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2023-02-13In recent years, there are more and more large-space and long-span steel structure production workshops, commercial shopping malls, gymnasium roof, terminal buildings, warehousing and logistics warehouses. High technical level. It is generally used in high-rise buildings or large-space, long-span buildings, as well as non-residential commercial streets at the bottom. With the increase in people’s fire and electricity consumption, the fire index is also on the rise. Although steel does not have combustion properties and has good fire resistance, once a fire occurs, the elastic modulus will drop significantly. When the temperature is close to 600°C, the strength and stiffness will basically be lost, which will cause the building to collapse instantly.
1 Fire characteristics
1.1 The steel structure is greatly affected by cold and heat and is easy to deform and collapse
1.1.1 The heating strength of the steel structure decreases rapidly
Steel structure buildings have a strong load-bearing capacity and large space. Generally, large-scale leisure and entertainment places, high-rise buildings, warehouses, etc. rely on roof trusses, columns, beams, etc. to build load-bearing. These steel structures are formed by riveting and welding. Some of the steel structures are beams and columns connected by round steel and flat steel. Angle steel is used to splice roof trusses, and the general bearing capacity is 400-450kg/m2. Generally, in a fire, steel components will not burn, but due to their poor fire resistance, their strength will change dramatically with the increase of temperature. In modern commercial buildings, some large-span leisure places and high-rise buildings are painted with fire-resistant paint according to fire-proof requirements. At 350°C, 500°C, and 600°C, the strength drops by 1/3, 1/2, and 2/3, respectively. Therefore, if the steel components of the main body of the building are not protected by fire-proof spraying when a fire occurs, the building will collapse in a short time under the influence of high temperature, causing casualties and property losses.
1.1.2 The sudden cooling and deformation of steel components will destroy the overall stability of the building
Most of the steel structure buildings are workshops, and the modern steel structure roofs are also equipped with components such as vents and air conditioners, burying fire hazards. Thermal expansion and contraction are the basic characteristics of steel. After a fire occurs in a steel structure building, firefighters will inevitably use water guns and water cannons to cool down. The security of insider combat operations.
1.1.3 The basic conditions are poor, and the fire-fighting facilities are easily damaged
Large-span steel structure buildings are equipped with sound fire-fighting facilities, temperature-sensing, smoke-sensing, automatic alarms, and other fire-fighting control systems according to the requirements of the fire department. Rapidly damaged, deformed, and collapsed within 20 minutes (Table 1), especially in some old steel structure production and processing factories, warehouses, and other places, the infrastructure is relatively weak, the fire-fighting facilities are not perfect, and the density of fire extinguishers and fire hydrants is not enough, which affects the timely fire fighting.
1.2 The ventilation condition is good, the combustion is sufficient, and it is easy to cause heavy casualties
1.2.1 Large volume, sufficient combustion conditions, high fire temperature
Large space and long-span steel structure shopping malls, warehouses, and other buildings generally have a relatively large volume of space, good air convection, and relatively many combustibles such as operating and storing goods, and the fire load density is high. People were evacuated. After the fire broke out, the fire was large, burning violently, spreading quickly, and having a high calorific value. At the same time, under the rapid thermal conductivity of the steel structure, the fire resistance is poor, and the interior decoration of the building is not decorated with flame-retardant materials, which increases the difficulty of fire rescue. The steel structure of the building is under the action of high temperature. The time for the collapse was delayed, and no more time was given for the rescue. Even if firefighters arrive at the scene, they cannot blindly attack inside. If the temperature cannot be controlled, it will cause more violent combustion and increase the risk of property damage and casualties.
1.2.2 It is easy to cause mass death and mass injury
First, when a fire breaks out, the people in the building are affected by the high-temperature smoke and toxic gases generated by the combustion, resulting in suffocation or poisoning. It is chaotic and difficult to evacuate; third, affected by unfavorable factors such as fire, high-temperature smoke, and easy collapse of buildings, it is difficult for firefighters to quickly carry out internal attacks to rescue people.
