The U.S. Environmental Protection Agency(EPA) in July 2002 issued an evaluation of the hazards of working around diesel exhaust from truck, bus, and other heavy-duty engines built before the mid-1990s-potential hazards faced by highway workers, laborers, maintenance workers, operating engineers, and others. The EPA concludes that exposure to diesel exhaust can make existing allergies and asthma worse, and that long-term exposure may cause lung damage or pose a lung cancer risk. The exhaust may contribute to pollution by nitrogen oxides, sulfur oxides, and others. Exhaust emissions must be cut in 2001 heavy-duty engines.

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=29060