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Wednesday, 16 February 2011 18:09

Post-Traumatic Stress Disorder and its Relation to Occupational Health and Injury Prevention

Beyond the broad concept of stress and its relationship to general health issues, there has been little attention to the role of psychiatric diagnosis in the prevention and treatment of the mental health consequences of work-related injuries. Most of the work on job stress has been concerned with the effects of exposure to stressful conditions over time, rather than to problems associated with a specific event such as a traumatic or life-threatening injury or the witnessing of an industrial accident or act of violence. At the same time, Post-traumatic Stress Disorder (PTSD), a condition which has received considerable credibility and interest since the mid-1980s, is being more widely applied in contexts outside of cases involving war trauma and victims of crime. With respect to the workplace, PTSD has begun to appear as the medical diagnosis in cases of occupational injury and as the emotional outcome of exposure to traumatic situations occurring in the workplace. It is often the subject of controversy and some confusion with respect to its relationship to work conditions and the responsibility of the employer when claims of psychological injury are made. The occupational health practitioner is called upon increasingly to advise on company policy in the handling of these exposures and injury claims, and to render medical opinions with respect to the diagnosis, treatment and ultimate job status of these employees. Familiarity with PTSD and its related conditions is therefore increasingly important for the occupational health practitioner.

The following topics will be reviewed in this article:

    • differential diagnosis of PTSD with other conditions such as primary depression and anxiety disorders
    • relationship of PTSD to stress-related somatic complaints
    • prevention of post-traumatic stress reactions in survivors and witnesses of psychologically traumatic events occurring in the workplace
    • prevention and treatment of complications of work injury related to post-traumatic stress.

           

          Post-traumatic Stress Disorder affects people who have been exposed to traumatizing events or conditions. It is characterized by symptoms of numbing, psychological and social withdrawal, difficulties controlling emotion, especially anger, and intrusive recollection and reliving of experiences of the traumatic event. By definition, a traumatizing event is one that is outside the normal range of everyday life events and is experienced as overwhelming by the individual. A traumatic event usually involves a threat to one’s own life or to someone close, or the witnessing of an actual death or serious injury, especially when this occurs suddenly or violently.

          The psychiatric antecedents of our current concept of PTSD go back to the descriptions of “battle fatigue” and “shell shock” during and after the World Wars. However, the causes, symptoms, course and effective treatment of this often debilitating condition were still poorly understood when tens of thousands of Vietnam-era combat veterans began to appear in the US Veterans Administration Hospitals, offices of family doctors, jails and homeless shelters in the 1970s. Due in large part to the organized effort of veterans’ groups, in collaboration with the American Psychiatric Association, PTSD was first identified and described in 1980 in the 3rd edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM III) (American Psychiatric Association 1980). The condition is now known to affect a wide range of trauma victims, including survivors of civilian disasters, victims of crime, torture and terrorism, and survivors of childhood and domestic abuse. Although changes in the classification of the disorder are reflected in the current diagnostic manual (DSM IV), the diagnostic criteria and symptoms remain essentially unchanged (American Psychiatric Association 1994).

          Diagnostic Criteria for Post-TraumaticStress Disorder

          A. The person has been exposed to a traumatic event in which both of the following were present:

          1. The person experienced, witnessed, or was confronted with an event or events that involved actual or threatened death or serious injury, or a threat to the physical integrity of self or others.
          2. The person’s response involved intense fear, helplessness or horror.

           

          B. The traumatic event is persistently re-experienced in one (or more) of the following ways:

          1. Recurrent and intrusive distressing recollections of the event, including images, thoughts or perceptions.
          2. Recurrent distressing dreams of the event.
          3. Acting or feeling as if the traumatic event were recurring.
          4. Intense psychological distress at exposure to internal or external cues that symbolize or resemble an aspect of the traumatic event.
          5. Physiological reactivity on exposure to internal or external cues that symbolize or resemble an aspect of the traumatic event.

           

          C. Persistent avoidance of stimuli associated with the trauma and numbing of general responsiveness (not present before the trauma), as indicated by three (or more) of the following:

          1. Efforts to avoid thoughts, feelings or conversations associated with the trauma.
          2. Efforts to avoid activities, places or people that arouse recollections of the trauma.
          3. Inability to recall an important aspect of the trauma.
          4. Markedly diminished interest or participation in significant activities.
          5. Feeling of detachment or estrangement from others.
          6. Restricted range of affect (e.g., unable to have loving feelings).
          7. Sense of a foreshortened future (e.g., does not expect to have a career, marriage, children or a normal life span).

           

          D. Persistent symptoms of increased arousal (not present before the trauma), as indicated by two (or more) of the following:

          1. Difficulty falling or staying asleep.
          2. Irritability or outbursts of anger.
          3. Difficulty concentrating.
          4. Hypervigilance.
          5. Exaggerated startle response.

           

          E. Duration of the disturbance (symptoms in criteria B, C and D) is more than 1 month.

           

          F. The disturbance causes clinically significant distress or impairment in social, occupational or other important areas of functioning.

          Specify if:

          Acute: if duration of symptoms is less than 3 months

          Chronic: if duration of symptoms is 3 months or more.

          Specify if:

          With Delayed Onset: if onset of symptoms is at least 6 months after the stressor.

          Psychological stress has achieved increasing recognition as an outcome of work-related hazards. The link between work hazards and post-traumatic stress was first established in the 1970s with the discovery of high incident rates of PTSD in workers in law enforcement, emergency medical, rescue and firefighting. Specific interventions have been developed to prevent PTSD in workers exposed to job-related traumatic stressors such as mutilating injury, death and use of deadly force. These interventions emphasize providing exposed workers with education about normal traumatic stress reactions, and the opportunity to actively surface their feelings and reactions with their peers. These techniques have become well established in these occupations in the United States, Australia and many European nations. Job-related traumatic stress, however, is not limited to workers in these high-risk industries. Many of the principles of preventive intervention developed for these occupations can be applied to programmes to reduce or prevent traumatic stress reactions in the general workforce.

          Issues in Diagnosis and Treatment

          Diagnosis

          The key to the differential diagnosis of PTSD and traumatic-stress-related conditions is the presence of a traumatic stressor. Although the stressor event must conform to criterion A—that is, be an event or situation that is outside of the normal range of experience—individuals respond in various ways to similar events. An event that precipitates a clinical stress reaction in one person may not affect another significantly. Therefore, the absence of symptoms in other similarly exposed workers should not cause the practitioner to discount the possibility of a true post-trauma reaction in a particular worker. Individual vulnerability to PTSD has as much to do with the emotional and cognitive impact of an experience on the victim as it does to the intensity of the stressor itself. A prime vulnerability factor is a history of psychological trauma due to a previous traumatic exposure or significant personal loss of some kind. When a symptom picture suggestive of PTSD is presented, it is important to establish whether an event that may satisfy the criterion for a trauma has occurred. This is particularly important because the victim himself may not make the connection between his symptoms and the traumatic event. This failure to connect the symptom with the cause follows the common “numbing” reaction, which may cause forgetting or dissociation of the event, and because it is not unusual for symptom appearance to be delayed for weeks or months. Chronic and often severe depression, anxiety and somatic conditions are often the result of a failure to diagnose and treat. Thus, early diagnosis is particularly important because of the often hidden nature of the condition, even to the sufferer him- or herself, and because of the implications for treatment.

          Treatment

          Although the depression and anxiety symptoms of PTSD may respond to usual therapies such as pharmacology, effective treatment is different from those usually recommended for these conditions. PTSD may be the most preventable of all psychiatric conditions and, in the occupational health sphere, perhaps the most preventable of all work-related injuries. Because its occurrence is linked so directly to a specific stressor event, treatment can focus on prevention. If proper preventive education and counselling are provided soon after the traumatic exposure, subsequent stress reactions can be minimized or prevented altogether. Whether the intervention is preventive or therapeutic depends largely on timing, but the methodology is essentially similar. The first step in successful treatment or preventive intervention is allowing the victim to establish the connection between the stressor and his or her symptoms. This identification and “normalization” of what are typically frightening and confusing reactions is very important for reduction or prevention of symptoms. Once the normalization of the stress response has been accomplished, treatment addresses the controlled processing of the emotional and cognitive impact of the experience.

          PTSD or conditions related to traumatic stress result from the sealing off of unacceptable or unacceptably intense emotional and cognitive reactions to traumatic stressors. It is generally considered that the stress syndrome can be prevented by providing the opportunity for controlled processing of the reactions to the trauma before the sealing off of the trauma occurs. Thus, prevention through timely and skilled intervention is the keystone for the treatment of PTSD. These treatment principles may depart from the traditional psychiatric approach to many conditions. Therefore, it is important that employees at risk of post-traumatic stress reactions be treated by mental health professionals with specialized training and experience in treating trauma-related conditions. The length of treatment is variable. It will depend on the timing of the intervention, the severity of the stressor, symptom severity and the possibility that a traumatic exposure may precipitate an emotional crisis linked to earlier or related experiences. A further issue in treatment concerns the importance of group treatment modalities. Victims of trauma can achieve enormous benefit from the support of others who have shared the same or similar traumatic stress experience. This is of particular importance in the workplace context, when groups of co-workers or entire work organizations are affected by a tragic accident, act of violence or traumatic loss.

          Prevention of Post-Traumatic Stress Reactionsafter Incidents of Workplace Trauma

          A range of events or situations occurring in the workplace may put workers at risk of post-traumatic stress reactions. These include violence or threat of violence, including suicide, inter-employee violence and crime, such as armed robbery; fatal or severe injury; and sudden death or medical crisis, such as heart attack. Unless properly managed, these situations can cause a range of negative outcomes, including post-traumatic stress reactions that may reach clinical levels, and other stress-related effects that will affect health and work performance, including avoidance of the workplace, concentration difficulties, mood disturbances, social withdrawal, substance abuse and family problems. These problems can affect not only line employees but management staff as well. Managers are at particular risk because of conflicts between their operational responsibilities, their feelings of personal responsibility for the employees in their charge and their own sense of shock and grief. In the absence of clear company policies and prompt assistance from health personnel to deal with the aftermath of the trauma, managers at all levels may suffer from feelings of helplessness that compound their own traumatic stress reactions.

          Traumatic events in the workplace require a definite response from upper management in close collaboration with health, safety, security, communications and other functions. A crisis response plan fulfils three primary goals:

          1. prevention of post-traumatic stress reactions by reaching affected individuals and groups before they have a chance to seal over
          2. communication of crisis-related information in order to contain fears and control rumours
          3. fostering of confidence that management is in control of the crisis and demonstrating concern for employees’ welfare.

           

          The methodology for the implementation of such a plan has been fully described elsewhere (Braverman 1992a,b; 1993b). It emphasizes adequate communication between management and employees, assembling of groups of affected employees and prompt preventive counselling of those at highest risk for post-traumatic stress because of their levels of exposure or individual vulnerability factors.

          Managers and company health personnel must function as a team to be sensitive for signs of continued or delayed trauma-related stress in the weeks and months after the traumatic event. These can be difficult to identify for manager and health professional alike, because post-traumatic stress reactions are often delayed, and they can masquerade as other problems. For a supervisor or for the nurse or counsellor who becomes involved, any signs of emotional stress, such as irritability, withdrawal or a drop in productivity, may signal a reaction to a traumatic stressor. Any change in behaviour, including increased absenteeism, or even a marked increase in work hours (“workaholism”) can be a signal. Indications of drug or alcohol abuse or change in moods should be explored as possibly linked to post-traumatic stress. A crisis response plan should include training for managers and health professionals to be alert for these signs so that intervention can be rendered at the earliest possible point.

          Stress-related Complications of Occupational Injury

          It has been our experience reviewing workers’ compensation claims up to five years post-injury that post-traumatic stress syndromes are a common outcome of occupational injury involving life-threatening or disfiguring injury, or assault and other exposures to crime. The condition typically remains undiagnosed for years, its origins unsuspected by medical professionals, claims administrators and human resource managers, and even the employee him- or herself. When unrecognized, it can slow or even prevent recovery from physical injury.

          Disabilities and injuries linked to psychological stress are among the most costly and difficult to manage of all work-related injuries. In the “stress claim”, an employee maintains he or she has been emotionally damaged by an event or conditions at work. Costly and hard to fight, stress claims usually result in litigation and in the separation of the employee. There exists, however, a vastly more frequent but seldom recognized source of stress-related claims. In these cases, serious injury or exposure to life-threatening situations results in undiagnosed and untreated psychological stress conditions that significantly affect the outcome of work-related injuries.

          On the basis of our work with traumatic worksite injuries and violent episodes over a wide range of worksites, we estimate that at least half of disputed workers’ compensation claims involve unrecognized and untreated post-traumatic stress conditions or other psychosocial components. In the push to resolve medical problems and determine the employee’s employment status, and because of many systems’ fear and mistrust of mental health intervention, emotional stress and psychosocial issues take a back seat. When no one deals with it, stress can take the form of a number of medical conditions, unrecognized by the employer, the risk manager, the health care provider and the employee him- or herself. Trauma-related stress also typically leads to avoidance of the workplace, which increases the risk of conflicts and disputes regarding return to work and claims of disability.

          Many employers and insurance carriers believe that contact with a mental health professional leads directly to an expensive and unmanageable claim. Unfortunately, this is often the case. Statistics bear out that claims for mental stress are more expensive than claims for other kinds of injuries. Furthermore, they are increasing faster than any other kind of injury claim. In the typical “physical-mental” claim scenario, the psychiatrist or psychologist appears only at the point—typically months or even years after the event—when there is a need for expert assessment in a dispute. By this time, the psychological damage has been done. The trauma-related stress reaction may have prevented the employee from returning to the workplace, even though he or she appeared visibly healed. Over time, the untreated stress reaction to the original injury has resulted in a chronic anxiety or depression, a somatic illness or a substance abuse disorder. Indeed, it is rare that mental health intervention is rendered at the point when it can prevent the trauma-related stress reaction and thus help the employee fully recover from the trauma of a serious injury or assault.

          With a small measure of planning and proper timing, the costs and suffering associated with injury-related stress are among the most preventable of all injuries. The following are the components of an effective post-injury plan (Braverman 1993a):

          Early intervention

          Companies should require a brief mental health intervention whenever a severe accident, assault or other traumatic event impacts on an employee. This evaluation should be seen as preventive, rather than as tied to the standard claims procedure. It should be provided even if there is no lost time, injury or need for medical treatment. The intervention should emphasize education and prevention, rather than a strictly clinical approach that may cause the employee to feel stigmatized. The employer, perhaps in conjunction with the insurance provider, should take responsibility for the relatively small cost of providing this service. Care should be taken that only professionals with specialized expertise or training in post-traumatic stress conditions be involved.

          Return to work

          Any counselling or assessment activity should be coordinated with a return-to-work plan. Employees who have undergone a trauma often feel afraid or tentative about returning to the worksite. Combining brief education and counselling with visits to the workplace during the recovery period has been used to great advantage in accomplishing this transition and speeding return to work. Health professionals can work with the supervisor or manager in developing gradual re-entry into job functioning. Even when there is no remaining physical limitation, emotional factors may necessitate accommodations, such as allowing a bank teller who was robbed to work in another area of the bank for part of the day as she gradually becomes comfortable returning to work at the customer window.

          Follow-up

          Post-traumatic reactions are often delayed. Follow-up at 1- and 6-month intervals with employees who have returned to work is important. Supervisors are also provided with fact sheets on how to spot possible delayed or long-term problems associated with post-traumatic stress.

          Summary: The Link between Post-Traumatic Stress Studies and Occupational Health

          Perhaps more than any other health science, occupational medicine is concerned with the relationship between human stress and disease. Indeed, much of the research in human stress in this century has taken place within the occupational health field. As the health sciences in general became more involved in prevention, the workplace has become increasingly important as an arena for research into the contribution of the physical and psychosocial environment to disease and other health outcomes, and into methods for the prevention of stress-related conditions. At the same time, since 1980 a revolution in the study of post-traumatic stress has brought important progress to the understanding of the human stress response. The occupational health practitioner is at the intersection of these increasingly important fields of study.

          As the landscape of work undergoes revolutionary transformation, and as we learn more about productivity, coping and the stressful impact of continued change, the line between chronic stress and acute or traumatic stress has begun to blur. The clinical theory of traumatic stress has much to tell us about how to prevent and treat work-related psychological stress. As in all health sciences, knowledge of the causes of a syndrome can help in prevention. In the area of traumatic stress, the workplace has shown itself to be an excellent place to promote health and healing. By being well acquainted with the symptoms and causes of post-traumatic stress reactions, occupational health practitioners can increase their effectiveness as agents of prevention.

           

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          Published in Mood and Affect
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          Wednesday, 16 February 2011 18:07

          Work-Related Anxiety

          Anxiety disorders as well as subclinical fear, worry and apprehension, and associated stress-related disorders such as insomnia, appear to be pervasive and increasingly prevalent in workplaces in the 1990s—so much so, in fact, that the Wall Street Journal has referred to the 1990s as the work-related “Age of Angst” (Zachary and Ortega 1993). Corporate downsizing, threats to existing benefits, lay-offs, rumours of impending lay-offs, global competition, skill obsolescence and “de-skilling”, re-structuring, re-engineering, acquisitions, mergers and similar sources of organizational turmoil have all been recent trends that have eroded workers’ sense of job security and have contributed to palpable, but difficult to precisely measure, “work-related anxiety” (Buono and Bowditch 1989). Although there appear to be some individual differences and situational moderator variables, Kuhnert and Vance (1992) reported that both blue-collar and white-collar manufacturing employees who reported more “job insecurity” indicated significantly more anxiety and obsessive-compulsive symptoms on a psychiatric checklist. For much of the 1980s and accelerating into the 1990s, the transitional organizational landscape of the US marketplace (or “permanent whitewater”, as it has been described) has undoubtedly contributed to this epidemic of work-related stress disorders, including, for example, anxiety disorders (Jeffreys 1995; Northwestern National Life 1991).