1.3 It is difficult to carry out firefighting operations
1.3.1 Difficulty in deep internal attack
When a fire occurs in a large-span steel structure, it will burn rapidly under the action of interior decoration materials after the fire. Thick smoke blocks the rescue line of sight and internal facilities hinder the fire protection instructions. . In addition, the decoration materials will release a large amount of harmful gas and hot smoke under the action of burning, which seriously affects the internal attack of firefighters. People will suffocate in about 3 minutes after inhaling the thick smoke and poisonous gas, which requires firefighters to go deep into the building to evacuate and rescue people, Cutting off and controlling the fire brings great difficulties. In addition, due to the large internal space of the building and the fast heat transmission speed of the steel structure, the support time will be shortened under the action of high temperature, and the risk of large-scale collapse will occur at any time, which will bring certain resistance to the rescue of firefighters and the evacuation of the masses.
1.3.2 It is difficult for internal attack fighters to withdraw quickly
Due to the large building volume, large space, and good convection, the fire spreads quickly, and the buildings above are easily affected by fireworks and barbecues, and collapsed objects are easy to fall, which affects the safety of internal attack fighters. The exact time of the collapse is difficult to predict. Once a dangerous situation arises, it is difficult for internal attack fighters to withdraw quickly in a short time.
2 Basic procedures for fire fighting and rescue operations
When fighting a fire in a steel structure building, saving people is the first principle, and at the same time avoiding the waste of water resources. Master the key points of rescue of steel structure buildings, avoid casualties caused by the sudden collapse of steel structures in a fire, and use rescue tactics skillfully to put out the fire with full effort.
2.1 Fire detection
To extinguish a fire in a steel structure building, fire rescue personnel should first consider the location of the fire and the fire water source, and dispatch a corresponding rescue team to take advantage of the coordination of fire rescue forces and the joint use of technical equipment resources to ensure that the fire is in a controllable state. After arriving at the scene of a fire accident, fire reconnaissance should be quickly carried out to study and judge the situation of the fire scene, accurately grasp the main aspects of the fire scene, establish an effective attack route, and accurately judge the direction of spread, fire source and weather conditions according to the characteristics of the burning site and building area. Calculate the number of people who need to be rescued at the fire scene, and timely deploy rescue personnel to support the fire scene.
2.1.1 External reconnaissance
After the fire rescue force arrives at the scene, the commander should immediately conduct external reconnaissance to understand the development and spread of the fire, and establish the main attack direction as soon as possible.
2.1.2 Ask insiders
While carrying out external observations, the reconnaissance team should promptly ask the insiders at the scene and inside the unit to accurately understand the location, number, location of the fire, whether there is any possibility of spread, whether there are flammable and explosive materials, whether Power failure, building structure, operation and availability of internal fire-fighting facilities, etc., whether the steel structure is deformed under high temperature, by judging the burning area and time and the temperature of the fire site, accurately predict whether there is a risk of collapse of the building, so as to organize internal attacks Rescue people, preventive attack fire control, key protective material transfer, separate fire extinguishing.
2.1.3 Internal reconnaissance
Timely fire detection inside buildings is an effective means to correctly grasp the fire situation and establish the main aspects of the fire scene. Quickly pass through the fire monitoring room for reconnaissance and various detection instruments (thermal imagers, thermometers, etc.), and focus on finding out the direction of fire spread, attack routes, burning materials, whether the building structure is likely to collapse, and trapped people Accurate location and rescue methods, etc., provide a detailed basis for command decision-making.
2.2 Actively evacuate and rescue trapped persons
If a fire breaks out in a crowded place such as a large commercial (supermarket), workshop, terminal building, etc., the personnel of the miniature fire station must actively evacuate the internal personnel while organizing the initial fire fighting; the fire rescue force should quickly carry out the evacuation. Rescue people and minimize casualties.
