Health error and critical tasks in remote afterloading brachytherapy: Approaches for improved system performance
Remote afterloading btachytherapy (RAB) is a medical process used in the treatment of cancer. RAB uses a computer-controlled device to remotely insert and remove radioactive sources, close to a target (or tumour) in the body. Problems related to the dose delivered during RAB have been reported and attributed to human error (Swann-D'Emilia, Chu and Daywalt 1990). Callan et al. (1995) evaluated human error and critical tasks associated with RAB in 23 sites in the United States. Evaluation included six phases:
Phase 1: Functions and tasks. Preparation for treatment was considered to be the most difficult task, as it was responsible for the greatest cognitive strain. In addition, distractions had the greatest effect on preparation.
Phase 2: Human-system interferences. Personnel were often unfamiliar with interfaces they used infrequently. Operators were unable to see control signals or essential information from their workstations. In many cases, information on the state of the system was not given to the operator.
Phase 3: Procedures and practices. Because procedures used to move from one operation to the next, and those used to transmit information and equipment between tasks, were not well defined, essential information could be lost. Verification procedures were often absent, poorly constructed or inconsistent.
Phase 4: Training policies. The study revealed the absence of formal training programmes at most sites.
Phase 5: Organizational support structures. Communication during RAB was particularly subject to error. Quality-control procedures were inadequate.
Phase 6: Identification and classification or circumstances favouring human error. In all, 76 factors favouring human error were identified and categorized. Alternative approaches were identified and evaluated.
Ten critical tasks were subject to error:
Treatment was the function associated with the greatest number of errors. Thirty treatment-related errors were analysed and errors were found to occur during four or five treatment sub-tasks. The majority of errors occurred during treatment delivery. The second-highest number of errors were associated with the planning of treatment and were related to the calculation of dose. Improvements of eqiupment and documentation are under way, in collaboration with manufacturers.
The National Institute for Occupational Safety and Health (NIOSH) studied lifting and other related injuries at two grocery warehouses (referred to hereafter as “Warehouse A” and “Warehouse B”) (NIOSH 1993a; NIOSH 1995). Both warehouses have engineered standards against which order selector performance is measured; those who fall below their standard are subject to disciplinary action. The data in table 1 are expressed in percentages of order selectors only, reporting either all injuries or back injuries alone each year.
Table 1. Back and all reported workplace injuries and illnesses involving order selectors at two grocery warehouses studied by NIOSH, 1987-1992.
Warehouse A: all injuries (%)
Warehouse B: all injuries (%)
Warehouse A: back injuries only (%)
Warehouse B: back injuries only (%)
Sources: NIOSH 1993a, 1995.
At the risk of generalizing these data beyond their context, by any reckoning, the magnitude of recordable injury and illness percentages in these warehouses are quite significant and considerably higher than the aggregate data for the industry as a whole for all job classifications. While the total injuries at Warehouse A show a slight decline, they actually increase at Warehouse B. But the back injuries, with the exception of 1992 at Warehouse B, are both quite stable and significant. In general terms, these data suggest that order selectors have virtually a 3 in 10 chance of experiencing a back injury involving medical treatment and/or lost time in any given year.
The US National Association of Grocery Warehouses of America (NAGWA), an industry group, reported that back strains and sprains accounted for 30% of all injuries involving grocery warehouses and that one-third of all warehouse workers (not just order selectors) will experience one recordable injury per year; these data are consistent with the NIOSH studies. Moreover, they estimated the cost of paying for these injuries (workers’ compensation primarily) at $0.61 per hour for the 1990-1992 period (almost US$1,270 per year per worker). They also determined that manual lifting was the primary cause of back injuries in 54% of all cases studied.
In addition to a review of injury and illness statistics, NIOSH utilized a questionnaire instrument which was administered to all grocery order selectors. At Warehouse A, of the 38 full-time selectors, 50% reported at least one injury in the last 12 months, and 18% of full-time selectors reported at least one back injury in the previous 12 months. For Warehouse B, 63% of the 19 full-time selectors reported at least one recordable injury in the last 12 months, and 47% reported having at least one back injury in the same period. Seventy per cent of full-time workers at Warehouse A reported significant back pain in the previous year, as did 47% of the full-time selectors at Warehouse B. These self-reported data closely correspond with the injury and illness survey data.
In addition to reviewing injury data regarding back injuries, NIOSH applied its revised lifting equation to a sample of lifting tasks of order selectors and found that all the sampled lifting tasks exceeded the recommended weight limit by significant margins, which indicates the tasks studied were highly stressful from an ergonomic point of view. In addition, compressive forces were estimated on the L5/S1 vertebral disc; all exceeded the recommended biomechanical limits of 3.4 kN (kilonewtons), which has been identified as an upper limit for protecting most workers from the risk of low-back injury.
Finally, NIOSH, using both energy expenditure and oxygen consumption methodologies, estimated energy demand on grocery order selectors in both warehouses. Average energy demands of the order selector exceeded the established criterion of 5 kcal/minute (4 METS) for an 8-hour day, which is recognized as moderate to heavy work for a majority of healthy workers. At Warehouse A, the working metabolic rate ranged from 5.4 to 8.0 kcal/minute, and the working heart rate ranged from 104 to 131 beats per minute; at Warehouse B, it was 2.6 to 6.3 kcal/minute, and 138 to 146 beats per minute, respectively.
Order selectors’ energy demands from continuous lifting at a rate of 4.1 to 4.9 lifts per minute would probably result in fatigued muscles, especially when working shifts of 10 or more hours. This clearly illustrates the physiological cost of work in the two warehouses studied to date. In summing up its findings, NIOSH reached the following conclusion concerning the risks faced by grocery warehouse order selectors:
In summary, all order assemblers (order selectors) have an elevated risk for musculoskeletal disorders, including low back pain, because of the combination of adverse job factors all contributing to fatigue, a high metabolic load and the workers’ inability to regulate their work rate because of the work requirements. According to recognized criteria defining worker capability and accompanying risk of low back injury, the job of order assembler at this work site will place even a highly selected work force at substantial risk of developing low back injuries. Moreover, in general, we believe that the existing performance standards encourage and contribute to these excessive levels of exertion (NIOSH 1995).
