Exposure

Definition of the exposure indicator
The most appropiate exposure measurement for occupational noise is the A-weighted
to damage human hearing. most commonly used epidemiological measurement of exposure. Exposure is initially
asessing the burden of disease. exposure above and below cut-off values, rather than as a distribution. limits in developed (usually 85 dB(A)) and many developing (usually 90 dB(A))

countries for an 8-hour day (Hessel & Sluis-Cremer, 1987; Alidrisi et al., 1990;
Shaikh, 1996; Hernandez-Gaytan et al., 2000; Osibogun, Igweze & Adeniran, 2000;
Sriwattanatamma & Breysse, 2000; Ahmed et al., 2001):
− minimum noise exposure: <85 dB(A)
− moderately high noise exposure: 85−90 dB(A)
− high noise exposure: >90 dB(A).
4.2 Determining the distribution of exposure in the population
The most accurate assessments of health impacts at the national level are obtained
from local exposure data, since population exposure distributions can vary between
countries. The most commonly used methods to assess health impacts are:
− area surveys: noise levels are measured at different sites across an area, such as
− dosimetry: a person’s cumulative exposure to noise over a period of time is
measured with a dosimeter;
− engineering surveys: noise is measured using a range of instruments.
Ideally, representative data will be available on the average levels of occupational
noise for all major occupations within the country, either from the published scientific
literature or from other sources of data. If such data are not available,
epidemiological surveys can be carried out to determine the distribution of noise
exposure by occupation. distribution will have to be estimated from existing sources of information. A reasonable estimate of the exposure distribution can be obtained by extrapolating
from existing data for studies undertaken elsewhere, provided that the data are from
similar occupational environments. determinant of exposure level is worker occupation. Industry-specific studies in the
perceived hearing loss, and 90% of coal miners have hearing impairment by age 52
Also, it is estimated that 70% of male metal/nonmetal miners will have hearing
impairment by age 60 years (NIOSH, 1991). workplace-specific factors will also influence the level of exposure. These factors
whether there are engineering and work practice controls; and whether personal
protective devices are used and properly maintained. developed countries than in developing countries). extrapolations should be made from data for comparable occupations in comparable
countries.
The Global Burden of Disease study estimated exposure distributions using an
occupational category approach, modified to reflect the different noise exposures for
occupations in different economic subsectors. national level, using country data where available, or by extrapolating from data for
other studies if local data are not available.
The first step is to assess the proportion of workers in each occupational category that
is exposed to at least moderately high occupational noise levels (>85 dB(A)); see
Table 4). If these data are not available from national surveys, the distribution can be
based on the results of a large survey in the USA (DHHS, 1986; NIOSH, 1998). For each occupational category, the proportion of production workers exposed to high
noise levels (i.e. >90 dB(A)) is estimated from a survey of over 9 million production
workers in the USA carried out by the USA Occupational Safety and Health
Administration in 1981 (cited in NIOSH 1991; DHHS, 1986). shown in bold font in Table 4. Of the 6 063 000 production workers with exposures
at or above 85 dB(A), 3 407 000 (or 56%) were exposed to noise levels above 90
dB(A). We therefore estimate that among production workers exposed at or above 85
dB(A), half were exposed at 85–90 dB(A), and half were exposed at >90 dB(A).
Exposures in the remaining occupational categories and economic subsectors are
estimated either by extrapolation from the most relevant subsector of the survey of
production workers (figures shown in italics in Table 4), or by expert judgement
the agricultural workers and sales and service workers exposed at or above 85 dB(A),
approximately 70% are exposed at 85–90 dB(A), and 30% at >90 dB(A). All
professional, administrative, and clerical workers with noise exposure at or above 85
dB(A) are assumed to be in the 85–90 dB(A) exposure level.
the country in which the assessment is undertaken. In developing countries, because
hearing conservation programmes are rare, the global assessment assumed that only
5% of the production workers would be exposed at the 85–90 dB(A) level, and 95%
would be exposed at the >90 dB(A) level. exposed at or above 85 dB(A) are assigned to the 85–90 dB(A) level, because
mechanization is not widespread in countries in WHO developing subregions (e.g.
The second step consists of defining the proportions of workers in each economic
subsector, by occupational category. These data may be available from national
proportion of workers in each occupation is multiplied by the proportion of workers in
the occupation exposed to moderately high, or high, noise levels). proportion of the working population in each economic subsector is determined by
gender. In the fifth step, these values are multiplied by the proportion of workers in
the occupational category exposed to the specific noise level. calculations is performed for all economic subsectors, and the results summed to give
the proportion of the total working population that is exposed at each noise level.
work, by defining the proportion of the working-age population that is currently
employed. the working-age population. Finally, the overall population exposure is given by
multiplying the proportion of the working population exposed at each exposure level,
by the proportion of the total population in work.
Table 5 summarizes these steps and the sources of data necessary to complete them,
and gives example calculations for the proportion of the male working-age population
in the USA that is exposed to moderately high noise levels. assessment of the exposure distribution, the calculations would be repeated for
exposure to high noise levels, and for females as well as males. Estimates for the prevalence of noise exposure, determined using the described
The figures assume there are equal employment rates
in all age groups of the working-age population.