Toxicity threats Insulation material Phenolic foam


Polyisocyanurate foam


Stone wool Glass wool ISO fire stage 2 – Well ventilated


3a – Small under ventilated 3b – Large under ventilated 2 – Well ventilated


3a – Small under ventilated 3b – Large under ventilated 2 – Well ventilated (NF)


Material-IC50/g m-3 (5 min exposure)


57 23 27 32 11 9


150


3a – Small under ventilated (NF) 226 3b – Large under ventilated (NF) 327 2 – Well ventilated (NF)


133


3a – Small under ventilated (NF) 191 3b Large under ventilated (NF)


362 Figure 7: NF indicates non flaming.


This could be expressed as: •


•


toxic hazard = flammability x smoke toxicity, or more precisely as;


toxic hazard = mass loss rate x toxic product yield


Toxic product yield can best be quantified at fixed ventilation conditions. This allows the individual fire stages 2, 3a and 3b to be distinguished. The steady state tube furnace (ISO 197003


Both of these provide the required indication of the material’s flammability.


By combining the flammability and smoke ) generates toxic


products under conditions of controlled ventilation, in effect at O concentrations from 5 to 21%. This forces combustion at any ventilation condition by allowing the heat flux on the sample to increase until steady burning is established. This provides a realistic assessment of toxic product yield over the full range of fire conditions. However, because the method is insensitive to the material’s flammability, to predict the toxic hazard, input of flammability data (usually measured at 21% O) is also required. In Europe, flammability is measured using the single burning item test (SBI). A 30 kW propane burner is placed in an internal corner formed by the sheet material under test. The SBI combines surface spread of flame with penetrative burning into the bulk of the material, giving a fairly realistic indication of a material’s flammability. Penetrative burning can also be measured using a cone calorimeter, giving a direct measurement of mass loss rate.


Material


Euroclass Minimum material- IC50


or


LC50 value


1 2 3 4 5 6


Figure 8


D B B E


C A2


20 5


15 30 10 70


Toxic hazard (1 lowest, 3 highest)


2 3 2 2 2 1


toxicity, a simple hazard classification can be derived, for example, classifying materials as low, medium or high smoke toxicity. Materials posing the greatest hazard can then be identified and their use avoided in high risk or other sensitive applications. The Euroclass, measured using the SBI test gives a robust indication of flammability. In combination with the minimum value of either the five minute material-IC50


, and/or the 30 minute material-LC50 , a


simple toxic hazard classification can be derived. The table in Figure 8 illustrates this approach. The following conclusions are drawn from the above: •


fire toxicity is the biggest cause of death and injury in fires, but is unregulated


• material composition has a big effect on fire toxicity


• combustible products drive fire growth and hence toxic gas production


• yields of CO and HCN increase dramatically as the fire grows


•


assessing fire toxicity is easy and an essential component of fire hazard assessment


Professor T Richard Hull is professor of chemistry and fire science at the University of Central Lancashire. For more information, view page 5


References 1.


Material-LC50/g m-3 (30 min exposure)


44 15 21 21 6 5


74


117 164 67


100 171


FOCUS


ISO 13571: 2012: Life-threatening components of fire. Guidelines for the estimation of time to compromised tenability in fires, ISO, Geneva.


2. ISO 13344: 2015: Estimation of the lethal toxic potency of fire effluents, ISO, Geneva.


3. ISO/TS 19700: 2016: Controlled equivalence ratio method for the determination of hazardous components of fire effluents – Steady-state tube furnace, ISO, Geneva.


www.frmjournal.com MARCH 2020 33


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