It is widely recognised that the greatest risk to life from a fire in a building is not from the fire itself, but from smoke and toxic fumes. It is not surprising therefore that there is currently much debate about whether construction products should be regulated for toxicity in the event of a fire. The protection of life is of paramount importance, so it is crucial to understand this issue in the context of what happens in a fire, where the balance of risk really lies, and how best to manage and mitigate that risk. So, the first question to address is how significant the contribution of the building envelope is compared to the contents of a burning building.
In July 2016, PU Europe commissioned Warrington Fire Gent to conduct a study into this very question, examining the contribution of the building fabric and the building contents during the three key phases of a fire: growth, fully developed, and decay. The tests performed also specifically examined the relative impact of using PIR insulation compared to mineral wool insulation in the building envelope build up.
Consequently, two tests were conducted based on the large-scale test as described in the ISO 9705 standard, with the content of a typical domestic room, including curtains, and armchair, a wastepaper bin and a TV cabinet. The building contents, configuration and internal volume of the ‘room’ were the same for both tests, and the only change to the building fabric build up was the insulation type, the thickness of which was determined to achieve the same U-value (80mm for the PIR, 140mm for the mineral wool). A penetration in the shape of a socket was also included to create a realistic scenario.
In both instances, flashover was caused by the contents of the room. The flashover occurred 7’24” after ignition of the chair in the MW test, and 6’55” in the PIR test. In both tests, a second peak of the Heat Release Rate (HRR) was observed after 13-15min caused by the collapse and subsequent ignition of the TV cabinet.
The insulation was not exposed to the fire until about 20 minutes into the test and did not start to contribute to the toxicity levels until the decay phase, after flashover had occurred.
Toxicity levels were monitored at each stage, and both constructions followed very similar patterns, with a minor variation in concentrations of specific toxins. The levels of acrolein were slightly higher for mineral wool than for PIR, and vice versa for HCN. To assess the relative toxicity of the gases released in both fires, the Fractional Effective Dose (FED) and Fractional Effective Concentration (FEC) were computed. In both tests, the increase and the absolute values were significantly lower than the peak values reached during flashover. By far the highest level of toxicity occurred in the early phases of the fire which, along with the flashover events, means that the burning contents of the room posed the greatest risk to life.
Full details of the test are available to download from the PU Europe website:
On a much wider scale, the question has also been looked at in some detail by the European Commission, and in 2018 they published the results of their “Study to evaluate the need to regulate within the Framework of Regulation (EU) 305/2011 on the toxicity of smoke produced by construction products in fires”, which can be downloaded in full from the European Fire Safety Alliance website:
The results reflected the view that the greatest risk is in the home and is from the contents of buildings, not from the construction products in the building envelope. The conclusion was that the “responses received do not agree that regulation of toxicity of smoke from construction products is required” and that “interviewees believe there would be limited benefits from regulating specifically for the toxicity of smoke from construction products. Some interviewees believed that there could be greater benefits if the flammability (and hence smoke toxicity) of furnishings and fittings was addressed across all Member States”.
We cannot legislate for every eventuality, or to regulate every product for the many different, potentially lethal toxins that they can all produce in a fire, including some ‘non-combustible’ construction products. What we can do is apply our knowledge, expertise and common sense to create buildings that are fundamentally safe, without stifling innovation, making it harder to meet other requirements, or over-regulating aspects that do not present the real risk to life safety. What is crucial is to ensure that proper early warning systems are installed to alert occupants to the presence of a fire, that people are educated about the importance of maintaining these, and that there are adequate escape routes in buildings.
Let us work together to improve building design, quality of construction, and our understanding of how products perform in the context of a construction, not as isolated samples in a laboratory, or by focussing exclusively on one potential toxin or another. Let us truly understand the nature of risk and act in an informed and measured way to mitigate it where it will make a difference.