The current prescriptive rules for designing the fire resistance of steel, concrete, masonry and timber members are based solely on the results and observations from standard fire resistance tests.

Basically, the test involves subjecting a structural member to a heated furnace environment for the desired duration. The resulting fire resistance rating is expressed as the time in minutes that the member is able to withstand exposure to the standard fire before a specified failure criteria is reached. Based on these tests, structural members are classified into fire resistance categories, for instance R30, R60, R90, R180, …, R240. The number of tests necessary for classification varies from country to country. The standard test methods in the UK for determining the fire resistance of beams, columns, roof assemblies etc. are complied with either British Standard BS476 or European Standards EN1363 and ENV13381 or the International Standard ISO 834.

It is noteworthy that the latest Eurocode EN1363-1(1999) has revised the method of measuring the heating curve, by replacing the bead thermocouple with the plate thermocouple, in an attempt to standardise furnaces across Europe. At first sight the effect of changing the type of thermocouple used to measure the heat input would appear to be insignificant. However, using the plate thermocouple results in the tested members being subjected to more heat during the early stages of the test. This may result in some members failing the test to EN1363-1 despite having passed the BS476 test.