Objectives Recently, diesel motor exhaust (DME) has been classified as a known human carcinogen. We used data from epidemiological studies of diesel exposures to perform a quantitative risk assessment to calculate DME exposure levels, expressed as elemental carbon (EC), corresponding to acceptable risk (AR) and maximum tolerable risk (MTR) levels of 4 to 10⁻⁵ and 4 to 10⁻³ for the lifetime excess probability of dying from lung cancer.

Methods Previously published slope estimates (n=14) of the exposure–response curve (ERC) for EC exposure and lung cancer were used in life-table analyses to calculate EC exposure levels corresponding to the specified AR and MTR levels.

Results Considered ERC slope factors ranged from 0.00060 to 0.0012 natural logarithm of the relative rate (InRR) per μg/m³ years based on different selections of studies and study-specific risk estimates. Exposure limits based on these slope factors were between 0.009–0.017 and 0.85–1.67 μg/m³ EC for the AR and MTR, respectively.

Conclusions Derived exposure limits based on the AR and MTR are around or well below 1 μg/m³ EC. Such limits are below current occupational exposure levels, and in some instances even below environmental exposure levels. Although uncertainties exist in the exact slope factors, these results indicate that an acceptable excess lung cancer mortality risk can only be achieved at very low DME exposure levels, suggesting that diesel engines using older technologies should be removed from the workplace when possible or emissions strictly controlled.