Chronic obstructive pulmonary disease mortality: The Diesel Exhaust in Miners Study (DEMS).

•Underground miners are more highly exposed to diesel exhaust than surface miners.•Surface miners had increased COPD mortality risk from diesel in traditional models.•Underground miners also at higher risk for COPD mortality after correcting for survivor bias.•Surface miners had higher mortality risk than underground miners, despite lower exposure.•Reducing diesel exhaust exposure among miners may reduce the number of COPD deaths.