          The problems of occupational stress and work-related psychological disorders appear to be global in nature, but there is a dearth of statistics outside of the United States documenting their nature and extent (Cooper and Payne 1992). The international data that are available, mostly from European countries, seem to confirm similar adverse mental health effects of job insecurity and high-strain employment on workers as those seen in US workers (Karasek and Theorell 1990). However, because of the very real stigma associated with mental disorders in most other countries and cultures, many, if not most, psychological symptoms, such as anxiety, related to work (outside of the United States) go unreported, undetected and untreated (Cooper and Payne 1992). In some cultures, these psychological disorders are somatized and manifested as “more acceptable” physical symptoms (Katon, Kleinman and Rosen 1982). A study of Japanese government workers has identified occupational stressors such as workload and role conflict as significant correlates of mental health in these Japanese workers (Mishima et al. 1995). Further studies of this kind are needed to document the impact of psychosocial job stressors on workers’ mental health in Asia, as well as in the developing and post-Communist countries.

          Definition and Diagnosis of Anxiety Disorders

          Anxiety disorders are evidently among the most prevalent of mental health problems afflicting, at any one time, perhaps 7 to 15% of the US adult population (Robins et al. 1981). Anxiety disorders are a family of mental health conditions which include agoraphobia (or, loosely, “houseboundness”), phobias (irrational fears), obsessive-compulsive disorder, panic attacks and generalized anxiety. According to the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM IV), symptoms of a generalized anxiety disorder include feelings of “restlessness or feeling keyed up or on edge”, fatigue, difficulties with concentration, excess muscle tension and disturbed sleep (American Psychiatric Association 1994). An obsessive-compulsive disorder is defined as either persistent thoughts or repetitive behaviours that are excessive/unreasonable, cause marked distress, are time consuming and can interfere with a person’s functioning. Also, according to DSM IV, panic attacks, defined as brief periods of intense fear or discomfort, are not actually disorders per se but may occur in conjunction with other anxiety disorders. Technically, the diagnosis of an anxiety disorder can be made only by a trained mental health professional using accepted diagnostic criteria.

          Occupational Risk Factors for Anxiety Disorders

          There is a paucity of data pertaining to the incidence and prevalence of anxiety disorders in the workplace. Furthermore, since the aetiology of most anxiety disorders is multifactorial, we cannot rule out the contribution of individual genetic, developmental and non-work factors in the genesis of anxiety conditions. It seems likely that both work-related organizational and such individual risk factors interact, and that this interaction determines the onset, progression and course of anxiety disorders.

          The term job-related anxiety implies that there are work conditions, tasks and demands, and/or related occupational stressors that are associated with the onset of acute and/or chronic states of anxiety or manifestations of anxiety. These factors may include an overwhelming workload, the pace of work, deadlines and a perceived lack of personal control. The demand-control model predicts that workers in occupations which offer little personal control and expose employees to high levels of psychological demand would be at risk of adverse health outcomes, including anxiety disorders (Karasek and Theorell 1990). A study of pill consumption (mostly tranquilizers) reported for Swedish male employees in high-strain occupations supported this prediction (Karasek 1979). Certainly, the evidence for an increased prevalence of depression in certain high-strain occupations in the United States is now compelling (Eaton et al. 1990). More recent epidemiological studies, in addition to theoretical and biochemical models of anxiety and depression, have linked these disorders not only by identifying their co-morbidity (40 to 60%), but also in terms of more fundamental commonalities (Ballenger 1993). Hence, the Encyclopaedia chapter on job factors associated with depression may provide pertinent clues to occupational and individual risk factors also associated with anxiety disorders. In addition to risk factors associated with high-strain work, a number of other workplace variables contributing to employee psychological distress, including an increased prevalence of anxiety disorders, have been identified and are briefly summarized below.

          Individuals employed in dangerous lines of work, such as law enforcement and firefighting, characterized by the probability that a worker will be exposed to a hazardous agent or injurious activity, would also seem to be at risk of heightened and more prevalent states of psychological distress, including anxiety. However, there is some evidence that individual workers in such dangerous occupations who view their work as “exhilarating” (as opposed to dangerous) may cope better in terms of their emotional responses to work (McIntosh 1995). Nevertheless, an analysis of stress symptomatology in a large group of professional firefighters and paramedics identified a central feature of perceived apprehension or dread. This “anxiety stress pathway” included subjective reports of “being keyed up and jittery” and “being uneasy and apprehensive.” These and similar anxiety-related complaints were significantly more prevalent and frequent in the firefighter/paramedic group relative to a male community comparison sample (Beaton et al. 1995).

          Another worker population evidently at risk of experiencing high, and at times debilitating, levels of anxiety are professional musicians. Professional musicians and their work are exposed to intense scrutiny by their supervisors; they must perform before the public and must cope with performance and pre-performance anxiety or “stage fright”; and they are expected (by others as well as by themselves) to produce “note-perfect performances” (Sternbach 1995). Other occupational groups, such as theatrical performers and even teachers who give public performances, may have acute and chronic anxiety symptoms related to their work, but very little data on the actual prevalence or significance of such occupational anxiety disorders have been collected.

          Another class of work-related anxiety for which we have little data is “computer phobics”, people who have responded anxiously to the advent of computing technology (Stiles 1994). Even though each generation of computer software is arguably more “user-friendly”, many workers are uneasy, while other workers are literally panicked by challenges of “techno-stress”. Some fear personal and professional failure associated with their inability to acquire the necessary skills to cope with each successive generation of technology. Finally, there is evidence that employees subjected to electronic performance monitoring perceive their jobs as more stressing and report more psychological symptoms, including anxiety, than workers not so monitored (Smith et al. 1992).

          Interaction of Individual and Occupational Risk Factors for Anxiety

          It is likely that individual risk factors interact with and may potentiate the above-cited organizational risk factors at the onset, progression and course of anxiety disorders. For example, an individual employee with a “Type A personality” may be more prone to anxiety and other mental health problems in high-strain occupational settings (Shima et al. 1995). To offer a more specific example, an overly responsible paramedic with a “rescue personality” may be more on edge and hypervigilant while on duty then another paramedic with a more philosophical work attitude: “You can’t save them all” (Mitchell and Bray 1990). Individual worker personality variables may also serve to potentially buffer attendant occupational risk factors. For instance, Kobasa, Maddi and Kahn (1982) reported that corporate managers with “hardy personalities” seem better able to cope with work-related stressors in terms of health outcomes. Thus, individual worker variables need to be considered and evaluated within the context of the particular occupational demands to predict their likely interactive impact on a given employee’s mental health.

          Prevention and Remediation ofWork-related Anxiety

          Many of the US and global workplace trends cited at the beginning of this article seem likely to persist into the foreseeable future. These workplace trends will adversely impact workers’ psychological and physical health. Psychological job enhancement, in terms of interventions and workplace redesign, may deter and prevent some of these adverse effects. Consistent with the demand-control model, workers’ well-being can be improved by increasing their decision latitude by, for example, designing and implementing a more horizontal organizational structure (Karasek and Theorell 1990). Many of the recommendations made by NIOSH researchers, such as improving workers’ sense of job security and decreasing work role ambiguity, if implemented, would also likely reduce job strain and work-related psychological disorders considerably, including anxiety disorders (Sauter, Murphy and Hurrell 1992).

          In addition to organizational policy changes, the individual employee in the modern workplace also has a personal responsibility to manage his or her own stress and anxiety. Some common and effective coping strategies employed by US workers include separating work and non-work activities, getting sufficient rest and exercise, and pacing oneself at work (unless, of course, the job is machine paced). Other helpful cognitive-behavioural alternatives in self-managing and preventing anxiety disorders include deep-breathing techniques, biofeedback-aided relaxation training, and meditation (Rosch and Pelletier 1987). In certain cases medications may be necessary to treat a severe anxiety disorder. These medications, including antidepressants and other anxiolytic agents, are generally available only by prescription.

           

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          Wednesday, 16 February 2011 18:06

          Depression

          Depression is an enormously important topic in the area of workplace mental health, not only in terms of the impact depression can have on the workplace, but also the role the workplace can play as an aetiological agent of the disorder.

          In a 1990 study, Greenberg et al. (1993a) estimated that the economic burden of depression in the United States that year was approximately US$ 43.7 billion. Of that total, 28% was attributable to direct costs of medical care, but 55% was derived from a combination of absenteeism and decreased productivity while at work. In another paper, the same authors (1993b) note:

          “two distinguishing features of depression are that it is highly treatable and not widely recognized. The NIMH has noted that between 80% and 90% of individuals suffering from a major depressive disorder can be treated successfully, but that only one in three with the illness ever seeks treatment.… Unlike some other diseases, a very large share of the total costs of depression falls on employers. This suggests that employers as a group may have a particular incentive to invest in programs that could reduce the costs associated with this illness.”

          Manifestations

          Everyone feels sad or “depressed” from time to time, but a major depressive episode, according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM IV) (American Psychiatric Association 1994), requires that several criteria be met. A full description of these criteria is beyond the scope of this article, but portions of criterion A, which describes the symptoms, can give one a sense of what a true major depression looks like:

          A. Five (or more) of the following symptoms have been present during the same 2-week period and represent a change from previous functioning; at least one of the symptoms is number 1 or 2.

          1. depressed mood most of the day, nearly every day
          2. markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day
          3. significant weight loss when not dieting or weight gain, or decrease or increase in appetite nearly every day
          4. insomnia or hypersomnia nearly every day
          5. psychomotor agitation or retardation nearly every day
          6. fatigue or loss of energy nearly every day
          7. feelings of worthlessness or excessive or inappropriate guilt nearly every day
          8. diminished ability to think or concentrate, or indecisiveness nearly every day
          9. recurrent thoughts of death, recurrent suicidal ideation, with or without a plan, or a suicide attempt.

           

          Besides giving one an idea of the discomfort suffered by a person with depression, a review of these criteria also shows the many ways depression can impact negatively on the workplace. It is also important to note the wide variation of symptoms. One depressed person may present barely able to move to get out of bed, while others may be so anxious they can hardly sit still and describe themselves as crawling out of their skin or losing their mind. Sometimes multiple physical aches and pains without medical explanation may be a hint of depression.

          Prevalence

          The following passage from Mental Health in the Workplace (Kahn 1993) describes the pervasiveness (and increase) of depression in the workplace:

          “Depression … is one of the most common mental health problems in the workplace. Recent research … suggests that in industrialized countries the incidence of depression has increased with each decade since 1910, and the age at which someone is likely to become depressed has dropped with every generation born after 1940. Depressive illnesses are common and serious, taking a tremendous toll on both workers and workplace. Two out of ten workers can expect a depression during their lifetime, and women are one and a half times more likely than men to become depressed. One out of ten workers will develop a clinical depression serious enough to require time off from work.”

          Thus, in addition to the qualitative aspects of depression, the quantitative/epidemiological aspects of the disease make it a major concern in the workplace.

          Related Illnesses

          Major depressive disorder is only one of a number of closely related illnesses, all under the category of “mood disorders”. The most well known of these is bipolar (or “manic-depressive”) illness, in which the patient has alternating periods of depression and mania, which includes a feeling of euphoria, a decreased need for sleep, excessive energy and rapid speech, and can progress to irritability and paranoia.

          There are several different versions of bipolar disorder, depending on the frequency and severity of the depressive and manic episodes, the presence or absence of psychotic features (delusions, hallucinations) and so on. Similarly, there are several different variations on the theme of depression, depending on severity, presence or absence of psychosis, and types of symptom most prominent. Again, it is beyond the scope of this article to delineate all of these, but the reader is again referred to DSM IV for a complete listing of all the different forms of mood disorder.

          Differential Diagnosis

          The differential diagnosis of major depression involves three major areas: other medical disorders, other psychiatric disorders and medication-induced symptoms.

          Just as important as the fact that many patients with depression first present to their general practitioners with physical complaints is the fact that many patients who initially present to a mental health clinician with depressive complaints may have an undiagnosed medical illness causing the symptoms. Some of the most common illnesses causing depressive symptoms are endocrine (hormonal), such as hypothyroidism, adrenal problems or changes related to pregnancy or the menstrual cycle. Particularly in older patients, neurological diseases, such as dementia, strokes or Parkinson’s disease, become more prominent in the differential diagnosis. Other illnesses that can present with depressive symptoms are mononucleosis, AIDS, chronic fatigue syndrome and some cancers and joint diseases.

          Psychiatrically, the disorders which share many common features with depression are the anxiety disorders (including generalized anxiety, panic disorder and post-traumatic stress disorder), schizophrenia and drug and alcohol abuse. The list of medications that can cause depressive symptoms is quite lengthy, and includes pain medications, some antibiotics, many anti-hypertensives and cardiac drugs, and steroids and hormonal agents.

          For further detail on all three areas of the differential diagnosis of depression, the reader is referred to Kaplan and Sadock’s Synopsis of Psychiatry (1994), or the more detailed Comprehensive Textbook of Psychiatry (Kaplan and Sadock 1995).

          Workplace Aetiologies

          Much can be found elsewhere in this Encyclopaedia regarding workplace stress, but what is important in this article is the manner in which certain aspects of stress can lead to depression. There are many schools of thought regarding the aetiology of depression, including biological, genetic and psychosocial. It is in the psychosocial realm that many factors relating to the workplace can be found.

          Issues of loss or threatened loss can lead to depression and, in today’s climate of downsizing, mergers and shifting job descriptions, are common problems in the work environment. Another result of frequently changing job duties and the constant introduction of new technologies is to leave workers feeling incompetent or inadequate. According to psychodynamic theory, as the gap between one’s current self image and “ideal self” widens, depression ensues.

          An animal experimental model known as “learned helplessness” can also be used to explain the ideological link between stressful workplace environments and depression. In these experiments, animals were exposed to electric shocks from which they could not escape. As they learned that none of the actions they took had any effect on their eventual fate, they displayed increasingly passive and depressive behaviours. It is not difficult to extrapolate this model to today’s workplace, where so many feel a sharply decreasing amount of control over both their day-to-day activities and long-range plans.

          Treatment

          In light of the aetiological link of the workplace to depression described above, a useful way of looking at the treatment of depression in the workplace is the primary, secondary, tertiary model of prevention. Primary prevention, or trying to eliminate the root cause of the problem, entails making fundamental organizational changes to ameliorate some of the stressors described above. Secondary prevention, or trying to “immunize” the individual from contracting the illness, would include such interventions as stress management training and lifestyle changes. Tertiary prevention, or helping to return the individual to health, involves both psychotherapeutic and psychopharmacological treatment.

          There is an increasing array of psychotherapeutic approaches available to the clinician today. The psychodynamic therapies look at the patient’s struggles and conflicts in a loosely structured format that allows explorations of whatever material may come up in a session, however tangential it may initially appear. Some modifications of this model, with boundaries set in terms of number of sessions or breadth of focus, have been made to create many of the newer forms of brief therapy. Interpersonal therapy focuses more exclusively on the patterns of the patient’s relationships with others. An increasingly popular form of therapy is cognitive therapy, which is driven by the precept, “What you think is how you feel”. Here, in a very structured format, the patient’s “automatic thoughts” in response to certain situations are examined, questioned and then modified to produce a less maladaptive emotional response.

          As rapidly as the psychotherapies have developed, the psychopharmacological armamentarium has probably grown even faster. In the few decades before the 1990s, the most common medications used to treat depression were the tricyclics (imipramine, amitriptyline and nortriptyline are examples) and the monoamine oxidase inhibitors (Nardil, Marplan and Parnate). These medications act on neurotransmitter systems thought to be involved with depression, but also affect many other receptors, resulting in a number of side effects. In the early 1990s, several new medications (fluoxetine, sertraline, Paxil, Effexor, fluvoxamine and nefazodone) were introduced. These medications have enjoyed rapid growth because they are “cleaner” (bind more specifically to depression-related neurotransmitter sites) and can thus effectively treat depression while causing much fewer side effects.

          Summary

          Depression is extremely important in the world of workplace mental health, both because of depression’s impact on the workplace, and the workplace’s impact on depression. It is a highly prevalent disease, and very treatable; but unfortunately frequently goes undetected and untreated, with serious consequences for both the individual and the employer. Thus, increased detection and treatment of depression can help lessen individual suffering and organizational losses.

           

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          Published in Mood and Affect
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          Wednesday, 16 February 2011 18:04

          Work-Related Psychosis

          Psychosis is a general term often used to describe a severe impairment in mental functioning. Usually, this impairment is so substantial that the individual is unable to carry on normal activities of daily living, including most work activities. More formally, Yodofsky, Hales and Fergusen (1991) define psychosis as:

          “A major mental disorder of organic or emotional origin in which a person’s ability to think, respond emotionally, remember, communicate, interpret reality and behave appropriately is sufficiently impaired so as to interfere grossly with the capacity to meet the ordinary demands of life. [Symptoms are] often characterized by regressive behaviour, inappropriate mood, diminished impulse control and such abnormal mental context as delusions and hallucinations [p. 618].”

          Psychotic disorders are comparatively rare in the general population. Their incidence in the workplace is even lower, probably due to the fact that many individuals who frequently become psychotic often have problems maintaining stable employment (Jorgensen 1987). Precisely how rare it is, is difficult to estimate. However, there are some suggestions that the prevalence within the general population of psychoses (e.g., schizophrenia) is less than 1% (Bentall 1990; Eysenck 1982). While psychosis is rare, individuals who are actively experiencing a psychotic state usually exhibit profound difficulties in functioning at work and in other aspects of their lives. Sometimes acutely psychotic individuals exhibit behaviours which are engaging, inspiring or even humorous. For example, some individuals who suffer from bipolar illness and are entering a manic phase exhibit high energy and grand ideas or plans. For the most part, however, psychosis is associated with behaviours which evoke reactions such as discomfort, anxiety, anger or fear in co-workers, supervisors and others.

          This article will first provide an overview of the various neurological conditions and mental states in which psychosis can occur. Then, it will review workplace factors potentially associated with the occurrence of psychosis. Finally, it will summarize treatment approaches for managing both the psychotic worker and the work environment (i.e., medical management, return-to-work clearance procedures, workplace accommodations and workplace consultations with supervisors and co-workers).

          Neurological Conditions and Mental Stateswithin which Psychosis Occurs

          Psychosis can occur within a number of diagnostic categories identified in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM IV) (American Psychiatric Association 1994). At this point, there is no commonly agreed upon definitive diagnostic set. The following are widely accepted as medical conditions within which psychoses arise.