The Entangling Net: Alaska’s Commercial Fishing Women Tell Their Lives, by Leslie Leyland Fields (Urbana: University of Illinois Press, 1996), is the story, based on the author’s own experience and interviews, of some of the women who worked as commercial fishers in the waters of the Pacific Ocean and the Gulf of Alaska surrounding Kodiak Island and the Aleutian Islands. The following excerpts capture some of the flavour of these women’s experience, why they chose this line of work and what it entailed.
The last black cod season started May 15. It was two gals and two guys. The skipper wanted a crew that could bait gear fast; that was what he was looking for. ... To start out, all we were trying to do is turn hooks. Its a numbers game. Ideally you run 18,000-20,000 hooks a day. And so we’d have four people baiting at all times and one person hauling gear. The people baiting would rotate coiling the gear. We went back to the traditional way of fishing. Most Kodiak boats will let the gear fall into a tub, kind of on its own, then you bring that tub back and bait it. On the old halibut schooners they hand coil everything so they’re able to offspin every hook. They try to make a really nice coil so when you take it back you can bait it twice as fast. The first couple of days we looked at the time it was taking to bait the messy skates (the long lines on which the hooks are attached). I refuse to bait another skate like that, so then we all started hand coiling our own. When you do that you’re able to move from your baiting station. We really worked long hours, often twenty-four hours, then we go into the next day and work through that night until about 2:00 A.M. and the next day another twenty hours. Then we’d lie down for about three hours. Then we’d get back up and go another twenty-four hours and a couple of hours down. The first week we averaged ten hours of sleep all together—we figured it out. So we joked, twenty-four on, one off.
I had never fished that hard before. When it opened, we fished Saturday, all through Saturday, all through Sunday and half of Monday. So well over fifty-six hours with no sleep, working as hard, as fast as high paced as you can push yourself. Then we laid down for like three hours. You get up. You are so stiff! Then we brought in a trip, just over 40,000 pounds in four days, so we virtually had been up those entire four days. That was a good load. It was really motivational. I make a thousand dollars a day. ... It’s the shorter seasons, the shorter longline seasons, are what are driving the boats back to these schedules. ... with a three-week season, you’re almost forced to unless you can rotate a person down (let them sleep) (pp. 31-33).
But the reason I feel lucky is because we were out there, a woman running a boat with an all-women crew, and we were doing it. And we were doing it as well as anybody else in the fleet, so I never felt intimidated in thinking, “Oh, a woman can’t do this, can’t figure it out, or is not capable of it” because the first job I ever had was with women and we did fine. So I had that confidence factor from the beginning of my deckhand career... (p. 35).
When you’re on a boat, you don’t have a life, you don’t have any physical space, you don’t have any time to yourself. It’s all the boat, the fishing, for four months straight...(p. 36).
I have a little bit of protection on some of the winds but pretty much I’ll get all of it. ... There’s also a lot of tide here. You dump these anchors off; you’ve got fifteen or twenty anchors, some of them three hundred pounders, to try to hold one net in place. And every time you go out there the net’s twisted in some different shape and you have to drag these anchors around. And the weather is not very nice most of the time. You’re always fighting the wind. It’s a challenge, a physical challenge instead of a mental challenge... (p. 37).
Beating the docks (going from boat to boat seeking a job) was the worst thing. After I did it for a while I realized that probably there’s only 15 percent of the boats that you even have a possibility of being hired on because the rest of them will not hire women. Mostly because their wives won’t let them or there’s another woman on the boat already or they are just flat out sexist—they don’t want women. But between those three factors, the number of boats you could get hired on was so slim that it was discouraging. But you had to find out which boats those were. That means walking the docks...(p. 81).
I was thinking about the question you asked earlier. Why women are increasingly drawn to this. I don’t know. You wonder if there are increasing numbers of women coal mining or trucking. I don’t know if it has something to do with Alaska and the whole lure of being able to partake of something that formerly was withheld from you, or maybe its a breed of women who have been raised or somehow have been grown up to understand that certain barriers that supposedly were there are not legitimate. Even withstanding all the dangers, it’s an important experience and it’s very viable, very—I hate to use the word “fulfilling,” but it is very fulfilling. I loved, I loved getting a string of pots over perfectly and not having to ask anyone to help me with one of the doors once and getting all the massive wads of bait that you sort of swoop under the pot in the middle. ...There are elements to it you can’t find in any other type of experience. It’s almost like farming. It’s so elemental. It calls on such an elemental process. Since biblical times we’ve been talking about these kind of people. There’s this ethos surrounding it that’s very ancient. And to be able to go to that and draw on it. It gets into this whole mystical realm (p.44).
It’s very lonely being the only woman on a boat. I make a point of never getting involved with guys on a romantic level or anything. Friends. I’m always open to friends, but you always have to be careful that they don’t think it’s more. See, there are so many different levels of guys. I don’t want to be friends with the drunkards and cocaine addicts. But definitely the more respectable people I became friends with. And I have maintained male friendships and female friendships. There’s a lot of loneliness though. I found out that laugh therapy helps. I go out on the back deck and just laugh to myself and feel better (p. 61).
Leslie Leyland Fields
Each (woman) asked only for equal treatment and equal opportunity. This doesn’t come automatically in a job where you need the strength to land a swinging 130-pound crab pot, the endurance to withstand thirty-six straight hours of work without sleep, the moxie to run a 150-horsepowered seine skiff at full speed near reefs, and special hands-on skills like diesel engine repair and maintenance, net mending, operating hydraulics. These are the powers that win the day and the fish; these are the powers fishing women must prove to disbelieving men. And not least of all, there is active resistance from an unexpected quarter—other women, the wives of men who fish (p. 53).
This is part of what I know of being a skipper. ... You alone hold the lives of two, three or four people in your hands. Your boat payments and insurance costs run you in the tens of thousands every year—you must catch fish. You manage a potentially volatile mix of personalities and work habits. You must have extensive knowledge of navigation, weather patterns, fishing regulations; you must be able to operate and repair to some degree the array of high-tech electronics that are the brains of the boat. ... The list goes on.
Why does anyone willingly hoist and carry such a load? There is another side, of course. To state it positively, there is independence in skippering, a degree of autonomy seldom found in other professions. You alone control the life within your ark. You can decide where you are going to fish, when the boat goes, how fast it goes, how long and hard the crew will work, how long everyone sleeps, the weather conditions you will work in, the degrees of risk you will take, the kind of food you eat... (p. 75).
