Source:http://linkedlifedata.com/resource/umls/id/C1518534
NCI: Studies of carcinogens encountered through occupational exposure. The carcinogens can be of any type: chemicals, electromagnetic fields, UV, viruses, etc. Many of these agents may also be commonly encountered outside the occupational environment (e.g., UV) but in such cases they are not coded in this category; for farmers and sailors, UV is an occupational carcinogen. Epidemiologic studies will usually clearly identify occupational carcinogens but in experimental studies or analyses of carcinogenic mechanisms, a judgment must be made as to whether the primary means of exposure is occupational and thus requires selection of SIC 28; for example, one could be exposed to benzene in various settings, but the most frequent exposure risk would be occupational. For chemicals with which you are unfamiliar, consult the Merck Index to determine whether the chemical is used in manufacturing, agriculture, or other occupational setting.