On the safety problems in building fire prevention

2022-07-25
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The growth rate of the number of urban buildings is one of the signs that people evaluate the development and changes of their construction. However, the relative concentration of urban buildings has also promoted the concentration of urban population. The use of fire and the concentration and increase of power consumption have led to the frequent occurrence of building fires, which have taken the lives of many people and caused huge losses to the lives and property of the broad masses of the people. For example, the Hengyang fire, which caused a nationwide sensation, caused the heroic sacrifice of 20 fire officers and soldiers; Another 53 people were killed and 70 injured in the fire at Zhongbai commercial building in Jilin City, Jilin Province. Therefore, based on many years' practical experience in fire protection supervision of construction projects and understanding of relevant fire protection codes, the author believes that it is necessary to discuss the design safety and fire fighting and rescue of building fires, so as to reduce the loss of life and property caused by fires. The following article on the building fire design, fire fighting officers and soldiers and other aspects, to talk about their superficial views

I. issues needing attention in building fire protection design

in order to avoid and reduce the harm of fire to buildings, in addition to meeting the code for fire protection design of buildings and code for fire protection design of high rise civil buildings and the special fire protection requirements of various buildings, the following issues should be paid attention to according to the different characteristics of buildings:

1. Design of reinforced concrete components

reinforced concrete columns The fire endurance of beams and slabs is very important, especially the columns. In case of fire, once there is a problem, the building will collapse in a very short time. The author observed the buildings with many fires, and found that the protective layer of reinforced concrete components was separated from the reinforcement after the fire, and some of them had fallen off. After analysis, it was considered that the reason for this phenomenon was related to the thickness of the protective layer of the reinforcement. The thinner the protective layer, the worse the fire resistance. At present, the minimum protective layer thickness of reinforcement required by the code is to protect the reinforcement from corrosion without considering the impact of high temperature on the reinforcement in case of fire. In order to avoid excessive deformation of reinforcement in case of fire and reduce the bonding force between reinforcement and concrete, the protective layer thickness of reinforcement should be appropriately increased in the design; Especially for the protective layer of prestressed reinforced concrete members, the minimum thickness specified in the code is smaller than that of ordinary concrete members, so the fire resistance performance is even worse. Protective measures such as increasing the thickness of the protective layer of reinforcement or plastering the lower surface after hoisting must be taken to improve the fire resistance limit and meet the requirements of fire safety. In addition, the section size of the member also has a great impact on the fire resistance performance. For the sake of safety, the section size of the column at the bottom layer and important parts should be appropriately increased

2. Design of steel members

in the quality supervision work, the author saw that some steel members did not require fire prevention treatment in the design. We know that the fire resistance of steel members is very poor. Under high temperature, the strength and bearing capacity of steel members decline very quickly. In order to ensure the strength and bearing capacity of members before the fire, it is required to paste or paint thermal insulation fireproof protective layer on the surface of members in the design to improve the fire resistance limit of steel members. Therefore, it is very important to record the tensile force value of each experimental section immediately and accurately for the success or failure of the experiment

3. Design of special components

for cantilevered components and components that are easy to lose stability, combustible materials cannot be used to maintain balance, so as to prevent combustible materials from burning and causing component collapse in case of fire. For example, a fire broke out in a warehouse, and the roof truss could be seen clearly when the fire spread to the wood. Because the cornice of the warehouse was high, the firefighters stood on the ground and used water guns to put out the fire. They found the picked out awning board, so four firefighters stood on one awning board successively and used water guns to shoot water at the roof truss. Just as they were concentrating on the fire, the wooden roof truss pressed on the awning beam was burnt out and the roof truss collapsed, The results of the experiment showed that when the awning overturned and the four firefighters did not react, they fell with the awning, were pressed under the awning and died heroically on the spot

4. Design of complex building

in recent years, there are many buildings with commercial buildings on the ground floor and residential buildings on the upper part. Due to the large power consumption of commercial buildings and a large variety of goods. Such as careless use of electricity and smoking, these rooms will cause fire. In order to prevent the impact of fire in commercial buildings on the upper residential buildings, fire barriers shall be set between commercial buildings and residential buildings in the design, and there shall be independent stair entrances and exits to completely separate them, so that the flow of personnel and the flow of goods and goods can be separated into two channels without interference with each other

in addition, the commercial buildings on the ground floor usually have large doors and windows. In order to prevent the fire from entering through the doors and windows after a fire, cornices, sunshades, balconies, awnings or verandas should be set at the upper part of the doors and windows to prevent the upward flame from deflecting outward after being blocked and away from the upper window, so as to achieve the purpose of fire prevention

