FOCUS Firefighter health
size of PAH strongly influences its distribution between the gas and condensed phases, and is of direct relevance to its toxicity. Smaller PAHs (fewer than four fused rings – for example naphthalene and phenanthrene) mainly exist in the gas phase. The tendency to adsorb onto organic carbon (such as soot particles) increases with increasing molecular size, so the larger compounds (more than four fused rings, such as benzo[a]pyrene [BaP]) occur in the atmosphere mainly as particulates. Historically, BaP has been identified as the most toxic PAH species and it is used as a reference toxicant for other PAHs. However, recent studies have identified 7,12- dimethylbenzo(a)anthracene as being 20 times more toxic than benzo(a)anthracene, and twice that of BaP. Both compounds have been identifi ed in deposits collected from fi refi ghters’ working environments. While relationships have been established
to show the links between exposure to PAHs and cancer, plus atmospheric particulates and respiratory and cardiovascular diseases (acute lower respiratory illness, cerebrovascular disease, ischaemic heart disease, chronic obstructive pulmonary disease and lung cancer); the specifi c agents responsible have not been positively identifi ed.
Figure 2: a range of polycyclic aromatic hydrocarbons
Volatile and semi volatile organic compounds Complex mixtures of volatile and semi volatile organic compounds (VOCs/SVOCs) are generated as incomplete combustion products during unwanted fi res, and many of them are known to be signifi cantly damaging to human health and the environment. Important examples of these compounds are benzene, styrene and phenol, formed in the majority of fi res. Benzene is of particular toxicological signifi cance as it is a precursor of carcinogenic PAHs, as well as being a known carcinogen in its own right. The unreactive chemistry of these compounds makes them environmentally persistent, and they bioaccumulate in fatty tissues.
Polycyclic aromatic hydrocarbons PAHs are fairly large molecules composed of several aromatic rings fused together. They are human toxicants, carcinogens and environmental pollutants, and agglomerate into combustion derived particulates. The molecular
36 MARCH 2020
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Particulate matter Smoke contains particulate matter which is suffi ciently small to pose a respiratory hazard. The World Health Organisation estimates a staggering 0.5% increase in daily mortality per
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