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This document provides guidance for fire safety engineering that is applicable for fires in enclosed spaces. It is intended to be used in conjunction with models for analysis of the initiation and development of fire, fire spread, impact of heat, radiation, and limited visibility, smoke formation and movement, chemical species generation, transport and decay, and people movement, as well as fire detection and suppression, given in the normative references in clause 2. This document is intended to be used only within this context. This document establishes procedures to evaluate the effects of life-threatening components from fire environments in terms of the probability of compromised tenability of a targeted human population at accumulated time intervals. It makes possible the estimation of the time at which people can experience compromised tenability due to smoke, heat and toxic fire effluent. The most critical hazard is that which causes compromised tenability at the earliest time. The time-dependent production of smoke and toxic fire effluent and the thermal environment of a fire are determined by the rate of fire growth, the yields of the various fire gases produced from the involved fuels, the decay characteristics of those fire gases and the ventilation pattern (see A.1). Once these are determined, the methodology presented in this International Document can be used for the estimation of the time at which individuals can be expected to experience compromised tenability. This document establishes procedures to evaluate the life-threatening components from fire environments in terms of the probability of a targeted human population at accumulated time intervals. It makes possible the estimation of the time at which people in enclosed spaces can experience compromised tenability (see A.2). It enables an estimation of compromised tenability for each predicted Cxt (Concentration x time) of components from fire environments. In addition, the time to untenability due to the impact of heat and of smoke (visibility) needs to be considered. The impact leading to attain compromised tenability at FED = 1 earliest is considered the most critical. The non-lethal threshold-based derivation of the occurrence of compromised tenability also protects from post-exposure mortality. Details for assessing the impact of heat and smoke will be given in ISO 13571-5. This method is intended to assess the escape capability of people in an environment, where generally adult and not handicapped people are expected, as for example in industrial and working surroundings. In addition, susceptible people are covered in this document based on the already included adjustment factors explained below. For the escape capability of hyper-susceptible people, no meaningful additional assessment factors can be defined, but this document can be applied in a meaningful way for places where it can be assumed that hyper-susceptible or helpless people will always get assistance for escape, like in child care units or hospitals. This document covers all fire stages including smouldering fires or other scenarios where high emissions of CO2 can be expected, as CO2 is considered as a toxicant per se for higher concentrations. Recent fire tests have shown that in some fire scenarios CO2 can be found in relevant concentrations [19-21] and has to be considered as a toxicant per se. For applying this document the basic information given in ISO 13344, and in ISO 19706 also is relevant.[58,59]