BS ISO 19706:2011 pdf download – Guidelines for assessing the fire threat to people
4 General principles
4.1 Fire effluent and escape time
4.1.1 Life safety in a fire is greatly enhanced if the time available for occupants to escape exceeds the time required for them to escape and is threatened if the time required exceeds the time available.
188.8.131.52 As specified in ISO/TR 13387-8, the time required for escape includes the time from ignition of a fire to its detection, the time from its detection to an evacuation warning to occupants, an occupant’s pre-movement time (the time between becoming aware of an emergency and initiating egress) and the actual travel time to a place of safety.
184.108.40.206 The time available for escape is the interval between the time of ignition and the time after which conditions become untenable, such that occupants are unable to take effective action to accomplish their own escape to a place of safe refuge. Guidelines for estimation of the time available for escape are specified in ISO 13571:2007. It involves procedures to evaluate the life threat components in a fire hazard analysis, e.g. toxic gases, heat and smoke obscuration, in terms of the status of exposed subjects at discrete time intervals. The time at which occupants’ exposure exceeds a threshold criterion represents the time available for escape. Users of ISO 13571:2007 have the flexibility to set such criteria according to their chosen life safety objectives. Thus, an estimated time available for escape might or might not be equivalent to an ASET (available safe escape time).
4.1.2 The quantity and nature of the fire effluent are prime factors in estimating the time available for escape. The effluent nature is a function not only of the product from which it is generated, but also of the conditions under which the product participates in the fire and the nature of the fire.
4.2 Effects of fire effluent on people During and following a fire, the products of combustion can have lethal and sub-lethal effects on occupants of the facility and responders to the fire. The severity of the effects depends on the composition of the effluent, the extent of the exposure and the physical condition of the subject. Information relative to the effects on people can be extracted from physical and chemical characterization of the effluent (e.g. using ISO 13571:2007), from estimation of the toxic potency of fire effluent (e.g. using ISO 13344) or from accidental exposures of people to the chemical and thermal components of the effluent. The effects of the effluent on people are not unique in severity or immediacy, but fall into a distribution. This is due to the range of sensitivity of people to the fire effluent and variations in the progress of a fire.
4.3 Use of fire-effluent data Because the effect of the fire effluent on people depends on factors beyond the combustible(s) as a source of the effluent, it is necessary that the fire-effluent composition data be combined with additional information about the facility, the fire and the people into a fire hazard or risk assessment, rather than being used alone as an indicator of fire hazard or risk.
4.4 Data accuracy and uncertainty All measurements, calculations and assumptions are characterized by a degree of uncertainty. The utility of the outcome of a fire hazard or risk assessment depends on knowing the uncertainties in the assessment methodology and the uncertainties in the input data. This International Standard addresses the uncertainty in the characterization of fire effluent, the measurement of effluent effects and the accuracy of the measurements.
5 Significance and use
5.1 The projected response of people to fire effluent frequently determines the fire-safety design limits for occupancy. This International Standard provides guidelines on the type of effluent information required to enable such a projection and how to use the data.
5.2 The information derived using the guidelines in this International Standard is for use in fire hazard and risk assessment