With the rapid development of economic construction, the production and storage rooms of enterprises are becoming larger and larger, and steel structure workshops are more and more adopted by manufacturers due to their advantages of high strength, light weight, large span, convenient lifting construction and short construction time.
The steel structure workshop has the characteristics of good fire resistance. Without fire treatment, it will not burn by itself.
In the context of the absence of clear provisions in the current fire regulations, it is particularly important how to adopt reasonable smoke prevention and exhaust measures to avoid and reduce the casualties of large-space building fires and ensure the safe evacuation of personnel.
1. Characteristics of smoke from the building fire
The occurrence of fire and the development of fire have dual characteristics of randomness and certainty. When the combustibles in the factory warehouse form a high temperature, rising fire plume. When the plume is diffused by the four sides of the box under the ceiling of the room, the surface of the ceiling slowly spreads to the four sides, and when it reaches a certain thickness, it will slowly expand like the middle of the room, and will gradually thicken under the ceiling. Smoke layer. When the fire reaches its full development stage, the temperature of the hot flue gas layer is almost the same as the central temperature.
If there is an opening to the outside in the room (such as doors and windows), when the thickness of the flue gas layer is lower than the height of the upper edge of the opening, the flue gas can flow out of the room. The opening serves to exhaust smoke outward. In the development of building fires, the emission of flue gas is very important. The size of the flue gas emission rate determines the change in the height of the flue gas layer. When the emission rate is greater than the flue gas production rate, the height of the flue gas layer will gradually increase, and eventually remain at a height that does not threaten people.
2. The rationalized performance of steel structure fire
The mechanical properties of steel vary with the temperature. When the temperature increases, the general tendency of steel yield strength, tensile strength, and elastic modulus is reduced, but it does not change much when it is below 150℃.
In the early 1990s, the fire resistance limits of exposed steel beams were verified, and the fire resistance limits of I36b and I40b standard I-beams were confirmed to be 15min and 16min, respectively (the internal temperature of the steel beam reached the critical temperature: average temperature 538℃, maximum temperature 649 ℃). Therefore, if ordinary building steel without fire protection is used as the main body of the building, once a fire occurs, the building will quickly collapse, causing serious losses to people's lives and property safety.
3. Comparison of various smoke exhaust methods
In building smoke prevention and exhaust engineering, three commonly used methods are natural smoke exhaust, mechanical pressurized air supply smoke prevention, and mechanical smoke exhaust.
Natural smoke exhaust and mechanical smoke exhaust are common methods for controlling the decline of smoke. Compared with mechanical smoke exhaust, the natural smoke exhaust has its own advantages. The first is that there is no large power equipment, and the operation and maintenance costs are also small, and it can also be used as ventilation. The second is to set up a smoke exhaust port on the ceiling, and the natural smoke exhaust effect is good.
Especially for large space buildings due to consideration of setting natural smoke exhaust
1) The tall space in the large space building has a strong smoke storage function;
2) Large space buildings usually have large areas of daylighting or ventilation belts on the ceiling or sidewalls, which can be used in combination with natural smoke exhaust;
3) The amount of mechanical smoke exhaust is very large, which brings great difficulty to design and construction;
4) Due to the large and spacious internal space, the mechanical exhaust may cause the mixing of smoke and air. Excessively concentrated mechanical ventilation exhaust will directly discharge a large amount of fresh air just added, forming a so-called "circulation short circuit."
Requirements for natural smoke extraction
At present, there are basically three types of anti-smoke design methods:
(1) Volume ventilation method;
(2) The design method of calculation formula based on the mathematical model;
(3) Analyze and evaluate the design method with the help of computer simulation software, namely the performance-based design method
Qingdao Yili Steel Structure Engineering Co., Ltd.'s main business is architectural steel structure design, budgeting, consulting, production, and steel structure detailing business. For different customer groups, our company can provide various professional services.