ABSTRACT: Assessing health risks associated with potential exposure to chemicals from petroleum or petrochemical operations requires the consideration of multiple exposure pathways. These pathways include ingestion of water, food, or soil, inhalation of vapors or airborne particulate, and dermal absorption from contaminated soil, water, or by direct skin contact. To estimate the exposures for each pathway, a number of variables related to exposure, that is, exposure factors, are needed. Some categories of exposure factors include physiologic factors (e.g., body weight), time-activity factors (e.g., time spent at home), and contact rate factors (e.g., soil ingestion rate). This manual is organized by exposure factor category and includes a description of selected exposure factors commonly used in risk assessments, a brief summary, and an evaluation of the current scientific data supporting a recommended point value for each factor, and available information on the known distributions. It is hoped that this information will promote consistency and quality among various risk assessment activities
