Evacuation in Complex Environments - Industrial Fire Journal

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Fourth International Symposium on Tunnel Safety and Security, Frankfurt am Main, Germany, March 17-19, 2010 A comment from the participants during discussions after the experiment revealed that communication between the participants on the TBM and between the participants on the TBM and persons outside the tunnel did not work properly. Communications over the radio during the experiment was sometimes in Swedish, which made it difficult for participants not understanding Swedish to follow the conversation. The formal procedure is that all communication shall be in English. The participants also mentioned that there was a lack of information regarding the situation from persons outside the tunnel. As there was no clear sign of a fire at the TBM the situation was rather ambiguous for the participants when they were sitting in the refuge chambers. One person also mentioned that he was anxious that someone had not noticed the fire alarm and still be at a place in the TBM. The information about the exact number of persons on the TBM during the experiment was uncertain to the persons supposed to be the only ones at the machine. EVACUATION MODELLING The evacuation model used for investigating the possibility for tunnel workers to safely evacuate a tunnel compares the time for evacuation with the time for untenable conditions to occur. The model is based on a one-dimensional approach of smoke spread in the tunnel. This means that the smoke temperature, gas concentrations, visibility etc only depend of the distance from the fire and the time. The vertical variation is ignored and it is assumed that homogenous conditions apply, which is true at a distance from the fire. Close to the fire the model will provide a not so good prediction of the conditions. The smoke spread and subsequently the spread of toxic gases, temperature etc are calculated using the model provided by Ingason [6] and only need to have a HRR curve as an input. It is assumed that the fire is located in the most remote part of the tunnel construction site, i.e. where the actual tunnel is excavated. The evacuation model is based on the assumption that a person continues to move away from a fire, after an initial pre-movement time, at a speed that depends on the smoke conditions, i.e. the visibility. Reduction in visibility reduces the walking speed. The person can initially already be at a distance away from the fire. The movement continues as long as the person is conscious and that depends on the accumulated toxic dose of the smoke gases, mainly carbon monoxide, carbon dioxide, low oxygen concentration and elevated temperature. The toxic accumulation is derived using the Fractional Effective Dose theory proposed by Purser [7]. It is assumed that unconsciousness occur when the person has accumulated a toxic dose equivalent to FED = 1,0. A preliminary analysis was made on the Hallandsås rail tunnel using a 30 MW fire as the first assumption. The fire peaks at 30 MW at approximately 13 minutes from the fire start. The ventilation air supply to the construction site is assumed to result in a supply air velocity of 0,5 m/s across the tunnel section. Some of the results from this initial analysis are presented in table 2 which show whether or not evacuation is possible and how far from the fire a safe refuge must be located. Table 2. Basic results from the sample analysis. Scenario Pre-movement time, sec Initial distance between person and fire, m Distance when FED = 1,0 occurs, m Time when FED = 1,0 occurs, minutes 1 60 0 - never 2 120 0 250 22 3 120 50 - never 4 120 30 - never 5 150 30 300 25 188
Fourth International Symposium on Tunnel Safety and Security, Frankfurt am Main, Germany, March 17-19, 2010 From analysing the different scenarios it is evident that as long as the evacuation can be initiated with only a small delay most of the occupants in the tunnel can evacuate safely. But if they respond slowly or are close to the fire so they already are within a smoky section they will have difficulties to escape. One shall, though, be aware of that in this case the fire is rather large and only a small part of the analysis is presented. But the purpose with these results is to demonstrate that it is quite easy to perform an evacuation analysis of the tunnel construction site in order to get an idea of the fire threat. Additional analyses, for example regarding heat radiation on the workers, have to be performed to get a broader picture of the workers’ safety. DISCUSSION Evacuating from a complex environment can be difficult to perform without any additional improvements of the environment or additional information or education of the persons subjected to the environment. The experiment shows that the outcome of an evacuation can depend on the attitudes among the persons in the environment even if that factor is not part of the environment but rather as an external factor associated to how the environment is used. However, given the conditions the overall impression is that the evacuation was prompt and efficient. The response time was very short for most of the participants indicating that they were trained to handle the situation. The attitudes regarding safety in the case of a fire among the participants given from the questionnaires showed that they were aware of the seriousness if the situation was for real. Working in building sites, industries etc may need to use different equipment, cranes or machinery that cannot be shut down immediately at the time the fire alarm starts. Because of safety reasons some equipment need a shutting down period before it is safe to leave the work place. There is no simple solution for handling these problems but care has to be taken to prepare for emergency closure procedures of such equipment. Mainly this is a management procedure and the first priority in the case where the fire alarm starts must be to shut down the equipment instead of questioning the reason for the alarm. This problem was not tested in a fully realistic manner as the TBM was shut down for maintenance and only running in stand by mode. Some traditional maintenance work provided some insights into the problem. A quick response will most likely require a clear and understandable signal that can be readily heard from all relevant locations. The fire alarm in the TBM was possible to be heard from all locations in the machine which contributed to the fast response. This is most important for cases when visual access is limited which usually is the situation for these locations as it defines the complex environment. The use of fire alarm is therefore essential. The evacuation from the TBM clearly shows the need to use a fire alarm as this was the first sign of an unusual condition in the tunnel. Initially it was assumed that the walking speed should be lower than what can be expected in other occupancies. But this turned out to be wrong. In the TBM the participants walked at least as fast as shoppers in a warehouse even if the walking paths were not as smooth as in the warehouse. The reason for this could be that most of the persons, mostly men, working in this type of environment are rather strong and well fit for the job. It must be assumed that they are slightly better suited for moving in the narrow passages and along uneven surfaces. In most cases it can also be assumed that the persons are familiar to the environment at least after spending some time in, for this case, the TBM. However, in many other complex environments narrow passages may still be a problem even if the persons are familiar with the conditions. Climbing a ladder through a narrow hole in a floor is much more difficult that using a stair. Elimination of difficult passages should therefore be considered if possible. 189
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