Terms

In the field of occupational noise, the terms regulation, standard, and legislation are often used interchangeably, even though technically they may have slightly different meanings. A standard is a codified set of rules or guidelines, much like a regulation, but it can be developed under the auspices of a consensus group, such as the International Organization for Standardization (ISO). Legislation consists of laws prescribed by legislating authorities or by local governing bodies.

Many national standards are called legislation. Some official bodies use the terms standards and regulations as well. The Council of the European Communities (CEC) issues Directives. All members of the European Community needed to “harmonize” their noise standards (regulations or legislation) with the 1986 EEC Directive on occupational noise exposure by the year 1990 (CEC 1986). This means that the noise standards and regulations of the member countries had to be at least as protective as the EEC Directive. In the United States, a regulation is a rule or order prescribed by a government authority and is usually more in the nature of a formality than a standard.

Some nations have a code of practice, which is somewhat less formal. For example, the Australian national standard for occupational exposure to noise consists of two short paragraphs setting forth mandatory rules, followed by a 35-page code of practice which provides practical guidance on how the standard should be implemented. Codes of practice usually do not have the legal force of regulations or legislation.

Another term that is used occasionally is recommendation, which is more like a guideline than a mandatory rule and is not enforceable. In this article, the term standard will be used generically to represent noise standards of all degrees of formality.

Consensus Standards

One of the most widely used noise standards is ISO 1999, Acoustics: Determination of Occupational Noise Exposure and Estimate of Noise-Induced Hearing Impairment (ISO 1990). This international consensus standard represents a revision of an earlier, less detailed version and it can be used to predict the amount of hearing loss expected to occur in various centiles of the exposed population at various audiometric frequencies as a function of exposure level and duration, age and sex.

The ISO is currently very active in the area of noise standardization. Its technical committee TC43, “Acoustics”, is working on a standard to evaluate the effectiveness of hearing conservation programmes. According to von Gierke (1993), TC43’s Subcommittee 1 (SC1) has 21 working groups, some of which are considering more than three standards each. TC43/SC1 has issued 58 noise-related standards and 63 additional standards are in a state of revision or preparation (von Gierke 1993).

Damage-Risk Criteria

The term damage-risk criteria refers to the risk of hearing impairment from various levels of noise. Many factors enter into the development of these criteria and standards in addition to the data describing the amount of hearing loss resulting from a certain amount of noise exposure. There are both technical and policy considerations.

The following questions are good examples of policy considerations: What proportion of the noise-exposed population should be protected, and how much hearing loss constitutes an acceptable risk? Should we protect even the most sensitive members of the exposed population against any loss of hearing? Or should we protect only against a compensable hearing handicap? It amounts to a question of which hearing loss formula to use, and different governmental bodies have varied widely in their selections.

In earlier years, regulatory decisions were made that allowed substantial amounts of hearing loss as an acceptable risk. The most common definition used to be an average hearing threshold level (or “low fence”) of 25 dB or greater at the audiometric frequencies 500, 1,000, and 2,000 Hz. Since that time, the definitions of “hearing impairment” or “hearing handicap” have become more restrictive, with different nations or consensus groups advocating different definitions. For example, certain US government agencies now use 25 dB at 1,000, 2,000, and 3,000 Hz. Other definitions may incorporate a low fence of 20 or 25 dB at 1,000, 2,000, and 4,000 Hz, and may include a broader range of frequencies.

In general, as definitions include higher frequencies and lower “fences” or hearing threshold levels, the acceptable risk becomes more stringent and a higher percentage of the exposed population will appear to be at risk from given levels of noise. If there is to be no risk of any hearing loss from noise exposure, even in the more sensitive members of the exposed population, the permissible exposure limit would have to be as low as 75 dBA. In fact, the EEC Directive has established an equivalent level (L_eq) of 75 dBA as the level at which the risk is negligible, and this level has also been put forward as a goal for Swedish production facilities (Kihlman 1992).

Overall, the prevailing thought on this subject is that it is acceptable for a noise-exposed workforce to lose some hearing, but not too much. As for how much is too much, there is no consensus at this time. In all probability, most nations draft standards and regulations in an attempt to keep the risk at a minimum level while taking technical and economic feasibility into account, but without coming to consensus on such matters as the frequencies, fence, or percentage of the population to be protected.

