Toxicity in fire is one of the least regulated elements of fire even though it’s one of the deadliest aspects in fire incidents. With the exception of mass transport (ships, buses, trains, etc.), toxicity of fires is left completely unregulated in all construction projects. In the last 20 years or so, the focus is being shifted to the fire engineering aspect of researching fires, so mainly prevention of ignition and fire growth towards reducing peak heat release rates. This has taken away a lot of research from the chemical aspect of fires, i.e. how toxic they can be.
As much as combustible materials can increase the growth and severity of fires, they also highly contribute to an increased concentration of toxicants, an issue that has been reflected by fire fighters as well. The increased usage of plastics in manufacturing led to covering that up with flame retardants. Though those are usually effective in delaying ignition and decreasing fire growth, their resulting toxicity levels can be quite alarming. This can aid in meeting the required regulations, but the results can be devastating from a fire safety perspective. Those regulations are also usually lacking in terms of fire toxicity.
Fire toxicity is an issue within all phases of the fire. Initially is it embodied in the gases that are released from the burning object itself, especially when those gases condensate on cooler surfaces such as walls and floors. Moreover, the effect continues with the residues left by the fire in forms of fire debris or larger particulates that can lead to contamination of the environment itself, for years to come.
The toxic products yielded in fires depend upon the ventilation conditions, which are in turn dictated by the various fire scenarios, be it flaming or non-flaming (smouldering) fires. Toxic product yield also depends on the chemical composition of the materials burning, which is where fire retardants can have a huge effect. For example, an upholstered furniture fire can yield very different toxic levels than PVC windows, this is due to a completely different “cocktail” of toxicants present in each.
It has been found that smouldering fires do not play a major role in toxicant levels as long as the room is not fully sealed, as long as the effect is a short term one. On the other hand, well ventilated fires, as the first phase of the fire, can lead to an immediate effect of disorientation due to smoke obscuration, sensory irritation, impaired normal breathing, etc. However, people usually still have enough time to evacuate the room of fire origin. Yet, if there are high levels of halogenated products, they will release irritants with high concentrations that can make evacuation much more difficult. Inorganic irritants can exacerbate the irritating and choking effects of the smoke.
As the fire keeps growing, it will reach the phase of an under ventilated fire, due to the decrease in oxygen levels. Most fatalities occur at that stage as there would be the highest concentrations of toxic gases. Smoke levels will also be much higher and containing an increased number of particulates comprising different mixtures of chronic toxicants. It’s important to distinguish here that when the fire is contained within the room of origin, it is considered under ventilated. However, if it progresses to other areas, then it is called post flashover fire, becoming even more lethal.
Building Construction Materials
Same as the building contents, building construction materials can have a huge effect on fire toxicity levels. This can be mainly seen in the usage of insulation materials in construction. Most insulation materials contain nitrogen, which will release hydrogen cyanides and other nitrogen oxide irritants. Some materials can have similar levels of nitrogen but can react and decompose differently in a fire and hence release completely different levels of irritants and toxic components.
Therefore, choosing materials based on the toxicity levels beside their fire performance is essential. It should also be noted that material compositions of common insulation materials are highly changing over the years, hence also up to date information must always be obtained and reviewed. Unfortunately, those changes are usually due to manufacturers adding more fire retardants into materials to be able to meet updated regulations, as well as trying to make the materials cheaper. All of those have an opposite effect and can highly increase toxicity levels.
As for mineral wool insulation, also known as stone wool, it is not release toxicants by itself. However, to form into in those plain homogenous panels, it is usually bonded with a cover of polyurethane, which in turn contains nitrogen and releases toxicants when burning. Thus, the whole insulation makeup would need to be tested for toxicants rather than only parts of it. Newer versions of specific brands have been lately resorting to using non-organic metal binders instead, which in turn do not release any toxicants into the fire.
Smoke levels and colours can be directly related to the type of toxicants burning. For example, the highly used insulation materials Styrofoam (expanded polystyrene) contains benzene, which in turn releases black smoke when burning. White smoke, on the other hand, is directly relevant to irritants such as chlorine and bromine. Nevertheless, the fire scenario itself can highly affect or alter those indicators. A fun fact about Styrofoam smoke is that even though it’s highly toxic and a known carcinogen, it releases a floral scent when burning.
To wrap it up ...
As a conclusion, it is highly noticeable that the emphasis on fire toxicity is definitely lagging behind other issues, especially when it comes to building regulations. The problem at hand exceeds the issue of Aluminium Composite Panels (ACM) that are cladding towers, it’s about the effect that these and other materials can have on human lives, whether it is fatal or long-term consequences.
Assessing fire toxicity can be relatively easy, as long as the fuel is known and well-studied, which is why increased research in the field is what’s required. As soon as this becomes an essential component of fire hazard assessment, regulations can then be amended to include a well informed and knowledgeable decision. Modern building practice needs to go hand in hand with the regulations, in all its various aspects. Only then can we say that we’re aiming for a holistic approach to fire safety, beyond the issue of travel distances and door widths.
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Amani er en libanesisk arkitektingeniør med en spesiell interesse for fagfeltet sikkerhet. Hun har også en Mastergrad i brannsikkerhet fra Høgskulen på Vestlandet (HVL), som hun var ferdig med i 2020. Hun har siden begynnelsen av 2021 jobbet som Graduate Fire Engineer ved Arup UK, og skriver med brennende engasjement for Brennaktuelt.no på fritiden.