In 1992, forty-four vessels in Alaska sunk, eighty-seven people were rescued from sinking vessels, thirty-five died. In Spring 1988 forty-four died after ice fog moved in and consumed boats and crew. To put those numbers in perspective, the National Institute for Occupational Safety and Health reports that the annual death rate for all U.S. Occupations is 7 per 100,000 workers. For commercial fishing in Alaska, the rate jumps to 200 per 100,000, making it the most deadly job in the country. For crab fishermen, whose season runs through the winter, the rate climbs to 660 per 100,000, or almost 100 times the national average (p. 98).
I’m only five feet tall and I weigh one hundred pounds and so men have a protective instinct toward me. I’ve had to surmount that my whole life to actually get in and do anything. The only way I’ve been able to get past is by being quicker and knowing what I’m doing. It’s about leverage. ... You have to slow down. You have to use your head in a different way and your body in a different way. I think its important that people know how small I am because if I can do it, it means any woman can do it... (p. 86).
I really believe in the North Pacific Vessel Owner’s Association, they offer some really good courses, one of which is Medical Emergencies at Sea. I think anytime you take any kind of marine tech class you’re doing yourself a favor (p. 106).
Developed such a sense of independence and strength. Things I thought I could never do I learned I would do out here. It’s just opened a whole new world for myself as a young woman. becoming a woman, I don’t know. There are so many possibilities now because I know I can do “a man’s job,” you know? There’s a lot of power that comes with that (p. 129).
Copyright 1997 by the Board of Trustees of the University of Illinois. Used with the permission of the University of Illinois Press.
3.1.1. The competent authority, or a body approved or recognised by the competent authority, should establish systems and specific criteria for classifying a chemical as hazardous and should progressively extend these systems and their application. Existing criteria for classification established by other competent authorities or by international agreement may be followed, if they are consistent with the criteria and methods outllined in this code, and this is encouraged where it may assist uniformity of approach. The results of the work of the UNEP/ILO/WHO International Programme on Chemical Safety (IPCS) coordinating group for the harmonisation of classification of chemicals should be considered when appropriate. The responsibilities and role of competent authorities concerning classification systems are set out in paragraphs 2.1.8 (criteria and requirements), 2.1.9 (consolidated list) and 2.1.10 (assessment of new chemicals).
3.1.2. Suppliers should ensure that chemicals they supplied have been classified or that they have been identified and their properties assessed (see paragraphs 2.4.3 (assessment) and 2.4.4 (classification)).
3.1.3. Manufacturers or importers, unless exempted, should give to the competent authority information about chemical elements and compounds not yet included in the consolidated classification list compiled by the competent authority, prior to their use at work (see paragraph 2.1.10 (assessment of new chemicals)).
3.1.4. The limited quantities of a new chemical required for research and development purposes may be produced by, handled in, and transported between laboratories and pilot plant before all hazards of this chemical are known in accordance with national laws and regulations. All available information found in literature or known to the employer from his or her experience with similar chemicals and applications should be fully taken into account, and adequate protection measures should be applied, as if the chemical were hazardous. The workers involved must be informed about the actual hazard information as it becomes known.
3.2. Criteria for classification
3.2.1. The criteria for the classification of chemicals should be based upon their intrinsic health and physical hazards, including:
3.3. Method of classification
3.3.1. The classification of chemicals should be based on available sources of information, e.g.:
3.3.2. Certain classification systems in use may be limited to particular classes of chemicals only. An example is the WHO Recommended classification of pesticides by hazard and guidelines to classification, which classifies pesticides by degree of toxicity only and principally by acute risks to health. Employers and workers should understand the limitations of any such system. Such systems can be useful to complement a more generally applicable system.
3.3.3. Mixtures of chemicals should be classified based on the hazards exhibited by the mixtures themselves. Only if mixtures have not been tested as a whole should they be classified on the basis of intrinsic hazards of their component chemicals.
Source: ILO 1993, Chapter 3.
A systematic approach to safety requires an efficient flow of information from the suppliers to the users of chemicals on potential hazards and correct safety precautions. In addressing the need for a written hazard communication programme, the ILO Code of Practice Safety in the Use of Chemicals at Work (ILO 1993) states, “The supplier should provide an employer with essential information about hazardous chemicals in the form of a chemical safety data sheet.” This chemical safety data sheet or material safety data sheet (MSDS) describes the hazards of a material and provides instructions on how the material can be safely handled, used and stored. MSDSs are produced by the manufacturer or importer of hazardous products. The manufacturer must provide distributors and other customers with MSDSs upon first purchase of a hazardous product and if the MSDS changes. Distributors of hazardous chemicals must automatically provide MSDSs to commercial customers. Under the ILO Code of Practice, workers and their representatives should have a right to an MSDS and to receive the written information in forms or languages they easily understand. Because some of the required information might be intended for specialists, further clarification may be needed from the employer. The MSDS is only one source of information on a material and, therefore, it is best used along with technical bulletins, labels, training and other communications.
The requirements for a written hazard communication programme are outlined in at least three major international directives: the US Occupational Safety and Health Administration (OSHA) Hazard Communication Standard, Canada’s Workplace Hazardous Materials Information System (WHMIS) and the European Community’s Commission Directive 91/155/EEC. In all three directives, the requirements for preparing a complete MSDS are established. Criteria for the data sheets include information about the identity of the chemical, its supplier, classification, hazards, safety precautions and the relevant emergency procedures. The following discussion details the type of required information included in the 1992 ILO Code of Practice Safety in the Use of Chemicals at Work. While the Code is not intended to replace national laws, regulations or accepted standards, its practical recommendations are intended for all those who have a responsibility for ensuring the safe use of workplace chemicals.
The following description of chemical safety data sheet content corresponds with section 5.3 of the Code:
Chemical safety data sheets for hazardous chemicals should give information about the identity of the chemical, its supplier, classification, hazards, safety precautions and the relevant emergency procedures.
The information to be included should be that established by the competent authority for the area in which the employer’s premises are located, or by a body approved or recognized by that competent authority. Details of the type of information that should be required are given below.
