Fire Toxicity Assessment
Death in fire may be caused either by gases which are directly toxic or which cause such irritation that they impair vision and breathing, preventing escape, or by smoke which not only impairs escape ability by visual obscuration, but also contains particulate matter which is sufficiently small to pose a respiratory hazard. Combustion toxicity is highly dependent on fire conditions. It depends on material, ventilation condition, oxygen depletion, and fuel geometry.
There are now criteria for assessing smoke toxicity for materials used in buildings and how it must be measured, ISO 13344 (Estimation of lethal toxic potency of fire effluents) and how that data must be used, ISO 13571 (Life threat from fires – Guidance on the estimation of time available for escape using fire data). Toxic substances in smoke are also a major concern for the disposal of plastic wastes via incineration, e.g. the dioxin problem.
Steady State Tube Furnace (Steady State Tube Furnace) A specially designed apparatus to burn polymeric materials under different fire conditions, particularly to look at the yields of toxic products, which are highly dependant on the fire conditions. It achieves this by burning materials at a fixed rate in a controlled air supply, independent of the flammability of the material. The furnace conditions are chosen to represent real fire conditions from early stages to post-flashover, and permits the collection of smoke and other effluents for detailed analysis with the sophisticated analytical equipment available (Electrochemical, NDIR, paramagnetic oxygen analysis, FTIR and GCMS).
The French Railway Test
(NF X 70-100) This is a static tube furnace test, where the different fire conditions are approximated by changing the furnace temperature setting, with a fixed air flow. Thus at 600°C the pyrolysis rate will be relatively slow so the combustion conditions will be well ventilated, whereas at 800°C the pyrolysis will be rapid and the fire condition underventilated.
The Acid Gas Test
(EN 50297-2-3:1998) This test has been incorporated into the Euroclassification of cables as part of the Construction Products Directive, introducing an additional acidity classification. This standard uses an apparatus similar to the NF X 70-100 in which a static sample is decomposed in a stream of flowing air in the middle of the tube furnace, above 935°C, and the effluent is collected in bubblers prior to analysis.