Steady state tube furnace
A steady-state tube furnace (BS 7990, IEC 60695-7-50, ISO/TS 19700) is the only method that has been shown to replicate the high toxicity of fully developed fires on a bench scale. The steady-state tube furnace generates fire effluents as a function of fire conditions (temperature and ventilation) so that the toxic product yields at each stage of fire growth may be determined directly.
This apparatus is designed to burn polymeric materials under different fire scenarios, particularly to look at the yields of toxic products, which are highly dependent on the fire conditions (temperature, oxygen). 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 permit the collection of smoke and other effluents for detailed analysis with the sophisticated analytical equipment available (electrochemical sensors, FTIR, HPIC etc.).
Until recently, fire toxicity was only specified for certain high-risk applications, such as transport. 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).
The apparatus has been used very successfully as a research tool, establishing a correlation between CO and HCN yields (the most toxic components in most fire gases) and the equivalence ratio (actual to stoichiometric fuel/air ratio). These data show an excellent correlation to large scale tests.