(a) Chemical product and company identification
The name should be the same as that used on the label of the hazardous chemical, which may be the conventional chemical name or a commonly used trade name. Additional names may be used if these help identification. The full name, address and telephone number of the supplier should be included. An emergency telephone number should also be given, for contact in the event of an emergency. This number may be that of the company itself or of a recognized advisory body, so long as either can be contacted at all times.
(b) Information on ingredients (composition)
The information should allow employers to identify clearly the risks associated with a particular chemical so that they may conduct a risk assessment, as outlined in section 6.2 (Procedures for assessment) of this code. Full details of the composition should normally be given but may not be necessary if the risks can be properly assessed. The following should be provided except where the name or concentration of an ingredient in a mixture is confidential information which can be omitted in accordance with section 2.6:
(c) Hazard identification
The most important hazards, including the most significant health, physical and environmental hazards, should be stated clearly and briefly, as an emergency overview. The information should be compatible with that shown on the label.
(d) First-aid measures
First-aid and self-help measures should be carefully explained. Situations where immediate medical attention is required should be described and the necessary measures indicated. Where appropriate, the need for special arrangements for specific and immediate treatment should be emphasized.
(e) Firefighting measures
The requirements for fighting a fire involving a chemical should be included; for example:
Information should also be given on the properties of the chemical in the event of fire and on special exposure hazards as a result of combustion products, as well as the precautions to be taken.
(f) Accidental release measures
Information should be provided on the action to be taken in the event of an accidental release of the chemical. The information should include:
(g) Handling and storage
Information should be given about conditions recommended by the supplier for safe storage and handling, including:
(h) Exposure controls and personal protection
Information should be given on the need for personal protective equipment during use of a chemical, and on the type of equipment that provides adequate and suitable protection. Where appropriate, a reminder should be given that the primary controls should be provided by the design and installation of any equipment used and by other engineering measures, and information provided on useful practices to minimize exposure of workers. Specific control parameters such as exposure limits or biological standards should be given, along with recommended monitoring procedures.
(i) Physical and chemical properties
A brief description should be given of the appearance of the chemical, whether it is a solid, liquid or gas, and its colour and odour. Certain characteristics and properties, if known, should be given, specifying the nature of the test to determine these in each case. The tests used should be in accordance with the national laws and criteria applying at the employer’s workplace and, in the absence of national laws or criteria, the test criteria of the exporting country should be used as guidance. The extent of the information provided should be appropriate to the use of the chemical. Examples of other useful data include:
(j) Stability and reactivity
The possibility of hazardous reactions under certain conditions should be stated. Conditions to avoid should be indicated, such as:
Where hazardous decomposition products are given off, these should be specified along with the necessary precautions.
(k) Toxicological information
This section should give information on the effects on the body and on potential routes of entry into the body. Reference should be made to acute effects, both immediate and delayed, and to chronic effects from both short- and long-term exposure. Reference should also be made to health hazards as a result of possible reaction with other chemicals, including any known interactions, for example, resulting from the use of medication, tobacco and alcohol.
(l) Ecological information
The most important characteristics likely to have an effect on the environment should be described. The detailed information required will depend on the national laws and practice applying at the employer’s workplace. Typical information that should be given, where appropriate, includes the potential routes for release of the chemical which are of concern, its persistence and degradability, bioaccumulative potential and aquatic toxicity, and other data relating to ecotoxicity (e.g., effects on water treatment works).
(m) Disposal considerations
Safe methods of disposal of the chemical and of contaminated packaging, which may contain residues of hazardous chemicals, should be given. Employers should be reminded that there may be national laws and practices on the subject.
(n) Transport information
Information should be given on special precautions that employers should be aware of or take while transporting the chemical on or off their premises. Relevant information given in the United Nations Recommendations on the Transport of Dangerous Goods and in other international agreements may also be included.
(o) Regulatory information
Information required for the marking and labelling of the chemical should be given here. Specific national regulations or practices applying to the user should be referred to. Employers should be reminded to refer to the requirements of national laws and practices.
(p) Other information
Other information which may be important to workers’ health and safety should be included. Examples are training advice, recommended uses and restrictions, references, and sources of key data for compiling the chemical safety data sheet, the technical contact point and date of issue of the sheet.
In a case-control study looking at environmental and occupational factors for congenital malformations (Kurppa et al. 1986), 1,475 cases were identified from the Finnish Register of Congenital Malformations during the period between 1976 and 1982 (see table 1). A mother whose delivery immediately preceded a case, and was in the same district, served as a control for that case. Exposure to visual display units (VDUs) during the first trimester of pregnancy was assessed using face-to-face interviews conducted either at the clinic during a post-natal visit, or at home. The classification of probable or obvious VDU use was determined by occupational hygienists, blind to the pregnancy outcomes, using job titles and the responses to open-ended questions asking to describe the ordinary work day. There was no evidence of increased risk either among women who reported exposure to VDUs (OR 0.9; 95% CI 0.6 – 1.2), or among women whose job titles indicated possible exposure to VDUs (235 cases/255 controls).
A cohort of Swedish women from three occupational groups was identified through a linkage of occupational census and the Medical Birth Registry during 1980–1981 (Ericson and Källén 1986). A case-base study was conducted within that cohort: cases were 412 women hospitalized for spontaneous abortion and an additional 110 with other outcomes (such as perinatal death, congenital malformations and birthweight below 1500 g). Controls were 1,032 women of similar age who had infants without any of these characteristics, chosen from the same registry. Using crude odds ratios, there was an exposure–response relation between VDU exposure in estimated hours per week (divided into five-hour categories) and pregnancy outcomes (excluding spontaneous abortion). After controlling for smoking and stress, the effect of VDU use on all adverse pregnancy outcomes was not significant.
Focusing on one of three occupational groups identified from a previous study by Ericson a cohort study was conducted using 4,117 pregnancies among social security clerks in Sweden (Westerholm and Ericson 1986). Rates of hospitalized spontaneous abortion, low birthweight, perinatal mortality and congenital malformations in this cohort were compared to rates in the general population. The cohort was divided into five exposure groups defined by trade union and employer representatives. No excesses were found for any of the studied outcomes. The overall relative risk for spontaneous abortion, standardized for mothers’ age was 1.1 (95% CI 0.8 – 1.4).