Presenting the Damage-Risk Criteria

Criteria for noise-induced hearing loss may be presented in either of two ways: noise-induced permanent threshold shift (NIPTS) or percentage risk. NIPTS is the amount of permanent threshold shift remaining in a population after subtracting the threshold shift that would occur “normally” from causes other than occupational noise. The percentage risk is the percentage of a population with a certain amount of noise-induced hearing impairment after subtracting the percentage of a similar population not exposed to occupational noise. This concept is sometimes called excess risk. Unfortunately, neither method is without problems.

The trouble with using NIPTS alone is that it is difficult to summarize the effects of noise on hearing. The data are usually set out in a large table showing noise-induced threshold shift for each audiometric frequency as a function of noise level, years of exposure and population centile. The concept of percentage risk is more attractive because it uses single numbers and appears easy to understand. But the trouble with percentage risk is that it can vary enormously depending on a number of factors, particularly the height of the hearing threshold level fence and the frequencies used to define hearing impairment (or handicap).

With both methods, the user needs to be sure that the exposed and non-exposed populations are carefully matched for such factors as age and non-occupational noise exposure.

National Noise Standards

Table 1 gives some of the main features of the noise exposure standards of several nations. Most of the information is current as of this publication, but some standards may have been recently revised. Readers are advised to consult the newest versions of the national standards.

Table 1. Permissible exposure limits (PEL), exchange rates, and other requirements for noise exposure according to nation

a PEL = Permissible exposure limit.

b Exchange rate. Sometimes called the doubling rate or time/intensity trading ratio, this is the amount of change in noise level (in dB) allowed for each halving or doubling of exposure duration.

c Like the PEL, the levels initiating the requirements for engineering controls and audiometric testing also, presumably, are average levels.

Sources: Arenas 1995; Gunn; Embleton 1994; ILO 1994. Published standards of various nations have been further consulted.

Notes to table 1.

¹ Levels for engineering controls, hearing tests, and other elements of the hearing conservation programme are defined in a code of practice.

² There is some variation among the individual Canadian provinces: Ontario, Quebec and New Brunswick use 90 dBA with a 5-dB exchange rate; Alberta, Nova Scotia and Newfoundland use 85 dBA with a 5-dB exchange rate; and British Columbia uses 90 dBA with a 3-dB exchange rate. All require engineering controls to the level of the PEL. Manitoba requires certain hearing conservation practices above 80 dBA, hearing protectors and training on request above 85 dBA, and engineering controls above 90 dBA.

³ The Council of the European Communities (86/188/EEC) and Germany (UVV Larm-1990) state that it is not possible to give a precise limit for the elimination of hearing hazards and the risk of other health impairments from noise. Therefore the employer is obliged to reduce the noise level as far as possible, taking technical progress and the availability of control measures into account. Other EC nations may have adopted this approach as well.

⁴ Those countries comprised by the European Community were required to have standards that at least conformed to the EEC Directive by January 1, 1990.

⁵ China requires different levels for different activities: e.g., 70 dBA for precision assembly lines, processing workshops and computer rooms; 75 dBA for duty, observation and rest rooms; 85 dBA for new workshops; and 90 dBA for existing workshops.

⁶ Germany also has noise standards of 55 dBA for mentally stressful tasks and 70 dBA for mechanized office work.

⁷ Recommendation.

⁸ The Netherlands’ noise legislation requires engineering noise control at 85 dBA “unless this cannot be reasonably demanded”. Hearing protection must be provided above 80 dBA and workers are required to wear it at levels above 90 dBA.

⁹ New Zealand requires a maximum of 82 dBA for a 16-hour exposure. Ear muffs must be worn in noise levels exceeding 115 dBA.

¹⁰ Norway requires a PEL of 55 dBA for work requiring a large amount of mental concentration, 85 dBA for work requiring verbal communication or great accuracy and attention, and 85 dBA for other noisy work settings. Recommended limits are 10 dB lower. Workers exposed to noise levels greater than 85 dBA should wear hearing protectors.

