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Toxicology – Burning Questions

Professor Mike Holmes, Head of the Graduate Research School, and Emma Sandon-Hesketh went to meet with Dr Anna Stec, to talk about her research and work internationally in the field of toxicology.

Could you give a brief outline of  what your research is about?

My research is about combustion and fire toxicology, which is a multi-disciplinary area. It starts from the physical aspects of combustion such as how much heat is released in fires. It is then about understanding how different materials, such as polymers burn under different fire conditions. A polyurethane foam sofa will burn differently to a plastic coated cable, with different combustion products being released. We use analytical chemistry to identify and quantify fire products or effluents released. Using existing hazard assessment models, it is possible to estimate the main hazards to humans, incapacitation or lethality, which can prevent a safe escape. Although my research focuses on the whole cycle, the main question I am always trying to answer is, “What is released from fires and how hazardous is it to humans?”. Many people believe that the biggest killer in a fire is carbon monoxide. In fact, it is more likely, particularly if nitrogen containing materials are being burnt, to be hydrogen cyanide, which is 25 times more toxic than carbon monoxide.

Anna Stec

Do the chemicals released depend upon the temperature of the burning?

Fire toxicity is closely related to the material, which is being burnt, and to the ventilation conditions such as temperature and oxygen. Smouldering or oxidative pyrolysis i.e. decomposition or transformation of a compound caused by heat in an oxygen containing atmosphere, is a non-flaming fire scenario related to a gradual increase in the local concentrations of smoke and toxic gases over a long period, such as carbon monoxide from smouldering furnishings . Once flaming starts, the effluent toxicity of a well-ventilated fire decreases briefly, until the fire grows rapidly to consume the available oxygen. If we look at the fire statistics, which are very well established in the UK, most fire deaths are from under-ventilated fires in the room of fire origin. In the US, there are more fire deaths outside the room of fire origin or on a different floor as the homes tend to be bigger with more open layouts, hence the fire can spread more easily. Under-ventilated fires are the most dangerous for humans because the fires are usually large, and the toxicity is very high. If we look at the yield of toxic products such as carbon monoxide, hydrogen cyanide, organo-irritants, and smoke, they increase by a factor between 10 and 50 as the fire changes from well ventilated to under ventilated.

Has this changed the way in which we design and build buildings?

I am a UK Principal Expert with the International Standards Organisation (ISO) "Fire Threat to Human and Environment" group, which gives me insight into what is happening with the regulations. What we are trying to change are the regulations regarding the flammability and the toxicity of materials used in buildings. A problem for the fire safety engineer is that whilst all fire stages need to be considered to address different scenarios for fire hazard analysis, well-ventilated flaming is well understood and quantified, whilst the more toxicologically significant under-ventilated flaming is often oversimplified or ignored. Although no bench-scale test can

re-create exactly the decomposition conditions in a full-scale fire, we have been developing, over the last five years, in the fire laboratory at UCLan, an ISO standard to generate and quantify fire effluents under the full range of fire conditions. The steady state tube furnace method has been developed specifically to replicate a range of large scale fire stages, characterising the fire behaviour of materials under controlled and well-defined laboratory conditions. The other standard that I am leading now is for the analytical measurement of fire toxicity and the analysis of gases and vapours in fire effluents. This involves six countries, and around 52 participants. I am also taking forward a standard for the characterisation of nano-particles in fires.

So nano-particles are things like smoke particles, are they?

Fire smoke is associated with visual obscuration, and with the toxicity of the gases and particles. Nano-particles are the particles, which have the size smaller than 100nm. There are three threats to humans from particles. First they are the major source of heat radiation from flames, resulting in flame spread and fire growth. Second when inhaled they are transported into the respiratory tract and depending on their shape or size, can damage the lungs. Finally, they can act as vehicles for the transport of other noxious substances into the lungs, e.g. acid gases.

Can you tell from an autopsy from someone who has died in a fire, whether it is nano-particles that have killed them?

If you look at the fire statistics, most of the people who die in a fire do so through inhalation of toxic gases. In the UK and elsewhere, the remit of the forensic pathologist does not extend to consideration of the toxicants present in a fire. It is to establish the cause of death, and not the agents responsible. At present, it is almost impossible for the pathologist to form any useful opinion about the effects of individual components of fire effluents, since the only analysis carried out is the examination of the airways and lung and blood-carbon monoxide levels. We have a very strong collaboration with Warsaw Medical University where they are doing post mortem analysis and looking at what the toxicants are. If you have particles or smoke found in the respiratory tract, then it will be visible, demonstrating the person was inhaling the particles during the fire.

So hopefully, I will have soon more results to provide a better answer.

Can I go back to a point you made earlier about your research changing some of the standards for buildings. What sort of changes are they?

We have a large diversity in the testing of materials and products commonly found in houses or used in transportation such as those used on ships, or trains or planes. Once we set the standard, it becomes a regulation that has to be met. A major example of this is the heat release rate standard, which indicates material flammability. The argument I am having now, is that if a material does not ignite, it does not mean it cannot be toxic; it can still produce high levels of toxicants. Twenty years ago there were few publications on fire toxicity. Now there is a big increase in the topic and, through the standards we are making, people are becoming aware that this topic is important.

I know there are things like fire retardant paints, that when heated, bubble, protecting the under-lying surface from the fire. Can you tell me about these?

China is extremely good in terms of developing new fire retardants and creating new products, but they do not check their flammability and toxicity. For fire retardants, there is starting to be a change because the most common flame retardants are chlorinated or brominated which generate corrosive gases when heated. Now, they are going for an approach based on alumina, silica or phosphorus, which is a much more expensive approach.

That brings us nicely to China. Could we explore your involvement in the new Institute for Nano-technology and Bioengineering based there?

We have established a collaboration with the University of Science and Technology of China (USTC) in Hefei, which has the only Chinese national laboratory of fire science. The good thing is that they have six different departments, including Fire Chemistry, Fire Analysis, Fire Building and Computer Modelling Section. They have around 250 post graduate students, and are internationally leading in terms of fire chemistry. The project started in November 2011 with six professors there; each is head of a different department: Fire Combustion and Chemistry, Fire Retardancy, Analytical Chemistry, Large Scale Testing, Fire Modelling, and High Altitude Low Pressure Test Methods located in Lhasa. Therefore, given their productivity, and these facilities, it is a wonderful opportunity to exploit the unique expertise of UCLan in fire toxicity and mechanisms of fire retardancy, with the complementary expertise of China’s leading fire laboratory.

In terms of testing, do they have large scale facilities?

They have a lot of large scale test methods that we are not able to have here because of the space and the cost. They have a full-scale room connected with a corridor, which is the standard test method for testing the flammability and toxicity of any product. They also have a five-floor building where we can look at the smoke, fire gases and particle distribution, and how this relates to aspects of toxicity. They also have a high altitude, low pressure test environment to enable testing for fires in such things as aircraft. We have two post doctoral research fellows, and four research assistants each of whom work on an individual project within the team. One of the aspects of the collaboration is to correlate small-scale tests, which we have in UCLan, with the large scale burning at USTC. The other aspects are the analytical measurements and particle assessments on a large scale with the particle size distribution and identification of toxicants present on nanoparticles. This collaborative research will establish fire toxicity as a key requirement in fire safety, develop new products of low fire toxicity and develop models to predict the fire behaviour of materials. This places UCLan in a unique position to lead on rapid prototyping of new fire safe materials. In addition, it will increase the fire safety of general consumer and building products, and provide industries with the know-how to meet the new stringent environmental and fire hazard regulations.