Dr Jim Glockling, technical director of the Fire Protection Association (FPA), discusses whether it is time to consider toxicity under fire when selecting building materials for certain high risk situations and occupancies.
The built environment lags behind other areas, such as transport, in its consideration of fire toxicity as part of the material selection requirement – is it time for that to change?
In today’s civilised society, as we go about our daily business our wellbeing is afforded many protections against perils of varying types and likelihood. In the case of fire many of these protections are quite visible and well understood by all – they are part of our upbringing: the fire extinguisher in the corridor; the sprinkler head and smoke detector in the ceiling; the hose reel on the wall; and the myriad of signage denoting the presence of fuels, need to control ignition sources, routes of escape, and fire doors, to name but a few. Other protections are less obvious such as the size of the space, its layout and the fire properties of the materials forming the structure. In certain special situations, these protections are extended even further to consider toxicity. Whether you are sitting on a train, on the London Underground, flying on a plane or travelling by boat, the likelihood is that the materials surrounding you have been specifically selected to ensure that when there is a fire, the toxicity of the products resulting from their involvement will have a lower chance of impeding your escape, or indeed disabling you all together. On this point let’s be clear – we are not talking about whether the materials can natively sustain burning or not; it is an evaluation of whether, under the influence of fire, the presence of these materials will act to make the overall threat greater by producing toxic byproducts. This is very different to the selection of materials on the basis of whether they are natively ‘combustible’ or not.Error, group does not exist! Check your syntax! (ID: 2)
But clearly these are very special circumstances; in transport situations you are often remote from help, with your safety assured only by the ability of the inbuilt passive systems to keep you properly separated from the fire, and the performance of active systems such as sprinklers to protect you from the threat at your location or any area you must pass through. This is clearly not a situation you ever find in the built environment … or is it? Is the plight of a person at the top of a high rise building, or someone of limited mobility in a lower environment, not basically exactly the same as someone far out to sea on a boat? They are all dependant on inbuilt protection, rather than their ability to allow you to leave the scene, or others’ ability to arrive and provide help.
Why has the potential toxicity of building materials under fire been neglected as a consideration for so many years? One issue is that the perceived threat from the unregulated contents of a room probably present a much higher and more immediate threat to any toxins that might ingress the occupied space first. This assumption is obviously dependant upon a number of key assumptions. Firstly, that the world is a perfect place and that what is drawn on paper is what gets delivered at the end of the day with computer assisted design (CAD) level accuracy – I think you need to look no further than the recent large hotel, care home, and apartment fires to make a judgement on that. Even if build quality could be tightened up to the point of installation perfection, there is still the human element – the fire door most likely propped open with a fire extinguisher emptied of its contents in the last student water fight, or the broken door closer never replaced. Cynical possibly, but even when everything is done right, we have to question whether our Building Regulations appropriately separate people from fire toxins. In the recent FPA / RISCAuthority study looking at the implications of penetrating (legal) rainscreen cladding systems with legally un-firestopped plastic vents (the external envelope of the building is not considered a fire compartment bounding wall), it was found that enough toxic products entered through a 100mm kitchen vent into an occupied 50m3 room to cause incapacitation and possibly death within 10 minutes of the fire breaking in to the part of the cladding housing the vent. All of this without breaking into the occupied space – an external fire internal to the cladding system. How does this scenario figure with ‘stay put’ policies?
Toxicity is a complex area. The FPA work demonstrated graphically the need to burn the materials with accuracy if you are to truly understand the toxic threat. The degree of ventilation is crucial – burning the same insulating material in the open poses a very different toxic threat than would be achieved if burning in the underventilated confines of, for example, a cladding system void.
There seems to be a growing desire within Europe to open up the debate on fire toxicity in the built environment, greatly added to by other worrying studies on the long term cancer causing toxins in soil following major fires, and indeed the result of firefighter exposure to these over their careers. In this respect debates around ‘combustibility’ are unhelpful – we all need to be talking about material ‘participation’. Some materials do not natively burn – if they do, this can often be adjusted by the use of fire retarding agents, but what if that simply exchanges a burning threat for a toxic threat when fire acts upon them? – is that an OK thing to do? The answer is that it is if it’s not measured. Surely it’s time for a more balanced view on the total threat materials pose to occupants – especially for those who by merit of the complexity of the environment they occupy, or constraints on their own physicality, might just need more protection from what at the end of the day is the biggest known killer in fire – smoke toxicity.