Occupational noise

1. Introduction
Physically, there is no difference between sound and noise. Sound is a sensory
perception and noise corresponds to undesired sound. By extension, noise is any
unwarranted disturbance within a useful frequency band (NIOSH, 1991). Noise is
present in every human activity, and when assessing its impact on human well-being
it is usually classified either as occupational noise (i.e. noise in the workplace), or as
environmental noise, which includes noise in all other settings, whether at the
community, residential, or domestic level (e.g. traffic, playgrounds, sports, music).
This guide concerns only occupational noise; the health effects of environmental noise
are covered in a separate publication (de Hollander et al., 2004).
High levels of occupational noise remain a problem in all regions of the world. exposed to hazardous noise (NIOSH, 1998). (12−15% of the workforce) are exposed to noise levels defined as hazardous by WHO
Although noise is associated with almost every work activity, some
activities are associated with particularly high levels of noise, the most important of
flying commercial jets. Occupations at highest risk for NIHL include those in
manufacturing, transportation, mining, construction, agriculture and the military.
The situation is improving in developed countries, as more widespread appreciation of
Data for developing
countries are scarce, but available evidence suggests that average noise levels are well
above the occupational level recommended in many developed nations (Suter, 2000;
The average noise levels in developing countries may be
There are therefore several reasons to assess the burden of disease from occupational
noise at country or subnational levels. Occupational noise is a widespread risk factor,
with a strong evidence base linking it to an important health outcome (hearing loss).
It is also distinct from environmental noise, in that it is by definition associated with
An assessment of the burden of disease associated with occupational noise can help
guide policy and focus research on this problem. occupational noise (WHO/FIOH, 2001).
2. The risk factor and its health outcomes
2.1 Measuring noise levels
There are a variety of metrics for quantifying noise levels, the most useful of which
for measuring sound as a health hazard is described in de Hollander et al. (2004). In
account for the sensitivity of people to noise. These corrections depend on the noise
frequency and characteristics (impulse, intermittent or continuous noise levels), and
the source of noise. The following measures are most relevant for assessing
occupational noise levels.
Sound pressure level. The sound pressure level (L) is a measure of the air vibrations
that make up sound. Because the human ear can detect a wide range of sound
pressure levels (from 20 μPa to 200 Pa), they are measured on a logarithmic scale
with units of decibels (dB) to indicate the loudness of a sound.
Sound level. frequencies. To account for the perceived loudness of a sound, a spectral sensitivity
factor is used to weight the sound pressure level at different frequencies (A-filter).
These A-weighted sound pressure levels are expressed in units of dB(A).
Equivalent sound levels. When sound levels fluctuate in time, which is often the case
for occupational noise, the equivalent sound level is determined over a specific time
period. In this guide, the A-weighted sound level is averaged over a period of time
A common exposure period, T, in occupational
studies and regulations is 8 h, and the parameter is designated by the symbol, LAeq,8h.

2.2 Disease outcomes related to the risk factor
In general, the health consequences of a given level of occupational noise are likely to
review has therefore been carried out of all well-designed epidemiological studies that
link occupational noise exposure to health outcomes, regardless of where the study
The review of the literature indicates that noise has a series of health effects, in
addition to hearing impairment (Table 1). with noise in the workplace. Other consequences of workplace noise, such as
annoyance, hypertension, disturbance of psychosocial well-being, and psychiatric
disorders have also been described (de Hollander et al., 2004).
For occupational noise, the best characterized health outcome is hearing impairment.
The first effects of exposure to excess noise are typically an increase in the threshold
of hearing (threshold shift), as assessed by audiometry. hearing thresholds of an average 10 dB or more at 2000, 3000 and 4000 Hz in either
ear (poorer hearing) (NIOSH, 1998). NIHL is measured by comparing the threshold
of hearing at a specified frequency with a specified standard of normal hearing, and is
reported in units of decibel hearing loss (dBHL).
Threshold shift is the precursor of NIHL, the main outcome of occupational noise. It
accompanied by tinnitus. Because hearing impairment is usually gradual, the affected
worker will not notice changes in hearing ability until a large threshold shift has
occurred. Noise-induced hearing impairment occurs predominantly at higher
frequencies (3000−6000 Hz), with the largest effect at 4000 Hz. increases in severity with continued exposure.
− social isolation;
− impaired communication with coworkers and family;
− decreased ability to monitor the work environment (warning signals, equipment
sounds);
− increased injuries from impaired communication and isolation;
− anxiety, irritability, decreased self-esteem;
− lost productivity;
− expenses for workers’ compensation and hearing aids.
2.3 The strength of the evidence for disease outcomes
The mechanisms linking occupational noise to the health outcomes described in the
countries or regions. strength of relationships, other studies are usually relevant for assessing the strength
of evidence for causality.