2.2.1 Evacuation and rescue
When evacuating and rescuing people, we should focus on the rescue principles of exit first, interior first, passage first, room second, fire scene first, periphery first, danger first, general rescue first, and carry out a rescue in a scientific and orderly manner. One is to use the on-site broadcasting system to stabilize the emotions of the trapped people and guide them to evacuate themselves; the other is to guide the evacuation by firefighters, set up a rescue team, carry corresponding protective equipment, and go deep into the interior to evacuate and rescue the trapped people. When attacking and rescuing people from inside, the fire should be cut off, and the fire near the trapped people in the fire scene should be extinguished with jets of water guns, the smoke should be dispersed, and evacuation channels should be opened. If a long-range water cannon or a large-caliber water cannon should be used on the periphery, it should be aimed at the steel structure under high temperatures to delay the collapse time and buy time for rescue. If the number of floors of the steel structure building is high, a high-altitude spray vehicle can be used to carry out high-altitude fire fighting.
2.2.2 Attack and Rescue
The situation of the trapped people: one is waiting for rescuers at the window of the building; the other is the trapped people trapped in the fire scene who cannot escape. Efficient and quick means and methods should be adopted for rescue: first, 9m pull ladders and 15m metal pull ladders can be erected on the lower floors for rescue; Fire-fighting and rescue air cushion rescue; third, under the cover of spray or spray water guns, demolish building components to forcibly open life-saving passages for rescue; fourth, helicopter lifting rescue can also be used if conditions permit.
2.3 Defensive offense
After the fire rescue force arrives at the scene, they must be good at grasping the main aspects of the fire scene while organizing evacuation to save people. The forces on the scene in the first battle are generally relatively weak. To avoid the wrong combat action of a full-scale attack, we must resolutely implement the combat guiding ideology of “saving people first, scientific rescue” and the combat principle of “blocking first and then destroying”, and laying out fire extinguishing water guns (cannons) The position controls the spread of the fire, and the fire is blocked and controlled within a certain range. If this is the case, it can be said that the fire fighting is half successful; if it cannot be controlled, the fire will develop into a passive situation where the fire is raging and burning, and the trapped people cannot be effectively rescued.
2.4 Timely internal fire extinguishing
When the fire is effectively controlled, it is necessary to seize the favorable opportunity to quickly organize an internal attack to rescue people and put out the fire. Effective measures and methods should be adopted in rescuing people and extinguishing fires, which can not only save people and extinguish the fire, but also reduce or avoid casualties.
2.5 Search for victims
For the victims who were not rescued in the fire, when the fire is in the decline stage, it is necessary to organize an internal attack to search and rescue the victims in due course.
2.6 Elimination of residual fire
In the later stage of fire extinguishing, some of the remaining combat forces should be divided into divisions to quickly and completely eliminate the residual fire.
2.7 Site Handover
After the search and rescue and residual fire are completely extinguished, the scene should be handed over to the unit and public security organs, and the scene should be protected to facilitate the investigation of the cause of the fire accident in the later stage.
3 Fire Fighting and Rescue Combat Techniques and Tactics
After the fire rescue force arrives at the fire scene, the commander must make a decisive decision based on the development of the fire scene and the burning time, and should not shoot water blindly because of the smog and open flames. The commander approaches the fire scene after judging that the building is not in danger of collapsing, and implements internal and external attacks to extinguish the fire. The fire truck should occupy a favorable water source position, and the water gun should be used as an internal attack and key defense.
3.1 Combination of fire fighting and evacuation, some sacrifices must be made during the attack
The focus of fire fighting operations is effective evacuation and rescue of people and rapid fire control. Combatants must concentrate their main force to control key parts of the fire scene. Do not disperse or deploy combat forces on all sides. There are both attack surfaces and smoke exhaust and heat dissipation openings. During the attack, they must enter quickly. Water should be used to extinguish the fire inside the fire scene. During the rescue, some items should be discarded, and property and parts that have no protection value should be discarded to ensure that the combat forces in the main attack form a joint force.
3.2 The internal attack is the main and auxiliary external attack, and an effective defensive position is set up
While carrying out internal attack, interception and fire control, demolition and smoke exhaust and heat release, use high-power fire trucks with guns and high-speed spray vehicles to forcibly suppress the fire on the periphery. Note that firefighting forces should use the nearby water source of the building, and should also be connected with the steel structure where the fire started. Buildings keep a certain distance. And arrange a certain protective position to prevent being affected by high-temperature fireworks, causing new fire points, and making rescue and evacuation more difficult. The focus is on the upper or lower floors of the building and adjacent buildings.