¹¹ These levels apply to the OSHA noise standard, covering workers in general industry and the maritime trades. The US military services require standards that are somewhat more stringent. The US Air Force and the US Army both use an 85-dBA PEL and a 3-dB exchange rate.

Table 1 clearly shows the trend of most nations to use a permissible exposure limit (PEL) of 85 dBA, whereas about half of the standards still use 90 dBA for compliance with requirements for engineering controls, as allowed by the EEC Directive. The vast majority of the nations listed above have adopted the 3-dB exchange rate, except for Israel, Brazil and Chile, all of which use the 5-dB rule with an 85-dBA criterion level. The other notable exception is the United States (in the civilian sector), although both the US Army and the US Air Force have adopted the 3-dB rule.

In addition to their requirements to protect workers against hearing loss, several nations include provisions for preventing other adverse effects of noise. Some nations state the need to protect against the extra-auditory effects of noise in their regulations. Both the EEC Directive and the German standard acknowledge that workplace noise involves a risk for the health and safety of workers beyond hearing loss, but that current scientific knowledge of the extra-auditory effects does not enable precise safe levels to be set.

The Norwegian standard includes a requirement that noise levels must not exceed 70 dBA in work settings where speech communication is necessary. The German standard advocates noise reduction for the prevention of accident risks, and both Norway and Germany require a maximum noise level of 55 dBA to enhance concentration and prevent stress during mental tasks.

Some countries have special noise standards for different kinds of workplaces. For example, Finland and the United States have noise standards for motor vehicle cabs, Germany and Japan specify noise levels for offices. Others include noise as one of many regulated hazards in a particular process. Still other standards apply to specific types of equipment or machines, such as air compressors, chain saws and construction equipment.

In addition, some nations have promulgated separate standards for hearing protection devices (such as the EEC Directive, the Netherlands and Norway) and for hearing conservation programmes (such as France, Norway, Spain, Sweden and the United States.)

Some nations use innovative approaches to attack the occupational noise problem. For example, the Netherlands has a separate standard for newly constructed workplaces, and Australia and Norway give information to employers for instructing manufacturers in the provision of quieter equipment.

There is little information about the degree to which these standards and regulations are enforced. Some specify that employers “should” take certain actions (as in codes of practice or guidelines), while most specify that employers “shall”. Standards that use “shall” are more apt to be mandatory, but individual nations vary widely in their ability and inclination to secure enforcement. Even within the same nation, enforcement of occupational noise standards may vary considerably with the government in power.

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The Pervasive Nature of Occupational Noise

Noise is one of the most common of all the occupational hazards. In the United States, for example, more than 9 million workers are exposed to daily average A-weighted noise levels of 85 decibels (abbreviated here as 85 dBA). These noise levels are potentially hazardous to their hearing and can produce other adverse effects as well. There are approximately 5.2 million workers exposed to noise above these levels in manufacturing and utilities, which represents about 35% of the total number of workers in US manufacturing industries.

Hazardous noise levels are easily identified and it is technologically feasible to control excessive noise in the vast majority of cases by applying off-the-shelf technology, by redesigning the equipment or process or by retrofitting noisy machines. But all too often, nothing is done. There are several reasons for this. First, although many noise control solutions are remarkably inexpensive, others can be costly, especially when the aim is to reduce the noise hazard to levels of 85 or 80 dBA.

One very important reason for the absence of noise control and hearing conservation programmes is that, unfortunately, noise is often accepted as a “necessary evil”, a part of doing business, an inevitable part of an industrial job. Hazardous noise causes no bloodshed, breaks no bones, produces no strange-looking tissue, and, if workers can manage to get through the first few days or weeks of exposure, they often feel as though they have “got used” to the noise. But what has most likely happened is that they have started to incur a temporary hearing loss which dulls their hearing sensitivity during the work day and often subsides during the night. Thus, the progress of noise-induced hearing loss is insidious in that it creeps up gradually over the months and years, largely unnoticed until it reaches handicapping proportions.