          Neurological and general medical conditions

          Delusional symtomatology can be caused by a range of neurological disorders affecting the limbic system or basal ganglia, where cerebral cortical functioning remains intact. Partial complex seizure episodes are often preceded by olfactory hallucinations of peculiar smells. To an external observer, this seizure activity may appear to be simple staring or day-dreaming. Cerebral neoplasms, especially in temporal and occipital areas, can cause hallucinations. Also, delirium-causing diseases, such as Parkinson’s, Huntington’s, Alzheimer’s, and Pick’s, can result in altered states of consciousness. Several sexually transmitted diseases such as tertiary syphilis and AIDS can also produce psychosis. Lastly, deficiencies of certain nutrients, such as B-12, niacin, folic acid and thiamine, have the potential of causing neurological problems which can result in psychosis.

          Psychotic symptoms such as hallucinations and delusions also occur among patients with various general medical conditions. These include several systemic diseases, such as hepatic encephalopathy, hypercalcaemia, diabetic ketoacidosis, and malfunction of endocrine glands (i.e., adrenal, thyroid, parathyroid and pituitary). Sensory and sleep deprivation have also been shown to cause psychosis.

          Mental states

          Schizophrenia is probably the most widely known of the psychotic disorders. It is a progressively deteriorating condition which usually has an insidious onset. A number of specific subcategories have been identified including paranoid, disorganized, catatonic, undifferentiated and residual types. People who suffer from this disorder often have limited work histories and often do not remain in the workforce. Occupational impairment among schizophrenics is very common, and many schizophrenics lose their interest or will to work as the disease progresses. Unless a job is of very low complexity, it is usually very difficult for them to stay employed.

          Schizophreniform disorder is similar to schizophrenia, but an episode of this disorder is of short duration, usually lasting less than six months. Generally, persons with this disorder have good premorbid social and occupational functioning. As the symptoms resolve, the person returns to baseline functioning. Consequently, the occupational impact of this disorder may be significantly less than in cases of schizophrenia.

          Schizoaffective disorder also has a better prognosis than schizophrenia but a worse prognosis than affective disorders. Occupational impairment is quite common in this group. Psychosis is also sometimes observed in major affective disorders. With appropriate treatment, occupational functioning among workers suffering from major affective disorders is generally substantially better than for those with schizophrenia or schizoaffective disorders.

          Severe stressors such as losing a loved one or losing one’s job can result in a brief reactive psychosis. This psychotic disorder is probably observed more frequently in the workplace than other types of psychotic disorder, especially with schizoid, schizotypal and borderline features.

          Delusional disorders are probably relatively common in the workplace. There are several types. The erotomanic type typically believes that another person, usually of a higher social status, is in love with them. Sometimes, they harass the person who they believe is in love with them by attempting contact via telephone calls, letters or even stalking. Often, individuals with these disorders are employed in modest occupations, living isolated and withdrawn lives with limited social and sexual contact. The grandiose type usually exhibits delusions of inflated worth, power, knowledge or a special relationship with a deity or a famous person. The jealous type believes inaccurately that their sexual partner has been unfaithful. The persecutory type believes inaccurately that they (or someone to whom they are close) are being cheated, maligned, harassed or in other ways malevolently treated. These persons are often resentful and angry and may resort to violence against those they believe to be hurting them. They rarely want to seek help, as they do not think there is anything wrong with them. Somatic types develop delusions, contrary to all evidence, that they are afflicted with infections. They can also believe that a part of their body is disfigured, or worry about having a bad body odour. These workers with delusional beliefs can often create work-related difficulties.

          Work-related chemical factors

          Chemical factors such as mercury, carbon disulphide, toluene, arsenic and lead have been known to cause psychosis in blue-collar workers. For example, mercury has been found to be responsible for causing psychosis in workers in the hat industry, appropriately named the “Mad Hatter’s psychosis” (Kaplan and Sadock 1995). Stopford (personal communication, 6 November 1995) suggests that carbon disulphide was found to cause psychosis among workers in France in 1856. In the United States, in 1989, two brothers in Nevada purchased a carbon disulphide compound to kill gophers. Their physical contact with this chemical resulted in severe psychosis—one brother shooting a person and the other shooting himself due to severe confusion and psychotic depression. The incidence of suicide and homicide increases thirteenfold with exposure to carbon disulphide. Further, Stopford reports that exposure to toluene (used in making explosives and dyestuffs) is known to cause acute encephalopathy and psychosis. Symptoms can manifest also as memory loss, mood changes (e.g., dysphoria), deterioration in eye-hand coordination and speech impediments. Hence, some organic solvents, especially those found in the chemical industry, have a direct influence on the human central nervous system (CNS), causing biochemical changes and unpredictable behaviour (Levi, Frandenhaeuser and Gardell 1986). Special precautions, procedures and protocols have been established by the US Occupational Safety and Health Administration (OSHA), National Institute for Occupational Safety and Health (NIOSH) and the chemical industry to ensure minimum risk to employees working with toxic chemicals in their work environments.

          Other factors

          A number of medications can cause delirium which in turn can result in psychosis. These include antihypertensives, anticholinergics (including a number of medications used to treat the common cold), antidepressants, anti-tuberculosis medicines, anti-Parkinson’s disease medicines, and ulcer medicines (such as cimetidine). Further, substance-induced psychosis can be caused by a number of licit and illicit drugs which are sometimes abused, such as alcohol, amphetamines, cocaine, PCP, anabolic steroids and marijuana. The delusions and hallucinations which result are usually temporary. Although the content may vary, persecutory delusions are quite common. In alcohol-related hallucinations a person may believe that he or she is hearing voices which are threatening, insulting, critical or condemning. Sometimes, these insulting voices speak in the third person. As with individuals exhibiting paranoid or persecutory delusions, these individuals should be carefully evaluated for dangerousness to self or others.

          Post-partum psychosis is comparatively uncommon in the workplace, but is worth noting as some women are returning to work more quickly. It tends to occur in new mothers (or more rarely fathers), usually within two to four weeks after delivery.

          In a number of cultures, psychosis may result from various commonly held beliefs. A number of culturally based psychotic reactions have been described, including episodes such as “koro” in South and East Asia, “qi-gong psychotic reaction” within Chinese populations, “piblokto” in Eskimo communities and “whitigo” among several American Indian groups (Kaplan and Sadock 1995). The relationship of these psychotic phenomena to various occupational variables does not appear to have been studied.

          Workplace Factors Associated with the Occurrence of Psychosis

          Although information and empirical research on work-related psychosis are extremely scarce, due in part to the low prevalence in the work setting, researchers have noted a relationship between psychosocial factors in the work environment and psychological distress (Neff 1968; Lazarus 1991; Sauter, Murphy and Hurrell 1992; Quick et al. 1992). Significant psychosocial stressors on the job, such as role ambiguity, role conflicts, discrimination, supervisor-supervisee conflicts, work overload and work setting have been found to be associated with greater susceptibility to stress-related illness, tardiness, absenteeism, poor performance, depression, anxiety and other psychological distress (Levi, Frandenhaeuser and Gardell 1986; Sutherland and Cooper 1988).

          Stress appears to have a prominent role in the complex manifestations of various types of physiological and psychological disorders. In the workplace, Margolis and Kroes (1974) believe that occupational stress occurs when some factor or combination of factors at work interact with the worker to disrupt his or her psychological or physiological homeostasis. These factors can be external or internal. External factors are the various pressures or demands from the external environment which stem from a person’s occupation, as well as from marriage, family or friends, whereas internal factors are the pressures and demands a worker places upon him- or herself—for example, by being “ambitious, materialistic, competitive and aggressive” (Yates 1989). It is these internal and external factors, separately or in combination, which can result in occupational distress whereby the worker experiences significant psychological and physical health problems.

          Researchers have speculated on whether severe or cumulative stress, known as “stress-induced arousal”, originating from the work environment, could induce work-related psychotic disorders (Bentall, Dohrenwend and Skodol 1990; Link, Dohrenwend and Skodol 1986). For example, there is evidence linking hallucinatory and delusional experiences to specific stressful events. Hallucinations have been associated with stress-induced arousal occurring as a result of mining accidents, hostage situations, chemical-factory explosions, wartime exposure, sustained military operations and loss of a spouse (Comer, Madow and Dixon 1967; Hobfoll 1988; Wells 1983).

          DeWolf (1986) believes that either the exposure to or interaction of multiple stressful conditions over an extended period of time is a complex process whereby some workers experience psychological health-related problems. Brodsky (1984) found in her examination of 2,000 workers who were her patients over 18 years that: (1) the timing, frequency, intensity and duration of unpleasant work conditions were potentially harmful, and she believed that 8 to 10% of the workforce experienced disabling psychological, emotional and physical health-related problems; and (2) workers react to work-related stress in part as “a function of perceptions, personality, age, status, life stage, unrealized expectations, prior experiences, social support systems and their capacity to respond adequately or adapt.” In addition, psychological distress can potentially be exacerbated by the worker feeling a sense of uncontrollability (e.g., inability to make decisions) and unpredictability in the work environment (e.g., corporate downsizing and reorganizing) (Labig 1995; Link and Stueve 1994).

          Specific examination of the work-related “antecedents” of workers experiencing psychosis has received limited attention. The few researchers who have empirically examined the relationship between psychosocial factors in the work environment and severe psychopathology have found a relationship between “noisome” work conditions (i.e., noise, hazardous conditions, heat, humidity, fumes and cold) and psychosis (Link, Dohrenwend and Skodol 1986; Muntaner et al. 1991). Link, Dohrenwend and Skodol (1986) were interested in understanding the types of jobs schizophrenics had when they experienced their first schizophrenic episode. First full-time occupations were examined for workers who experienced: (a) schizophrenic or schizophrenic-like episodes; (b) depression; and (c) no psychopathology. These researchers found that noisome work conditions existed among more blue-collar than white-collar professions. These researchers concluded that noisome work conditions were potentially significant risk factors in the manifestation of psychotic episodes (i.e., schizophrenia).

          Muntaner et al. (1991) replicated the findings of Link, Dohrenwend and Skodol (1986) and examined in greater detail whether various occupational stressors contributed to increased risk of developing or experiencing psychoses. Three types of psychotic condition were examined using the criteria of DSM III—schizophrenia; schizophrenia criterion A (hallucinations and delusions); and schizophrenia criterion A with affective episode (psychotic-affective disorder). Participants in their retrospective study were from a larger Epidemiologic Catchment Area (ECA) study examining the incidence of psychiatric disorders across five sites (Connecticut, Maryland, North Carolina, Missouri and California). These researchers found that psychosocial work characteristics (i.e., high physical demands, lack of control over work and working conditions—noisome factors) placed participants at increased risk of psychotic occurrences.

          As illustrations, in the Muntaner et al. (1991) study, people in construction trade occupations (i.e., carpenters, painters, roofers, electricians, plumbers) were 2.58 times more likely to experience delusions or hallucinations than people in managerial occupations. Workers in housekeeping, laundry, cleaning and servant-type occupations were 4.13 times more likely to become schizophrenic than workers in managerial occupations. Workers who identified themselves as writers, artists, entertainers and athletes were 3.32 times more likely to experience delusions or hallucinations in comparison to workers in executive, administrative and managerial occupations. Lastly, workers in occupations such as sales, mail and message delivery, teaching, library science and counselling were more at risk of psychotic, affective disorders. It is important to note that the associations between psychotic conditions and occupational variables were examined after alcohol and drug use was controlled for in their study.

          A significant difference between blue-collar and white-collar professions is the types of psychological demand and psychosocial stress placed on the worker. This is illustrated in the findings of Muntaner et al. (1993). They found an association between a work environment’s cognitive complexity and psychotic forms of mental illness. The most frequent occupations held by schizophrenic patients during their last full-time job were characterized by their low level of complexity in dealing with people, information and objects (e.g., janitors, cleaners, gardeners, guards). A few researchers have examined some of the consequences of first episodic psychosis relative to employment, job performance and capacity to work (Jorgensen 1987; Massel et al. 1990; Beiser et al. 1994). For example, Beiser and co-workers examined occupational functioning after the first episode of psychosis. These researchers found 18 months after the first episode that the “psychosis compromise[d] occupational functioning”. In other words, there was a higher post-morbid decline among schizophrenic workers than among those suffering from affective disorders. Similarly, Massel et al. (1990) found that the work capacity of psychotics (e.g., people with schizophrenia, affective disorders with psychotic features or atypical psychotic disorders) was impaired in comparison to non-psychotics (e.g., people with affective disorders without psychotic features, anxiety disorders, personality disorders and substance abuse disorders). Psychotics in their study showed marked thought disturbance, hostility and suspiciousness which correlated with poor work performance.

          In summary, our knowledge about the relationship between work-related factors and psychosis is in the embryonic stage. As Brodsky (1984) states, “the physical and chemical hazards of the workplace have received considerable attention, but the psychological stresses associated with work have not been as widely discussed, other than in relation to managerial responsibilities or to the coronary-prone behaviour pattern”. This means that research on the topic of work-related psychosis is vitally needed, especially since workers spend an average of 42 to 44% of their lives working (Hines, Durham and Geoghegan 1991; Lemen 1995) and work has been associated with psychological well-being (Warr 1978). We need to have a better understanding of what types of occupational stressor under what types of condition influence which types of psychological disorder. For example, research is needed to determine whether there are stages which workers move through based upon intensity, duration and frequency of psychosocial stress in the work environment, in conjunction with personal, social, cultural and political factors occurring in their daily lives. We are dealing with complex issues which will require in-depth inquiries and ingenious solutions.

          Acute Management of the Psychotic Worker

          Typically, the primary role of persons in the workplace is to respond to an acutely psychotic worker in a manner which facilitates the person being transported safely to an emergency room or psychiatric treatment facility. The process may be greatly facilitated if the organization has an active employee assistance programme and a critical incident response plan. Ideally, the organization will train key employees in advance for emergency crisis responses and will have a plan in place for coordinating as needed with local emergency response resources.

          Treatment approaches for the psychotic worker will vary depending upon the specific type of underlying problem. In general, all psychotic disorders should be evaluated by a professional. Often, immediate hospitalization is warranted for the safety of the worker and the workplace. Thereafter, a thorough evaluation can be completed to establish a diagnosis and develop a treatment plan. The primary goal is to treat the underlying cause(s). However, even prior to conducting a comprehensive evaluation or initiating a comprehensive treatment plan, the physician responding to the emergency may need to focus initially on providing symptomatic relief. Providing a structured, low-stress environment is desirable. Neuroloptics may be used to help the patient calm down. Benzodiazepines may help reduce acute anxiety.

          After managing the acute crisis, a comprehensive evaluation may include collecting a detailed history, psychological testing, a risk assessment to establish dangerousness to self or others and careful monitoring of response to treatment (including not only response to medications, but also to psychotherapeutic interventions). One of the more difficult problems with many patients who exhibit psychotic symptomatology is treatment compliance. Often these individuals tend not to believe that they have serious difficulties, or, even if they recognize the problem, they are sometimes inclined to decide unilaterally to discontinue treatment prematurely. In these instances, family members, co-workers, treating clinicians, occupational health personnel and employers are sometimes placed in awkward or difficult situations. Sometimes, for the safety of the employee and the workplace, it becomes necessary to mandate compliance with treatment as a condition for returning to the job.

           

           

          Managing the Psychotic Worker and the Work Environment

          Case example

          A skilled worker on the third shift at a chemical plant began to exhibit unusual behaviour as the company began to modify its production schedule. For several weeks, instead of leaving work after his shift ended, he began to stay for several hours discussing his concerns about increased job demands, quality control and changes in production procedures with his counterparts on the morning shift. He appeared quite distressed and behaved in a manner which was atypical for him. He had formerly been somewhat shy and distant, with an excellent job performance history. During this period of time, he became more verbal. He also approached individuals and stood close to them in a manner which several co-workers reported made them feel uncomfortable. While these co-workers later reported that they felt his behaviour was unusual, no one notified the employee assistance programme (EAP) or management of their concerns. Then, suddenly one evening, this employee was observed by his co-workers as he began to shout incoherently, walked over to a storage area for volatile chemicals, laid down on the ground and began to flick a cigarette lighter on and off. His co-workers and supervisor interfered and, after consultation with the EAP, he was taken by ambulance to a nearby hospital. The treating physician determined that he was acutely psychotic. After a brief treatment period he was successfully stabilized on medications.

          After several weeks, his treating physician felt he was able to return to his job. He underwent a formal return-to-work evaluation with an independent clinician and was judged ready to return to work. While his company doctor and the treating physician determined that it was safe for him to return, his co-workers and supervisors expressed substantial concerns. Some employees noted that they might be harmed if this episode were repeated and the chemical storage areas ignited. The company took steps to increase security in safety sensitive areas. Another concern also surfaced. A number of workers stated that they believed this individual might bring a weapon to work and start shooting. None of the professionals involved in treating this worker or in evaluating him for return to work believed that there was a risk of violent behaviour. The company then elected to bring in mental health professionals (with the worker’s consent) to assure co-workers that the risk of violent behaviour was exceedingly low, to provide education on mental illnesses, and to identify proactive steps that co-workers could take to facilitate the return to work of a colleague who had undergone treatment. However, in this situation, even after this educational intervention, co-workers were unwilling to interact with this worker, further compounding the return-to-work process. While the legal rights of individuals suffering from mental disorders, including those associated with psychotic states, have been addressed by the Americans with Disabilities Act, practically speaking the organizational challenges to effectively managing occurrences of psychosis at work are often as great or greater than the medical treatment of psychotic workers.

           

           

          Return to Work

          The primary question to be addressed after a psychotic episode is whether the employee can safely return to his or her current job. Sometimes organizations permit this decision to be made by the treating clinicians. However, ideally, the organization should require their occupational medical system to conduct an independent fitness-for-duty evaluation (Himmerstein and Pransky 1988). In the fitness-for-duty evaluation process a number of key pieces of information should be reviewed, including the treating clinician’s evaluation, treatment and recommendations, as well as the worker’s prior job performance and the specific features of the job, including the required job tasks and the organizational environment.