Evidence is usually assessed on the grounds of biological plausibility, strength and
consistency of association, independence of confounding variables and reversibility
(Hill, 1965). psychosocial well-being, psychiatric disorders, and effects on performance are
plausible outcomes, but are only weakly supported by epidemiological evidence.
Other plausible outcomes include biochemical effects, immune system effects, and
birth-weight effects, but again there is limited evidence to support these outcomes.
There is stronger evidence of noise-based annoyance, defined as “a feeling of
resentment, displeasure, discomfort, dissatisfaction or offence which occurs when
noise interferes with someone’s thoughts, feelings or daily activities” (Passchier-
Vermeer, 1993). Noise annoyance is always assessed at the level of populations,
There is consistent evidence for annoyance in populations
about 42 dB(A). doubt that annoyance from noise adversely affects human well-being.
A recent meta-analysis reviewed the effects of occupational and environmental noise
on a variety of cardiovascular risks, including hypertension, use of anti-hypertension
drugs, consultation with a general practitioner or specialist, use of cardiovascular
medicines, angina pectoris, myocardial infarction and prevalence of ischaemic heart
disease (van Kempen et al., 2002). The analysis showed an association with
hypertension, but only limited evidence for an association with the other health
outcomes. Reasons for the limited evidence included methodological weaknesses,
such as poor (retrospective) exposure assessment, poorly controlled confounding
variables, and selection bias (such as the “healthy worker” effect, where the studied
work through disability). individual studies, and summary relative risks were statistically significant in only a
limited number of cases. Overall, the causal link is plausible, and the meta-analysis
provides support for further investigation of cardiovascular effects in the future.
the meta-analysis. Global Burden of Disease study, and methods for estimating the cardiovascular
effects of noise were not defined (Concha-Barrientos et al., 2004). This guide does
not therefore provide information for assessing the cardiovascular effects of noise at
national or local levels. the physical properties of noise and damage to the hearing system). supported by epidemiological studies that compared the prevalence of hearing loss in
different categories of occupations, or in particularly noisy occupations (e.g. Arndt et
al., 1996; Waitzman & Smith, 1998; Hessel, 2000; Palmer, Pannett & Griffin, 2001).
The studies showed a strong association between occupational noise and NIHL, an
effect that increased with the duration and magnitude of the noise exposure. For
example, the risk for “blue-collar” construction workers was 2 to >3.5-fold greater
(Table 2). exposure to vibrations, ototoxic drugs and some chemicals, the association with
occupational noise remains robust after accounting for these influences. epidemiological evidence for an effect of high levels of occupational exposure on
hearing loss in unborn children (e.g. Lalande, Hetu & Lambert, 1986), but there was
Global Burden of Disease study, and it is not covered further in this guide.
3.4 Health outcomes to include in the burden of disease assessment
The selection of a health outcome should be made principally on the strength of the
evidence of causality and on the availability of information for quantifying health
impacts. It is also important that the health outcome has been assessed within the
study population, or can reasonably be extrapolated from other populations. several possible sources for health statistics, including national health statistics, a
national burden of disease study, or “prior estimates” provided by WHO. More
(Prüss-Üstün et al., 2003).
Depending on the aim of the study, it may be preferable to assess disease burden in
terms of attributable disease incidence, or overall disease burden, using summary
measures of population health such as DALYs (Murray, Salomon & Mathers, 2000).
with the health burden from other risk factors. A goal of burden of disease
assessments is to maximize the compatibility of frameworks for assessing the burden
of disease for risk factors. associated with each disease.
health outcomes often assessed in national health statistics and as part of WHO
burden of disease assessments. se. Should annoyance cause other health outcomes, such as hypertension and
associated cardiovascular disease, then other outcomes could be considered. comparative disability weights independently, to take them from other studies (e.g. de
Hollander et al., 2004), or to extrapolate them from similar health outcomes. You
should be aware that an independent assessment of the severity of such outcomes
introduces additional uncertainty when the results are compared with other risk factors
This guide follows the previous global assessment of occupational noise, in that only
the effects of occupational noise on NIHL are assessed. Several definitions of hearing
impairment are available in the literature. In the occupational setting, hearing
impairment is generally defined as “ a binaural pure-tone average for the frequencies
Sriwattanatamma & Breysse, 2000). correspond to the WHO definition of disabling hearing loss (i.e. with an associated
disability weight, and corresponding to a quantifiable burden of disease). This level
of hearing impairment is defined as “permanent unaided hearing threshold level for
4000 kHz” (Table 3). prevalence of hearing loss that corresponds to the WHO definition, as it is preferable
for burden of disease assessments. procedure is supported by large epidemiological studies, and should therefore