Acceptable Noise Levels

In estimating the risks, three or more stages, requiring the input of different disciplines.

The first step, hazard identification, is to determine the qualitative nature of the potential adverse consequences of contaminants (chemical, radiation, noise, etc.) and the strength of the evidence it may have that effect. This happens, for chemical hazards, building on the results of science of toxicology and epidemiology. For other types of risks, engineering or other disciplines are involved.

The second stage of chemical risk assessment, the dose-response analysis is to determine the relationship between dose and the likelihood or impact of the effect (evaluation of the dose-response). The complexity of this step in many contexts derives mainly from the need to extrapolate from laboratory animals (eg mouse, rat) to humans and / or from high to lower doses. In addition, differences between individuals due to genetics or other factors mean that the risk may be higher for particular groups, called susceptible populations. An alternative to the dose-response estimation is to determine an effect unlikely to produce observable effects. To develop such a dose, to account for largely unknown effects of extrapolations from animals to humans, increased variability in humans, or missing data, a conservative approach is often adopted by including factors of safety the estimate of "security" dose, usually a factor of 10 for each stage unknown.

The third step, exposure quantification, is to determine the amount of a contaminant (dose) that individuals and populations receive. This is done by examining the results of the discipline of the exposure assessment. As different location, lifestyles and other factors that may influence the amount of contaminants that is received, a range or distribution of possible values is generated in this step. Particular care is taken to determine the exposure of the susceptible population (s).

Finally, the results of the three steps above are then combined to produce a risk estimate. Due to the sensitivity and different exposures, this risk can vary within a population. Decisions based on the application of risk assessment are sometimes based on a standard of protection for those most at risk. This raises the question of how small a segment of the population must be protected.

If the risk is higher for a particular subpopulation because of the freak show rather than sensitivity, there is risk to consider strategies to further reduce exposure to this sub-group. If a person identifiable subpopulation is more vulnerable due to inherent genetic or other factors, there is a political choice to define policies to protect the general population that are protective of these groups (as is currently done for children where data exist, or made under the Clean Air Act to populations such as asthmatics) or if the group is too small, or high costs. Sometimes, a position that should at least limit the risk of the most sensitive to a certain level of risk above which it seems so unfair to leave out the risk.

Idea not to increase the lifetime risk of more than one in a million has become commonplace in the discourse of public health and policy. How the consensus on this particular figure is not clear. In some respects, this figure has the characteristics of a mythical number. In another sense, the figure provides a numerical basis to consider that a negligible increase in risk. In part one in a million mark rose early in the history of public health risk assessment in risk assessment is an analysis of quenching the existing statutory language such as the prohibition Delaney clause of any use of carcinogens in place or where environmental laws have been using.