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Risk and Safety: Overview


Risk and safety are polyvalent concepts with numerous and overlapping ethical complexities in relation to science and technology. As such they are dealt with in a number of different entries.

In technical terms, scientific phenomena may exhibit certainty, risk, or uncertainty. Situations of certainty have a probability of 1. For example, all things being equal, it is certain (probability = 1) that water freezes when cooled below 0° Celsius. Cases of risk have some numerical probability between 0 and 1, based on a known or assumed model of what causes the outcome under study. For instance, the risk of tossing "heads" on a fair coin has a probability of 0.5, because the model is known. In risk assessment, the risk of something is typically defined as the average annual estimated probability of causing a fatality. Cases of uncertainty cannot be defined a priori in terms of probabilities, because of inadequate knowledge. To assign legitimate or scientifically valid probabilities, one needs experimental or frequency/statistical data; an example is data on automobile accidents for drivers of a given age. In many cases of uncertainty there may simply be no adequate data.

Despite the name, "risk assessors" typically do not assess cases of risk (with known or well-established probability between 0 and 1), but situations of great uncertainty.When people have "risk" knowledge, they do not need risk assessment. In part because they address uncertainty in extremely complex situations, risk assessments usually err between four to six orders of magnitude (Shrader-Frechette 1991). That is, fatalities predicted by risk assessments typically are (later proved to be) wrong by factors of 10,000 to 1,000,000. Most predictions are too low and exhibit an "overconfidence bias" in favor of some technology (Kahneman and Tversky 2000; Kahneman, Slovic, and Tversky 1982).

It is against this technical background that the following entries on risk need to be read: "Risk Assessment," "Risk Ethics," and "Risk Perception." Other entries—such as "Risk and Emotion" and "Risk Society"—make an effort to move beyond the more strictly technical understanding of risk.

There is no technical concept of safety analogous to that of risk. Nevertheless, according to an influential analysis by William W. Lowrance, safety can be defined in terms of risk: "A thing is safe if its risks are judged to be acceptable" (1976, p. 8). Mike W. Martin and Roland Schinzinger pointed out as early as 1983 that this definition needs a qualifier: The judgment of acceptability needs to be done with adequate knowledge. Free consent is not enough; it must be free and informed.

Langdon Winner, however, has gone further and warned against defining safety in terms of risk. According to Winner, traditional efforts to promote safety had a clear goal of eliminating certain "workplace dangers" or "health hazards." But when the promotion of safety involves assessing risks in terms of their acceptability, the goal fades into "studying, weighing, comparing, and judging circumstances about which no simple consensus is available" (1986, p. 143). It is against this critical background that the articles on "Safety Engineering: Historical Emergence," "Safety Engineering: Practices," and "Safety Factors" need to be considered.

There are also a number of articles that are related to the concepts of risk and safety. Among these it is useful to mention "Exposure Limits" and "Hazards." Even more specific topics include "Radiation" and "Regulatory Toxicology."



Kahneman, Daniel, and Amos Tversky, eds. (2000). Choices, Values, and Frames. New York: Russell Sage Foundation; Cambridge, UK: Cambridge University Press.

Kahneman, Daniel; Paul Slovic; and Amos Tversky, eds. (1982). Judgment under Uncertainty: Heuristics and Biases. Cambridge, UK: Cambridge University Press.

Lowrance, William W. (1976). Of Acceptable Risk: Science and the Determination of Safety. Los Altos, CA: William Kaufmann.

Martin, Mike W., and Roland Schinzinger. (1983). Ethics in Engineering. New York: McGraw-Hill. 4th edition, 2005.

National Research Council. Committee on Risk Characterization. (1996). Understanding Risk: Informing Decisions in a Democratic Society. Washington, DC: National Academy Press.

Resnik, Michael D. (1987). Choices: An Introduction to Decision Theory. Minneapolis: University of Minnesota Press. A good introduction to distinctions between certainty, risk, and uncertainty.

Shrader-Frechette, Kristin S. (1991). Risk and Rationality: Philosophical Foundations for Populist Reforms. Berkeley: University of California Press.

Winner, Langdon. (1986). The Whale and the Reactor: A Search for Limits in an Age of High Technology. Chicago: University of Chicago Press.

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