FOCUS
A deadly cocktail Richard Hull charts the origins of smoke toxicity and explains how it can be assessed effectively to provide regulators with much needed information
transport industries. Simple assessment of smoke toxicity of commercial materials would provide the information designers and regulators need to avoid using the most dangerous products in places where fi re deaths occur most often. In the UK, as elsewhere, the majority of fi re deaths and most fi re injuries result from inhalation of toxic smoke. The cause of fatalities and injuries from UK dwelling fi res in 2018/19 is shown in Figure 1 (see page 31). The UK’s fi re statistics show a progressive shift
S
from burns to toxic gas inhalation as the leading causes of both death and injury, since they were fi rst published in 1955. This can be attributed to the increasing proportion of synthetic plastics in the fuel of unwanted fires, and to the increasing reliance on flame retardants to limit their flammability. Bulk synthetic polymers such as polyethylene, polypropylene, polystyrene and polyesters are more fl ammable than the wood, cotton and wool they have replaced. It has been shown that gas phase fl ame retardants increase the toxicity of smoke.
30 MARCH 2020
www.frmjournal.com
MOKE TOXICITY is the greatest cause of death and injury in unwanted fi res, yet is completely unregulated outside of the mass
It is this combination of greater fl ammability
and increased smoke toxicity that has driven up the proportion of smoke toxicity deaths and injuries to burns. Flammability is fairly well understood and regulated in most high risk applications. In the UK this includes construction products, electrical and electronic goods, furniture and children’s toys. Flammability covers a range of properties such as ignitability, fl ame spread and heat release. The usual worst case scenario for fl ammability is an atmospheric concentration of oxygen (O) of 21%. Conversely, smoke toxicity tends to be lowest at an O concentration of 21%, when the main products are carbon dioxide (CO2
) and water. In
an enclosure fi re, even with the windows and doors open, the ventilation rate is fi xed, and – provided there is suffi cient fuel – the fi re quickly becomes ventilation controlled. At this stage, the yields (masses of toxic products for a given mass of fuel) of carbon monoxide (CO) and hydrogen cyanide (HCN) can increase by factors of between ten and 25, creating a highly toxic fi re effl uent. It has been established that this small, under ventilated stage of burning is responsible for the majority of fi re deaths in the UK.
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