Diesel exhaust causes cancer, the World Health Organisation's cancer agency declared on Tuesday, June 12, 2012, a ruling it said could make exhaust as important a public health threat as second-hand cigarette smoke.The risk of getting cancer from diesel fumes is small but, since so many people breathe in the fumes in some way, the science panel said raising the status of diesel exhaust to carcinogen from "probable carcinogen" was an important shift.Kurt Straif, director of the International Agency for Research on Cancer, the cancer arm of the WHO, said: "It's on the same order of magnitude as passive smoking. This could be another big push for countries to clean up exhaust from diesel engines."MAJOR TECH ADVANCESSince so many people are exposed to engine exhausts, Straif said, there could be many cases of lung cancer connected to the contaminant. He said the fumes affected groups including pedestrians, ship passengers and crew, railway workers, truck drivers, mechanics, miners and people operating heavy machinery.A US group that represents diesel engine makers says major technological advances in the last decade have cut emissions from trucks and buses by more than 95% for nitrogen oxides, particulate and sulphur emissions.The new classification followed a weeklong discussion in Lyon, France, by an expert panel organised by the IARC. The panel's decision stands as the ruling for the IARC.The last time the agency considered the status of diesel exhaust was in 1989 when it was labeled a "probable" carcinogen. Reclassifying diesel exhaust as carcinogenic puts it into the same category as other known hazards such as asbestos, alcohol and ultraviolet radiation.Experts said current diesel engines emitted less fumes but further studies were needed to assess potential dangers. The US government, however, still classifies diesel exhaust as a "likely" carcinogen. Vincent Cogliano of the US Environmental Protection Agency, said: "We don't have enough evidence to say these new engines are zero risk, but they are certainly lower-risk than before." NO SURPRISESome experts said the new classification wasn't surprising. Ken Donaldson, a professor of respiratory toxicology at the University of Edinburgh who was not part of the IARC panel, said: "It's pretty well-known that if you get enough exposure to diesel, it's a carcinogen."Donaldson said the thousands of particles, including some harmful chemicals, in the exhaust could cause inflammation in the lungs and, over time, that could lead to cancer but he added that lung cancer was caused by multiple factors and that other things - such as smoking - were far more deadly.He said the people most at risk were those whose jobs exposed them to high levels of diesel exhaust: truck drivers, mechanics or miners."For the man on the street, nothing has changed," he said. "It's a known risk but a low one for the average person, so people should go about their business as normal... you could wear a mask if you want to, but who wants to walk around all the time with a mask on?"