5. Design of special rooms

for some rooms where it is difficult to drain water after ponding, drainage holes shall be set at appropriate parts. In case of fire, the water used by firefighters for fire fighting can be discharged smoothly to reduce the load weight of the floor. Refuge balconies are set in some parts to provide a place to escape smoke and fire for those who are too late to evacuate. They can also be used as positions for firefighters and water gunners

II. Safety issues that fire officers and soldiers should pay attention to when fighting fires

through the observation and analysis of the fire fighting situation of many building fires, the author believes that fire officers and soldiers should have some knowledge of building fire prevention, and should avoid dangerous building components when fighting fires, so as to achieve the purpose of protecting themselves from fighting fires. Specific attention should be paid to the following points:

1. For buildings with fires, according to the structural type, The fire resistance limit of each component shall be preliminarily determined. When the load-bearing component reaches the fire resistance limit, it shall not enter the building again

2. For non combustible components, do not shoot too much water. For example, reinforced concrete columns, beams, slabs, etc. begin to expand under the action of high temperature in the event of a fire. When washed by the water jet, the surface cools sharply, causing surface shrinkage. In the case of internal expansion and external contraction, the concrete skin often falls off, damaging the protective layer of the reinforcement and exposing the reinforcement. Before the fire is completely extinguished, the reinforcement is directly affected by the high temperature of the flame and immediately loses its strength, Damage to the whole structure; However, if the steel members with higher temperature are cooled suddenly by water jetting, the deformation of the steel members will be accelerated and the structure will collapse in advance

3. Because the fire resistance of prestressed reinforced concrete members is not as good as that of ordinary reinforced concrete members, in case of fire, the reinforcement will be heated and extended, which will cause prestress loss and reduce the bearing capacity of the structure. The collapse is relatively sudden. During fire fighting, pay attention to observe the deformation and cracks, and avoid them immediately if there are deformation and cracks

4. For cantilevered members, unstable members and members that change the stress in case of fire, pay attention to observe whether they can lose stability, overturn, break, etc. to prevent people from being injured by collapse

5. The fire resistance of solid brick wall is relatively good, but the empty bucket wall and hollow brick wall are prone to deformation and damage in case of fire, and the fire extinguishing water may push the wall down. The adobe wall is not afraid of fire, but it will collapse in case of water gun jet impact or water absorbed by the root to extinguish the fire

6. The cooperation with Alibaba on the roof or the building on fire is not just a one-time cooperation. There are fewer people on the ordinary business cooperation board, and they should not concentrate. They should walk steadily, explore and move forward, listen to the movement, see the deformation, and do not stand on the eaves and the edges of components. In the roof and on the floor, pay attention to avoid stepping empty, climbing on the "probe plate" or stepping on the structure that will be damaged, so as to prevent falling into various shafts

7. During fire fighting, pay attention to the spread of smoke and radiant heat, be optimistic about the wind direction, select a favorable location, and try not to damage the original load-bearing structure, so as to avoid collapse due to insufficient bearing capacity

8. Before the wood structure is damaged, there is usually a symbolic sound. When extinguishing the fire, pay attention to the sound of structural deformation, observe the erosion of the structural section, and feel the temperature. When the fire has broken through the roof shell, it indicates that the roof is in danger of collapse. When extinguishing the fire, it should be hidden in a safe place where people will not be injured by the roof collapse

9. Before the wall collapses, the soil or bricks are mostly dropped from the top of the wall, and then a large area is poured with a "bang". The sequence of house collapse is generally the ceiling first, then the roof, and finally the wall. Most of the external walls collapse inward

there is a close relationship between the fire protection design of building engineering and fire accidents. In the fire protection design of buildings, we should carefully consider the adverse factors when a fire occurs and adopt effective design to improve the fire resistance of buildings; When the majority of fire officers and soldiers understand the knowledge of building fire prevention, they can reduce the casualties in fire fighting

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