Nils Johansson

A Monte Carlo analysis of the effect of heat release rate uncertainty on available safe egress time

Available safe egress time is an important criterion to determine occupant safety in performance-based fire protection design of buildings. There are many factors affecting the calculation of available safe egress time, such as heat release rate, smoke toxicity and the geometry of the building. Heat release rate is the most critical factor. Due to the variation of fuel layout, initial ignition location and many other factors, significant uncertainties are associated with heat release rate. Traditionally, fire safety engineers prefer to ignore these uncertainties, and a fixed value of heat release rate is assigned based on experience. This makes the available safe egress time results subjective. To quantify the effect of uncertainties in heat release rate on available safe egress time, a Monte Carlo simulation approach is implemented for a case study of a single hypothetical fire compartment in a commercial building. First, the effect of deterministic peak heat release rate and fire growth rate on the predicted available safe egress time is studied. Then, the effect of uncertainties in peak heat release rate and fire growth rate are analyzed separately. Normal and log-normal distributions are employed to characterize peak heat release rate and fire growth rate, respectively. Finally, the effect of uncertainties in both peak heat release rate and fire growth rate on available safe egress time are analyzed. Illustrations are also provided on how to utilize probabilistic functions, such as the cumulative density function and complementary cumulative distribution function, to help fire safety engineers develop proper design fires. (Less)

Detection of a typical arson fire scenario – comparison between experiments and simulations

Abstract in Undetermined Between one and two school fires occur in Sweden every day. In most cases, arson is the cause of the fire. The most severe fires generally start outside the building and spread up along the facade and into the attic through ventilation openings in the eaves. Linear heat detectors can be placed on facades to detect these types of fires. Such devices detect fire when short-circuited at a specific temperature. In this article, an attempt to simulate linear heat detectors is presented. Data from small-scale and full-scale experiments are compared with these simulations. The small-scale experiments and simulations demonstrate that the cable failure model in Fire Dynamics Simulator can be used to predict detection in linear heat detectors that use short-circuiting as the means of signaling an overheated condition. The full-scale experiments provide a measure of the uncertainties involved, as well as the possibility of using simulations of linear heat detectors in a fire engineering design. (Less)

How could the fire fatalities have been prevented? An analysis of 144 cases during 2011-2014 in Sweden : An analysis

Approximately 80%–90% of all fire-related fatalities take place in residential occupancies. The risk groups are well known, but the effectiveness of different measures has been less investigated. In this article, fire investigations from 144 unintentional fatal residential fires have been systematically analyzed and technical measures that would have been effective in preventing each fatality have been identified. The result shows that, generally, a thermally activated suppression system (e.g. sprinkler) has the highest potential effectiveness (68%) followed by a detector-activated system in bedroom and living room (59%) or smoke alarm (37%). For smokers with home care, however, the potential effectiveness of a thermally activated suppression system and home smoke alarm was significantly lower (31% and 14%, respectively). This indicates that different measures are effective for different groups. In one-fifth of the cases, the victim could have evacuated but chose not to do so, primarily to attempt to extinguish the fire.

Response of stone wool–insulated building barriers under severe heating exposures

This article presents the experimental results of stone wool–layered sandwich constructions, with either steel or gypsum claddings, tested under four different heating exposures: 7 kW/m2 incident radiant heat flux exposure, 60 kW/m2 incident radiant heat flux exposure, parametric time–temperature curve exposure and ISO 834 standard time–temperature exposure. The test apparatus used were a movable radiant panel system, a mid-scale furnace (1.5 m3) and a large-scale furnace (15 m3). The results show that reduced-scale tests are capable of reproducing the heat transferred through the construction at large scale provided there is limited mechanical degradation. The results indicate that the availability of oxygen is fundamental to the fire behaviour of the sandwich composites tested. Reactions occurring in stone wool micro-scale testing, such as oxidative combustion of the binder or crystallisation of the fibres, have a limited effect on the temperature increase when wool is protected from air entrainment.