Learning Objective

Define risk and risk assessment.

Explain how the four steps of risk assessment help determine adverse health effects.

Threats to our health, particularly from toxic chemicals in the environment, make big news. Many of these stories are more sensational than factual. If they were completely accurate, people would be dying everywhere—but in fact, human health is generally better today than at any time in our history, and our life expectancy continues to increase rather than decline. This does not mean that you should ignore chemicals that humans introduce into the environment. Nor does it mean you should discount the stories that the news media sometimes sensationalize. These stories serve an important role in getting the regulatory wheels of the government moving to protect us as much as possible from the dangers of our technological and industrialized world.

Risk is inherent in all our actions and in everything in our environment. All of us take risks every day of our lives. Walking on stairs involves a small risk, but a risk nonetheless, because sometimes people die from falls on stairs. Using household appliances is slightly risky, because sometimes people die from electrocution when they operate appliances with faulty wiring or use appliances in an unsafe manner. Driving or riding in a car, or flying in a jet, has risks that are easier for most of us to recognize. Yet few of us hesitate to get in a car or board a plane because of the associated risk. It is important to have an adequate understanding of the nature and size of risks before deciding what actions are appropriate to avoid them.

Although we sometimes speak of percentages, probabilities of risk are always calculated as fractions. If a risk is certain to occur, its probability is 1; if it is certain not to occur, its probability is 0. Most probabilities of risk are some number between 0 and 1. For example, according to the American Cancer Society, in 2002 about 170,000 Americans who smoked died of cancer. This translates into a probability of risk of 0.00059, or about 6 of every 10,000 Americans. (Table 4-1 shows probabilities of risk of dying in a given year by selected causes.)

Table 4-1 Probability of Risk of Dying by Selected Causes, 1998
Cause of death U.S. deaths in 1998 Probability of risk
Cardiovascular disease 940,600 3.5 of every 1,000 people
Cancer (all types) 541,500 2.0 of every 1,000 people
Accidents (including motor vehicle) 97,800 3.6 of every 10,000 people
Suicide 30,600 1.1 of every 10,000 people
Homicide 18,300 0.7 of every 10,000 people
Accidental falls 16,274 0.6 of every 10,000 people
Accidental poisonings by drugs 9,838 3.6 of every 100,000 people
Accidental drownings 3,964 1.5 of every 100,000 people
Fire 3,255 1.2 of every 100,000 people
Accidents by firearms 726 2.6 of every 1,000,000 people
Accidents (airplane) 692 2.5 of every 1,000,000 people

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