The chances are [the British Medical Association] will claim that a cigarette smoked in a car exposes passengers to either 23 or 27 times more secondhand smoke than they would get from a whole night in a smoky bar. Both of these statistics are obviously absurd.
In the end they plumped for the "23 times" figure despite it being thoroughly debunked in the Canadian Medical Association Journal, which offered this advice to advocates:
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.
Did that stop the BMA resurrecting this zombie statistic?
It did not. Not only are the BMA bandying around a figure for which there is "no evidence in the scientific literature", but they have added a fresh layer of nonsense to it.
There is evidence to suggest that the levels of SHS present in vehicles can contribute to a serious health hazard for adults and children.
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.
In the studies a number of ventilation conditions were assessed, where airflow parameters included average driving speed, presence of air conditioning and open windows. Realistic ventilation is described as driving at average roads speeds with all four windows completely open.
The BMA seem to be suffering from undiagnosed pseudologia fantastica. Their new briefing paper supplies three references for their bizarre claim about "realistic ventilation". Only one of the named studies experimented with a scenario in which all the windows were open. The researchers called it 'Condition 3' (PM is particulate matter)...
At the other extreme, in Condition 3 (all windows open all the way while driving), the PM2.5 level was the lowest (M = 60.4 μg/m3, range = 15.7 to 220.5 μg/m3).
And how does that compare to a "smoky pub"?
To provide some context about the PM2.5 levels recorded in this study, in a recent report of PM2.5 levels in Irish pubs throughout the world, the average level of PM2.5 in 48 Irish pubs that allowed smoking was 340 μg/m3.
Pedants and sceptics would say that there is a bit of a difference between "23 times higher" and "82% lower" but what the hell, eh? If the BMA says it, it must be true.