But clearly there is no such thing as a safe level of cigarette smoke exposure.

VOA: special.2009.06.03

"The people that are at the highest level of passive smoke are actually the ones reporting exposure in their own homes.

VOA: standard.2010.06.15

To accurately assess the level of second-hand smoke exposure, researchers tested for cotinine, which is produced when nicotine is metabolized.

VOA: standard.2010.06.15

Her stance was backed by the British Heart Foundation and Cancer Research UK, who said there was no safe level of smoke and that the ban on smoking indoors should be absolute.

BBC: Wales smoking ban forced Casualty story change says

Minutes after she left her bedroom on the lower level and went upstairs, the smoke alarm went off and she saw "thick black smoke" coming from downstairs.

BBC: The fire at Lakanal House in Camberwell in July 2009

The image is grainy, but good enough to be able to fly at very low level at night, although rain, fog, or smoke adversely affect it.

BBC: News | In Depth | Military Fact Files