This International Standard is one of many tools available for use in fre safety engineering. It is intended to be used in conjunction with models for analysis of the initiation and development of fre, fre spread, smoke formation and movement, chemical species generation, transport and decay, and people movement, as well as fre detection and suppression. This International Standard is to be used only within this context.This International Standard is intended to address the consequences of human exposure to the life-threatening components of fre. The time-dependent concentrations of fre effuents and the thermal environment of a fre are determined by the rate of fre growth, the yields of the various fre gases produced from the involved fuels, the decay characteristics of those fre gases and the ventilation pattern (see A.1). Once these are determined, the methodology presented in this International Standard can be used for the estimation of the time at which individuals can be expected to experience compromised tenability.With care, this guidance can also be applied to estimation of the time limit for rescuing people who are immobile due to injury, medical condition, etc.This International Standard establishes procedures to evaluate the life-threatening components of fre hazard analysis in terms of the status of exposed human subjects at discrete time intervals. It makes possible the estimation of the time at which occupants can experience compromised tenability (see A.2). It enables estimation of a compromised tenability endpoint for each of the fre effuent components, with the most important endpoint being the earliest to occur.