AbstractEquations have been developed which give the time available for escape or rescue, i.e., the time interval between detection and blockage of the escape route by smoke, heat or toxic gases. Alternative assumptions are explored concerning exponential vs power law fire growth and an extended fire plume vs uniform filing of the building. The equations are developed in such a form that the threat variable by which the fire is detected is not necessarily the same threat variable which first blocks the escape route. A number of interesting results have been obtained, and numerical values of key parameters measured in various test fires at Factory Mutual Research are tabulated. It is shown that for many polymeric fuels smoke will block the escape route well before temperature or toxicity becomes excessive. In such cases, if the fire, assumed to be growing exponentially, is detected by its smoke, the detector being located in the escape route, then the escape time, surprisingly, is independent of the smokiness of the material as well as the size and shape of the building. It is determined only by the growth rate constant (doubling time) of the fire and the sensitivity of the detector.