3.3 Form an echelon cover formation and establish the awareness of storming close combat
When carrying out internal fire fighting, in order to prevent the high-temperature smoke from invading the combatants, it is necessary to form an echelon cover attack formation to ensure the safety of the combatants themselves and create good combat conditions. At the same time, this kind of firefighting takes a long time. In order to ensure the efficiency of the operation, the firefighting should be carried out in a rotating manner.
3.4 Organize water supply to the fire site and use water sources reasonably
When a fire breaks out in large-span steel structure shopping malls, factory buildings, and warehouse logistics buildings, it is difficult to fight the fire, the duration is long, and the water consumption is large. The key is to ensure the uninterrupted water supply of the water gun (cannon) positions in key parts. It is particularly important to allocate and use water sources reasonably. One is to adopt the formation mode of water supply; the other is to occupy the nearest water source to directly discharge water; the third is to adopt the remote water supply mode for water supply. In the arrangement of the fire water gun position, the periphery should be cooled by spraying water from a long distance. After eliminating the risk of the main body of the steel structure collapsing, focus on extinguishing the fire on doors, windows and other parts, increase the density of the jet, and gradually approach the fire point to carry out fire extinguishing operations.
4 Combat Operation Requirements and Precautions
4.1 Enhance the safety awareness of fire-fighting operations
①Personnel who perform internal skills should strengthen personal protection, and if necessary, they should be supplemented by water guns to prevent burns from high-temperature airflow. ② Accurately grasp the use time of the air respirator to ensure that there is enough remaining air to safely withdraw from the building. ③ Set up safety officers to accurately judge and grasp the time of building deformation and collapse. Firefighters at all levels should carry out evacuation and rescue under the premise of protecting their own safety, so that the commander can take corresponding measures.
4.2 Pay attention to the protection measures of steel components
① When cooling the water gun positions, spraying and flowering should be the main focus. It is possible to avoid the use of vehicle-mounted guns and high-speed spray guns to directly impact the load-bearing components of the steel structure, so as to achieve the purpose of internal cooling and peripheral spraying. The cooling treatment of the main body structure ensures that it is within the non-collapsible temperature. The cooling force should be evenly distributed to avoid sudden cooling, the steel structure will shrink instantly, and the collapse time will be accelerated. ② When demolishing smoke exhaust and heat dissipation, the correct location should be selected, and blind demolition of load-bearing components is prohibited, so as to avoid the weakening of the overall building stability due to wrong demolition.
4.3 Correctly choose smoke and heat release measures
① Make full use of the openings of the building itself for smoke exhaust and heat release and demolish and enlarge the openings if necessary. ②Reasonably select the location of the opening of the demolition according to the wind direction, so as to avoid the wrong location of the demolition, which may cause the fire to spread and expand. ③ During demolition, spray water guns should be installed to carry out cover operations, and fire-fighting gloves and air respirators should be worn to prevent burns by hot smoke flow during demolition.
4.4 Ensuring unimpeded communication on the scene of firefighting and rescue
Steel structure buildings generally shield the signal of the opponent station very seriously, and relying solely on the handheld station cannot carry out normal communication. Therefore, communication technology upgrades should be strengthened to ensure unobstructed rescue. The communication assistant must formulate an on-site communication guarantee plan according to the on-site situation, set up relay stations, communication base stations, and 4G individual equipment as appropriate, and use communication command vehicles or fire telephones to communicate to ensure smooth communication.
Steel structure fire fighting In addition to mastering the combustion characteristics and precautions of building structures, fire prevention awareness should also be strengthened in daily life. Understand the fire-fighting water source, fire-fighting equipment, rescue facilities, fire-fighting exits, fire prevention awareness and escape self-rescue ability of the staff in the building around the building, especially if the steel structure is corroded or not sprayed with fire-proof paint, it should be solved in time.
