Towards harmonized standard fire resistance testing

Abstract

All fire resistance test furnaces in the EU will shortly be operated in accordance with EN 1363-1 (ISO 834-1 ), which specifies the temperature-time characteristic of the furnace gases 100 mm from the test specimen. However, even though a test centre complies with this standard, differences in furnace construction, fuel used and mode of operation can significantly change the effective heat flux at the surface of the test specimen. This in turn influences the heating rate and hence the assigned fire resistance time of the test specimen. For example, a comparison between valid fire resistance tests on identical samples of two types of steel beam carried out during 1989 in furnaces at TNO, Delfi, and WRFC, Warrington (both gas-fired furnaces), indicated a 30% difference in the assigned fire resistance times even though the observed limiting temperatures of the steel beams were similar in each instance. There is evidence that the specimens tested at TNO were subjected to significantly higher incident heat fluxes during the early stages of the test. To achieve harmonized fire resistance testing it is necessary to subject all test specimens to the same incident heat flux-time characteristic. This will involve furnace standardization and the development of methods for the measurement and control of the incident heat flux at the surface of the test specimen. Some indication is given concerning the form of the incident heat flux-time characteristic envisaged for an improved test procedure.