Smoking in cars: just how toxic is it?

Yesterday's decision by the House of Lords to back a Labour amendment that would ban adults from smoking in a car when children are present was big news this morning, with the Daily Mail leading with the story on its front page.

Speaking in advance of the Lords debate, Labour's Shadow Public Health Minister Luciana Berger told listeners to Radio 4's Today programme that:

"A single cigarette can create concentrations of tobacco smoke in a car that is 23 times more toxic than in a typical house."

This was echoed by Baroness Howe during the debate, who told peers that "We also know that tobacco smoke pollution levels in vehicles can be 23 times greater than in a house."

However this wasn't the only statistic about the dangers of smoking while driving doing the rounds. Lord Hunt, who led the debate for the opposition, and Baroness Tyler both referenced a different comparison, which noted that:

"within the confines of a stationary car with a roof and the windows closed, a single cigarette can create concentrations of smoke 11 times greater than in the average smoky pub."

So what do we know about the evidence behind these claims?

Smoky cars and smoky bars

Lord Hunt's figure is one we've seen before. Back in 2011, Full Fact corrected a mistake made in a report by the British Medical Association (BMA), which initially claimed that "the concentration of toxins in a smoke-filled vehicle is 23 times greater than that of a smoky bar."

When we checked the research, we found that it didn't support the claim, so we raised the issue with the BMA who amended the claim so that it read: "a smoke-filled vehicle could be up to 11 times greater than that of a smoky bar." This was supported by the evidence provided, and we're pleased that it was this accurate figure that was picked up by Lord Hunt.

How smoky is a 'typical house'?

Luciana Berger's claim sounds very similar to the initial, uncorrected version of the BMA statistic. However it does have one crucial difference: rather than comparing a smoky car to a smoky bar, Ms Berger compares the toxicity of smoking in a vehicle to smoking in a "typical house".

We contacted Labour's health team to find out more, and were sent a research paper which concluded that the average smoke concentration in a home ranged between 65 and 90 ?g/m³ (micrograms per cubic metre), depending upon where the cigarette was being smoked. For the purposes of this research, a 'typical house' is actually a one- or two-bedroomed flat, and the smoke concentration changed depending upon how many cigarettes were being smoked, and in which rooms.

However Labour haven't yet been able to provide us with anything that suggests that smoking in a car is 23 times more toxic. In fact, if we compare the concentration of smoke in a 'typical house' with the research referenced by the BMA on the concentration of smoke recorded in a car, the result is much more striking.

The paper referenced by the BMA found that in a stationary car with the windows closed, the concentration of second hand smoke was 3,800 ?g/m³, over 40 times the concentration levels recorded in the home. With the air conditioning on, the concentration of smoke fell to 844 ?g/m³ (approximately 10 times the concentration recorded in a home) and when smoking next to an open window, it fell further to 223 ?g/m³ (around two and a half times the highest concentration level seen in the home).

So while there is certainly some evidence to support the notion that smoking in a car is more harmful than in the home, we haven't yet seen anything that suggests its 23 times more dangerous.