A cohort study involving 1,820 births was conducted among women having ever worked at the Norwegian Postal Giro Centre between 1967–1984 (Bjerkedal and Egenaes 1986). The rates of stillbirth, first-week death, perinatal death, low and very low birthweight, preterm birth, multiple births and congenital malformations were estimated for pregnancies occurring during employment at the centre (990 pregnancies), and pregnancies occurring before or after employment at the centre (830 pregnancies). Rates of adverse pregnancy outcomes were also estimated for three six-year periods, (1967–1972), (1973–1978) and (1979–1984). Introduction of VDUs began in 1972, and were extensively used by 1980. The study concluded that there was no indication that introduction of VDUs in the centre had led to any increase in the rate of adverse pregnancy outcomes.
A cohort of 9,564 pregnancies was identified through logs of urine pregnancy tests from three California clinics in 1981–1982 (Goldhaber, Polen and Hiatt. 1988). Coverage by a Northern California medical plan was a requirement to be eligible for the study. Pregnancy outcomes were found for all but 391 identified pregnancies. From this cohort, 460 of 556 spontaneous abortion cases (<28 weeks), 137 of 156 congenital abnormality cases and 986 of 1,123 controls (corresponding to every fifth normal birth in the original cohort), responded to a retrospective postal questionnaire on chemical environmental exposures including pesticides and VDU use during pregnancy. Odds ratios for women with first trimester VDU use over 20 hours per week, adjusted for eleven variables including age, previous miscarriage or birth defect, smoking and alcohol, were 1.8 (95% CI 1.2 – 2.8) for spontaneous abortion and 1.4 (95% CI 0.7 – 2.9) for birth defects, when compared to working women who did not report using VDUs.
In a study conducted in 11 hospital maternity units in the Montreal area over a two-year period (1982–1984), 56,012 women were interviewed on occupational, personal and social factors after delivery (51,855) or treatment for spontaneous abortion (4,127) (McDonald et al. 1988).These women also provided information on 48,637 previous pregnancies. Adverse pregnancy outcomes (spontaneous abortion, stillbirth, congenital malformations and low birthweight) were recorded for both current and previous pregnancies. Ratios of observed to expected rates were calculated by employment group for current pregnancies and previous pregnancies. Expected rates for each employment group were based on the outcome in the whole sample, and adjusted for eight variables, including age, smoking and alcohol. No increase in risk was found among women exposed to VDUs.
A cohort study comparing rates of threatened abortion, length of gestation, birthweight, placental weight and pregnancy-induced hypertension between women who used VDUs and women who did not use VDUs was carried out among 1,475 women (Nurminen and Kurppa 1988).The cohort was defined as all non-cases from a previous case-control study of congenital malformations. Information about risk factors was collected using face-to-face interviews. The crude and adjusted rate ratios for the outcomes studied did not show statistically significant effects for working with VDUs.
A case-control study involving 344 cases of hospitalized spontaneous abortion occurring at three hospitals in Calgary, Canada, was conducted in 1984–1985 (Bryant and Love 1989). Up to two controls (314 prenatal and 333 postpartum) were chosen among women having delivered or susceptible of delivering at the study hospitals. The controls were matched to each case on the basis of age at last menstrual period, parity, and intended hospital of delivery. VDU use at home and at work, before and during pregnancy, was determined through interviews at the hospitals for postnatal controls and spontaneous abortion, and at home, work, or the study office for prenatal controls. The study controlled for socioeconomic and obstetric variables. VDU use was similar between the cases and both the prenatal controls (OR=1.14; p=0.47) and postnatal controls (OR=0.80; p=0.2).
A case-control study of 628 women with spontaneous abortion, identified through pathology specimen submissions, whose last menstrual period occurred in 1986, and 1,308 controls who had live births, was carried out in one county in California (Windham et al. 1990). The controls were randomly selected, in a two-to-one ratio, among women matched for date of last menstrual period and hospital. Activities during the first 20 weeks of pregnancy were identified through telephone interviews. The participants were also asked about VDU use at work during this period. Crude odds ratios for spontaneous abortion and VDU use less than 20 hours per week (1.2; 95% CI 0.88 – 1.6), and at least 20 hours per week (1.3; 95% CI 0.87 – 1.5), showed little change when adjusted for variables including employment group, maternal age, prior foetal loss, alcohol consumption and smoking. In a further analysis among the women in the control group, risks for low birthweight and intrauterine growth retardation were not significantly elevated.
A case-control study was conducted within a study base of 24,352 pregnancies occurring between 1982 and 1985 among 214,108 commercial and clerical employees in Denmark (Brandt and Nielsen 1990). The cases, 421 respondents among the 661 women who gave birth to children with congenital abnormalities and who were working at the time of pregnancy, were compared to 1,365 respondents among the 2,252 randomly selected pregnancies among working women. Pregnancies, and their outcomes, and employment were determined through a linkage of three databases. Information on VDU use (yes/no/hours per week), and job-related and personal factors such as stress, exposure to solvents, life-style and ergonomic factors were determined through a postal questionnaire. In this study, the use of VDUs during pregnancy was not associated with an increased risk of congenital abnormalities.
Using the same study base as in the previous study on congenital abnormalities (Brandt and Nielsen 1990) 1,371 of 2,248 women whose pregnancies ended in a hospitalized spontaneous abortion were compared to 1,699 randomly selected pregnancies (Nielsen and Brandt 1990). While the study was carried out among commercial and clerical workers, not all of the pregnancies corresponded to times when the women were gainfully employed as commercial or clerical workers. The measure of association used in the study was the ratio of the rate of VDU use among women with a spontaneous abortion to the rate of VDU use among the sample population (representing all pregnancies including those ending in spontaneous abortion). The adjusted rate ratio for any exposure to VDU and spontaneous abortion was 0.94 (95% CI 0.77 – 1.14).
A case-control study was carried out among 573 women who gave birth to children with cardiovascular malformations between 1982 and 1984 (Tikkanen and Heinonen 1991). The cases were identified through the Finnish register of congenital malformations. The control group consisted of 1,055 women, randomly selected among all hospital deliveries during the same time period. VDU use, recorded as never, regular or occasional, was assessed through an interview conducted 3 months after the delivery. No statistically significant association was found between VDU use, at work or at home, and cardiovascular malformations.
