First, ensure that the main structure of the building has sufficient fire stability.
At present, most high-rise buildings at home and abroad are mainly steel structures. Although its integrity and stability are good, its fire resistance is poor. The tensile and load-bearing properties of steel will drop sharply due to the increase of temperature. Usually, at 450 ~ 650 degrees Celsius, the bearing capacity will be lost, deformation will occur, and steel columns and beams will be bent and cannot be used any more. In general, the fire resistance limit of unprotected steel structures is only 15 minutes. Therefore, the construction industry and the fire protection industry still have a long way to go to solve this problem.
(1) Fire rating and material selection. China is divided into four fire resistance grades according to the fire resistance grade of ordinary building structures (high-rise buildings must be Grade I or Grade II). The fire resistance limit of a building depends on the fire resistance limit and combustion performance of components, which are stipulated in different fire resistance grades. The fire resistance limit of a member mainly refers to the time (in hours) from the time when the member is damaged by fire (such as losing its supporting capacity). The materials of components can be divided into combustible materials (such as wood), refractory materials (such as asphalt concrete and particleboard) and nonflammable materials (such as bricks, stones and metals) according to their combustion performance.
(two) the building should choose the component materials and construction methods according to its fire resistance rating. For example, the first-class fire-resistant load-bearing walls and columns must be incombustible with a fire resistance limit of 3 hours (such as 180 mm thick walls or columns made of bricks or concrete with a thickness of 300×300 mm), the beams must be incombustible with a fire resistance limit of 2 hours, and the protective layer of steel bars must be greater than 30 mm thick. The fire stability of the main structure must be ensured in the design, so as to win enough evacuation time and make the building easy to repair after the fire. The partition wall and ceiling should have the necessary fire resistance, and the interior decoration and furniture display should use incombustible or flame retardant materials as far as possible, such as fire-proof ceiling materials, carpets, curtains, etc., in order to reduce the occurrence of fire and control the spread of fire.
Second, do a good job in fire separation and safe passage design
In high-rise buildings, about 70% people suffocate because of toxic smoke, and smoke is the invisible killer in the fire. Therefore, we should fully consider the importance of setting up smoke control system in buildings. The horizontal velocity of flue gas is 0.3 and 0.8m/s, and the vertical diffusion velocity is 3.4m/s. When the flue gas is unimpeded, it only takes about 1min to spread to a building with dozens of floors. The flow speed of smoke greatly exceeds the evacuation speed of people. Stairwells, elevator shafts and various vertical tube wells are important ways for the vertical spread of fire in high-rise buildings, and it is easy to form "stack effect". Stairwells and their antechambers or shared antechambers are places for temporary refuge and evacuation in case of fire, and fire elevators and their antechambers are the main channels for firefighters to enter high-rise buildings for fire fighting.
(1) Fire distance: In order to prevent the fire from spreading through radiant heat, buildings should keep a certain distance. The fire spacing between Class I and Class II fire-resistant civil buildings shall not be less than 6 meters, and the fire spacing between Class III and Class IV fire-resistant civil buildings shall be 7 meters and 9 meters respectively. It is difficult to evacuate people when there is a fire in a high-rise building, so the ladder truck needs a larger working radius. Therefore, the fire prevention spacing of high-rise buildings with the same and second fire resistance ratings should not be less than13m, and the fire prevention spacing of buildings with the same and third fire resistance ratings should not be less than15m and18m. There are many flammable items in the workshop, so the fire prevention distance should be increased. For example, the fire prevention distance between the first and second-class fire-resistant workshops or civil buildings should not be less than 10 m, and the fire prevention distance between the third and fourth-class fire-resistant workshops and other buildings should not be less than 12 and 14 m. Factories or warehouses that produce or store flammable and explosive materials should be far away from buildings.
(2) Fire zoning: In order to prevent the spread of fireworks in the building, fire zoning must be carried out, that is, the building is divided into several areas by using a firewall. Firewalls should be installed in buildings with the first and second fire resistance rating exceeding 150m, and the maximum allowable area of partition wall is 2500m2. The indexes of the above-mentioned third and fourth fire-resistant buildings are 100m2, 1200m2 and 60m2 respectively. The fire zone area of Class I and II fire-resistant high-rise buildings is limited to 1000m2 or 1500m2, and the basement is controlled within 500m2. The firewall shall be incombustible, with a fire resistance limit of 4 hours. If there is a hole, Class A fire doors and windows should be installed, and all kinds of pipes should not pass through the firewall. If you can't install a firewall, you can install a fire shutter and protect it with a water curtain.