Another important reason why the hazards of noise are not always recognized is that there is a stigma attached to the resulting hearing impairment. As Raymond Hétu has demonstrated so clearly in his article on rehabilitation from noise-induced hearing loss elsewhere in this Encyclopaedia, people with hearing impairments are often thought of as elderly, mentally slow and generally incompetent, and those at risk of incurring impairments are reluctant to acknowledge either their impairments or the risk for fear of being stigmatized. This is an unfortunate situation because noise-induced hearing losses become permanent, and, when added to the hearing loss that naturally occurs with ageing, can lead to depression and isolation in one’s middle and old age. The time to take preventive steps is before the hearing losses begin.

The Scope of Noise Exposure

As mentioned above, noise is especially prevalent in the manufacturing industries. The US Department of Labor has estimated that 19.3% of the workers in manufacturing and utilities are exposed to daily average noise levels of 90 dBA and above, 34.4% are exposed to levels above 85 dBA, and 53.1% to levels above 80 dBA. These estimates should be fairly typical of the percentage of workers exposed to hazardous levels of noise in other nations. The levels are likely to be somewhat higher in less developed nations, where engineering controls are not used as widely, and somewhat lower in nations with stronger noise control programmes, such as the Scandinavian countries and Germany.

Many workers throughout the world experience some very hazardous exposures, well above 85 or 90 dBA. For example, the US Labor Department has estimated that nearly half a million workers are exposed to daily average noise levels of 100 dBA and above, and more than 800,000 to levels between 95 and 100 dBA in the manufacturing industries alone.

Figure 1 ranks the noisiest manufacturing industries in the United States in descending order according to the percentage of workers exposed above 90 dBA and gives estimates of noise-exposed workers by industrial sector.

Figure 1. Occupational noise exposure—the US experience

Research Needs

In the following articles of this chapter, it should become clear to the reader that the effects on hearing of most types of noise are well-known. Criteria for the effects of continuous, varying and intermittent noise were developed some 30 years ago and remain essentially the same today. This is not true, however, of impulse noise. At relatively low levels, impulse noise seems to be no more damaging and possibly less so than continuous noise, given equal sound energy. But at high sound levels, impulse noise appears to be more damaging, especially when a critical level (or, more correctly, a critical exposure) is exceeded. Further research needs to be performed to define more exactly the shape of the damage/risk curve.

Another area that needs to be clarified is the adverse effect of noise, both on hearing and on general health, in combination with other agents. Although the combined effects of noise and ototoxic drugs are fairly well known, the combination of noise and industrial chemicals is of growing concern. Solvents and certain other agents appear to be increasingly neurotoxic when experienced in conjunction with high levels of noise.

Around the world, noise-exposed workers in the manufacturing industries and the military receive the major share of attention. There are, however, many workers in mining, construction, agriculture and transportation who are also exposed to hazardous levels of noise, as pointed out in figure 1. The unique needs associated with these occupations need to be assessed, and noise control and other aspects of hearing conservation programmes need to be extended to these workers. Unfortunately, the provision of hearing conservation programmes to noise-exposed workers does not guarantee that hearing loss and the other adverse effects of noise will be prevented. Standard methods to evaluate the effectiveness of hearing conservation programmes do exist, but they can be cumbersome and are not widely used. Simple evaluation methods need to be developed that can be used by small as well as large companies, and those with minimal resources.

The technology exists to abate most noise problems, as mentioned above, but there is a large gap between the existing technology and its application. Methods need to be developed by which information on all kinds of noise control solutions can be disseminated to those who need it. Noise control information needs to be computerized and made available not only to users in developing nations but to industrialized nations as well.

Future Trends

In some countries there is a growing trend to place more emphasis on non-occupational noise exposure and its contribution to the burden of noise-induced hearing loss. These kinds of sources and activities include hunting, target shooting, noisy toys and loud music. This focus is beneficial in that it highlights some potentially significant sources of hearing impairment, but it can actually be detrimental if it diverts attention from serious occupational noise problems.

A very dramatic trend is evident among the nations belonging to the European Union, where standardization for noise is progressing at an almost breathless pace. This process includes standards for product noise emissions as well as for noise exposure standards.

The standard-setting process is not moving rapidly at all in North America, especially in the United States, where regulatory efforts are at a standstill and movement toward deregulation is a possibility. Efforts to regulate the noise of new products were abandoned in 1982 when the Noise Office in the US Environmental Protection Agency was closed, and occupational noise standards may not survive the deregulatory climate in the current US Congress.