A cohort study was carried out among 730 married women who reported pregnancies between 1983 and 1986 (Schnorr et al. 1991). These women were employed as either directory assistance operators or as general telephone operators at two telephone companies in eight southeastern states in the United States. Only the directory assistance operators used VDUs at work. VDU use was determined through company records. Spontaneous abortion cases (foetal loss at 28 weeks’ of gestation or earlier) were identified through a telephone interview; birth certificates were later used to compare women’s reporting with pregnancy outcomes and when possible, physicians were consulted. Strengths of electric and magnetic fields were measured at very low and extremely low frequencies for a sample of the workstations. The VDU workstations showed higher field strengths than those not using VDUs. No excess risk was found for women who used VDUs during the first trimester of pregnancy (OR 0.93; 95% CI 0.63 – 1.38), and there was no apparent exposure–response relation when looking at time of VDU use per week.
A cohort of 1,365 Danish commercial and clerical workers who were gainfully employed at the time of pregnancy, and identified through a previous study (Brandt and Nielsen 1990; Nielsen and Brandt 1990), was used to study fecundability rates, in relation to VDU use (Brandt and Nielsen 1992). Fecundability was measured as time from stopping birth control use to time of conception, and was determined through a postal questionnaire. This study showed an increased relative risk for prolonged waiting to pregnancy for the subgroup with at least 21 weekly hours of VDU use. (RR 1.61; 95% CI 1.09 – 2.38).
A cohort of 1,699 Danish commercial and clerical workers, consisting of women employed and unemployed at the time of pregnancy, identified through the study reported on in the previous paragraph, was used to study low birthweight (434 cases), preterm birth (443 cases), small for gestational age (749 cases), and infant mortality (160 cases), in relation to VDU use patterns (Nielsen and Brandt 1992). The study failed to show any increased risk for these adverse pregnancy outcomes among women with VDU use.
In a case-control study, 150 nulliparous women with clinically diagnosed spontaneous abortion and 297 nulliparous working women attending a hospital in Reading, England for antenatal care between 1987 and 1989 were interviewed (Roman et al. 1992). The interviews were conducted face to face at the time of their first antenatal visit for the controls, and three weeks after the abortion for women with spontaneous abortion. For women who mentioned VDU use, estimates of time of exposure in hours per week, and calendar time of first exposure were assessed. Other factors such as overtime, physical activity at work, stress and physical comfort at work, age, alcohol consumption and previous miscarriage were also assessed. Women who worked with VDUs had an odds ratio for spontaneous abortion of 0.9 (95% CI 0.6 – 1.4), and there was no relation with the amount of time spent using VDUs. Adjusting for other factors such as maternal age, smoking, alcohol and previous spontaneous abortion did not alter the results.
From a study base of bank clerks and clerical workers in three companies in Finland, 191 cases of hospitalized spontaneous abortion and 394 controls (live births) were identified from Finnish medical registers for 1975 to 1985 (Lindbohm et al. 1992). Use of VDUs was defined using workers’ reports and company information. Magnetic field strengths were retrospectively assessed in a laboratory setting using a sample of the VDUs which had been used in the companies. The odds ratio for spontaneous abortion and working with VDUs was 1.1 (95% CI 0.7 – 1.6). When VDU users were separated in groups according to the field strengths for their VDU models, the odds ratio was 3.4 (95% CI 1.4 – 8.6) for workers who had used VDUs with a high magnetic field strength in the extremely low frequency bandwidth (0.9 μT), compared to those working with VDUs with field strength levels below the detection limits (0.4 μT). This odds ratio changed only slightly when adjusted for ergonomic and mental work-load factors. When comparing workers exposed to high magnetic field strengths to workers not exposed to VDUs, the odds ratio was no longer significant.
A study, looking at adverse pregnancy outcomes and fertility, was carried out among female civil servants working for the British Government tax offices (Bramwell and Davidson 1994). Of the 7,819 questionnaires mailed in the first stage of the study, 3,711 were returned. VDU use was determined through this first questionnaire. Exposure was assessed as hours per week of VDU use during pregnancy. One year later, a second questionnaire was sent out to assess the incidence of adverse pregnancy outcomes among these women; 2,022 of the original participants responded. Possible confounders included pregnancy history, ergonomic factors, job stressors, caffeine, alcohol, cigarette and tranquillizer consumption. There was no relationship between exposure as assessed one year previously and the incidence of adverse pregnancy outcomes.
In general there is a square root relationship between thickness d of a static air layer and air velocity v. The exact function depends on the size and shape of the surface, but for the human body a useful approximation is:
Still air acts as an insulating layer with a conductivity (a material constant, regardless of the shape of the material) of .026 W/mK, which has a heat transfer coefficient h (units of ) (the conductive property of a slab of material) of:
Radiant heat flow () between two surfaces is approximately proportional to their temperature difference:
where T is the average absolute temperature (in Kelvin) of the two surfaces, is the absorption coefficient and is the Stefan-Boltzmann constant ( ). The amount of radiation exchange is inversely related to the number of intercepting layers (n):
Clothing insulation () is defined by the following equations:
where is intrinsic insulation, is (adjacent) air insulation, is total insulation, is average skin temperature, is the average temperature of the outer surface of the clothing, is air temperature, is the dry heat flow (convective and radiant heat) per unit of skin area and is the clothing area factor. This coefficient has been underestimated in older studies, but more recent studies converge to the expression
Often I is expressed in the unit clo; one clo equals .
McCullough et al. (1985) deduced a regression equation from data on a mix of clothing ensembles, using thickness of the textile (, in mm) and percentage covered body area () as determinants. Their formula for the insulation of single clothing items () is:
The evaporative resistance R (units of s/m) can be defined as:
(or sometimes , in )
For fabric layers, the air equivalent () is the thickness of air that provides the same resistance to diffusion as the fabric does. The associated vapour and latent heat () flows are:
where D is the diffusion coefficient (), C the vapour concentration () and the heat of evaporation (2430 J/g).
(from Lotens 1993). is related to R by:
D is the diffusion coefficient for water vapour in air, .
I. Index of thermal stress (ITS)
The improved heat balance equation is:
where is the evaporation required to maintain heat balance, is the solar load, and metabolic heat production H is used instead of metabolic rate to account for external work. An important improvement is the recognition that not all sweat evaporates (e.g., some drips) hence required sweat rate is related to required evaporation rate by:
where nsc is the efficiency of sweating.
