The World Health Organization has officially decreed that inhaling diesel fumes can cause lung cancer and has added the fumes to its list of Group 1 Carcinogens - things known to cause cancer in humans. It's in the same group with arsenic, strontium-90, neutron radiation and being a painter - making it worse than second hand smoke.

According to The New York Times, scientists said that you need to be concerned if your job or environment places you are in direct long term contact with diesel exhaust. This goes for miners and toll collectors. One study showed miners being subjected to diesel fumes for years had lung cancer risk that was seven times greater than nonsmokers.

Walking by an accelerating diesel car won't be an issue and as one scientist said: "I don't think it's bad to have a diesel car. I don't think it's good to breathe its exhaust." Captain Obvious.