The concept of an Environmental Noise Impact Analysis (ENIA) is central to the philosophy of managing environmental noise. An ENIA should be required before implementing any project that would significantly increase the level of environmental noise in a community (typically, greater than a 5dB increase).
The first step in performing an ENIA is to develop a baseline description of the existing noise environment. Next, the expected level of noise from a new source is added to the baseline exposure level to produce the new overall noise level.
If the new total noise level is expected to cause an unacceptable impact on human health, trade-off analyses should then be performed to assess the cost, technical feasibility and community acceptance of noise mitigation measures.
It is strongly recommended that countries develop standardized procedures for performing ENIAs (Finegold et al. 1998; SABS 1998).
Assessment of Adverse Effects of Noise on Human Health
In setting noise standards, the adverse health effects from which the population is to be protected need to be defined. Health effects range from hearing impairment to sleep disturbance, speech interference to annoyance.
The distinction between adverse and non-adverse effects sometimes poses considerable difficulties. More serious noise effects, such as hearing impairment or permanent threshold shift, are generally accepted as adverse.
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Consideration of health effects that are both temporary and reversible, or that involve functional changes with uncertain clinical significance, requires a judgment on whether these less-serious effects should be considered when deriving guideline values.
Judgments as to the adversity of health effects may differ between countries, because of factors such as cultural backgrounds and different levels of health status.
Estimation of the Population at Risk
The population at risk is that part of the population in a given country or community that is exposed to enhanced levels of noise. Each population has sensitive groups or sub-populations that are at higher risk of developing health effects due to noise exposure.
Sensitive groups include individuals impaired by concurrent diseases or other physiological limitations and those with specific characteristics that make them more vulnerable to noise.
The sensitive groups in a population may vary across countries due to differences in medical care, nutritional status, lifestyle and demographic factors, prevailing genetic factors, and whether endemic or debilitating diseases are prevalent.
Calculation of Exposure-Response Relationships
In developing standards, regulators should consider the degree of uncertainty in the exposure- response relationships provided in the noise guidelines.
Differences in the population structure (age, health status), climate (temperature, humidity) and geography (altitude, environment) can influence the prevalence and severity of noise-related health effects. In consequence, modified exposure-response relationships may need to be applied when setting noise standards.
Assessment of Risks and their Acceptability
In the absence of distinct thresholds for the onset of health effects, regulators must determine what constitutes an acceptable health risk for the population and select an appropriate noise standard to protect public health.
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This is also true in cases where thresholds are present, but where it would not be feasible to adopt noise guidelines as standards because of economical and/or technical constraints. The acceptability of the risks involved, and hence the standards selected, will depend on several factors.
These include the expected incidence and severity of the potential effects, the size of the population at risk, the perception of related risks, and the degree of scientific uncertainty that the effects will occur at any given noise level.
For example, if it is suspected that a health effect is severe and the size of the population at risk is large, a more cautious approach would be appropriate than if the effect were less troubling, or if the population were smaller.
Again, the acceptability of risk may vary among countries because of differences in social norms, and the degree of adversity and risk perception by the general population and stakeholders. Risk acceptability is also influenced by how the risks associated with noise compare with risks from other pollution sources or human activities.
In summary, more serious noise effects, such as hearing impairment or permanent threshold shift, are generally accepted as adverse. The first step in performing an ENIA is to develop a baseline description of the existing noise environment.
In the absence of distinct thresholds for the onset of health effects, regulators must determine what constitutes an acceptable health risk for the population.
The concept of an environmental noise impact analysis (ENIA) is vital to the philosophy of managing environmental noise. In setting noise standards, the adverse health effects from which the population is to be protected need to be defined.