The developing nations appear to be in the process of adopting and revising noise standards. These standards are tending toward conservatism, in that they are moving toward a permissible exposure limit of 85 dBA, and toward an exchange rate (time/intensity trading relation) of 3 dB. How well these standards are enforced, especially in burgeoning economies, is an open question.

The trend in some of the developing nations is to concentrate on controlling noise by engineering methods rather than to struggle with the intricacies of audiometric testing, hearing protection devices, training and record keeping. This would appear to be a very sensible approach wherever feasible. Supplementation with hearing protectors may be necessary at times to reduce exposures to safe levels.

The Effects of Noise

Certain of the materials which follow have been adapted from Suter, AH, “Noise and the conservation of hearing”, Chapter 2 in Hearing Conservation Manual (3rd ed.), Council for Accreditation in Occupational Hearing Conservation, Milwaukee, WI, USA (1993).

Loss of hearing is certainly the most well-known adverse effect of noise, and probably the most serious, but it is not the only one. Other detrimental effects include tinnitus (ringing in the ears), interference with speech communication and with the perception of warning signals, disruption of job performance, annoyance and extra-auditory effects. Under most circumstances, protecting workers’ hearing should protect against most other effects. This consideration provides additional support for companies to implement good noise control and hearing conservation programmes.

Hearing impairment

Noise-induced hearing impairment is very common, but it is often underrated because there are no visible effects and, in most cases, no pain. There is only a gradual, progressive loss of communication with family and friends, and a loss of sensitivity to sounds in the environment, such as birdsong and music. Unfortunately, good hearing is usually taken for granted until it is lost.

These losses may be so gradual that individuals do not realize what has happened until the impairment becomes handicapping. The first sign is usually that other people do not seem to speak as clearly as they used to. The hearing-impaired person will have to ask others to repeat themselves, and he or she often becomes annoyed with their apparent lack of consideration. Family and friends will often be told, “Don’t shout at me. I can hear you, but I just can’t understand what you’re saying.”

As the hearing loss becomes worse, the individual will begin to withdraw from social situations. Church, civic meetings, social occasions and theatre begin to lose their attraction and the individual will choose to stay at home. The volume of the television becomes a source of contention within the family, and other family members are sometimes driven out of the room because the hearing-impaired person wants it so loud.

Presbycusis, the hearing loss that naturally accompanies the ageing process, adds to the hearing handicap when the person with noise-induced hearing loss becomes older. Eventually, the loss may progress to such a severe stage that the individual can no longer communicate with family or friends without great difficulty, and then he or she is indeed isolated. A hearing aid may help in some cases, but the clarity of natural hearing will never be restored, as the clarity of vision is with eyeglasses.

Occupational hearing impairment

Noise-induced hearing impairment is usually considered an occupational disease or illness, rather than an injury, because its progression is gradual. On rare occasions, an employee may sustain immediate, permanent hearing loss from a very loud event such as an explosion or a very noisy process, such as riveting on steel. In these circumstances the hearing loss is sometimes referred to as an injury and is called “acoustic trauma”. The usual circumstance, however, is a slow decrease in hearing ability over many years. The amount of impairment will depend on the level of the noise, the duration of the exposure and the susceptibility of the individual worker. Unfortunately, there is no medical treatment for occupational hearing impairment; there is only prevention.

The auditory effects of noise are well documented and there is little controversy over the amount of continuous noise that causes varying degrees of hearing loss (ISO 1990). That intermittent noise causes hearing loss is also uncontested. But periods of noise that are interrupted by periods of quiet can offer the inner ear an opportunity to recover from temporary hearing loss and may therefore be somewhat less hazardous than continuous noise. This is true mainly for outdoor occupations, but not for inside settings such as factories, where the necessary intervals of quiet are rare (Suter 1993).

Impulse noise, such as the noise from gunfire and metal stamping, also damages hearing. There is some evidence that the hazard from impulse noise is more severe than that from other types of noise (Dunn et al. 1991; Thiery and Meyer-Bisch 1988), but this is not always the case. The amount of damage will depend mainly on the level and duration of the impulse, and it may be worse when there is continuous noise in the background. There is also evidence that high-frequency sources of impulse noise are more damaging than those composed of lower frequencies (Hamernik, Ahroon and Hsueh 1991; Price 1983).

