In 2017 , a famous occupational site counted 6 types of high-risk occupations: firefighters, policemen, doctors, reporters, salespersons, and taxi drivers.

Firefighters are well-deserved high-risk occupations. Firefighters who died in the Tianjin bombings in 2015 are equivalent to those in the past decade. In the fire scene, the causes of firefighters’ casualties include falling, electric shocks, explosions, collapses, siege by fire, and poisoning.

Therefore, firefighters must improve their professional skills, enhance personal protection awareness and avoid casualties.

Causes of building collapse in fire

It is common for buildings to collapse in fires in steel structures because of changes in the nature of the steel as it manifests itself in the fire. At ambient temperature, temperature of the steel will increase as the room temperature increases, when the steel temperature was raised to 600 ~ C, the strength will fall 2/3, resulting in reduced carrying capacity. The plasticity of steel is obviously enhanced with the increase of its own temperature, and it shows that the steel is more easily deformed. The temperature of steel components that have not been fireproofed exceeds 600°C within 15 minutes . Decreased strength and increased plasticity are important reasons for the collapse of steel structures.

From the above characteristics, the instability of steel structures in fires is a major threat to firefighters' personal safety. In 2010 , in a fire squadron handling a steel structure factory building, the steel structure of the building was not fire-proofed. Due to prolonged exposure to high temperatures, deformation of the building steel columns occurred outwards, and the external wall that was closely attached to the steel column was supported. The force collapsed outward, as shown in Figure 2 . Three firefighters who set up water gun positions at the gates of the factory's outer walls were smashed by wall fragments because they could not retreat in time. In which a firefighter because of his injuries sacrifice.

Avoid casualties

A sufficiently high fire field temperature and burning time in a fire will inevitably cause partial or overall collapse of a steel structure.

(1) Fire fighters should fully understand the building structure and set up fire safety personnel.

In the “six-familiar” work of daily operational readiness, they should accurately understand the construction situation. Including the structure of the building, the position of the load-bearing components, the purpose of construction, the storage of materials inside the building, whether the building components are fire-protected, whether the fire-proof coating is effective, and whether the built-in fire-extinguishing system inside the building is intact and effective. By mastering this information, we can roughly judge the time when the building structure collapsed and the form of the collapsed structure. In addition, during the process of firefighting and rescue, investigative teams and firefighters should be set up to keep track of the development of the fire. Including the building burning time, the range of fire, the temperature of the fire, the color change of the steel components in the fire, and the threat of the steel components of the building under fire.

This information helps to determine the stability of steel structures and helps to weigh the fire fighting methods of fire fighters on the fire and on the outside. Therefore, we should grasp the daily “six familiars” and the opportunity of fire scene investigation to fully understand the building structure.

(2) When setting up water guns and water guns in fire fighting, maintain a safe distance from the building.

In steel constructions with long burning time, if there are no personnel trapped inside and there is no need to evacuate precious materials, the fire extinguishing will be mainly external attack. The fourteenth article of the "Safety Principles for Public Security Fire Fighting Training" clearly stipulates that when fighting fires in large-span steel structures and warehouses, priority should be given to the use of long-range, large-flow jets such as water guns, moving guns, and remote control guns. The implement implements cooling, blocking, and extinguishing. Minimize the number of firefighters around the building . In the event that the water supply to the fire site is limited to the transport of water, the amount of water in the fire can hardly meet the needs of high-powered water guns and guns, and water can only be extinguished in the form of water guns. In this case, the firefighters on the water gun position will be threatened by the collapse of the building.

The location of the water gun positions is also an important factor affecting the safety of firefighters. When the water gun positions were set too close to the external wall and caused the building to collapse, the three firefighters in the water gun position had no time to evacuate and were trapped by the wall beams. It can be seen that the outer wall of a steel structure is not a safe support for water gun positions in a fire. Therefore, the location of water guns and artillery arrays must pay attention to a certain safety distance and ensure that firefighters can withdraw smoothly from the first time.

(3) The building can be demolished properly.

For a steel structure building, the cost of building construction is not high. If the fire is in a state of complete combustion, no one is trapped inside. After the scene, a large excavation equipment can be used to partially remove the external wall of the building. On the one hand, an increase in the size of the exhaust outlet makes it easier for firefighters to see the location of the fire in the building. On the other hand, it eliminates the uncertainty of the collapse of buildings in fires and the security threats to firefighters, so as to remove obstacles for firefighting attacks. For the fire burning under the fire collapse, firefighters can use close combat methods to extinguish the fire.

(4) Cooling protection of load-bearing components during fire extinguishing.

The fire-resistant coating of steel structures can delay the temperature rise of steel components in fires and cannot completely isolate the high temperature. Therefore, in order to ensure the firefighters' own safety, in order to ensure the safety of the firefighters in the steel structure building fire field that requires internal attack, the load-bearing components inside the building must be cooled to extend the time of deformation of the steel structure. If the fire building is in the form of a single-story steel structure, it is necessary to cool the beams and pillars that are greatly affected by heat radiation, the color steel plate wall of the building, and the steel girder, steel truss, and color steel plate roof above the combustion; for multi-layer and high-rise steel Structural buildings should be cooled by shooting water on the fire floor and the upper floor to cool the floor beams and other components.

This article is edited and compiled by China Rescue Equipment Network. Please indicate the link.