Chapter 3
Risk Analysis
One of the tasks of the environmental engineer is to understand and reduce the risks
from hazards from environmental pollution to the environment and to public health in
both long and short term. In particular the environmental engineer frequently is asked
to estimate or project future risks, then to use science, engineering, and technology
to design facilities andor processes to prevent or mitigate those risks. To accomplish
this objective the risks associated with various hazards must initially be evaluated and
Risk analysis is introduced here as a tool of the environmental engineer that crosses
the boundaries of science, engineering, and risk analysis. This chapter is not a com-
prehensive treatise on risk analysis; rather, it includes those elements of risk analysis
that an environmental engineer most importantly must understand and use.
quantified.
Most pollution control and environmental laws were enacted in the early 1970s in order
to protect public health and welfare.' Throughout this text a substance is considered
a pollutant if it has been perceived to have an adverse effect on human health or the
environment. In recent years increasing numbers of substances appear to pose such
threats; for example the Clean Air Act listed seven hazardous substances between
1970 and 1989 and now lists approximately 300! The environmental engineer thus has
one more task to face: determine the comparative risks from various environmental
pollutants and, further, which risk(s) is it most important to decrease or eliminate.
Adverse effects on human health are often difficult to identify and to determine.
Even when an adverse effect on health has been identified, it is still difficult to recognize
those components of the individual's environment associated with the adverse effect.
Risk analysts refer to these components as riskfucrors. In general a risk factor should
meet the following conditions:
0 Exposure to the risk factor precedes appearance of the adverse effect.
0 The risk factor and the adverse effect are consistently associated. That is, the
adverse effect is not usually observed in the absence of the risk factor.ISee Chapters 11, 17, and 21 for the details of air, water, and land laws and regulations in the
United States.
33