          If the occupational medical physician is not trained in psychiatric or psychological fitness-for-duty evaluation, then the evaluation should be performed by an independent mental health professional who is not the treating clinician. If some aspects of the job pose safety risks, then specific work restrictions should be developed. These restrictions may range from minor alterations in work activities or work schedule to more significant modifications such as alternate job placement (e.g., a light-duty assignment or a job transfer to an alternate position). In principle, these work restrictions are not different in kind from other restrictions commonly provided by occupational health physicians, such as specifying the amount of weight which a worker may be cleared to lift following a musculoskeletal injury.

          As is evident in the case example above, the return to work often raises challenges not only for the affected worker, but also for co-workers, supervisors and the broader organization. While professionals are obligated to protect the confidentiality of the affected worker to the fullest extent permitted by law, if the worker is willing and competent to sign an appropriate release of information, then the occupational medical system can provide or coordinate consultation and educational interventions to facilitate the return-to-work process. Often, coordination between the occupational medical system, the employee assistance programme, supervisors, union representatives and co-workers is critical to a successful outcome.

          The occupational health system should also periodically monitor the worker’s readjustment to the workplace in collaboration with the supervisor. In some instances, it may be necessary to monitor the worker’s compliance with a medication regimen recommended by the treating physician—for example, as a precondition for being permitted to engage in certain safety-sensitive job tasks. More importantly, the occupational medical system must consider not only what is best for the worker, but also what is safe for the workplace. The occupational medical system may also play a critical role in assisting the organization in complying with legal requirements such as the Americans with Disabilities Act as well as in interfacing with treatments provided under the organization’s health care plan and/or the workers’ compensation system.

          Prevention Programming

          At present, there is no literature on specific prevention or early intervention programmes for reducing the incidence of psychosis in the workforce. Employee assistance programmes may play a crucial role in the early identification and treatment of psychotic workers. Since stress may contribute to the incidence of psychotic episodes within working populations, various organizational interventions which identify and modify organizationally created stress may also be helpful. These general programmatic efforts may include job redesign, flexible scheduling, self-paced work, self-directed work teams and microbreaks, as well as specific programming to reduce the stressful impact of reorganization or downsizing.

          Conclusion

          While psychosis is a comparatively rare and multiply determined phenomenon, its occurrence within working populations raises substantial practical challenges for co-workers, union representatives, supervisors and occupational health professionals. Psychosis may occur as a direct consequence of a work-related toxic exposure. Work-related stress may also increase the incidence of psychosis among workers who suffer from (or are at risk of developing) mental disorders which place them at risk of psychosis. Additional research is needed to: (1) better understand the relationship between workplace factors and psychosis; and (2) develop more effective approaches for managing psychosis in the workplace and reduce its incidence.

           

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          Published in 5. Mental Health
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          Wednesday, 16 February 2011 17:49

          Work and Mental Health

          This chapter provides an overview of major types of mental health disorder that can be associated with work—mood and affective disorders (e.g., dissatisfaction), burnout, post-traumatic stress disorder (PTSD), psychoses, cognitive disorders and substance abuse. The clinical picture, available assessment techniques, aetiological agents and factors, and specific prevention and management measures will be provided. The relationship with work, occupation or branch of industry will be illustrated and discussed where possible.

          This introductory article first will provide a general perspective on occupational mental health itself. The concept of mental health will be elaborated upon, and a model will be presented. Next, we will discuss why attention should be paid to mental (ill) health and which occupational groups are at greatest risk. Finally, we will present a general intervention framework for successfully managing work-related mental health problems.

          What Is Mental Health: A Conceptual Model

          There are many different views about the components and processes of mental health. The concept is heavily value laden, and one definition is unlikely to be agreed upon. Like the strongly associated concept of “stress”, mental health is conceptualized as:

          • a state—for example, a state of total psychological and social well-being of an individual in a given sociocultural environment, indicative of positive moods and affects (e.g., pleasure, satisfaction and comfort) or negative ones (e.g., anxiety, depressive mood and dissatisfaction).
          • a process indicative of coping behaviour—for example, striving for independence, being autonomous (which are key aspects of mental health).
          • the outcome of a process—a chronic condition resulting either from an acute, intense confrontation with a stressor, such as is the case in a post-traumatic stress disorder, or from the continuing presence of a stressor which may not necessarily be intense. This is the case in burnout, as well as in psychoses, major depressive disorders, cognitive disorders and substance abuse. Cognitive disorders and substance abuse are, however, often considered as neurological problems, since pathophysiological processes (e.g., degeneration of the myelin sheath) resulting from ineffective coping or from the stressor itself (alcohol use or occupational exposition to solvents, respectively) can underlie these chronic conditions.

           

          Mental health may also be associated with:

          • Person characteristics like “coping styles”—competence (including effective coping, environmental mastery and self-efficacy) and aspiration are characteristic of a mentally healthy person, who shows interest in the environment, engages in motivational activity and seeks to extend him- or herself in ways that are personally significant.

          Thus, mental health is conceptualized not only as a process or outcome variable, but also as an independent variable—that is, as a personal characteristic that influences our behaviour.

          In figure 1 a mental health model is presented. Mental health is determined by environmental characteristics, both in and outside the work situation, and by characteristics of the individual. Major environmental job characteristics are elaborated upon in the chapter “Psychosocial and organizational factors”, but some points on these environmental precursors of mental (ill) health have to be made here as well.

          Figure 1. A model for mental health.

          MEN010F1

          There are many models, most of them stemming from the field of work and organizational psychology, that identify precursors of mental ill health. These precursors are often labelled “stressors”. Those models differ in their scope and, related to this, in the number of stressor dimensions identified. An example of a relatively simple model is that of Karasek (Karasek and Theorell 1990), describing only three dimensions: psychological demands, decision latitude (incorporating skill discretion and decision authority) and social support. A more elaborate model is that of Warr (1994), with nine dimensions: opportunity for control (decision authority), opportunity for skill use (skill discretion), externally generated goals (quantitative and qualitative demands), variety, environmental clarity (information about consequences of behaviour, availability of feedback, information about the future, information about required behaviour), availability of money, physical security (low physical risk, absence of danger), opportunity for interpersonal contact (prerequisite for social support), and valued social position (cultural and company evaluations of status, personal evaluations of significance). From the above it is clear that the precursors of mental (ill) health are generally psychosocial in nature, and are related to work content, as well as working conditions, conditions of employment and (formal and informal) relationships at work.

          Environmental risk factors for mental (ill) health generally result in short-term effects such as changes in mood and affect, like feelings of pleasure, enthusiasm or a depressed mood. These changes are often accompanied by changes in behaviour. We may think of restless behaviour, palliative coping (e.g., drinking) or avoiding, as well as active problem-solving behaviour. These affects and behaviours are generally accompanied by physiological changes as well, indicative of arousal and sometimes also of a disturbed homeostasis. When one or more of these stressors remains active, the short-term, reversible responses may result in more stable, less reversible mental health outcomes like burnout, psychoses or major depressive disorder. Situations that are extremely threatening may even immediately result in chronic mental health disorders (e.g., PTSD) which are difficult to reverse.

          Person characteristics may interact with psychosocial risk factors at work and exacerbate or buffer their effects. The (perceived) coping ability may not only moderate or mediate the effects of environmental risk factors, but may also determine the appraisal of the risk factors in the environment. Part of the effect of the environmental risk factors on mental health results from this appraisal process.

          Person characteristics (e.g., physical fitness) may not only act as precursors in the development of mental health, but may also change as a result of the effects. Coping ability may, for example, increase as the coping process progresses successfully (“learning”). Long-term mental health problems will, on the other hand, often reduce coping ability and capacity in the long run.

          In occupational mental health research, attention has been particularly directed to affective well-being—factors such as job satisfaction, depressive moods and anxiety. The more chronic mental health disorders, resulting from long-term exposure to stressors and to a greater or lesser extent also related to personality disorders, have a much lower prevalence in the working population. These chronic mental health problems have a multitude of causal factors. Occupational stressors will consequently be only partly responsible for the chronic condition. Also, people suffering from these kinds of chronic problem will have great difficulty in maintaining their position at work, and many are on sick leave or have dropped out of work for quite a long period of time (1 year), or even permanently. These chronic problems, therefore, are often studied from a clinical perspective.

          Since, in particular, affective moods and affects are so frequently studied in the occupational field, we will elaborate on them a little bit more. Affective well-being has been treated both in a rather undifferentiated way (ranging from feeling good to feeling bad), as well as by considering two dimensions: “pleasure” and “arousal” (figure 2). When variations in arousal are uncorrelated with pleasure, these variations alone are generally not considered to be an indicator of well-being.

          Figure 2. Three principal axes for the measurement of affective well-being.

          MEN010F2

          When, however, arousal and pleasure are correlated, four quadrants can be distinguished:

          1. Highly aroused and pleased indicates enthusiasm.
          2. Low aroused and pleased indicates comfort.
          3. Highly aroused and displeased indicates anxiety.
          4. Low aroused and displeased indicates depressed mood (Warr 1994).

           

          Well-being can be studied at two levels: a general, context-free level and a context-specific level. The work environment is such a specific context. Data analyses support the general notion that the relation between job characteristics and context-free, non-work mental health is mediated by an effect on work-related mental health. Work-related affective well-being has commonly been studied along the horizontal axis (Figure 2) in terms of job satisfaction. Affects related to comfort in particular have, however, largely been ignored. This is regrettable, since this affect might indicate resigned job satisfaction: people may not complain about their jobs, but may still be apathetic and uninvolved (Warr 1994).

          Why Pay Attention to Mental Health Issues?

          There are several reasons that illustrate the need for attention to mental health issues. First of all, national statistics of several countries indicate that a lot of people drop out of work because of mental health problems. In the Netherlands, for example, for one-third of those employees who are diagnosed as disabled for work each year, the problem is related to mental health. The majority of this category, 58%, is reported to be work related (Gründemann, Nijboer and Schellart 1991). Together with musculoskeletal problems, mental health problems account for about two-thirds of those who drop out for medical reasons each year.

          Mental ill health is an extensive problem in other countries as well. According to the Health and Safety Executive Booklet, it has been estimated that 30 to 40% of all sickness absence from work in the UK is attributable to some form of mental illness (Ross 1989; O’Leary 1993). In the UK, it has been estimated that one in five of the working population suffers each year from some form of mental illness. It is difficult to be precise about the number of working days lost each year because of mental ill health. For the UK, a figure of 90 million certified days—or 30 times that lost as a result of industrial disputes—is widely quoted (O’Leary 1993). This compares with 8 million days lost as a result of alcoholism and drink-related diseases and 35 million days as a result of coronary heart disease and strokes.

          Apart from the fact that mental ill health is costly, both in human and financial terms, there is a legal framework provided by the European Union (EU) in its framework directive on health and safety at work (89/391/EEC), enacted in 1993. Although mental health is not as such an element which is central to this directive, a certain amount of attention is given to this aspect of health in Article 6. The framework directive states, among other things, that the employer has:

          “a duty to ensure the safety and health of workers in every aspect related to work, following general principles of prevention: avoiding risks, evaluating the risks which cannot be avoided, combating the risks at source, adapting the work to the individual, especially as regards the design of workplaces, the choice of work equipment and the choice of work and production methods, with a view, in particular, to alleviating monotonous work and work at a predetermined work rate and to reduce their effects on health.”

          Despite this directive, not all European countries have adopted framework legislation on health and safety. In a study comparing regulations, policies and practices concerning mental health and stress at work in five European countries, those countries with such framework legislation (Sweden, the Netherlands and the UK) recognize mental health issues at work as important health and safety topics, whereas those countries which do not have such a framework (France, Germany) do not recognize mental health issues as important (Kompier et al. 1994).

          Last but not least, prevention of mental ill health (at its source) pays. There are strong indications that important benefits result from preventive programmes. For example, of the employers in a national representative sample of companies from three major branches of industry, 69% state that motivation increased; 60%, that absence due to sickness decreased ; 49%, that the atmosphere improved; and 40%, that productivity increased as a result of a prevention programme (Houtman et al. 1995).

          Occupational Risk Groups of Mental Health

          Are specific groups of the working population at risk of mental health problems? This question cannot be answered in a straightforward manner, since hardly any national or international monitoring systems exist which identify risk factors, mental health consequences or risk groups. Only a “scattergram” can be given. In some countries national data exist for the distribution of occupational groups with respect to major risk factors (e.g., for the Netherlands, Houtman and Kompier 1995; for the United States, Karasek and Theorell 1990). The distribution of the occupational groups in the Netherlands on the dimensions of job demands and skill discretion (figure 3) agree fairly well with the US distribution shown by Karasek and Theorell, for those groups that are in both samples. In those occupations with high work pace and/or low skill discretion, the risk of mental health disorders is highest.

          Figure 3. Risk for stress and mental ill health for different occupational groups, as determined by the combined effects of work pace and skill discretion.

          MEN010F3

          Also, in some countries there are data for mental health outcomes as related to occupational groups. Occupational groups that are especially prone to drop out for reasons of mental ill health in the Netherlands are those in the service sector, such as health care personnel and teachers, as well as cleaning personnel, housekeepers and occupations in the transport branch (Gründemann, Nijboer and Schellart1991).

          In the United States, occupations which were highly prone to major depressive disorder, as diagnosed with standardized coding systems (i.e., the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM III)) (American Psychiatric Association 1980), are juridicial employees, secretaries and teachers (Eaton et al. 1990). 

          Management of Mental Health Problems

          The conceptual model (figure 1) suggests at least two targets of intervention in mental health issues:

          1. The (work) environment.
          2. The person—either his or her characteristics or the mental health consequences.

          Primary prevention, the type of prevention that should prevent mental ill health from occurring, should be directed at the precursors by alleviating or managing the risks in the environment and increasing the coping ability and capacity of the individual. Secondary prevention is directed at the maintenance of people at work who already have some form of (mental) health problem. This type of prevention should embrace the primary prevention strategy, accompanied by strategies to make both employees and their supervisors sensitive to signals of early mental ill health in order to reduce the consequences or prevent them from getting worse. Tertiary prevention is directed at the rehabilitation of people who have dropped out of work due to mental health problems. This type of prevention should be directed at adapting the workplace to the possibilities of the individual (which is often found to be quite effective), along with individual counselling and treatment. Table 1 provides a schematic framework for the management of mental health disorders at the workplace. Effective preventive policy plans of organizations should, in principle, take into account all three types of strategy (primary, secondary and tertiary prevention), as well as be directed at risks, consequences and person characteristics.

          Table 1. A schematic overview of management strategies on mental health problems, and some examples.

          Type of
          prevention

          Intervention level
           

          Work environment

          Person characteristics and/or health outcomes

          Primary

          Redesign of task content

          Redesign of communication structure

          Training groups of employees on signalling and handling specific work- related problems (e.g., how to manage time pressure, robberies etc.)

          Secondary

          Introduction of a policy on how to act in case of absenteeism (e.g., training supervisors to discuss absence and return with employees concerned)

          Provide facilities within the organization, especially for risk groups (e.g., counsellor for sexual harassment)

          Training in relaxation techniques

          Tertiary

          Adaptation of an individual workplace

          Individual counselling

          Individual treatment or therapy (may also be with medication)

           

          The schedule as presented provides a method for systematic analysis of all possible types of measure. One can discuss whether a certain measure belongs somewhere else in the schedule; such a discussion is, however, not very fruitful, since it is often the case that primary preventive measures can work out positively for secondary prevention as well. The proposed systematic analysis may well result in a large number of potential measures, several of which may be adopted, either as a general aspect of the (health and safety) policy or in a specific case.

          In conclusion: Although mental health is not a clearly defined state, process or outcome, it covers a generally agreed upon area of (ill) health. Part of this area can be covered by generally accepted diagnostic criteria (e.g., psychosis, major depressive disorder); the diagnostic nature of other parts is neither as clear nor as generally accepted. Examples of the latter are moods and affects, and also burnout. Despite this, there are many indications that mental (ill) health, including the more vague diagnostic criteria, is a major problem. Its costs are high, both in human and financial terms. In the following articles of this chapter, several mental health disorders—moods and affects (e.g., dissatisfaction), burnout, post-traumatic stress disorder, psychoses, cognitive disorders and substance abuse—will be discussed in much more depth with respect to the clinical picture, available assessment techniques, aetiological agents and factors, and specific prevention and management measures.

           

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          Published in 5. Mental Health
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          Wednesday, 16 February 2011 01:28

          Types of Lamps and Lighting

          A lamp is an energy converter. Although it may carry out secondary functions, its prime purpose is the transformation of electrical energy into visible electromagnetic radiation. There are many ways to create light. The standard method for creating general lighting is the conversion of electrical energy into light.

          Types of Light

          Incandescence

          When solids and liquids are heated, they emit visible radiation at temperatures above 1,000 K; this is known as incandescence.

          Such heating is the basis of light generation in filament lamps: an electrical current passes through a thin tungsten wire, whose temperature rises to around 2,500 to 3,200 K, depending upon the type of lamp and its application.

          There is a limit to this method, which is described by Planck’s Law for the performance of a black body radiator, according to which the spectral distribution of energy radiated increases with temperature. At about 3,600 K and above, there is a marked gain in emission of visible radiation, and the wavelength of maximum power shifts into the visible band. This temperature is close to the melting point of tungsten, which is used for the filament, so the practical temperature limit is around 2,700 K, above which filament evaporation becomes excessive. One result of these spectral shifts is that a large part of the radiation emitted is not given off as light but as heat in the infrared region. Filament lamps can thus be effective heating devices and are used in lamps designed for print drying, food preparation and animal rearing.

          Electric discharge

          Electrical discharge is a technique used in modern light sources for commerce and industry because of the more efficient production of light. Some lamp types combine the electrical discharge with photoluminescence.

          An electric current passed through a gas will excite the atoms and molecules to emit radiation of a spectrum which is characteristic of the elements present. Two metals are commonly used, sodium and mercury, because their characteristics give useful radiations within the visible spectrum. Neither metal emits a continuous spectrum, and discharge lamps have selective spectra. Their colour rendering will never be identical to continuous spectra. Discharge lamps are often classed as high pressure or low pressure, although these terms are only relative, and a high-pressure sodium lamp operates at below one atmosphere.

