Risk is the probability of harm resulting from various activities or exposures and, because it is a probability, it carries numerical values between zero and one. Risk assessment conjures up the concept of a specific methodological approach, extrapolating from sets of human and animal data under conditions of relatively intense exposure and developing quantitative estimates of risk at much less intense exposures experienced by human populations. Whatever methodology that is thought to be scientifically justifiable can be used, as long as the reasons for the choices have been explicitly set forth. As J. V. Rodericks concluded, risk assessment focuses explicit recognition of the various assumptions needed to reach conclusions about risk and the uncertainties their use introduces. Human exposure can be extrapolated from extensive quantification of chemical residues in air and on surfaces as well as from transfer to, deposition on, and penetration of the skin.