Smoke and mirrors? Is a smoky car 23 times more toxic than a smoky bar?

Published: 16 Nov 2011

The British Medical Association has now issued a correction to their original press release. See below for more details. 

"Toxin levels [when smoking in a car] can be 23 times higher than in a typical smoky bar", The Independent, 16 November 2011

Calls for smoking to be banned in cars appeared to be gathering momentum this morning, as the British Medical Association reported on the dangers associated with a cigarette while driving.

The Prime Minister faced questions on the matter at Prime Minister's Questions earlier this month.

Some media outlets, the Independent among them, picked out an eye-catching claim that air in a smoke-filled car contains 23 times the amount of damaging toxins than a smoky bar. But how reliable is this claim?

Analysis

The figure comes from a British Medical Association report, released today, which calls for a ban on smoking in private vehicles.

It does indeed note that:

"Further studies demonstrate that the concentration of toxins in a smoke-filled vehicle is 23 times greater than that of a smoky bar, even under realistic ventilation conditions" (p.4)

In support of this, the report cites three sources: a report by the Ontario Tobacco Research Unit, an article published in the New Zealand Medical Journal, and an article published in the American Journal of Preventative Medicine.

Full Fact looked into the report by the Ontario Tobacco Research Unit and found the following quote:

"According to a report by the Ontario Medical Association (OMA), TSP levels in vehicles can be 23 times greater than in a house."

This was the only potential source of the BMA's claim that we could find, and already we see significant differences to the BMA wording, with the frame of referencing being changed from a "smoky bar" to a "house".

It gets worse, however. Full Fact dug out the Ontario Medical Association report, cited above. This notes that:

"Based on the evidence that exposure to SHS in a vehicle is 23-times more toxic than in a house due to the smaller enclosed space, the state of Colorado drafted a bill that would impose fines on adults caught smoking in cars when a child is present."

The footnote attached to this quote cited an article that appeared in the rather less medically-inclined Rocky Mountain News; a Colorado newspaper.

Unable to pursue this particular paper-trail any further, Full Fact went back to the other sources the BMA originally cited, in the hope that they would provide some substantive evidence of its claims (or at least something more substantive than an article in a regional newspaper).

The article cited from the New Zealand Medical Journal does make a comparison between the air quality in a "smoky pub" and that in a smoke-filled vehicle, but it is nowhere near the claim that the BMA makes. It says:

"Air quality in the car with the window partially or wholly down was therefore similar to that found in a typical smoky pub, whereas when smoking occurred with the window closed it was at least twice as bad as even the smokiest pub."

So the BMA claim seems to be the result of a conflation of two separate claims; one of dubious origins which provides the "23 times" figure, and the other which makes a much milder claim about the relative level of toxins in smoke-filled vehicles and smoky pubs.

The last of the BMA's sources - the article from the American Journal of Preventative Medicine — apparently provided no support for the claim that "the concentration of toxins in a smoke-filled vehicle is 23 times greater than that of a smoky bar".

However there was research readily available to cast doubt on the figure.

One article published in the Canadian Medical Association Journal entitled 'Second-hand smoke in cars: How did the "23 times more toxic" myth turn into fact?'concludes by saying:

"We recommend that researchers and organizations stop using the 23 times more toxic factoid because there appears to be no evidence for it in the scientific literature."

They go on to say that:

"Instead, advocates of smoking bans in cars should simply state that exposure to second-hand smoke in cars poses a significant health risk and that vulnerable children who cannot remove themselves from this smoky environment must be protected."

Conclusion

We have contacted the BMA to make it aware of the concerns we have about this "23 times more toxic" claim. Significant doubts have been raised over the figure, while the exact process through which the BMA has arrived at the estimate is not at all clear from the research cited.

Picture credit: multisanti

Update 17/11:  The British Medical Association has now issued a correction to their briefing paper, acknowledging that the '23 times more toxic' claim was incorrect. The claim has been revised down to 11 times more toxic. Naturally we will be checking to see if this claim fares any better under Full Fact scrutiny. If you would like to support this and the other work we do checking politicians', journalists' and interest groups' claims, please donate.

"17/11/2011 Headline :   CORRECTION TO BMA briefing paper: Smoking in vehicles — press release issued on Tuesday 15 November 2011 (publication date — 16 November 2011)

Please note, there is an error in the BMA briefing paper: Smoking in vehicles. On page 4, in the 3rd paragraph, the following sentence is incorrect: 

"Further studies demonstrate that the concentration of toxins in a smoke-filled vehicle is 23 times greater than that of a smoky bar, even under realistic ventilation conditions". a, 17, 18, 19 

THIS SENTENCE HAS BEEN REPLACED WITH: "Further studies demonstrate that the concentration of toxins in a smoke-filled vehicle could be up to 11 times greater than that of a smoky bar". a, 17, 18, 19 

We apologise for this error."


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