There is no doubt that the inhalation of toxic products formed during the combustion process is the major cause of fatalities that occur during fire catastrophes. There is however considerable dispute as to the best means to mitigate these hazards. Essentially two approaches are currently adopted ― the American and the European. In summary the US approach is that heat release is all important. Toxicity is directly linked to carbon monoxide, which in flashover fires is proportional to heat release. In Europe, the fire hazard model is different. Fire deaths are believed due to a two stage process - incapacitation followed by carbon monoxide poisoning. Therefore the focus is on controlling the smoke and irritant gases which cause incapacitation. In spite of the obvious concerns most cable specifications do not take toxicity/irritancy into account. A few, such as BS 7211, VDE 0250 pt 214 and 215, limit the acidity (irritancy) by a simple restriction of the halogen content of the combustion fumes (IEC60754-2). Consideration of the more general toxicity/irritancy problem is much more difficult. Animal testing is probably the most reliable approach but is very difficult to justify on moral grounds. The alternative is to identify and quantify critical components of the combustion fumes (NES 713, IMO MSC 41(64)). Toxicity is then estimated by assuming that the overall hazard is the sum of the component parts. The resulting parameter is known as the Fractional Effective Dose. A similar approach may be adopted in considering irritancy. ISO 130571 is a draft specification aimed at incorporating this type of analysis into a system of building hazard assessment. The purpose of this paper is to give an overview of the toxicity/irritancy of the main combustion products formed during the combustion of materials used in three types of data cable. The key difference to the methods cited above is the use of GC/MS, which ensures consideration of all components of the combustion process.
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