No matter what level of exposure of smoke you have, your lung cells know it and they are responding.

无论你暴露在何种程度的烟雾环境中，你的肺部细胞都知道并且会做出反应。

youdao

There is no safe level of exposure to second-hand tobacco smoke.

关于二手烟草烟雾，不存在安全接触水平。

youdao

If there's smoke in the cabin, get low and crawl below the level of the smoke and toxic fumes, so you can breathe until you get out of the plane.

如果机舱里有烟雾，把身体放低到烟雾与有毒气体的下面爬行，这样你能在你离开飞机前保持呼吸。

youdao

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