(3) Exit of safety evacuation passage: In order to reduce fire casualties, safety evacuation should be considered in architectural design. Generally speaking, there should be no less than two safety exits in public buildings, and more exits should be set in theaters, gymnasiums and other places with dense audiences. The safety exit on this floor is the stairs. Open stairwells can easily lead to the spread of fireworks and hinder evacuation. The closed stairwell can block smoke and facilitate evacuation. The smoke-proof stairwell is more conducive to evacuation because of the front room. High-rise buildings must be equipped with closed or smoke-proof stairwells, which should be arranged in two evacuation directions. Super-high-rise buildings should be added with temporary safety zones or refuge floors, and rooftop heliports can also be set up to evacuate from the air. Emergency lighting, evacuation direction indicator lights and safety exit lights should be set on the evacuation passage.
Third, strengthen the setting of alarm system and fire extinguishing device.
Automatic alarm device and automatic fire extinguishing device. The former detectors include temperature sensing, smoke sensing and light sensing. The latter is mainly automatic sprinkler equipment, and automatic fire extinguishing equipment such as carbon dioxide, dry powder or halon can be used for the parts that are not suitable for fire extinguishing with water. Buildings with automatic alarm devices and automatic fire extinguishing devices should be equipped with fire control centers to control and direct alarm, evacuation, fire fighting, smoke exhaust, fire doors and windows, fire elevators and emergency lighting. Considering that high-rise buildings are mainly self-defense and self-rescue, indoor fire water consumption is greater than outdoor. The water consumption of indoor fire hydrants is 40l/s (30l/s for residential buildings), that is, the water consumption of fire hydrants is 70l/s (50l/s for residential buildings), which is the upper limit of building fire water consumption stipulated in the code. Generally speaking, super high-rise buildings have two or more functions. Therefore, the fire duration is 3.00 hours (2.00 hours for residential buildings). Considering the municipal water supply situation, it can be determined whether to set up an outdoor fire pool and its capacity.
(1) Indoor fire hydrant installation scope: (1) High-rise building main body and podium; (2) The front room of the fire elevator or the front room shared with the smoke-proof stairwell is convenient for firefighters to put out the fire with fire hydrants and open channels as soon as possible; (3) setting refuge layer for self-rescue protection; (4) The roof or helipad is used to check the pressure of fire hydrants to prevent the fire from spreading to the top floor and protect personnel; (5) Indoor fire hydrant box should be equipped with fire reels for non-fire professionals to put out initial fires.
(2) Technical requirements for setting indoor fire hydrants: (1) The water filling column of fire hydrants needs hydraulic calculation, and it should not be less than 13m to avoid the influence of smoke and high heat on fire fighting and ensure the normal use of firefighters; (2) The distance between fire hydrants in high-rise buildings is not more than 30m, and the distance between fire hydrants in podium buildings is not more than 50m, so as to ensure that two full water columns reach any part of the same floor at the same time; (3) The district water supply system is adopted, including series water supply and parallel water supply. When the outlet pressure of hydrant bolt mouth is greater than 0.5Mpa, a pressure relief device should be set; (4) roof water tank. In order to meet the requirements of fire water consumption and fire water pressure in the early stage of fire, the height of roof water tank of super high-rise building should meet the hydrostatic pressure of fire hydrant at the most unfavorable point of 0. 15Mpa. If it cannot be met, pressurized facilities such as pneumatic water tank or pressure stabilizing pump should be set up.
In the mode of parallel water supply, the capacity of the divisional fire water tank should be the same as that of the high-level fire water tank. In case of fire, the fire water supplied by the fire pump will enter the high-level water tank, and the series water supply mode is allowed. (5) water pump adapter. Each partition within the water supply pressure range of the fire truck needs to be equipped with a water pump adapter. That is, according to the existing or future water supply capacity of fire engines, it is determined whether each partition should be equipped with a water pump adapter; (6) Anti-overpressure measures should be taken for the fire pipe network. The common method is to use a fire pump with a gentle flow-lift curve, and set up a safety valve and a drain valve to avoid the damage of ultra-high pressure to the water supply system.
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