Model development of untenable conditions during egress and stochastic evaluation in compartment fires
Abstract
This study aimed to develop an “improved simplified two-zone model authentication technology” in order to simulate the time to untenable conditions in compartments less than 200 m2 in area, which include smoke layer temperature, visibility, carbon monoxide concentration, fractional lethal dose, and radiation heat flux. Based on reliability-based design and structure function, this study focuses on constructing “the stochastic model of egress safety/failure in a compartment fire”. Moreover, stochastic parameters and probability distributions were assumed. Random numbers of parameters were generated by Monte Carlo simulation. After several simulations, the failure probability of occupants egress due to one or more than one of the untenable conditions was obtained. After constructing the model, 200 m 2 occupants in a ALA PUB disco ballroom located in Taichung, Taiwan were taken as an example. The simulation of polyurethane furniture fire was executed 100 times. The results showed that installation of automatic fire alarm equipments and emergency broadcasting equipments can substantially reduce the untenable conditions and failure probability of occupants egress. Some ideas for fire officers and future studies for fire researchers were also recommended.
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Introduction
The fire incident of an entertainment quarters (ALA PUB) occurred on March 06, 2011. It is situated in Chung Hsing Street, Taichung City, Taiwan. The fire broke out at 1 am. It first initiated from the stage area on the second floor, so customers staying on the mezzanine were unable to escape, thus resulting in 9 dead and 12 wounded. After the fire incident, public safety in discos, bars, and musical performance places (live house) that sell alcoholic beverages became the focus of attention.
Over the past decades, compartment fire has been investigated in detail and its growth is well understood. From these literatures [1–3], it appears that great progress has been made in the typical building compartment fires with vertical openings, such as door and window. As a typical enclosure, the buildings, such as underground structures, entertainment compartments, and bars, only have the horizontal ceiling vents. Compartment fire with vertical wall vents or horizontal ceiling vents might have different behaviors, because the flow exchange at the openings and vents is of considerable importance in the compartment fire growth and spread.
Conclusion
(A) This study used the “stochastic subdivided space personnel evacuation prediction model”, supplemented by the Monte Carlo simulation method, to assess the probability of personnel evacuation failure. Personnel may be faced with untenable conditions in entertainment quarters (discos) during evacuation process. The fire is initiated from PU (polyurethane) furniture in the quarters (where fire growth rate is according to the 2 t fire growth model, while the average fire growth rate is 0.059 kW/s². The untenable conditions faced by personnel include visibility less than 5 m, radiant heat flux greater than 2.5 kW/m², smoke layer temperature higher than 200 °C, fractional incapacitating dose of carbon monoxide in blood 30%, and lastly the concentration of carbon monoxide over 1,400 ppm.
(B) In this study, setting the accommodating capacity control limit for the entertainment quarter (discos) to 200 persons, equipped with automatic fire alarm and emergency broadcast equipment, the probability of failure in personnel evacuation due to one or more untenable conditions will be decreased by 13.3%. Such a decrease is close to the result of Nystedt [44]. Nystedt made a simulation with residential quarters equipped with smoke detectors, in which the risk of fire death was decreased by 11%. The apparent difference may be due to several factors. The fire growth model used by this study is different from Nystedt; the accommodating capacities for the business quarters are different; the personnel behavior and detector types used are different; and the standards for untenable conditions are also different. However, the installation of automatic fire alarms and emergency broadcast equipment will indeed reduce the probability of fire casualties overall.
(C) The personnel evacuation model developed by this study has made several assumptions. The fire is flaming combustion; people remaining in the compartment will listen to the automatic fire alarms and follow instructions from the emergency broadcast equipment to escape; no one stays behind to fight the fire, or opens the windows to release smoke. In fact, if considering the smoldering effect or that some people will not observe the fire warning and escape but choose to stay behind to assist the fire fighting or open the windows to release smoke, such circumstances should be discussed and elucidated separately with another research topic to analyze the probability of evacuation failures due to the above conditions.