Current occupational exposures are tightly controlled and are largely confined to workers in the petrochemical industry, vehicle
mechanics, firefighters, workers exposed to automobile emissions, and some other occupational groups. Typically, occupational
exposure levels are currently at or below 3.25 mg/m
3
(1 ppm), and environmental exposures are typically below 50g/m
3
(15 ppb). Smoking remains a significant source of exposure in both occupationally and non-occupationally exposed individuals.