Perceived Time Available: The Margin Of Safety In Fires

Abstract

The knowledge people have of the degree of fire threat is considered to be important to an understanding of the time people need for response. 'Time needed' is a psychological concept which varies in terms of the 'perceived' time available (PTA) to carry out various actions. A distinction is made between the objective and subjective (perceived) availabil ity of escape (or refuge) options: termed ODF and SDF 'Degrees of Freedom'. Analyses are presented of the time lag between the fire growth (ODF) and a person's knowledge of the degree of threat (SDF), also the diminishing availabil ity of escape routes. The time components of different 'Required Safe Egress Time' equations are discussed. An alternative equation is discussed. Two integrated levels of analysis are necessary in monitoring the timing of people's actions in fires (A) the psychological! social goal of the action: (B) the location of the action as a person moves around a building. Attempts to measure the duration of behaviour are discussed together with recommendations for future research. It is suggested that PTA should feature in any calculations of margins of safety in equations contrasting time needed and time avai 1ab1e •