This International Standard specifies a test method for determining the effective sealing capability of intumescent materials or systems in the context of sealing door–to–frame clearances in timber door assemblies. Intumescent seals extend the duration for which the gap between the leaf edge and the frame will satisfy the integrity criteria of the fire resistance test, and sealing systems can be compared using this method. The method is suitable for evaluating the efficacy of exposed intumescent sealing systems used in conjunction with timber fire resisting doors of up to 1 h fire resistance. It is not suitable for comparing concealed intumescent seals. The results can be applied to proven, single-acting, single-leaf, latched, timber door assemblies of sizes up to that given in the field of direct application. This International Standard is applicable to timber door assemblies whose intumescent seals have been tested in accordance with ISO 3008 and have satisfied the integrity and — if appropriate — the insulation criterion, whilst incorporating another form of heat-activated seal for a period appropriate to the application. The suitability of any sealing system for use on timber door assemblies of any other configuration (i.e. unlatched single doors, double leaf assemblies etc., or doors constructed of other materials) can only be evaluated by subjecting a full-sized door assembly, complete with seals, to testing in accordance with ISO 3008. The method does not provide any measure of the ability of the seal to resist the flow of smoke (although a gap that is sealed will provide a reduction in the flow of hot products of combustion) or any information as to the additional protection that could be needed at hardware/ironmongery positions.