Used indoors, sensible heat transfer is calculated from:
For outdoor conditions with solar load, is replaced with and allowance made for solar load (RS ) by:
The equations used are fits to experimental data and are not strictly rational.
Maximum evaporation heat loss is:
and efficiency of sweating is given by:
nsc = 1, если
nsc = 0.29, если
The index of thermal stress (ITS) in g/h is given by:
where is the required evaporation rate , 0.37 converts into g/h andnsc is the efficiency of sweating (McIntyre 1980).
II. Required sweat rate
Similar to the other rational indices, is derived from the six basic parameters (air temperature (), radiant temperature ( ), relative humidity air velocity (v), clothing insulation ( ), metabolic rate (M) and external work (W)). Effective radiation area values for posture (sitting = 0.72, standing = 0.77) are also required. From this the evaporation required is calculated from:
Equations are provided for each component (see table 8 and table 9). Mean skin temperature is calculated from a multiple linear regression equation or a value of 36°C is assumed.
From the required evaporation (Ereg) and maximum evaporation (Emax) and sweating efficiency (r), the following are calculated:
Required skin wettedness
Required sweat rate
III. Predicted 4-hour sweat rate (P4SR)
Steps taken to obtain the P4SR index value are summarized by McIntyre (1980) as follows:
If , increase wet bulb temperature by .
If the metabolic rate M > 63 , increase wet bulb temperature by the amount indicated in the chart (see figure 6).
If the men are clothed, increase the wet bulb temperature by .
The modifications are additive.
The (P4SR) is determined from figure 6. The P4SR is then:
IV. Heart rate
where M is metabolic rate, is air temperature in °C and Pa is vapour pressure in Mb.
Givoni and Goldman (1973) provide equations for predicting heart rate of persons (soldiers) in hot environments. They define an index for heart rate (IHR) from a modification of predicted equilibrium rectal temperature,
IHR is then:
where M = metabolic rate (watts), = mechanical work (watts), clo = thermal insulation of clothing, = air temperature, = total metabolic and environmental heat load (watts), = evaporative cooling capacity for clothing and environment (watts).
The equilibrium heart rate (in beats per minute) is then given by:
for IHR 225
that is, a linear relationship (between rectal temperature and heart rate) for heart rates up to about 150 beats per minute. For IHR >225:
that is, an exponential relationship as heart rate approaches maximum, where:
= equilibrium heart rate (bpm),
65 = assumed resting heart rate in comfortable conditions (bpm), and t = time in hours.
V. Wet bulb globe temperature index (WBGT)
Wet bulb globe temperature is given by:
for conditions with solar radiation, and:
for indoor conditions with no solar radiation, where Tnwb= temperature of a naturally ventilated wet bulb thermometer, Ta = air temperature, and Tg = temperature of a 150 mm diameter black globe thermometer.
There are several ways to define a dose of ionizing radiation, each appropriate for different purposes.
Absorbed dose resembles pharmacological dose the most closely. While pharmacological dose is the quantity of substance administered to a subject per unit weight or surface, radiological absorbed dose is the amount of energy transmitted by ionizing radiation per unit mass. Absorbed dose is measured in Grays (1 Gray = 1 joule/kg).
When individuals are exposed homogeneously—for example, by external irradiation by cosmic and terrestrial rays or by internal irradiation by potassium-40 present in the body—all organs and tissues receive the same dose. Under these circumstances, it is appropriate to speak of whole-body dose. It is, however, possible for exposure to be non-homogenous, in which case some organs and tissues will receive significantly higher doses than others. In this case, it is more relevant to think in terms of organ dose. For example, inhalation of radon daughters results in exposure of essentially only the lungs, and incorporation of radioactive iodine results in irradiation of the thyroid gland. In these cases, we may speak of lung dose and thyroid dose.
However, other units of dose that take into account differences in the effects of different types of radiation and the different radiation sensitivities of tissues and organs, have also been developed.
The development of biological effects (e.g., inhibition of cell growth, cell death, azoospermia) depends not only on the absorbed dose, but also on the specific type of radiation. Alpha radiation has a greater ionizing potential than beta or gamma radiation. Equivalent dose takes this difference into account by applying radiation-specific weighting factors. The weighting factor for gamma and beta radiation (low ionizing potential), is equal to 1, while that for alpha particles (high ionizing potential) is 20 (ICRP 60). Equivalent dose is measured in Sieverts (Sv).
In cases involving non-homogenous irradiation (e.g., the exposure of various organs to different radionuclides), it may be useful to calculate a global dose that integrates the doses received by all organs and tissues. This requires taking into account the radiation sensitivity of each tissue and organ, calculated from the results of epidemiological studies of radiation-induced cancers. Effective dose is measured in Sieverts (Sv) (ICRP 1991). Effective dose was developed for the purposes of radiation protection (i.e., risk management) and is thus inappropriate for use in epidemiological studies of the effects of ionizing radiation.
Collective dose reflects the exposure of a group or population and not of an individual, and is useful for evaluating the consequences of exposure to ionizing radiation at the population or group level. It is calculated by summing the individual received doses, or by multiplying the average individual dose by the number of exposed individuals in the groups or populations in question. Collective dose is measured in man-Sieverts (man Sv).
ILO 80th Session, 2nd June 1993
ILO 80th Session, 2nd June 1993
PART I. SCOPE AND DEFINITIONS
1. The purpose of this Convention is the prevention of major accidents involving hazardous substances and the limitation of the consequences of such accidents.…
For the purposes of this Convention:
(a) the term “hazardous substance” means a substance or mixture of substances which by virtue of chemical, physical or toxicological properties, either singly or in combination, constitutes a hazard;
(b) the term “threshold quantity” means for a given hazardous substance or category of substances that quantity, prescribed in national laws and regulations by reference to specific conditions, which if exceeded identifies a major hazard installation;
(c) the term “major hazard installation” means one which produces, processes, handles, uses, disposes of or stores, either permanently or temporarily, one or more hazardous substances or categories of substances in quantities which exceed the threshold quantity;
(d) the term “major accident” means a sudden occurrence—such as a major emission, fire or explosion—in the course of an activity within a major hazard installation, involving one or more hazardous substances and leading to a serious danger to workers, the public or the environment, whether immediate or delayed;
(e) the term “safety report“ means a written presentation of the technical, management and operational information covering the hazards and risks of a major hazard installation and their control and providing justification for the measures taken for the safety of the installation;
(f) the term “near miss” means any sudden event involving one or more hazardous substances which, but for mitigating effects, actions or systems, could have escalated to a major accident.