          Types of Luminescence

          Photoluminescence occurs when radiation is absorbed by a solid and is then re-emitted at a different wavelength. When the re-emitted radiation is within the visible spectrum the process is called fluorescence or phosphorescence.

          Electroluminescence occurs when light is generated by an electric current passed through certain solids, such as phosphor materials. It is used for self-illuminated signs and instrument panels but has not proved to be a practical light source for the lighting of buildings or exteriors.

          Evolution of Electric Lamps

          Although technological progress has enabled different lamps to be produced, the main factors influencing their development have been external market forces. For example, the production of filament lamps in use at the start of this century was possible only after the availability of good vacuum pumps and the drawing of tungsten wire. However, it was the large-scale generation and distribution of electricity to meet the demand for electric lighting that determined market growth. Electric lighting offered many advantages over gas- or oil-generated light, such as steady light that requires infrequent maintenance as well as the increased safety of having no exposed flame, and no local by-products of combustion.

          During the period of recovery after the Second World War, the emphasis was on productivity. The fluorescent tubular lamp became the dominant light source because it made possible the shadow-free and comparatively heat-free lighting of factories and offices, allowing maximum use of the space. The light output and wattage requirements for a typical 1,500 mm fluorescent tubular lamp is given in table 1.

          Table 1. Improved light output and wattage requirements of some typical 1,500 mm fluorescent tube lamps

          Rating (W)

          Diameter (mm)

          Gas fill

          Light output (lumens)

          80

          38

          argon

          4,800

          65

          38

          argon

          4,900

          58

          25

          krypton

          5,100

          50

          25

          argon

          5,100
          (high frequency gear)

           

          By the 1970s oil prices rose and energy costs became a significant part of operating costs. Fluorescent lamps that produce the same amount of light with less electrical consumption were demanded by the market. Lamp design was refined in several ways. As the century closes there is a growing awareness of global environment issues. Better use of declining raw materials, recycling or safe disposal of products and the continuing concern over energy consumption (particularly energy generated from fossil fuels) are impacting on current lamp designs.

          Performance Criteria

          Performance criteria vary by application. In general, there is no particular hierarchy of importance of these criteria.

          Light output: The lumen output of a lamp will determine its suitability in relation to the scale of the installation and the quantity of illumination required.

          Colour appearance and colour rendering: Separate scales and numerical values apply to colour appearance and colour rendering. It is important to remember that the figures provide guidance only, and some are only approximations. Whenever possible, assessments of suitability should be made with actual lamps and with the colours or materials that apply to the situation.

          Lamp life: Most lamps will require replacement several times during the life of the lighting installation, and designers should minimize the inconvenience to the occupants of odd failures and maintenance. Lamps are used in a wide variety of applications. The anticipated average life is often a compromise between cost and performance. For example, the lamp for a slide projector will have a life of a few hundred hours because the maximum light output is important to the quality of the image. By contrast, some roadway lighting lamps may be changed every two years, and this represents some 8,000 burning hours.

          Further, lamp life is affected by operating conditions, and thus there is no simple figure that will apply in all conditions. Also, the effective lamp life may be determined by different failure modes. Physical failure such as filament or lamp rupture may be preceded by reduction in light output or changes in colour appearance. Lamp life is affected by external environmental conditions such as temperature, vibration, frequency of starting, supply voltage fluctuations, orientation and so on.

          It should be noted that the average life quoted for a lamp type is the time for 50% failures from a batch of test lamps. This definition of life is not likely to be applicable to many commercial or industrial installations; thus practical lamp life is usually less than published values, which should be used for comparison only.

          Efficiency: As a general rule the efficiency of a given type of lamp improves as the power rating increases, because most lamps have some fixed loss. However, different types of lamps have marked variation in efficiency. Lamps of the highest efficiency should be used, provided that the criteria of size, colour and lifetime are also met. Energy savings should not be at the expense of the visual comfort or the performance ability of the occupants. Some typical efficacies are given in table 2.

          Table 2. Typical lamp efficacies

          Lamp efficacies

          		  

          100 W filament lamp

          14 lumens/watt

          58 W fluorescent tube

          89 lumens/watt

          400 W high-pressure sodium

          125 lumens/watt

          131 W low-pressure sodium

          198 lumens/watt

           

          Main lamp types

          Over the years, several nomenclature systems have been developed by national and international standards and registers.

          In 1993, the International Electrotechnical Commission (IEC) published a new International Lamp Coding System (ILCOS) intended to replace existing national and regional coding systems. A list of some ILCOS short form codes for various lamps is given in table 3.

          Table 3. International Lamp Coding System (ILCOS) short form coding system for some lamp types

          Type (code)

          Common ratings (watts)

          Colour rendering

          Colour temperature (K)

          Life (hours)

          Compact fluorescent lamps (FS)

          5–55

          good

          2,700–5,000

          5,000–10,000

          High-pressure mercury lamps (QE)

          80–750

          fair

          3,300–3,800

          20,000

          High-pressure sodium lamps (S-)

          50–1,000

          poor to good

          2,000–2,500

          6,000–24,000

          Incandescent lamps (I)

          5–500

          good

          2,700

          1,000–3,000

          Induction lamps (XF)

          23–85

          good

          3,000–4,000

          10,000–60,000

          Low-pressure sodium lamps (LS)

          26–180

          monochromatic yellow colour

          1,800

          16,000

          Low-voltage tungsten halogen lamps (HS)

          12–100

          good

          3,000

          2,000–5,000

          Metal halide lamps (M-)

          35–2,000

          good to excellent

          3,000–5,000

          6,000–20,000

          Tubular fluorescent lamps (FD)

          4–100

          fair to good

          2,700–6,500

          10,000–15,000

          Tungsten halogen lamps (HS)

          100–2,000

          good

          3,000

          2,000–4,000

           

          Incandescent lamps

          These lamps use a tungsten filament in an inert gas or vacuum with a glass envelope. The inert gas suppresses tungsten evaporation and lessens the envelope blackening. There is a large variety of lamp shapes, which are largely decorative in appearance. The construction of a typical General Lighting Service (GLS) lamp is given in figure 1.

          Figure 1. Construction of a GLS lamp

          LIG010F1

          Incandescent lamps are also available with a wide range of colours and finishes. The ILCOS codes and some typical shapes include those shown in table 4.

          Table 4. Common colours and shapes of incandescent lamps, with their ILCOS codes

          Colour/Shape

          Code

          Clear

          /C

          Frosted

          /F

          White

          /W

          Red

          /R

          Blue

          /B

          Green

          /G

          Yellow

          /Y

          Pear shaped (GLS)

          IA

          Candle

          IB

          Conical

          IC

          Globular

          IG

          Mushroom

          IM

           

          Incandescent lamps are still popular for domestic lighting because of their low cost and compact size. However, for commercial and industrial lighting the low efficacy generates very high operating costs, so discharge lamps are the normal choice. A 100 W lamp has a typical efficacy of 14 lumens/watt compared with 96 lumens/watt for a 36 W fluorescent lamp.

          Incandescent lamps are simple to dim by reducing the supply voltage, and are still used where dimming is a desired control feature.

          The tungsten filament is a compact light source, easily focused by reflectors or lenses. Incandescent lamps are useful for display lighting where directional control is needed.

          Tungsten halogen lamps

          These are similar to incandescent lamps and produce light in the same manner from a tungsten filament. However the bulb contains halogen gas (bromine or iodine) which is active in controlling tungsten evaporation. See figure 2.

          Figure 2. The halogen cycle

          LIG010F2

          Fundamental to the halogen cycle is a minimum bulb wall temperature of 250 °C to ensure that the tungsten halide remains in a gaseous state and does not condense on the bulb wall. This temperature means bulbs made from quartz in place of glass. With quartz it is possible to reduce the bulb size.

          Most tungsten halogen lamps have an improved life over incandescent equivalents and the filament is at a higher temperature, creating more light and whiter colour.

          Tungsten halogen lamps have become popular where small size and high performance are the main requirement. Typical examples are stage lighting, including film and TV, where                                                                                                                                 directional control and dimming are common requirements.

          Low-voltage tungsten halogen lamps

          These were originally designed for slide and film projectors. At 12 V the filament for the same wattage as 230 V becomes smaller and thicker. This can be more efficiently focused, and the larger filament mass allows a higher operating temperature, increasing light output. The thick filament is more robust. These benefits were realized as being useful for the commercial display market, and even though it is necessary to have a step-down transformer, these lamps now dominate shop-window lighting. See figure 3.

          Figure 3. Low-voltage dichroic reflector lamp

          LIG010F3

          Although users of film projectors want as much light as possible, too much heat damages the transparency medium. A special type of reflector has been developed, which reflects only the visible radiation, allowing infrared radiation (heat) to pass through the back of lamp. This feature is now part of many low-voltage reflector lamps for display lighting as well as projector equipment.

           

           

           

          Voltage sensitivity: All filament lamps are sensitive to voltage variation, and light output and life are affected. The move to “harmonize” the supply voltage throughout Europe at 230 V is being achieved by widening the tolerances to which the generating authorities can operate. The move is towards ±10%, which is a voltage range of 207 to 253 V. Incandescent and tungsten halogen lamps cannot be operated sensibly over this range, so it will be necessary to match actual supply voltage to lamp ratings. See figure 4.

          Figure 4. GLS filament lamps and supply voltage

          LIG010F4

          Discharge lamps will also be affected by this wide voltage variation, so the correct specification of control gear becomes important.

           

           

           

           

           

           

           

          Tubular fluorescent lamps

          These are low pressure mercury lamps and are available as “hot cathode” and “cold cathode” versions. The former is the conventional fluorescent tube for offices and factories; “hot cathode” relates to the starting of the lamp by pre-heating the electrodes to create sufficient ionization of the gas and mercury vapour to establish the discharge.

          Cold cathode lamps are mainly used for signage and advertising. See figure 5.

          Figure 5. Principle of fluorescent lamp

          LIG010F5

          Fluorescent lamps require external control gear for starting and to control the lamp current. In addition to the small amount of mercury vapour, there is a starting gas (argon or krypton).

          The low pressure of mercury generates a discharge of pale blue light. The major part of the radiation is in the UV region at 254 nm, a characteristic radiation frequency for mercury. Inside of the tube wall is a thin phosphor coating, which absorbs the UV and radiates the energy as visible light. The colour quality of the light is determined by the phosphor coating. A range of phosphors are available of varying colour appearance and                                                                                                                               colour rendering.

          During the 1950s phosphors available offered a choice of reasonable efficacy (60 lumens/watt) with light deficient in reds and blues, or improved colour rendering from “deluxe” phosphors of lower efficiency (40 lumens/watt).

          By the 1970s new, narrow-band phosphors had been developed. These separately radiated red, blue and green light but, combined, produced white light. Adjusting the proportions gave a range of different colour appearances, all with similar excellent colour rendering. These tri-phosphors are more efficient than the earlier types and represent the best economic lighting solution, even though the lamps are more expensive. Improved efficacy reduces operating and installation costs.

          The tri-phosphor principle has been extended by multi-phosphor lamps where critical colour rendering is necessary, such as for art galleries and industrial colour matching.

          The modern narrow-band phosphors are more durable, have better lumen maintenance, and increase lamp life.

          Compact fluorescent lamps

          The fluorescent tube is not a practical replacement for the incandescent lamp because of its linear shape. Small, narrow-bore tubes can be configured to approximately the same size as the incandescent lamp, but this imposes a much higher electrical loading on the phosphor material. The use of tri-phosphors is essential to achieve acceptable lamp life. See figure 6.

          Figure 6. Four-leg compact fluorescent

          LIG010F6

          All compact fluorescent lamps use tri-phosphors, so, when they are used together with linear fluorescent lamps, the latter should also be tri-phosphor to ensure colour consistency.

          Some compact lamps include the operating control gear to form retro-fit devices for incandescent lamps. The range is increasing and enables easy upgrading of existing installations to more energy-efficient lighting. These integral units are not suitable for dimming where that was part of the original controls.

           

           

           

           

          High-frequency electronic control gear: If the normal supply frequency of 50 or 60 Hz is increased to 30 kHz, there is a 10% gain in efficacy of fluorescent tubes. Electronic circuits can operate individual lamps at such frequencies. The electronic circuit is designed to provide the same light output as wire-wound control gear, from reduced lamp power. This offers compatibility of lumen package with the advantage that reduced lamp loading will increase lamp life significantly. Electronic control gear is capable of operating over a range of supply voltages.

          There is no common standard for electronic control gear, and lamp performance may differ from the published information issued by the lamp makers.

          The use of high-frequency electronic gear removes the normal problem of flicker, to which some occupants may be sensitive.

          Induction lamps

          Lamps using the principle of induction have recently appeared on the market. They are low-pressure mercury lamps with tri-phosphor coating and as light producers are similar to fluorescent lamps. The energy is transferred to the lamp by high-frequency radiation, at approximately 2.5 MHz from an antenna positioned centrally within the lamp. There is no physical connection between the lamp bulb and the coil. Without electrodes or other wire connections the construction of the discharge vessel is simpler and more durable. Lamp life is mainly determined by the reliability of the electronic components and the lumen maintenance of the phosphor coating.

          High-pressure mercury lamps

          High-pressure discharges are more compact and have higher electrical loads; therefore, they require quartz arc tubes to withstand the pressure and temperature. The arc tube is contained in an outer glass envelope with a nitrogen or argon-nitrogen atmosphere to reduce oxidation and arcing. The bulb effectively filters the UV radiation from the arc tube. See figure 7.

          Figure 7. Mercury lamp construction

          LIG010F7

          At high pressure, the mercury discharge is mainly blue and green radiation. To improve the colour a phosphor coating of the outer bulb adds red light. There are deluxe versions with an increased red content, which give higher light output and improved colour rendering.

          All high-pressure discharge lamps take time to reach full output. The initial discharge is via the conducting gas fill, and the metal evaporates as the lamp temperature increases.

          At the stable pressure the lamp will not immediately restart without special control gear. There is a delay while the lamp                                                                                                                             cools sufficiently and the pressure reduces, so that the normal                                                                                                                         supply voltage or ignitor circuit is adequate to re-establish the                                                                                                                           arc.

          Discharge lamps have a negative resistance characteristic, and so the external control gear is necessary to control the current. There are losses due to these control gear components so the user should consider total watts when considering operating costs and electrical installation. There is an exception for high-pressure mercury lamps, and one type contains a tungsten filament which both acts as the current limiting device and adds warm colours to the blue/green discharge. This enables the direct replacement of incandescent lamps.

          Although mercury lamps have a long life of about 20,000 hours, the light output will fall to about 55% of the initial output at the end of this period, and therefore the economic life can be shorter.

          Metal halide lamps

          The colour and light output of mercury discharge lamps can be improved by adding different metals to the mercury arc. For each lamp the dose is small, and for accurate application it is more convenient to handle the metals in powder form as halides. This breaks down as the lamp warms up and releases the metal.

          A metal halide lamp can use a number of different metals, each of which give off a specific characteristic colour. These include:

          • dysprosium—broad blue-green
          • indium—narrow blue
          • lithium—narrow red
          • scandium—broad blue-green
          • sodium—narrow yellow
          • thallium—narrow green
          • tin—broad orange-red

           

          There is no standard mixture of metals, so metal halide lamps from different manufacturers may not be compatible in appearance or operating performance. For lamps with the lower wattage ratings, 35 to 150 W, there is closer physical and electrical compatibility with a common standard.

          Metal halide lamps require control gear, but the lack of compatibility means that it is necessary to match each combination of lamp and gear to ensure correct starting and running conditions.

          Low-pressure sodium lamps

          The arc tube is similar in size to the fluorescent tube but is made of special ply glass with an inner sodium resistant coating. The arc tube is formed in a narrow “U” shape and is contained in an outer vacuum jacket to ensure thermal stability. During starting, the lamps have a strong red glow from the neon gas fill.

          The characteristic radiation from low-pressure sodium vapour is a monochromatic yellow. This is close to the peak sensitivity of the human eye, and low-pressure sodium lamps are the most efficient lamps available at nearly 200 lumens/watt. However the applications are limited to where colour discrimination is of no visual importance, such as trunk roads and underpasses, and residential streets.

          In many situations these lamps are being replaced by high-pressure sodium lamps. Their smaller size offers better optical control, particularly for roadway lighting where there is growing concern over excessive sky glow.

          High-pressure sodium lamps

          These lamps are similar to high-pressure mercury lamps but offer better efficacy (over 100 lumens/watt) and excellent lumen maintenance. The reactive nature of sodium requires the arc tube to be manufactured from translucent polycrystalline alumina, as glass or quartz are unsuitable. The outer glass bulb contains a vacuum to prevent arcing and oxidation. There is no UV radiation from the sodium discharge so phosphor coatings are of no value. Some bulbs are frosted or coated to diffuse the light source. See figure 8.

          Figure 8. High-pressure sodium lamp construction

          LIG010F8

          As the sodium pressure is increased, the radiation becomes a broad band around the yellow peak, and the appearance is golden white. However, as the pressure increases, the efficiency decreases. There are currently three separate types of high-pressure sodium lamps available, as shown in table 5.

          Table 5. Types of high-pressure sodium lamp

          Lamp type (code)

          Colour (K)

          Efficacy (lumens/watt)

          Life (hours)

          Standard

          2,000

          110

          24,000

          Deluxe

          2,200

          80

          14,000

          White (SON)

          2,500

          50

          		  

           

          Generally the standard lamps are used for exterior lighting, deluxe lamps for industrial interiors, and White SON for commercial/display applications.

          Dimming of Discharge Lamps

          The high-pressure lamps cannot be satisfactorily dimmed, as changing the lamp power changes the pressure and thus the fundamental characteristics of the lamp.

          Fluorescent lamps can be dimmed using high-frequency supplies generated typically within the electronic control gear. The colour appearance remains very constant. In addition, the light output is approximately proportional to the lamp power, with consequent saving in electrical power when the light output is reduced. By integrating the light output from the lamp with the prevailing level of natural daylight, a near constant level of illuminance can be provided in an interior.

