Description of BS 6401:1983 1983

1.1 This British Standard specifies a method for measuring the specific optical densities of smoke generated by materials when a specimen of specified form and thickness, of up to 25 mm in thickness, is exposed vertically to a radiant heat source of 2.5 W/cm2 in a closed cabinet, with or without the application of a pilot flame.

1.2 This method is not applicable to the testing of insulated wire and cable as it is not possible to obtain a satisfactory distribution of heat flux with such products.

1.3 Materials which melt and flow away from the direct impingement of heat flux do not give a smoke emission which is representative of current knowledge from real fire situations, and for these materials, this method may not be applicable.

1.4 The values of specific optical density measured by this method are specific to the form and thickness of the product tested. They are not necessarily valid when other variables are involved; in particular, different material thicknesses and densities.

1.5 The method is intended for research and development and not as a basis for building control purposes. No basis is provided for predicting the optical density of smoke which may be generated by the materials upon exposure to heat and flame under fire conditions nor has any correlation been established with measurements derived from other test methods (see B.1.7).

1.6 The repeatability of the measurement given by this method, both within and between laboratories tends to vary with the physical structure and chemical composition of the materials tested as well as the mode of test. In view of the poor inter-laboratory reproducibility attainable by this method, the resolution of the method tends to be poor and so is only applicable to distinguishing between materials which have substantial differences in smoke emission for each mode of test and which do not melt or drip during the test.

1.7 It is emphasized that smoke production from a material varies according to the irradiance level to which the specimen is exposed. In making use of the results of this method, it should be borne in mind that the results are based on exposure to one irradiance level (2.5 W/cm2) only. For details of the effect of heat flux variations, using the apparatus described in this method see B.2.

NOTE The titles of the publications referred to in this British Standard are listed on the inside back cover.

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