Hearing loss due to noise is often temporary at first. During the course of a noisy day, the ear becomes fatigued and the worker will experience a reduction in hearing known as temporary threshold shift (TTS). Between the end of one workshift and the beginning of the next the ear usually recovers from much of the TTS, but often, some of the loss remains. After days, months and years of exposure, the TTS leads to permanent effects and new amounts of TTS begin to build onto the now permanent losses. A good audiometric testing programme will attempt to identify these temporary hearing losses and provide for preventive measures before the losses become permanent.

Experimental evidence indicates that several industrial agents are toxic to the nervous system and produce hearing loss in laboratory animals, especially when they occur in combination with noise (Fechter 1989). These agents include (1) heavy metal hazards, such as lead compounds and trimethyltin, (2) organic solvents, such as toluene, xylene and carbon disulphide, and (3) an asphyxiant, carbon monoxide. Recent research on industrial workers (Morata 1989; Morata et al. 1991) suggests that certain of these substances (carbon disulphide and toluene) can increase the damaging potential of noise. There is also evidence that certain drugs which are already toxic to the ear can increase the damaging effects of noise (Boettcher et al. 1987). Examples include certain antibiotics and cancer chemotherapy drugs. Those in charge of hearing conservation programmes should be aware that workers exposed to these chemicals or using these drugs may be more susceptible to hearing loss, especially when exposed to noise in addition.

Non-occupational hearing impairment

It is important to understand that occupational noise is not the only cause of noise-induced hearing loss among workers, but hearing loss can also be caused by sources outside the workplace. These sources of noise produce what is sometimes called “sociocusis”, and their effects on hearing are impossible to differentiate from occupational hearing loss. They can only be surmised by asking detailed questions about the worker’s recreational and other noisy activities. Examples of sociocusic sources could be woodworking tools, chain saws, unmuffled motorcycles, loud music and firearms. Frequent shooting with large-calibre guns (without hearing protection) may be a significant contributor to noise-induced hearing loss, whereas occasional hunting with smaller-calibre weapons is more likely to be harmless.

The importance of non-occupational noise exposure and the resulting sociocusis is that this hearing loss adds to the exposure that an individual might receive from occupational sources. For the sake of workers’ overall hearing health, they should be counselled to wear adequate hearing protection when they engage in noisy recreational activities.

Tinnitus

Tinnitus is a condition that frequently accompanies both temporary and permanent hearing loss from noise, as well as other types of sensorineural hearing loss. Often referred to as a “ringing in the ears”, tinnitus may range from mild in some cases to severe in others. Sometimes individuals report that they are more bothered by their tinnitus than they are by their hearing impairment.

People with tinnitus are likely to notice it the most in quiet conditions, such as when they are trying to go to sleep at night, or when they are sitting in a sound-proof booth taking an audiometric test. It is a sign that the sensory cells in the inner ear have been irritated. It is often a precursor to noise-induced hearing loss and therefore an important warning signal.

Communication interference and safety

The fact that noise can interfere with or “mask” speech communication and warning signals is only common sense. Many industrial processes can be carried out very well with a minimum of communication among workers. Other jobs, however, such as those performed by airline pilots, railroad engineers, tank commanders and many others rely heavily on speech communication. Some of these workers use electronic systems that suppress the noise and amplify the speech. Nowadays, sophisticated communication systems are available, some with devices that cancel unwanted acoustic signals so that communication can take place more easily.

In many cases, workers just have to make do, straining to understand communications above the noise and shouting above it or signalling. Sometimes people may develop hoarseness or even vocal nodules or other abnormalities on the vocal cords from excessive strain. These individuals may need to be referred to for medical care.

People have learned from experience that in noise levels above about 80 dBA they have to speak very loudly, and in levels above 85 dBA they have to shout. In levels much above 95 dBA they have to move close together to communicate at all. Acoustical specialists have developed methods to predict the amount of communication that can take place in industrial situations. The resulting predictions are dependent upon the acoustical characteristics of both the noise and the speech (or other desired signal), as well as the distance between talker and listener.

