Assessment and Quantification of Contamination by Smoke Deposits

By Ian Wadsworth

Smoke produced during a fire can spread well beyond the area that is directly affected by the fire itself; often entering neighbouring premises. Smoke contains the airborne products of combustion in the solid, liquid and gaseous states. The composition of smoke is varied and often complex, depending on the nature of the fire, but typical constituents include: soot, polyaromatic hydrocarbons (PAH’s), halides (such as chloride), carbon monoxide, carbon dioxide and water vapour. Many constituents of smoke settle on, condense on or are adsorbed by solids with which they make contact.

Such ‘smoke deposits’, if not dealt with appropriately, can cause damage to both the fabric of a building and to property that is contained within it. In some instances the potential costs associated with this contamination can far exceed those associated with the direct effects of the fire. Knowledge of the potentially damaging effects of smoke deposits has recently spread to the wider community, on occasions giving rise to large claims for contaminated property and requiring insurers to establish the extent of contamination or damage that has actually occurred.

Chloride is a substance that is commonly entrained in smoke and its damaging effects are well understood, as are the processes and procedures employed to measure the chloride levels on a surface. Hence, this particular constituent of smoke will not be addressed in this article. However, insurers are increasingly facing claims for contamination by other substances, including soot and chemicals that cause residual odours to persist. Another increasingly common issue that arises for insurers is what proportion of the contamination that is present following a fire can be directly ascribed to the incident and what proportion pre-dated it. The following sections of this article provide an overview of some of the contamination issues that can be specifically addressed.

Claims Arising from Soot Penetration

Examination of a dismantled socketIn addition to its spread by fires, smoke can be transported in other ways. A recent matter concerned a claim that soot particles had entered numerous electrical sockets and conduits inside a large building that was nearing completion at the time. The soot originated from a malfunctioning diesel generator situated outside the building and was drawn into it via a ventilation system. Soot contamination of the internal surfaces of the building was extensive. However, comparative examinations of the soot derived from the generator with the interiors of the sockets and conduits confirmed the absence of soot, significantly reducing the size of the claim.

Claims Arising from Smoke Odours

A magnified view of a section of yarnFires often produce a variety of odorous compounds that may percolate into fabrics, garments and textiles. Odours arising from smoke deposits often persist, either reducing the value of the goods or requiring costly decontamination measures to be implemented. Hence it is important to ascertain the severity and extent of any such contamination.

A recent case in which Burgoynes was involved concerned a small fire that started in an electric motor within a loom in a large mill that produced yarn. The substances that burnt were principally grease, PVC-insulated cables and a large accumulation of fibre fragments. A considerable quantity of yarn at various stages of production was present in the mill at the time of the fire and the insured claimed that all of it was damaged by smoke deposits. Odour discrimination testing was undertaken on a representative sample of yarn to a recognised standard in order to determine the severity and extent of contamination by smoke deposits. These qualitative analyses were corroborated by undertaking quantitative chemical analyses, in which the unique constituents of the smoke were identified and used to determine the quantity of yarn that indicated the presence of smoke deposits. These investigations determined that the quantity of product that had been contaminated by smoke deposits was minimal.

Claims Arising from Deposit Accumulation

Depth profile sampling of depositsDust accumulation to varying extents is common in many premises and often this can have a dark colour, reminiscent of smoke deposits. Hence the first part of an assessment for contamination is to determine the composition and characteristics of any background matter and compare it to that of a known sample of smoke deposit arising from the fire. If the two substances are completely distinct chemically, the task is a relatively straightforward one. However, if both are identified as being derived from smoke, more detailed analyses are sometimes required to determine whether all of the substance(s) found originated from the fire or whether some pre-dated the fire. For example, smoke deposits are commonplace in a smoker’s dwelling and some industrial processes, such as in foundries that utilise oil quenching baths, also emit smoke. In such instances more detailed investigations and analyses are required to determine the compositions and therefore the origins of the deposits. In one instance involving a fire in a foundry, we analysed the compositions of the deposits found on structural steelwork at different levels throughout their thicknesses. This process of depth profiling enabled us to determine the proportion of the deposits that could be ascribed to the fire and the proportion that pre-dated it.

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