The Performance And Relevance Of Smoke Tests For Material Selection For Improved Safety In Fires

In the interests of society, it is necessary to provide a reasonable level of protection against hazards which the consumer cannot be expected to know anything about. The prospect, therefore, of a simple test for an assessment of the smoke producing potential of materials is therefore attractive to the Regulator. The objective of the work reported here is to assess the performance and relevance of smoke tests for material selection for improved safety in fires. The scientific principles of six of the standard test methods are thoroughly investigated and particular reference made to the variation of the test parameters, eg incident heat flux, in order to determine the sensitivity of such variation to the results. The tests are also examined in the light of results from large-scale investigative fires together with fundamental studies using laser diffraction techniques and chemical analysis. The results of the tests are given in terms of the comparison of measured smoke production from a standard range of materials selected on the basis of being representative of the wide range of polymer types available. The molecular structure of the polymers suggested a“ theoretical” ranking of the six materials in terms of their smoke producing potential. It is of interest that only one of the six methods examined agreed with this ranking. In simplistic terms, the aims of any smoke test should be to give an indication of the smoke producing potential of materials or assemblies, when that material or assembly is subjected to a heat flux under laboratory conditions modelled upon those that the material could quite reasonably encounter in its normal use, so that hazards can be identified and evaluated. In practice, many problems arise, particularly because the melting and burning behaviour of the materials themselves have been shown to have a direct bearing on the results. Scientific criticism can justifiably be levelled at many of the tests because of such factors as the volume of the test chamber and the associated problem of the ageing of the smoke prior to measurement. From this work it has been possible to suggest a specification for a smoke test based on the scientific principles established. On a comparison of this suggested specification with the parameters of the known tests, it was found that the specification of the draft International Organization for Standardization (ISO) test method - Draft Technical Report DTR 5924, comes closest to meeting the suggested criterion. It is also significant that this test method is the only test method, as mentioned above, to rank the polymers in the same order as the "theoretical” ranking. The objective of any test method is to provide data, data that is acceptable to end-us.er and/or specifiers. To achieve this, the results must be related to hazard to life in unwanted fire situations. The suggestion of 'worst case' testing, whilst being a widely accepted principle, would benefit from further work, particularly if the principle could be applied to the testing of composites.