           

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          Published in 46. Lighting
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          Wednesday, 16 February 2011 01:25

          Indoor Air: Ionization

          Ionization is one of the techniques used to eliminate particulate matter from air. Ions act as condensation nuclei for small particles which, as they stick together, grow and precipitate.

          The concentration of ions in closed indoor spaces is, as a general rule and if there are no additional sources of ions, inferior to that of open spaces. Hence the belief that increasing the concentration of negative ions in indoor air improves air quality.

          Some studies based on epidemiological data and on planned experimental research assert that increasing the concentration of negative ions in work environments leads to improved worker efficiency and enhances the mood of employees, while positive ions have an adverse affect. However, parallel studies show that existing data on the effects of negative ionization on workers’ productivity are inconsistent and contradictory. Therefore, it seems that it is still not possible to assert unequivocally that the generation of negative ions is really beneficial.

          Natural Ionization

          Individual gas molecules in the atmosphere can ionize negatively by gaining, or positively by losing, an electron. For this to occur a given molecule must first gain enough energy—usually called the ionization energy of that particular molecule. Many sources of energy, both of cosmic and terrestrial origin, occur in nature that are capable of producing this phenomenon: background radiation in the atmosphere; electromagnetic solar waves (especially ultraviolet ones), cosmic rays, atomization of liquids such as the spray caused by waterfalls, the movement of great masses of air over the earth’s surface, electrical phenomena such as lightning and storms, the process of combustion and radioactive substances.

          The electrical configurations of the ions that are formed this way, while not completely known yet, seems to include the ions of carbonation and H+, H3O+, O+, N+, OH–, H2O– and O2–. These ionized molecules can aggregate through adsorption on suspended particles (fog, silica and other contaminants). Ions are classified according to their size and their mobility. The latter is defined as a velocity in an electrical field expressed as a unit such as centimetres per second by voltage per centimetre (cm/s/V/cm), or, more compactly,

          Atmospheric ions tend to disappear by recombination. Their half-life depends on their size and is inversely proportional to their mobility. Negative ions are statistically smaller and their half-life is of several minutes, while positive ions are larger and their half-life is about one half hour. The spatial charge is the quotient of the concentration of positive ions and the concentration of negative ions. The value of this relation is greater than one and depends on factors such as climate, location and season of the year. In living spaces this coefficient can have values that are lower than one. Characteristics are given in table 1.

          Table 1. Characteristics of ions of given mobilities and diameter

          Mobility (cm2/Vs)

          Diameter (mm)

          Characteristics

          3.0–0.1

          0.001–0.003

          Small, high mobility, short life

          0.1–0.005

          0.003–0.03

          Intermediate, slower than small ions

          0.005–0.002

          >0.03

          Slow ions, aggregates on particulate matter
          (ions of Langevin)

           

          Artificial Ionization

          Human activity modifies the natural ionization of air. Artificial ionization can be caused by industrial and nuclear processes and fires. Particulate matter suspended in air favours the formation of Langevin ions (ions aggregated on particulate matter). Electrical radiators increase the concentration of positive ions considerably. Air-conditioners also increase the spatial charge of indoor air.

          Workplaces have machinery that produces positive and negative ions simultaneously, as in the case of machines that are important local sources of mechanical energy (presses, spinning and weaving machines), electrical energy (motors, electronic printers, copiers, high-voltage lines and installations), electromagnetic energy (cathode-ray screens, televisions, computer monitors) or radioactive energy (cobalt-42 therapy). These kinds of equipment create environments with higher concentrations of positive ions due to the latter’s higher half-life as compared to negative ions.

          Environmental Concentrations of Ions

          Concentrations of ions vary with environmental and meteorological conditions. In areas with little pollution, such as in forests and mountains, or at great altitudes, the concentration of small ions grows; in areas close to radioactive sources, waterfalls, or river rapids the concentrations can reach thousands of small ions per cubic centimetre. In the proximity of the sea and when the levels of humidity are high, on the other hand, there is an excess of large ions. In general, the average concentration of negative and positive ions in clean air is 500 and 600 ions per cubic centimetre respectively.

          Some winds can carry great concentrations of positive ions—the Föhn in Switzerland, the Santa Ana in the United States, the Sirocco in North Africa, the Chinook in the Rocky Mountains and the Sharav in the Middle East.

          In workplaces where there are no significant ionizing factors there is often an accumulation of large ions. This is especially true, for example, in places that are hermetically sealed and in mines. The concentration of negative ions decreases significantly in indoor spaces and in contaminated areas or areas that are dusty. There are many reasons why the concentration of negative ions also decreases in indoor spaces that have air-conditioning systems. One reason is that negative ions remain trapped in air ducts and air filters or are attracted to surfaces that are positively charged. Cathode-ray screens and computer monitors, for example, are positively charged, creating in their immediate vicinity a microclimate deficient in negative ions. Air filtration systems designed for “clean rooms” that require that levels of contamination with particulate matter be kept at a very low minimum seem also to eliminate negative ions.

          On the other hand, an excess of humidity condenses ions, while a lack of it creates dry environments with large amounts of electrostatic charges. These electrostatic charges accumulate in plastic and synthetic fibres, both in the room and on people.

          Ion Generators

          Generators ionize air by delivering a large amount of energy. This energy may come from a source of alpha radiation (such as tritium) or from a source of electricity by the application of a high voltage to a sharply pointed electrode. Radioactive sources are forbidden in most countries because of the secondary problems of radioactivity.

          Electric generators are made of a pointed electrode surrounded by a crown; the electrode is supplied with a negative voltage of thousands of volts, and the crown is grounded. Negative ions are expelled while positive ions are attracted to the generator. The amount of negative ions generated increases in proportion to the voltage applied and to the number of electrodes that it contains. Generators that have a greater number of electrodes and use a lower voltage are safer, because when voltage exceeds 8,000 to 10,000 volts the generator will produce not only ions, but also ozone and some nitrous oxides. The dissemination of ions is achieved by electrostatic repulsion.

          The migration of ions will depend on the alignment of the magnetic field generated between the emission point and the objects that surround it. The concentration of ions surrounding the generators is not homogeneous and diminishes significantly as the distance from them increases. Fans installed in this equipment will increase the ionic dispersion zone. It is important to remember that the active elements of the generators need to be cleaned periodically to insure proper functioning.

          The generators may also be based on atomizing water, on thermoelectric effects or on ultraviolet rays. There are many different types and sizes of generators. They may be installed on ceilings and walls or may be placed anywhere if they are the small, portable type.

          Measuring Ions

          Ion measuring devices are made by placing two conductive plates 0.75 cm apart and applying a variable voltage. Collected ions are measured by a picoamperemeter and the intensity of the current is registered. Variable voltages permit the measurement of concentrations of ions with different mobilities. The concentration of ions (N) is calculated from the intensity of the electrical current generated using the following formula:

          where I is the current in amperes, V is the speed of the air flow, q is the charge of a univalent ion (1.6x10–19) in Coulombs and A is the effective area of the collector plates. It is assumed that all ions have a single charge and that they are all retained in the collector. It should be kept in mind that this method has its limitations due to background current and the influence of other factors such as humidity and fields of static electricity.

          The Effects of Ions on the Body

          Small negative ions are the ones which are supposed to have the greatest biological effect because of their greater mobility. High concentrations of negative ions can kill or block the growth of microscopic pathogens, but no adverse effects on humans have been described.

          Some studies suggest that exposure to high concentrations of negative ions produces biochemical and physiological changes in some people that have a relaxing effect, reduce tension and headaches, improve alertness and cut reaction time. These effects could be due to the suppression of the neural hormone serotonin (5-HT) and of histamine in environments loaded with negative ions; these factors could affect a hypersensitive segment of the population. However, other studies reach different conclusions on the effects of negative ions on the body. Therefore, the benefits of negative ionization are still open to debate and further study is needed before the matter is decided.

           

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          Published in 45. Indoor Environmental Control
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          Wednesday, 16 February 2011 01:06

          Heating and Air-Conditioning Systems

          With regard to heating, a given person’s needs will depend on many factors. They can be classified into two main groups, those related to the surroundings and those related to human factors. Among those related to the surroundings one might count geography (latitude and altitude), climate, the type of exposure of the space the person is in, or the barriers that protect the space against the external environment, etc. Among the human factors are the worker’s energy consumption, the pace of work or the amount of exertion needed for the job, the clothing or garments used against the cold and personal preferences or tastes.

          The need for heating is seasonal in many regions, but this does not mean that heating is dispensable during the cold season. Cold environmental conditions affect health, mental and physical efficiency, precision and occasionally may increase the risk of accidents. The goal of a heating system is to maintain pleasant thermal conditions that will prevent or minimize adverse health effects.

          The physiological characteristics of the human body allow it to withstand great variations in thermal conditions. Human beings maintain their thermal balance through the hypothalamus, by means of thermal receptors in the skin; body temperature is kept between 36 and 38°C as shown in figure 1.

          Figure 1. Thermoregulatory mechanisms in human beings

          IEN050F1

          Heating systems need to have very precise control mechanisms, especially in cases where workers carry out their tasks in a sitting or a fixed position that does not stimulate blood circulation to their extremities. Where the work performed allows a certain mobility, the control of the system may be somewhat less precise. Finally, where the work performed takes place in abnormally adverse conditions, as in refrigerated chambers or in very cold climatic conditions, support measures may be undertaken to protect special tissues, to regulate the time spent under those conditions or to supply heat by electrical systems incorporated into the worker’s garments.

          Definition and Description of the Thermal Environment

          A requirement that can be demanded of any properly functioning heating or air conditioning system is that it should allow for control of the variables that define the thermal environment, within specified limits, for each season of the year. These variables are

            1. air temperature
            2. average temperature of the inside surfaces that define the space
            3. air humidity
            4. speeds and uniformity of speeds of air flow within the space

                   

                  It has been shown that there is a very simple relation between the temperature of the air and of the wall surfaces of a given space, and the temperatures that provide the same perceived thermal sensation in a different room. This relation can be expressed as

                  where

                  Teat = equivalent air temperature for a given thermal sensation

                  Tdbt = air temperature measured with a dry bulb thermometer

                  Tast = measured average surface temperature of the walls.

                  For example, if in a given space the air and the walls are at 20° C, the equivalent temperature will be 20°C, and the perceived sensation of heat will be the same as in a room where the average temperature of the walls is 15°C and the air temperature is 25°C, because that room would have the same equivalent temperature. From the standpoint of temperature, the perceived sensation of thermal comfort would be the same.

                  Properties of humid air

                  In implementing an air-conditioning plan, three things that must be taken into consideration are the thermodynamic state of the air in the given space, of the air outside, and of the air that will be supplied to the room. The selection of a system capable of transforming the thermodynamic properties of the air supplied to the room will then be based on the existing thermal loads of each component. We therefore need to know the thermodynamic properties of humid air. They are as follows:

                  Tdbt = the dry bulb temperature reading, measured with a thermometer insulated from radiated heat

                  Tdpt = the dew point temperature reading. This is the temperature at which nonsaturated dry air reaches the saturation point

                  W = a humidity relation that ranges from zero for dry air to Ws for saturated air. It is expressed as kg of water vapour by kg of dry air

                  RH = relative humidity

                  t* = thermodynamic temperature with moist bulb

                  v = specific volume of air and water vapour (expressed in units of m3/kg). It is the inverse of density

                  H = enthalpy, kcal/kg of dry air and associated water vapour.

                  Of the above variables, only three are directly measurable. They are the dry bulb temperature reading, the dew point temperature reading and relative humidity. There is a fourth variable that is experimentally measurable, defined as the wet bulb temperature. The wet bulb temperature is measured with a thermometer whose bulb has been moistened and which is moved, typically with the aid of a sling, through nonsaturated moist air at a moderate speed. This variable differs by an insignificant amount from the thermodynamic temperature with a dry bulb (3 per cent), so they can both be used for calculations without erring too much.

                  Psychrometric diagram

                  The properties defined in the previous section are functionally related and can be portrayed in graphic form. This graphic representation is called a psychrometric diagram. It is a simplified graph derived from tables of the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). Enthalpy and the degree of humidity are shown on the coordinates of the diagram; the lines drawn show dry and humid temperatures, relative humidity and specific volume. With the psychrometric diagram, knowing any two of the aforementioned variables enables you to derive all the properties of humid air.

                  Conditions for thermal comfort

                  Thermal comfort is defined as a state of mind that expresses satisfaction with the thermal environment. It is influenced by physical and physiological factors.

                  It is difficult to prescribe general conditions that should be met for thermal comfort because conditions differ in various work situations; different conditions could even be required for the same work post when it is occupied by different people. A technical norm for thermal conditions required for comfort cannot be applied to all countries because of the different climatic conditions and their different customs governing dress.

                  Studies have been carried out with workers that do light manual labour, establishing a series of criteria for temperature, speed and humidity that are shown in table 1 (Bedford and Chrenko 1974).

                  Table 1. Proposed norms for environmental factors

                  Environmental factor

                  Proposed norm

                  Air temperature

                  21 °C

                  Average radiant temperature

                  ≥ 21 °C

                  Relative humidity

                  30–70%

                  Speed of air flow

                  0.05–0.1 metre/second

                  Temperature gradient (from head to foot)

                  ≤ 2.5 °C

                   

                  The above factors are interrelated, requiring a lower air temperature in cases where there is high thermal radiation and requiring a higher air temperature when the speed of the air flow is also higher.

                  Generally, the corrections that should be carried out are the following:

                  The air temperature should be increased:

                  • if the speed of the air flow is high
                  • for sedentary work situations
                  • if clothing used is light
                  • when people must be acclimatized to high indoor temperatures.

                   

                  The air temperature should be decreased:

                  • if the work involves heavy manual labour
                  • when warm clothing is used.

                   

                  For a good sensation of thermal comfort the most desirable situation is one where the temperature of the environment is slightly higher than the temperature of the air, and where the flow of radiating thermal energy is the same in all directions and is not excessive overhead. The increase in temperature by height should be minimized, keeping feet warm without creating too much of a thermal load overhead. An important factor that has a bearing on the sensation of thermal comfort is the speed of the air flow. There are diagrams that give recommended air speeds as a function of the activity that is being carried out and the kind of clothing used (figure 2).

                  Figure 2. Comfort zones based on readings of overall temperatures and speed of air currents

                  IEN050F3

                  In some countries there are norms for minimal environmental temperatures, but optimal values have not yet been established. Typically, the maximum value for air temperature is given as 20°C. With recent technical improvements, the complexity of measuring thermal comfort has increased. Many indexes have appeared, including the index of effective temperature (ET) and the index of effective temperature, corrected (CET); the index of caloric overload; the Heat Stress Index (HSI); the wet bulb globe temperature (WBGT); and the Fanger index of median values (IMV), among others. The WBGT index allows us to determine the intervals of rest required as a function of the intensity of the work performed so as to preclude thermal stress under working conditions. This is discussed more fully in the chapter Heat and Cold.

                  Thermal comfort zone in a psychrometric diagram

                  The range on the psychrometric diagram corresponding to conditions under which an adult perceives thermal comfort has been carefully studied and has been defined in the ASHRAE norm based on the effective temperature, defined as the temperature measured with a dry bulb thermometer in a uniform room with 50 per cent relative humidity, where people would have the same interchange of heat by radiant energy, convection and evaporation as they would with the level of humidity in the given local environment. The scale of effective temperature is defined by ASHRAE for a level of clothing of 0.6 clo—clo is a unit of insulation; 1 clo corresponds to the insulation provided by a normal set of clothes—that assumes a level of thermal insulation of 0.155 K m2W–1, where K is the exchange of heat by conduction measured in Watts per square metre (W m–2) for a movement of air of 0.2 m s–1 (at rest), for an exposure of one hour at a chosen sedentary activity of 1 met (unit of metabolic rate=50 Kcal/m2h). This comfort zone is seen in figure 2 and can be used for thermal environments where the measured temperature from radiant heat is approximately the same as the temperature measured by a dry bulb thermometer, and where the speed of air flow is below 0.2 m s–1 for people dressed in light clothing and carrying out sedentary activities.

                  Comfort formula: The Fanger method

                  The method developed by PO Fanger is based on a formula that relates variables of ambient temperature, average radiant temperature, relative speed of air flow, pressure of water vapour in ambient air, level of activity and thermal resistance of the clothing worn. An example derived from the comfort formula is shown in table 2, which can be used in practical applications for obtaining a comfortable temperature as a function of the clothing worn, the metabolic rate of the activity carried out and the speed of the air flow.

                  Table 2. Temperatures of thermal comfort (°C), at 50% relative humidity (based on the formula by PO Fanger)

                  Metabolism (Watts)

                  105

                  Radiating temperature

                  clo

                  20 °C

                  25 °C

                  30 °C

                  Clothing (clo)
                  0.5 Va /(m.sg–1)


                  0.2


                  30.7


                  27.5


                  24.3
                   

                  0.5

                  30.5

                  29.0

                  27.0
                   

                  1.5

                  30.6

                  29.5

                  28.3

                  Clothing (clo)
                  0.5 Va /(m.sg–1)


                  0.2


                  26.0


                  23.0


                  20.0
                   

                  0.5

                  26.7

                  24.3

                  22.7
                   

                  1.5

                  27.0

                  25.7

                  24.5

                  Metabolism (Watts)

                  157

                  Radiating temperature

                  clo

                  20 °C

                  25 °C

                  30 °C

                  Clothing (clo)
                  0.5 Va /(m.sg–1)


                  0.2


                  21.0


                  17.1


                  14.0
                   

                  0.5

                  23.0

                  20.7

                  18.3
                   

                  1.5

                  23.5

                  23.3

                  22.0

                  Clothing (clo)
                  0.5 Va /(m.sg–1)


                  0.2


                  13.3


                  10.0


                  6.5
                   

                  0.5

                  16.0

                  14.0

                  11.5
                   

                  1.5

                  18.3

                  17.0

                  15.7

                  Metabolism (Watts)

                  210

                  Radiating temperature

                  clo

                  20 °C

                  25 °C

                  30 °C

                  Clothing (clo)
                  0.5 Va /(m.sg–1)


                  0.2


                  11.0


                  8.0


                  4.0
                   

                  0.5

                  15.0

                  13.0

                  7.4
                   

                  1.5

                  18.3

                  17.0

                  16.0

                  Clothing (clo)
                  0.5 Va /(m.sg–1)


                  0.2


                  –7.0


                  /


                  /
                   

                  0.5

                  –1.5

                  –3.0

                  /
                   

                  1.5

                  –5.0

                  2.0

                  1.0

                   

                  Heating Systems

                  The design of any heating system should be directly related to the work to be performed and the characteristics of the building where it will be installed. It is hard to find, in the case of industrial buildings, projects where the heating needs of the workers are considered, often because the processes and workstations have yet to be defined. Normally systems are designed with a very free range, considering only the thermal loads that will exist in the building and the amount of heat that needs to be supplied to maintain a given temperature within the building, without regard to heat distribution, the situation of workstations and other similarly less general factors. This leads to deficiencies in the design of certain buildings that translate into shortcomings like cold spots, draughts, an insufficient number of heating elements and other problems.

