Air filtration. One of the axioms in ventilation is that it is always best to deal with a problem as near to its source as possible. Thus we have noted that extract should be close to the smokers. An alternative approach is to pass the ventilation air through some sort of filter. This will result in a reduction in the amounts of fresh air necessary and also save on the heating bills. Do not however assume that ventilation can always be reduced to 8 I/s.

Air filtration

That would only exchange one set of problems for another Environmental Tobacco Smoke (ETS) for an increase in CO2 levels and possible problems from the heat generated by closely packed bodies. The author’s conclusion is that one should still consider a minimum fresh air level of 24 I/s. There are a number of different types of filter available, each with its own respective merits. The restaurant in the author’s “local” uses an electrostatic precipitator- it’s brilliant.

The combination of high ceilings and filter means that smokers and non-smokers are mixed without problem, and the air is perfectly clear. Precipitators consist of an initial bank of positively charged ionising wires between co-planar grounded electrodes followed by a bank of grounded collection plates. Between each pair of collection plates is a positively charged repulsion plate.

Using relatively low voltages and currents of positive polarity, ozone formation is reduced to a minimum. Gas absorbers which burn off carbon monoxide is the presence of a catalyst can also be installed – most easily in a ducted system. Other types of filter which are available include absolute paper High Efficiency Particulate Air (HEPA) filters and those using other types of media.

How then, are we to know what is an acceptable indoor air quality? The American Society of Heating Refrigeration and AirConditioning Engineers (ASHRAE) defines this as air in which “there are no known contaminants at harmful concentrations as determined by cognisant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction”. That is indeed a tough target, but one to which we can all surely agree. How to calculate it without a substantial statistical survey is the real problem.

If this definition is accepted, and the air quality within a building is as good as that experienced in the external ambient atmosphere, then no one can expect more. This is not an impossible target and no doubt surprise will be expressed that tobacco smoke is not necessarily the dominant criteria. However, it must again be emphasised that the ventilation rates are higher than those which are currently specified. Let us therefore ensure that all public places have at least 8 I/s of fresh air per person but recognise that higher rates are necessary for any further improvement of indoor air quality towards that enjoyed outside in the fresh air.

Efficient ventilation is a definite plus in the promotion of all public places. It can provide an atmosphere which should satisfy the most fastidious. ETS is unpleasant, even if some of one’s friends are smokers, and one wishes to continue to have the opportunity to socialise with them. It is more than possible that ventilation can be installed that will allow one to do this in perfect safety even if ETS is proved to be a danger.


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In the light of the current debate, it should be emphasised that hot and cold tobacco smoke are very different both physically and chemically. Certainly, a well-designed and maintained ventilation system can ensure that the atmosphere within a public space need be no worse than that in the surrounding streets. The work of Dr Andrew Geens at the University of Glamorgan show this to be the case.