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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