In our daily life, there is a door that should be kept closed. Do you know which one is?
That is the normally closed fire door. But many people often leave it open for convenience. Once a fire breaks out, it may cause greater casualties.
Normal closed fire door is a kind of fire door, which refers to the door that can meet the requirements of fire resistance stability, integrity and heat insulation within a certain period of time. It is located in fire compartments, evacuation stairwells, and vertical shafts. Such as fire partitions with certain fire resistance.
In addition to the function of ordinary doors, fire doors also have the function of preventing the spread of fire and smoke, which can prevent the spread of fire within a certain period of time and ensure the evacuation of people.
Fire experts pointed out that the vertical flow velocity of smoke is 3 to 5 meters per second, which is 8 to 10 times the horizontal flow velocity and 5 times the fire spreading velocity. Take a 33-storey building as an example. Smoke can spread from the bottom to the top in about 30 seconds through the evacuation stairs without being blocked.
In order to verify the role of normally closed fire doors in a fire, someone once conducted an escape tunnel smoke experiment in an abandoned four-story family hotel.
The experiment simulates that the electric heater in the living room of the suite on the second floor is close to combustible materials to cause a fire. The experimenters set up three fire doors between the two bedrooms on the second floor and the living room, the living room and the evacuation passage. Suppose someone was trapped in one of the bedrooms when the fire broke out.
The normally closed fire door is closed. The fire is getting bigger and bigger after 4 minutes of the fire. At this time, the personnel trapped in the bedroom discovered the fire and prepared to escape.
Because the normally closed fire door is closed, smoke and flames did not spread to the escape route. The fire door played a very good role in preventing and preventing smoke, and the trapped people were successfully evacuated.
The normally closed fire door is in the open state. Less than 10 seconds after the fire door is opened, the corridor on the second floor is filled with toxic smoke and it spreads upwards rapidly. After 20 seconds, the smoke filled the evacuation passages of the entire building. If the trapped people choose to escape at this time, they will not be able to escape safely.
The experimenter tested the toxic gas content in the flue gas on-site with instruments and found that at a height of about 1.5 meters, the value of carbon monoxide was 200ppm, and the value of sulfur dioxide was 0.8ppm; and at a height of about 0.5 meters, the value of carbon monoxide was 42ppm, the sulfur dioxide value is 0.4ppm.
Firefighters pointed out that if you escape at this time, you should cover your mouth and nose with a wet towel, and bend down to evacuate.
If it is left open for a long time, the normally-closed fire door cannot return normally at light level, and may damage the door frame and door panel, making it lose the function of preventing smoke and fire. If the fire door fails, once a fire breaks out, it is easy for a 'small fire' to cause a 'catastrophe'.
According to the requirements of the national building design fire protection code, normally closed fire doors should be kept closed at ordinary times. When people open and pass, the door closer on the door will automatically close the fire door. Such a fire door can effectively block the attack of dense smoke and fire after a fire occurs. Keep the normally closed fire door in an open state. Once a fire occurs, the fire door will not be able to prevent the spread of the fire and prevent the spread of smoke.
What is the difference between a normally closed fire door and a normally open fire door?
The normally closed fire door is normally closed and needs to be pushed open when there are people walking around. The open state of normally closed fire doors has certain shortcomings. Because the place where the fire door is installed is usually the passage where people often walk, it causes certain contradictions. Especially in large shopping malls, there is a large flow of people. If a normally closed fire door is installed in the evacuation stairwell, the fire door will soon be damaged and fall off due to frequent opening and closing, which will not play the role of fire prevention and cause fire hazards.
Normally open fire doors are usually open, and will automatically close in case of fire. Because it is kept open at ordinary times, it is convenient for people to pass through, and it is convenient for ventilation and lighting. It can be closed by itself in case of fire, which plays a role of preventing smoke and fire, thus completely solving the inconvenience and fire door that the fire door is usually closed and the inconvenience caused to the passage of people Man-made damage caused by frequent switching, while ensuring fire safety. Therefore, in the evacuation stairwells of some large shopping malls, normally open fire doors should be installed, which are usually open. When a fire occurs, various sensors are used to control the door closers to close the doors.
Under what circumstances should a normally open or normally closed fire door be used?
Normal open fire doors should be used for fire doors installed in buildings where people often pass through. In other words, fire doors in public parts of the building (traffic core) including smoke-proof staircases, front rooms of fire elevators, and shared front rooms should be normally open fire doors, and fire doors in the evacuation aisles of the hall should also be normally open. fire-proof door.
Except for the positions where normally open fire doors are allowed, fire doors in other positions shall be normally closed fire doors. In other words, in the design, except for the normally open fire doors indicated in the drawings, all other fire doors should be normally closed fire doors. This requires that when the designer chooses a fire door, if the code requires a normally open fire door, it must be indicated in the door and window table, and the inspector can conduct an inspection based on this.