                  To end up with a good heating system in planning a building, the following are some of the considerations that should be addressed:

                  • Consider the proper placement of insulation to save energy and to minimize temperature gradients within the building.
                  • Reduce as much as possible the infiltration of cold air into the building to minimize temperature variations in the work areas.
                  • Control air pollution through localized extraction of air and ventilation by displacement or diffusion.
                  • Control the emissions of heat due to the processes used in the building and their distribution in occupied areas of the building.

                   

                  When heating is provided by burners without exhaust chimneys, special consideration should be given to the inhalation of the products of combustion. Normally, when the combustible materials are heating oil, gas or coke, they produce sulphur dioxide, nitrogen oxides, carbon monoxide and other combustion products. There exist human exposure limits for these compounds and they should be controlled, especially in closed spaces where the concentration of these gases can increase rapidly and the efficiency of the combustion reaction can decrease.

                  Planning a heating system always entails balancing various considerations, such as a low initial cost, flexibility of the service, energy efficiency and applicability. Therefore, the use of electricity during off-peak hours when it might be cheaper, for example, could make electric heaters cost-effective. The use of chemical systems for heat storage that can then be put to use during peak demand (using sodium sulphide, for example) is another option. It is also possible to study the placement of several different systems together, making them work in such a way that costs can be optimized.

                  The installation of heaters that are capable of using gas or heating oil is especially interesting. The direct use of electricity means consuming first-class energy that may turn out to be costly in many cases, but that may afford the needed flexibility under certain circumstances. Heat pumps and other cogeneration systems that take advantage of residual heat can afford solutions that may be very advantageous from the financial point of view. The problem with these systems is their high initial cost.

                  Today the tendency of heating and air conditioning systems is to aim to deliver optimal functioning and energy savings. New systems therefore include sensors and controls distributed throughout the spaces to be heated, obtaining a supply of heat only during the times necessary to obtain thermal comfort. These systems can save up to 30% of the energy costs of heating. Figure 3 shows some of the heating systems available, indicating their positive characteristics and their drawbacks.

                  Figure 3. Characteristics of the most common heating systems employed in worksites

                  IEN050F7

                  Air-conditioning systems

                  Experience shows that industrial environments that are close to the comfort zone during summer months increase productivity, tend to register fewer accidents, have lower absenteeism and, in general, contribute to improved human relations. In the case of retail establishments, hospitals and buildings with large surfaces, air conditioning usually needs to be directed to be able to provide thermal comfort when outside conditions require it.

                  In certain industrial environments where external conditions are very severe, the goal of heating systems is geared more to providing enough heat to prevent possible adverse health effects than to providing enough heat for a comfortable thermal environment. Factors that should be carefully monitored are the maintenance and proper use of the air-conditioning equipment, especially when equipped with humidifiers, because they can become sources of microbial contamination with the risks that these contaminants may pose to human health.

                  Today ventilation and climate-control systems tend to cover, jointly and often using the same installation, the needs for heating, refrigerating and conditioning the air of a building. Multiple classifications may be used for refrigerating systems.

                  Depending on the configuration of the system they may be classified in the following way:

                  • Hermetically sealed units, with refrigerating fluid installed at the factory, that can be opened and recharged in a repair shop. These are air-conditioning units normally used in offices, dwellings and the like.
                  • Semi-hermetic units of medium size, factory made, that are of larger size than home units and that can be repaired through openings designed for that purpose.
                  • Segmented systems for warehouses and large surfaces, which consist of parts and components that are clearly differentiated and physically separate (the compressor and the condenser are physically separate from the evaporator and the expansion valve). They are used for large office buildings, hotels, hospitals, large factories and industrial buildings.

                   

                  Depending on the coverage they provide, they can be classified in the following way:

                  • Systems for a single zone: one air treatment unit serves various rooms in the same building and at the same time. The rooms served have similar heating, refrigeration and ventilation needs and they are regulated by a common control (a thermostat or similar device). Systems of this type can end up being unable to supply an adequate level of comfort to each room if the design plan did not take into consideration the different thermal loads between rooms in the same zone. This may happen when there is an increase in the occupancy of a room or when lighting or other heat sources are added, like computers or copying machines, that were unforeseen during the original design of the system. Discomfort may also occur because of seasonal changes in the amount of solar radiation a room receives, or even because of the changes from one room to the next during the day.
                  • Systems for multiple zones: systems of this type can provide different zones with air at different temperatures and humidities by heating, cooling, humidifying or dehumidifying air in each zone and by varying the flow of air. These systems, even if they generally have a common and centralized air cooling unit (compressor, evaporator, etc.), are equipped with a variety of elements, such as devices that control the flow of air, heating coils and humidifiers. These systems are capable of adjusting the conditions of a room based on specific thermal loads, which they detect by means of sensors distributed in the rooms throughout the area they serve.
                  • Depending on the flow of air that these systems pump into the building they are classified in the following way:
                  • Constant volume (CV): these systems pump a constant flow of air into each room. Temperature changes are effected by heating or cooling the air. These systems frequently mix a percentage of outside air with recycled indoor air.
                  • Variable volume (VAV): these systems maintain thermal comfort by varying the amount of heated or cooled air supplied to each space. Even though they function primarily based on this mixing principle, they can also be combined with systems that change the temperature of the air they introduce into the room.

                   

                  The problems that most frequently plague these types of systems are excess heating or cooling if the system is not adjusted to respond to variations in thermal loads, or a lack of ventilation if the system does not introduce a minimal amount of outside air to renew the circulating indoor air. This creates stale indoor environments in which the quality of air deteriorates.

                  The basic elements of all air-conditioning systems are (see also figure 4):

                  • Units to retain solid matter, usually bag filters or electrostatic precipitators.
                  • Air heating or cooling units: heat is exchanged in these units by thermal exchange with cold water or refrigerating liquids, by forced ventilation in the summer and by heating with electrical coils or by combustion in the winter.
                  • Units to control humidity: in winter humidity can be added by directly injecting water vapour or by direct water evaporation; in the summer it can be removed by refrigerated coils that condense excess humidity in the air, or by a refrigerated water system in which moist air flows through a curtain of drops of water that is colder than the dew point of the moist air.

                   

                  Figure 4. Simplified schematic of air-conditioning system

                  IEN050F8

                   

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                  Published in 45. Indoor Environmental Control
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                  Wednesday, 16 February 2011 00:58

                  Ventilation Criteria for Nonindustrial Buildings

                  One of the chief functions of a building in which nonindustrial activities are carried out (offices, schools, dwellings, etc.) is to provide the occupants with a healthy and comfortable environment in which to work. The quality of this environment depends, to a large degree, on whether the ventilation and climatization systems of the building are adequately designed and maintained and function properly.

                  These systems must therefore provide acceptable thermal conditions (temperature and humidity) and an acceptable quality of indoor air. In other words, they should aim for a suitable mix of outside air with indoor air and should employ filtration and cleaning systems capable of eliminating pollutants found in the indoor environment.

                  The idea that clean outdoor air is necessary for well-being in indoor spaces has been expressed since the eighteenth century. Benjamin Franklin recognized that air in a room is healthier if it is provided with natural ventilation by opening the windows. The idea that providing great quantities of outside air could help reduce the risk of contagion for illnesses like tuberculosis gained currency in the nineteenth century.

                  Studies carried out during the 1930s showed that, in order to dilute human biological effluvia to concentrations that would not cause discomfort due to odours, the volume of new outside air required for a room is between 17 and 30 cubic metres per hour per occupant.

                  In standard No. 62 set in 1973, the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) recommends a minimum flow of 34 cubic metres of outside air per hour per occupant to control odours. An absolute minimum of 8.5 m3/hr/occupant is recommended to prevent carbon dioxide from surpassing 2,500 ppm, which is half of the exposure limit set for industrial settings.

                  This same organization, in standard No. 90, set in 1975—in the middle of an energy crisis—adopted the aforementioned absolute minimum leaving aside, temporarily, the need for greater ventilation flows to dilute pollutants such as tobacco smoke, biological effluvia and so forth.

                  In its standard No. 62 (1981) ASHRAE rectified this omission and established its recommendation as 34 m3/hr/occupant for areas where smoking is permitted and 8.5 m3/hr/occupant in areas where smoking is forbidden.

                  The last standard published by ASHRAE, also No. 62 (1989), established a minimum of 25.5 m3/hr/occupant for occupied indoor spaces independently of whether smoking is permitted or not. It also recommends increasing this value when the air brought into the building is not mixed adequately in the breathing zone or if there are unusual sources of pollution present in the building.

                  In 1992, the Commission of European Communities published its Guidelines for Ventilation Requirements in Buildings. In contrast with existing recommendations for ventilation standards, this guide does not specify volumes of ventilation flow that should be provided for a given space; instead, it provides recommendations that are calculated as a function of the desired quality of indoor air.

                  Existing ventilation standards prescribe set volumes of ventilation flow that should be supplied per occupant. The tendencies evidenced in the new guidelines show that volume calculations alone do not guarantee a good quality of indoor air for every setting. This is the case for three fundamental reasons.

                  First, they assume that occupants are the only sources of contamination. Recent studies show that other sources of pollution, in addition to the occupants, should be taken into consideration as possible sources of pollution. Examples include furniture, upholstery and the ventilation system itself. The second reason is that these standards recommend the same amount of outside air regardless of the quality of air that is being conveyed into the building. And the third reason is that they do not clearly define the quality of indoor air required for the given space. Therefore, it is proposed that future ventilation standards should be based on the following three premises: the selection of a defined category of air quality for the space to be ventilated, the total load of pollutants in the occupied space and the quality of outside air available.

                  The Perceived Quality of Air

                  The quality of indoor air can be defined as the degree to which the demands and requirements of the human being are met. Basically, the occupants of a space demand two things of the air they breathe: to perceive the air they breathe as fresh and not foul, stale or irritating; and to know that the adverse health effects that may result from breathing that air are negligible.

                  It is common to think that the degree of quality of the air in a space depends more on the components of that air than on the impact of that air on the occupants. It may thus seem easy to evaluate the quality of the air, assuming that by knowing its composition its quality can be ascertained. This method of evaluating air quality works well in industrial settings, where we find chemical compounds that are implicated in or derived from the production process and where measuring devices and reference criteria to assess the concentrations exist. This method does not, however, work in nonindustrial settings. Nonindustrial settings are places where thousands of chemical substances can be found, but at very low concentrations, sometimes a thousand times lower than the recommended exposure limits; evaluating these substances one by one would result in a false assessment of the quality of that air, and the air would likely be judged to be of a high quality. But there is a missing aspect that remains to be considered, and that is the lack of knowledge that exists about the combined effect of those thousands of substances on human beings, and that may be the reason why that air is perceived as being foul, stale or irritating.

                  The conclusion that has been reached is that traditional methods used for industrial hygiene are not well-adapted to define the degree of quality that will be perceived by the human beings that breathe the air being evaluated. The alternative to chemical analysis is to use people as measuring devices to quantify air pollution, employing panels of judges to make the evaluations.

                  Human beings perceive the quality of air by two senses: the olfactory sense, situated in the nasal cavity and sensitive to hundreds of thousands of odorous substances, and the chemical sense, situated in the mucous membranes of the nose and eyes, and sensitive to a similar number of irritating substances present in air. It is the combined response of these two senses that determines how air is perceived and that allows the subject to judge whether its quality is acceptable.

                  The olf unit

                  One olf (from Latin = olfactus) is the emission rate of air pollutants (bioeffluents) from a standard person. One standard person is an average adult who works in an office or in a similar nonindustrial workplace, sedentary and in thermal comfort with a hygienic standard equipment to 0.7 bath/day. Pollution from a human being was chosen to define the term olf for two reasons: the first is that biological effluvia emitted by a person are well-known, and the second is that there was much data on the dissatisfaction caused by such biological effluvia.

                  Any other source of contamination can be expressed as the number of standard persons (olfs) needed to cause the same amount of dissatisfaction as the source of contamination that is being evaluated.

                  Figure 1 depicts a curve that defines an olf. This curve shows how contamination produced by a standard person (1 olf) is perceived at different rates of ventilation, and allows the calculation of the rate of dissatisfied individuals—in other words, those that will perceive the quality of air to be unacceptable just after they have entered the room. The curve is based on different European studies in which 168 people judged the quality of air polluted by over a thousand people, both men and women, considered to be standard. Similar studies conducted in North America and Japan show a high degree of correlation with the European data.

                  Figure 1. Olf definition curve

                  IEN040F1

                  The decipol unit

                  The concentration of pollution in air depends on the source of contamination and its dilution as a result of ventilation. Perceived air pollution is defined as the concentration of human biological effluvia that would cause the same discomfort or dissatisfaction as the concentration of polluted air that is being evaluated. One decipol (from the Latin pollutio) is the contamination caused by a standard person (1 olf) when the rate of ventilation is 10 litres per second of noncontaminated air, so that we may write

                  1 decipol = 0.1 olf/(litre/second)

                  Figure 2, derived from the same data as the previous figure, shows the relation between the perceived quality of air, expressed as a percentage of dissatisfied individuals and in decipols.

                  Figure 2. Relation between the perceived quality of air expressed as a percentage of dissatisfied individuals and in decipols

                  IEN040F2

                  To determine the rate of ventilation required from the point of view of comfort, selecting the degree of air quality desired in the given space is essential. Three categories or levels of quality are proposed in Table 1, and they are derived from Figures 1 and 2. Each level corresponds to a certain percentage of dissatisfied people. The selection of one or another level will depend, most of all, on what the space will be used for and on economic considerations.

                  Table 1. Levels of quality of indoor air

                  Perceived air quality

                  Category
                  (quality level)

                  Percentage of dissatisfied
                  individuals

                  Decipols

                  Rate of ventilation required1
                  litres/second × olf

                  A

                  10

                  0.6

                  16

                  B

                  20

                  1.4

                  7

                  C

                  30

                  2.5

                  4

                  1 Assuming that outside air is clean and the efficiency of the ventilation system is equal to one.

                  Source: CEC 1992.

                   

                  As noted above, the data are the result of experiments carried out with panels of judges, but it is important to keep in mind that some of the substances found in air that can be dangerous (carcinogenic compounds, micro-organisms and radioactive substances, for example) are not recognized by the senses, and that the sensory effects of other contaminants bear no quantitative relationship to their toxicity.

                  Sources of Contamination

                  As was indicated earlier, one of the shortcomings of today’s ventilation standards is that they take into account only the occupants as the sources of contamination, whereas it is recognized that future standards should take all the possible sources of pollution into account. Aside from the occupants and their activities, including the possibility that they might smoke, there are other sources of pollution that contribute significantly to air pollution. Examples include furniture, upholstery and carpeting, construction materials, products used for decoration, cleaning products and the ventilation system itself.

                  What determines the load of pollution of air in a given space is the combination of all these sources of contamination. This load can be expressed as chemical contamination or as sensory contamination expressed in olfs. The latter integrates the effect of several chemical substances as they are perceived by human beings.

                  The chemical load

                  Contamination that emanates from a given material can be expressed as the rate of emission of each chemical substance. The total load of chemical pollution is calculated by adding all the sources, and is expressed in micrograms per second (μg/s).

                  In reality, it may be difficult to calculate the load of pollution because often little data are available on the rates of emission for many commonly used materials.

                  Sensory load

                  The load of pollution perceived by the senses is caused by those sources of contamination that have an impact on the perceived quality of air. The given value of this sensory load can be calculated by adding all the olfs of different sources of contamination that exist in a given space. As in the previous case, there is still not much information available on the olfs per square metre (olfs/m2) of many materials. For that reason it turns out to be more practical to estimate the sensory load of the entire building, including the occupants, the furnishings and the ventilation system.

                  Table 2 shows the pollution load in olfs by the occupants of the building as they carry out different types of activities, as a proportion of those who smoke and don’t smoke, and the production of various compounds like carbon dioxide (CO2), carbon monoxide (CO) and water vapour. Table 3 shows some examples of the typical occupancy rates in different kinds of spaces. And last, table 4 reflects the results of the sensory load—measured in olfs per square metre—found in different buildings.

                  Table 2. Contamination due to the occupants of a building

                   

                  Sensory load olf/occupant

                  CO2  
                                     (l/(hr × occupant))

                  CO3   
                                     (l/(hr × occupant))

                  Water vapour4
                  (g/(hr × occupant))

                  Sedentary, 1-1.2 met1

                  0% smokers

                  2

                  19

                  		  

                  50

                  20% smokers2

                  2

                  19

                  11x10-3

                  50

                  40% smokers2

                  3

                  19

                  21x10-3

                  50

                  100% smokers2

                  6

                  19

                  53x10-3

                  50

                  Physical exertion

                  Low, 3 met

                  4

                  50

                  		  

                  200

                  Medium, 6 met

                  10

                  100

                  		  

                  430

                  High (athletic),
                  10 met

                  20

                  170

                  		  

                  750

                  Children

                  Child care centre
                  (3–6 years),
                  2.7 met

                  1.2

                  18

                  		  

                  90

                  School
                  (14–16 years),
                  1.2 met

                  1.3

                  19

                  		  

                  50

                  1 1 met is the metabolic rate of a sedentary person at rest (1 met = 58 W/m2 of skin surface).
                  2 Average consumption of 1.2 cigarettes/hour per smoker. Average rate of emission, 44 ml of CO per cigarette.
                  3 From tobacco smoke.
                  4 Applicable to people close to thermal neutrality.

