This Technical Report specifies procedures for the design, performance and reporting of fire tests which are not performed using standardized test equipment, such as furnaces or test chambers, and which are primarily duration- or time-based. It is applicable to all “natural” fire tests, which set out to evaluate the behaviour of structural frames, rooms (or a suite of rooms forming part of a building), with respect to fully developed fire conditions, regardless of whether or not the heat input is by means of natural sources, e.g. cribs or burners. It is not applicable to “reaction-to-fire” large-scale tests, which are primarily designed to evaluate materials and for which the heating rate is slower and the maximum rate of heat release is lower than that which would occur at full development. In the context of this Technical Report “large” means tests in which the flame has a width of 1 m or more. This Technical Report is intended for use by the designers of fire tests (laboratories, regulatory authorities and researchers) and for those responsible for disseminating the information and applying the results in practice.