The mission of National Center for Environmental Assessment (NCEA) of EPA’s Office of Research and Development is to provide guidance and risk assessments aimed at protecting human health and the environment. To accomplish this mission, NCEA works to develop and improve the models, databases, tools, assumptions, and extrapolations used in risk assessments. This handbook is a tool developed by NCEA aimed at refining the assumptions used in exposure assessments and reducing uncertainty.
This handbook was first published in 1989 and updated in 1997 to provide statistical data on the various human factors used in assessing exposure. This revised version of the handbook provides the up-to-date data on these exposure factors. The recommended values are based solely on our interpretations of the available data. In many situations different values may be appropriate to use in consideration of policy, precedent or other factors.