                  Source: CEC 1992.

                   

                  Table 3. Examples of the degree of occupancy of  different buildings

                  Building

                  Occupants/m2

                  Offices

                  0.07

                  Conference rooms

                  0.5

                  Theatres, other large gathering places

                  1.5

                  Schools (classrooms)

                  0.5

                  Child-care centres

                  0.5

                  Dwellings

                  0.05

                  Source: CEC 1992.

                   

                  Table 4. Contamination due to the building

                   

                  Sensory load—olf/m2
                   

                  Average

                  Interval

                  Offices1

                  0.3

                  0.02–0.95

                  Schools (classrooms)2

                  0.3

                  0.12–0.54

                  Child care facilities3

                  0.4

                  0.20–0.74

                  Theatres4

                  0.5

                  0.13–1.32

                  Low-pollution buildings5

                  		  

                  0.05–0.1

                  1 Data obtained in 24 mechanically ventilated offices.
                  2 Data obtained in 6 mechanically ventilated schools.
                  3 Data obtained in 9 mechanically ventilated child-care centres.
                  4 Data obtained in 5 mechanically ventilated theatres.
                  5 Goal that should be reached by new buildings.

                  Source: CEC 1992.

                   

                  Quality of Outside Air

                  Another premise, one that rounds out the inputs needed for creation of ventilation standards for the future, is the quality of available outside air. Recommended exposure values for certain substances, both from inside and outside spaces, appear in the publication Air Quality Guidelines for Europe by the WHO (1987).

                  Table 5 shows the levels of perceived outside air quality, as well as the concentrations of several typical chemical pollutants found out of doors.

                  Table 5. Quality levels of outside air

                   

                  Perceived
                  air quality                  1

                  Environmental pollutants2
                   

                  Decipol

                  CO2 (mg/m3)

                  CO (mg/m3)

                  NO2 (mg/m3)

                  SO2 (mg/m3)

                  By the sea, in the  mountains

                  0

                  680

                  0-0.2

                  2

                  1

                  City, high quality

                  0.1

                  700

                  1-2

                  5-20

                  5-20

                  City, low quality

                  >0.5

                  700-800

                  4-6

                  50-80

                  50-100

                  1 The values of perceived air quality are daily average values.
                  2 The values of pollutants correspond to average yearly concentrations.

                  Source: CEC 1992.

                   

                  It should be kept in mind that in many cases the quality of outside air can be worse than the levels indicated in the table or in the guidelines of the WHO. In such cases air needs to be cleaned before it is conveyed into occupied spaces.

                  Efficiency of Ventilation Systems

                  Another important factor that will affect the calculation of the ventilation requirements for a given space is the efficiency of ventilation (Ev), which is defined as the relation between the concentration of pollutants in extracted air (Ce) and the concentration in the breathing zone (Cb).

                  Ev = Ce/Cb

                  The efficiency of ventilation depends on the distribution of air and the location of the sources of pollution in the given space. If air and the contaminants are mixed completely, the efficiency of ventilation is equal to one; if the quality of air in the breathing zone is better than that of extracted air, then the efficiency is greater than one and the desired quality of air can be attained with lower rates of ventilation. On the other hand, greater rates of ventilation will be needed if the efficiency of ventilation is less than one, or to put it differently, if the quality of air in the breathing zone is inferior to the quality of extracted air.

                  In calculating the efficiency of ventilation it is useful to divide spaces into two zones, one into which the air is delivered, the other comprising the rest of the room. For ventilation systems that work by the mixing principle, the zone where air is delivered is generally found above the breathing zone, and the best conditions are reached when mixing is so thorough that both zones become one. For ventilation systems that work by the displacement principle, air is supplied in the zone occupied by people and the extraction zone is usually found overhead; here the best conditions are reached when mixing between both zones is minimal.

                  The efficiency of ventilation, therefore, is a function of the location and characteristics of the elements that supply and extract air and the location and characteristics of the sources of contamination. In addition, it is also a function of the temperature and of the volumes of air supplied. It is possible to calculate the efficiency of a ventilation system by numerical simulation or by taking measurements. When data are not available the values in figure 3 can be used for different ventilation systems. These reference values take into consideration the impact of air distribution but not the location of sources of pollution, assuming instead that they are uniformly distributed throughout the ventilated space.

                  Figure 3. Effectiveness of ventilation in breathing zone according to different ventilation principles

                  IEN040F3

                  Calculating Ventilation Requirements

                  Figure 4 shows the equations used to calculate ventilation requirements from the point of view of comfort as well as that of protecting health.

                  Figure 4. Equations for calculating ventilation requirements

                  IEN040F4

                  Ventilation requirements for comfort

                  The first steps in the calculation of comfort requirements is to decide the level of quality of indoor air that one wishes to obtain for the ventilated space (see Table 1), and to estimate the quality of outside air available (see Table 5).

                  The next step consists in estimating the sensory load, using Tables 8, 9, and 10 to select the loads according to the occupants and their activities, the type of building, and the level of occupancy by square metre of surface. The total value is obtained by adding all the data.

                  Depending on the operating principle of the ventilation system and using Figure 9, it is possible to estimate the efficiency of ventilation. Applying equation (1) in Figure 9 will yield a value for the required amount of ventilation.

                  Ventilation requirements for health protection

                  A procedure similar to the one described above, but using equation (2) in Figure 3, will provide a value for the stream of ventilation required to prevent health problems. To calculate this value it is necessary to identify a substance or group of critical chemical substances which one proposes to control and to estimate their concentrations in air; it is also necessary to allow for different evaluation criteria, taking into account the effects of the contaminant and the sensitivity of the occupants that you wish to protect—children or the elderly, for example.

                  Unfortunately, it is still difficult to estimate the ventilation requirements for health protection owing to the lack of information on some of the variables that enter into the calculations, such as the rates of emission of the contaminants (G), the evaluation criteria for indoor spaces (Cv) and others.

                  Studies carried out in the field show that spaces where ventilation is required to achieve comfortable conditions the concentrations of chemical substances is low. Nevertheless, those spaces may contain sources of pollution that are dangerous. The best policy in these cases is to eliminate, to substitute or to control the sources of pollution instead of diluting the contaminants by general ventilation.

                   

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                  Published in 45. Indoor Environmental Control
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                  Wednesday, 16 February 2011 00:52

                  Aims and Principles of General and Dilution Ventilation

                  When pollutants generated at a worksite are to be controlled by ventilating the entire locale we speak of general ventilation. The use of general ventilation implies accepting the fact that the pollutant will be distributed to some degree through the entire space of the worksite, and could therefore affect workers who are far from the source of contamination. General ventilation is, therefore, a strategy that is the opposite of localized extraction. Localized extraction seeks to eliminate the pollutant by intercepting it as closely as possible to the source (see “Indoor air: methods for control and cleaning”, elsewhere in this chapter).

                  One of the basic objectives of any general ventilation system is the control of body odours. This can be achieved by supplying no less than 0.45 cubic metres per minute, m3/min, of new air per occupant. When smoking is frequent or the work is physically strenuous, the rate of ventilation required is greater, and may surpass 0.9 m3/min per person.

                  If the only environmental problems that the ventilation system must overcome are the ones just described, it is a good idea to keep in mind that every space has a certain level of “natural” air renewal by means of so-called “infiltration,” which occurs through doors and windows, even when they are closed, and through other sites of wall penetration. Air-conditioning manuals usually provide ample information in this regard, but it can be said that as a minimum the level of ventilation due to infiltration falls between 0.25 and 0.5 renewals per hour. An industrial site will commonly experience between 0.5 and 3 renewals of air per hour.

                  When used to control chemical pollutants, general ventilation must be limited to only those situations where the amounts of pollutants generated are not very high, where their toxicity is relatively moderate and where workers do not carry out their tasks in the immediate vicinity of the source of contamination. If these injunctions are not respected, it will be difficult to obtain acceptance for adequate control of the work environment because such high renewal rates must be used that the high air speeds will likely create discomfort, and because high renewal rates are expensive to maintain. It is therefore unusual to recommend the use of general ventilation for the control of chemical substances except in the case of solvents which have admissible concentrations of more than 100 parts per million.

                  When, on the other hand, the goal of general ventilation is to maintain the thermal characteristics of the work environment with a view to legally acceptable limits or technical recommendations such as the International Organization for Standardization (ISO) guidelines, this method has fewer limitations. General ventilation is therefore used more often to control the thermal environment than to limit chemical contamination, but its usefulness as a complement of localized extraction techniques should be clearly recognized.

                  While for many years the phrases general ventilation and ventilation by dilution were considered synonymous, today that is no longer the case because of a new general ventilation strategy: ventilation by displacement. Even though ventilation by dilution and ventilation by displacement fit within the definition of general ventilation we have outlined above, they both differ widely in the strategy they employ to control contamination.

                  Ventilation by dilution has the goal of mixing the air that is introduced mechanically as completely as possible with all the air that is already within the space, so that the concentration of a given pollutant will be as uniform as possible throughout (or so that the temperature will be as uniform as possible, if thermal control is the goal desired). To achieve this uniform mixture air is injected from the ceiling as streams at a relatively high speed, and these streams generate a strong circulation of air. The result is a high degree of mixing of the new air with the air already present inside the space.

                  Ventilation by displacement, in its ideal conceptualization, consists of injecting air into a space in such a way that new air displaces the air previously there without mixing with it. Ventilation by displacement is achieved by injecting new air into a space at a low speed and close to the floor, and extracting air near the ceiling. Using ventilation by displacement to control the thermal environment has the advantage that it profits from the natural movement of air generated by density variations that are themselves due to temperature differences. Even though ventilation by displacement is already widely used in industrial situations, the scientific literature on the subject is still quite limited, and the evaluation of its effectiveness is therefore still difficult.

                  Ventilation by Dilution

                  The design of a system of ventilation by dilution is based on the hypothesis that the concentration of the pollutant is the same throughout the space in question. This is the model that chemical engineers often refer to as a stirred tank.

                  If you assume that the air that is injected into the space is free of the pollutant and that at the initial time the concentration within the space is zero, you will need to know two facts in order to calculate the required rate of ventilation: the amount of the pollutant that is generated in the space and the level of environmental concentration that is sought (which hypothetically would be the same throughout).

                  Under these conditions, the corresponding calculations yield the following equation:

                  where

                  c(t) = the concentration of the contaminant in the space at time t

                  a = the amount of the pollutant generated (mass per unit of time)

                  Q = the rate at which new air is supplied (volume per unit of time)

                  V = the volume of the space in question.

                  The above equation shows that the concentration will tend to a steady state at the value a/Q, and that it will do so faster the smaller the value of Q/V, frequently referred to as “the number of renewals per unit of time”. Although occasionally the index of the quality of ventilation is regarded as practically equivalent to that value, the above equation clearly shows that its influence is limited to controlling the speed of stabilization of the environmental conditions, but not the level of concentration at which such a steady state will occur. That will depend only on the amount of the pollutant that is generated (a), and on the rate of ventilation (Q).

                  When the air of a given space is contaminated but no new amounts of the pollutant are generated, the speed of diminution of the concentration over a period of time is given by the following expression:

                  where Q and V have the meaning described above, t1 and t2 are, respectively, the initial and the final times and c1 and c2 are the initial and final concentrations.

                  Expressions can be found for calculations in instances where the initial concentration is not zero (Constance 1983; ACGIH 1992), where the air injected into the space is not totally devoid of the pollutant (because to reduce heating costs in the winter part of the air is recycled, for example), or where the amounts of the pollutant generated vary as a function of time.

                  If we disregard the transition stage and assume that the steady state has been achieved, the equation indicates that the rate of ventilation is equivalent to a/clim, where clim is the value of the concentration that must be maintained in the given space. This value will be established by regulations or, as an ancillary norm, by technical recommendations such as the threshold limit values (TLV) of the American Conference of Governmental Industrial Hygienists (ACGIH), which recommends that the rate of ventilation be calculated by the formula

                  where a and clim have the meaning already described and K is a safety factor. A value of K between 1 and 10 must be selected as a function of the efficacy of the air mixture in the given space, of the toxicity of the solvent (the smaller clim is, the greater the value of K will be), and of any other circumstance deemed relevant by the industrial hygienist. The ACGIH, among others, cites the duration of the process, the cycle of operations and the usual location of the workers with respect to the sources of emission of the pollutant, the number of these sources and their location in the given space, the seasonal changes in the amount of natural ventilation and the anticipated reduction in the functional efficacy of the ventilation equipment as other determining criteria.

                  In any case, the use of the above formula requires a reasonably exact knowledge of the values of a and K that should be used, and we therefore provide some suggestions in this regard.

                  The amount of pollutant generated may quite frequently be estimated by the amount of certain materials consumed in the process that generates the pollutant. So, in the case of a solvent, the amount used will be a good indication of the maximum amount that can be found in the environment.

                  As indicated above, the value of K should be determined as a function of the efficacy of the air mixture in the given space. This value will, therefore, be smaller in direct proportion to how good the estimation is of finding the same concentration of the pollutant at any point within the given space. This, in turn, will depend on how air is distributed within the space being ventilated.

                  According to these criteria, minimum values of K should be used when air is injected into the space in a distributed fashion (by using a plenum, for example), and when the injection and extraction of air are at opposite ends of the given space. On the other hand, higher values for K should be used when air is supplied intermittently and air is extracted at points close to the intake of new air (figure 1).

                  Figure 1. Schematic of air circulation in room with two supply openings

                  IEN030F1

                  It should be noted that when air is injected into a given space—especially if it is done at a high speed—the stream of air created will exert a considerable pull on the air surrounding it. This air then mixes with the stream and slows it down, creating measurable turbulence as well. As a consequence, this process results in intense mixing of the air already in the space and the new air that is injected, generating internal air currents. Predicting these currents, even generally, requires a large dose of experience (figure 2).

                  Figure 2. Suggested K factors for inlet and exhaust locations

                  IEN030F2

                  In order to avoid problems that result from workers’ being subjected to streams of air at relatively high speeds, air is commonly injected by way of diffusing grates designed in such a way that they facilitate the rapid mixing of new air with the air already present in the space. In this way, the areas where air moves at high speeds are kept as small as possible.

                  The stream effect just described is not produced near points where air escapes or is extracted through doors, windows, extraction vents or other openings. Air reaches extraction grates from all directions, so even at a relatively short distance from them, air movement is not easily perceived as an air current.

                  In any case, in dealing with air distribution, it is important to keep in mind the convenience of placing workstations, to the extent possible, in such a way that new air reaches the workers before it reaches the sources of contamination.

                  When in the given space there are important sources of heat, the movement of air will largely be conditioned by the convection currents that are due to density differences between denser, cold air and lighter, warm air. In spaces of this kind, the designer of air distribution must not fail to keep in mind the existence of these heat sources, or the movement of air may turn out to be very different from the one predicted.

                  The presence of chemical contamination, on the other hand, does not alter in a measurable way the density of air. While in a pure state the pollutants may have a density that is very different from that of air (usually much greater), given the real, existing concentrations in the workplace, the mix of air and pollutant does not have a density significantly different than the density of pure air.

                  Furthermore, it should be pointed out that one of the most common mistakes made in applying this type of ventilation is supplying the space only with air extractors, without any forethought given to adequate intakes of air. In these cases, the effectiveness of the extraction ventilators is diminished and, therefore, the actual rates of air extraction are much less than planned. The result is greater ambient concentrations of the pollutant in the given space than those initially calculated.

                  To avoid this problem some thought should be given to how air will be introduced into the space. The recommended course of action is to use immission ventilators as well as extraction ventilators. Normally, the rate of extraction should be greater than the rate of immission in order to allow for infiltration through windows and other openings. In addition, it is advisable to keep the space under slightly negative pressure to prevent the contamination generated from drifting into areas that are not contaminated.

                  Ventilation by Displacement

                  As mentioned above, with ventilation by displacement one seeks to minimize the mixing of new air and the air previously found in the given space, and tries to adjust the system to the model known as plug flow. This is usually accomplished by introducing air at slow speeds and at low elevations in the given space and extracting it near the ceiling; this has two advantages over ventilation by dilution.

                  In the first place, it makes lower rates of air renewal possible, because pollution concentrates near the ceiling of the space, where there are no workers to breathe it. The average concentration in the given space will then be higher than the clim value we have referred to before, but that does not imply a higher risk for the workers because in the occupied zone of the given space the concentration of the pollutant will be the same or lower than a clim.

                  In addition, when the goal of ventilation is the control of the thermal environment, ventilation by displacement makes it possible to introduce warmer air into the given space than would be required by a system of ventilation by dilution. This is because the warm air that is extracted is at a temperature several degrees higher than the temperature in the occupied zone of the space.

                  The fundamental principles of ventilation by displacement were developed by Sandberg, who in the early 1980s developed a general theory for the analysis of situations where there were nonuniform concentrations of pollutants in enclosed spaces. This allowed us to overcome the theoretical limitations of ventilation by dilution (which presupposes a uniform concentration throughout the given space) and opened the way for practical applications (Sandberg 1981).

                  Even though ventilation by displacement is widely used in some countries, particularly in Scandinavia, very few studies have been published in which the efficacy of different methods are compared in actual installations. This is no doubt because of the practical difficulties of installing two different ventilation systems in a real factory, and because the experimental analysis of these types of systems require the use of tracers. Tracing is done by adding a tracer gas to the air ventilation current and then measuring the concentrations of the gas at different points within the space and in the extracted air. This sort of examination makes it possible to infer how air is distributed within the space and to then compare the efficacy of different ventilation systems.

                  The few studies available that have been carried out in actual existing installations are not conclusive, except as regards the fact that systems that employ ventilation by displacement provide better air renewal. In these studies, however, reservations are often expressed about the results in so far as they have not been confirmed by measurements of the ambient level of contamination at the worksites.

                   

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                  Published in 45. Indoor Environmental Control
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