BS 476 was first published as a single volume in 1932. A revision was published in three parts as follows:
— Part 1:1953: Fire tests on building materials and structures;
— Part 2:1955: Flammability test for thin flexible materials;
— Part 3:1958: External fire exposure roof test.
In the present revision the three sections of Part 1, covering tests for combustibility of materials, surface spread of flame on materials and fire resistance of structures, have been prepared as separate parts and given new part numbers. As each of these parts is issued it will supersede the corresponding section of Part 1. Part 2:1955 is being withdrawn as a result of publication of BS 2782, “Methods of testing plastics”, Part 5, “Miscellaneous methods”, which includes Method 508, “Flammability”. In order to avoid confusion none of the new parts will be numbered 1 or 2. Part 3:1958 is under revision. Additional parts for ignitability and fire propagation tests are in preparation. This in effect means that the standard will comprise the following parts:
— Part 3: External fire exposure roof tests;
— Part 4: Non-combustibility test for materials;
— Part 5: Ignitability test for materials;
— Part 6: Fire propagation test for materials;
— Part 7: Surface spread of flame test for materials;
— Part 8: Fire resistance tests for elements of building construction.
Other tests being studied may result in the issue of further parts. The need for a glossary covering terms used in BS 476 has been established and this will be published separately as a British Standard glossary of terms and definitions associated with fire.
The present standard replaces the combustibility test specified in BS 476-1.1:1953 and is issued under the authority of the Fire Standards Committee. The test has been revised and renamed in the light of practical experience in the United Kingdom and of joint investigation and discussion in an international context. The name “non-combustibility test” was thought on balance to be more logical than “combustibility test” and in line with the proposals of the International Organization for Standardization (ISO).
Consideration was given to the possibility of using a bomb calorimeter but it was decided not to recommend a test on this basis. The new test recommends that a continuous recording of the furnace temperature is made and requires observations as to whether a sample produces a flame. Materials are classified as combustible or non-combustible by identifying those which make little or no thermal contribution to the heat of the furnace and do not produce a flame, and by calling the remainder “combustible”.
Three samples are required instead of six as in the earlier test, but the sample size remains practically unchanged. A long steel cone is now attached to the bottom of the testing furnace to act as an air-flow stabilizer. As part of BSI’s programme of metrication this standard is expressed in metric terms. The metric values are given in SI units. For further information reference should be made to BS 37631) and PD 56862).
