Saturday, 21 August 2010

Safe levels of secondary smoke confirmed

Remember this piece from the Staffordshire Sentinal where a West Midlands environmental health officer was quoted describing a study that a study 'found a child [in a car] inhales three times the amount of smoke that would be considered safe to inhale over the course of a day'?

The study referred to is not online, but a powerpoint presentation that shows the results of a similar study can be seen here. The lead author of this presentation is Hilary Wareing, Co-director of the Tobacco Control Collaborating Centre, Warwick, who also authored the study featured in the newspaper article.

The authors compare the exposure of children to smoke in a car with the EU allowable daily exposure of 25ug/m^3. Conveying a sense of shock, they say that children absorb three times more smoke in a ten-minute (or an eighty-minute) journey than is permitted by the European Union in 24 hours.

The maximum length of journey undertaken in either study was 83 minutes. This is roughly one-seventeenth of day. Giving the exposure of smoke during a journey as three times the EU permitted level would be accurate only if the journey was 24 hours long and the smoke exposure was constant throughout.

The authors don't seem at all concerned by the length of exposure to smoke: the powerpoint graphs don't include the length of time exposed. They find that 'concentrations of PM2.5 found in all journeys, even when a single cigarette was smoked, were three and a half times higher than the recommended daily exposure'. In other words regardless of the number of cigarettes smoked (and the length of the journey undertaken), exposure was constant. They also find that 'open windows or an active ventilation system resulted in lower concentrations but levels remained above the EU daily exposure limit'. This acknowledgement that managing the air makes a difference is a significant one. (The quotations are taken from the paper version of the single-author version of the study, hard copy only.)

Concentrations of fine particulate matter, which is measured by PM2.5, provide a limited indication of the dangers presented by aerial pollutants. Actual toxicity matters, as well as particle size. As Michael McFadden observes:
[the environmental officer quoted by the Staffordshire Sentinal] is equating the FPM 2.5 produced by cars, commercial high temperature incineration, and general industrial and chemical processes with the FPM 2.5 produced by the quiet low-temperature combustion of tobacco and pretending they are the same thing just because the particles are the same size. That's actually not much different than comparing a teaspoon of arsenic crystals with a teaspoon of sugar crystals and concluding they are equally dangerous to eat because the crystals are the same size ....
Finally, as noted above: FPM 2.5 is VERY disproportionately produced by tobacco burning at smoking temperatures. That's why the Antis have turned it into their holy grail for talking about "smoking pollution." It actually has nothing to do, all by itself, with any determination of the "danger" of the pollution involved except that such small particles, just like vapors, can go deep into the lungs.
All that said, the admissions that one can measure smoke exposure, and also reduce its concentration by air management systems, are important, especially coming from a tobacco control organisation.

1 comment:

Unknown said...

A very thorough piece Belinda, your command of the science is inspiring. All those figures just hurt my head.

Great post.