It is generally known that noise can interfere with safety, but only a few studies have documented this problem (e.g., Moll van Charante and Mulder 1990; Wilkins and Acton 1982). There have been numerous reports, however, of workers who have got clothing or hands caught in machines and have been seriously injured while their co-workers were oblivious to their cries for help. To prevent communication breakdowns in noisy environments, some employers have installed visual warning devices.

Another problem, recognized more by noise-exposed workers themselves than by professionals in hearing conservation and occupational health, is that hearing protection devices may sometimes interfere with the perception of speech and warning signals. This appears to be true mainly when the wearers already have hearing losses and the noise levels fall below 90 dBA (Suter 1992). In these cases, workers have a very legitimate concern about wearing hearing protection. It is important to be attentive to their concerns and either to implement engineering noise controls or to improve the kind of protection offered, such as protectors built into an electronic communication system. In addition, hearing protectors are now available with a flatter, more “high fidelity” frequency response, which may improve workers’ abilities to understand speech and warning signals.

Effects on job performance

The effects of noise on job performance have been studied both in the laboratory and in actual working conditions. The results have shown that noise usually has little effect on the performance of repetitive, monotonous work, and in some cases can actually increase job performance when the noise is low or moderate in level. High levels of noise can degrade job performance, especially when the task is complicated or involves doing more than one thing at a time. Intermittent noise tends to be more disruptive than continuous noise, particularly when the periods of noise are unpredictable and uncontrollable. Some research indicates that people are less likely to help each other and more likely to exhibit antisocial behaviour in noisy environments than in quiet ones. (For a detailed review of the effects of noise on job performance see Suter 1992).

Annoyance

Although the term “annoyance” is more often connected with community noise problems, such as airports or race-car tracks, industrial workers may also feel annoyed or irritated by the noise of their workplace. This annoyance may be related to the interference of speech communication and job performance described above, but it may also be due to the fact that many people have an aversion to noise. Sometimes the aversion to noise is so strong that a worker will look for employment elsewhere, but that opportunity is not often feasible. After a period of adjustment, most will not appear to be bothered as much, but they may still complain about fatigue, irritability and sleeplessness. (The adjustment will be more successful if young workers are properly fitted with hearing protectors from the start, before they develop any hearing loss.) Interestingly, this kind of information sometimes surfaces after a company starts a noise control and hearing conservation programme because the workers would have become aware of the contrast between earlier and subsequently improved conditions.

Extra-auditory effects

As a biological stressor, noise can influence the entire physiological system. Noise acts in the same way that other stressors do, causing the body to respond in ways that may be harmful in the long run and lead to disorders known as the “stress diseases”. When facing danger in primitive times, the body would go through a series of biological changes, preparing either to fight or to run away (the classic “fight or flight” response). There is evidence that these changes still persist with exposure to loud noise, even though a person may feel “adjusted” to the noise.

Most of these effects appear to be transitory, but with continued exposure some adverse effects have been shown to be chronic in laboratory animals. Several studies of industrial workers also point in this direction, while some studies show no significant effects (Rehm 1983; van Dijk 1990). The evidence is probably strongest for cardiovascular effects such as increased blood pressure, or changes in blood chemistry. A significant set of laboratory studies on animals showed chronic elevated blood pressure levels resulting from exposure to noise around 85 to 90 dBA, which did not return to baseline after cessation of the exposure (Peterson et al. 1978, 1981 and 1983).

Studies of blood chemistry show increased levels of the catecholamines epinephrine and norepinephrine due to noise exposure (Rehm 1983), and a series of experiments by German investigators found a connection between noise exposure and magnesium metabolism in humans and animals (Ising and Kruppa 1993). Current thinking holds that the extra-auditory effects of noise are most likely mediated psychologically, through aversion to noise, making it very difficult to obtain dose-response relationships. (For a comprehensive overview of this problem, see Ising and Kruppa 1993.)

Because the extra-auditory effects of noise are mediated by the auditory system, meaning that it is necessary to hear the noise for adverse effects to occur, properly fitted hearing protection should reduce the likelihood of these effects in just the way it does with hearing loss.

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