Exhaust from diesel engines brings a complex mixture of soot and gases to roadways, cities, farms, and other places. Health concerns about diesel exhaust relate not only to cancer, but also to other health problems such as lung and heart diseases. Studies have raised concerns over the years about the connection between diesel exhaust and cancer in workers with heavy exposure to exhaust from diesel engines. Men with the heaviest and most prolonged exposures, such as railroad workers, heavy equipment operators, miners, and truck drivers, have been found to have higher lung cancer death rates than unexposed workers. The International Agency for Research on Cancer (IARC), which is part of the World Health Organization (WHO), today classified diesel engine exhaust as carcinogenic to humans.