PART II. GENERAL PRINCIPLES
1. In the light of national laws and regulations, conditions and practices, and in consultation with the most representative organizations of employers and workers and with other interested parties who may be affected, each Member shall formulate, implement and periodically review a coherent national policy concerning the protection of workers, the public and the environment against the risk of major accidents.
2. This policy shall be implemented through preventive and protective measures for major hazard installations and, where practicable, shall promote the use of the best available safety technologies.
1. The competent authority, or a body approved or recognized by the competent authority, shall, after consulting the most representative organizations of employers and workers and other interested parties who may be affected, establish a system for the identification of major hazard installations as defined in Article 3(c), based on a list of hazardous substances or of categories of hazardous substances or of both, together with their respective threshold quantities, in accordance with national laws and regulations or international standards.
2. The system mentioned in paragraph 1 above shall be regularly reviewed and updated.
The competent authority, after consulting the representative organizations of employers and workers concerned, shall make special provision to protect confidential information transmitted or made available to it in accordance with Articles 8, 12, 13 or 14, whose disclosure would be liable to cause harm to an employer’s business, so long as this provision does not lead to serious risk to the workers, the public or the environment.
PART III. RESPONSIBILITIES OF EMPLOYERS IDENTIFICATION
Employers shall identify any major hazard installation within their control on the basis of the system referred to in Article 5.
1. Employers shall notify the competent authority of any major hazard installation which they have identified:
(a) within a fixed time-frame for an existing installation;
(b) before it is put into operation in the case of a new installation.
2. Employers shall also notify the competent authority before any permanent closure of a major hazard installation.
In respect of each major hazard installation employers shall establish and maintain a documented system of major hazard control which includes provision for:
(a) the identification and analysis of hazards and the assessment of risks including consideration of possible interactions between substances;
(b) technical measures, including design, safety systems, construction, choice of chemicals, operation, maintenance and systematic inspection of the installation;
(c) organizational measures, including training and instruction of personnel, the provision of equipment in order to ensure their safety, staffing levels, hours of work, definition of responsibilities, and controls on outside contractors and temporary workers on the site of the installation;
(d) emergency plans and procedures, including:
(i) the preparation of effective site emergency plans and procedures, including
emergency medical procedures, to be applied in case of major accidents or threat
thereof, with periodic testing and evaluation of their effectiveness and revision as
(ii) the provision of information on potential accidents and site emergency plans to
authorities and bodies responsible for the preparation of emergency plans and
procedures for the protection of the public and the environment outside the site of
(iii) any necessary consultation with such authorities and bodies;
(e) measures to limit the consequences of a major accident;
(f) consultation with workers and their representatives;
(g) improvement of the system, including measures for gathering information and analysing accidents and near misses. The lessons so learnt shall be discussed with the workers and their representatives and shall be recorded in accordance with national law and practice.…
* * *
PART IV. RESPONSIBILITIES OF COMPETENT AUTHORITIES
OFF-SITE EMERGENCY PREPAREDNESS
Taking into account the information provided by the employer, the competent authority shall ensure that emergency plans and procedures containing provisions for the protection of the public and the environment outside the site of each major hazard installation are established, updated at appropriate intervals and coordinated with the relevant authorities and bodies.
The competent authority shall ensure that:
(a) information on safety measures and the correct behaviour to adopt in the case of a major accident is disseminated to members of the public liable to be affected by a major accident without their having to request it and that such information is updated and redisseminated at appropriate intervals;
(b) warning is given as soon as possible in the case of a major accident;
(c) where a major accident could have transboundary effects, the information required in (a) and (b) above is provided to the States concerned, to assist in cooperation and coordination arrangements.
The competent authority shall establish a comprehensive siting policy arranging for the appropriate separation of proposed major hazard installations from working and residential areas and public facilities, and appropriate measures for existing installations. Such a policy shall reflect the General Principles set out in Part II of the Convention.
1. The competent authority shall have properly qualified and trained staff with the appropriate skills, and sufficient technical and professional support, to inspect, investigate, assess, and advise on the matters dealt with in this Convention and to ensure compliance with national laws and regulations.
2. Representatives of the employer and representatives of the workers of a major hazard installation shall have the opportunity to accompany inspectors supervising the application of the measures prescribed in pursuance of this Convention, unless the inspectors consider, in the light of the general instructions of the competent authority, that this may be prejudicial to the performance of their duties.
The competent authority shall have the right to suspend any operation which poses an imminent threat of a major accident.
PART V. RIGHTS AND DUTIES OF WORKERS AND THEIR REPRESENTATIVES
The workers and their representatives at a major hazard installation shall be consulted through appropriate cooperative mechanisms in order to ensure a safe system of work. In particular, the workers and their representatives shall:
(a) be adequately and suitably informed of the hazards associated with the major hazard installation and their likely consequences;
(b) be informed of any orders, instructions or recommendations made by the competent authority;
(c) be consulted in the preparation of, and have access to, the following documents:
(i) the safety report;
(ii) emergency plans and procedures;
(iii) accident reports;
(d) be regularly instructed and trained in the practices and procedures for the prevention of major accidents and the control of developments likely to lead to a major accident and in the emergency procedures to be followed in the event of a major accident;
(e) within the scope of their job, and without being placed at any disadvantage, take corrective action and if necessary interrupt the activity where, on the basis of their training and experience, they have reasonable justification to believe that there is an imminent danger of a major accident, and notify their supervisor or raise the alarm, as appropriate, before or as soon as possible after taking such action;
(f) discuss with the employer any potential hazards they consider capable of generating a major accident and have the right to notify the competent authority of those hazards.
Workers employed at the site of a major hazard installation shall:
(a) comply with all practices and procedures relating to the prevention of major accidents and the control of developments likely to lead to a major accident within the major hazard installation;
(b) comply with all emergency procedures should a major accident occur.
PART VI. RESPONSIBILITY OF EXPORTING STATES
When, in an exporting member State, the use of hazardous substances, technologies or processes is prohibited as a potential source of a major accident, the information on this prohibition and the reasons for it shall be made available by the exporting member State to any importing country.
Source: Excerpts, Convention No. 174 (ILO 1993).