[en] This three-part report provides quantitative estimates of the risk of cancer and other diseases among persons exposed to hazardous substances in the workplace. The risk estimates presented are based on a comprehensive review of recent epidemiologic studies. Primary emphasis was placed on studies of workers exposed to hazardous chemicals under conditions typical of a given industry over a working lifetime. Despite finding over 100 chemicals associated with increased incidence of disease, convincing dose-response trends existed for only a few. Although there were notable exceptions (arsenic, asbestos, PAH's, etc.), it was generally impossible to estimate risk-per-unit of dose in a manner analogous to calculations which exist for radiation exposure. The principal reason for this is the lack of adequate environmental monitoring data for the specific chemicals, locations, and time periods needed to estimate individual cumulative doses. In addition to analyzing risk in terms of increased incidence of specific diseases, we also examined life expectancy and years of life lost due to cancer in four selected occupational groups via a life table model which allowed for competing risks. The resulting estimates indicated that the overall life expectancy of these groups was generally greater than that of the general population but that the workers suffered greater loss of life expectancy (LLE) due to cancer than their counterparts in the general population. Published estimates of LLE due to radiation induced cancer indicate that at doses of less than or equal to 0.5 rem/y, radiation workers are projected to suffer less LLE than any of the four non-nuclear cohorts examined. At 5 rem/y (the MPD) or higher, LLE may be greater than one or more of the cohorts examined. This is Volume I of a three volume series. 12 references