Ranking the carcinogenic hazards of occupational exposures: Exposure-Potency Index (EPI) values for nine volatile industrial chemicals.

Employers, employees, and occupational health professionals need a a simple index to rank carcinogens according to their potential danger at exposure levels which are commonly encountered in workplaces. We describe such an index, the Exposure-Potency Index (EPI). This simple proportion, dose level (mg/kg body weight/day) to which workers are permitted to be exposed/cancer-causing dose (mg/kg body weight/day) in test animals, permits comparisons among carcinogens. We have calculated this index for inhalation exposures to 1,3-butadiene, 1,2-dibromo-3-chloropropane (DBCP), 1,2-dibromoethane (EDB), ethylene oxide, formaldehyde, methylene chloride, propylene oxide, tetrachloroethylene (perchloroethylene), and trichloroethylene (TCE). The permitted worker exposure levels have frequently been close to the levels which induce tumors in laboratory animals. More recently, Permissible Exposure Limits (PEL's) for for some chemicals have been markedly reduced, and this is reflected in lowered EPI values. Combining EPI values with information on the numbers of exposed workers provides a simple means of identifying and ranking dangers to populations of workers.