دانلود رایگان مقاله اثر محیط ساخته شده بر روی طراحی آتش سوزی

Abstract

Design fires are often used to the evaluate performance based designs by fire protection engineers all over the world and can be an invaluable tool if used properly. One potential big issue however is the fact that the exact same design fire is recommended by authorities in similar building types despite the fact that some building characteristics, such as building material, can differ greatly. This paper focused on investigating several key characteristics of a building (building material, openings, room floor area size and ceiling height) and its effect on the design fire using computational fluid dynamics. When well to moderately insulating materials was used the design fire growth rate and maximum heat release rate was in many cases significantly increased, especially if the room was well ventilated, the ceiling height was relatively low and the room floor area was moderate. However, using thermally thin materials (steel sheet) or materials with large heat storing capacity (concrete) very little change was seen on the growth rate or maximum heat release rate. In conclusion it was recommended that one should take precaution when using recommended design fires in buildings with certain characteristics since it potentially can overestimate the safety in such case.

6. Conclusions

It has been shown that the building material used in a fire compartment might influence the growth rate of a design fire in a significant way; insulating wall/ceiling materials will probably increase the growth rate which in turn will mean that the time to critical conditions will be shorter compared to the expected result. However, if the building material used is thermally thin or has a large heat storing capacity the influence is rather negligible. The maximum heat release rate and transient behavior of the fire was shown to be very dependent on ventilation factor in combination with the building material; with only one door opening present the initial fire growth was rapid due to radiative feedback but was then hampered by the oxygen depletion which caused the heat release rate to decrease significantly during the course of the simulation duration. The heat release rate increased slowly over time but never reached above the preset maximum (5000 kW). This applied to all building materials. Using 4 door openings however allowed the initial peak heat release rate to become larger for the insulated and drywall compartments which meant an increase in calculated growth rate. Since more air was supplied more combustion could occur inside the compartment and this increased the temperature of the walls and hot gasses and hence the radiative feedback became more intense. Further it was shown that the room floor area might have a significant effect on the growth rate and maximum heat release rate; with one door opening a larger room (floor area 20 20 m) would have a higher initial peak heat release rate than the smaller rooms, (5 5 and 10 10 m) but they would all get oxygen depleted soon thereafter and behave similarly for the rest of the simulation. If there were four door openings present the radiative feedback would overpower the oxygen depletion and the smaller the room the higher the maximum heat release rate and growth rate. 0