How Indoor Fire Happens

Smoke detector hanging from ceiling is effective to predict indoor fire. Building fires initially start in a room or part of the interior. Then it spread from there to adjacent rooms or areas, to entire floors, and finally to the entire building. Its development process can be roughly divided into three stages: initial stage, comprehensive development and decline.

occupancy smoke sensor
occupancy smoke sensor
The initial stages of an indoor fire

After an indoor fire occurs, it is initially limited to the combustion of combustibles at the ignition point. After the local combustion is formed, the following three situations may occur. one is that the combustibles that initially catch fire are burned out. The speed is maintained to burn. The third is that there are enough combustibles and good ventilation conditions. Still the fire develops rapidly to the entire room. Smoke detector hanging from ceiling beeps and flashes to remind people.

At this stage, the local temperature at the ignition point is relatively high, the burning area is not large, and the temperature of each point in the room is unbalanced. Due to the influence of the combustion performance, distribution and ventilation, heat dissipation and other conditions of combustibles, the development of combustion is mostly slow. While it is possible to form a fire, or it may self-extinguish midway. Moreover, the combustion development is unstable. The duration of the initial stage of the fire is variable.

The comprehensive development stage of indoor fire

As the combustion time continues, the combustibles in the room continuously release combustible gas under the action of high temperature. When the temperature in the room reaches 400–600 ℃, flashover will occur. Flashover is one of the most significant characteristics of indoor fires, and it marks that indoor fires have entered a comprehensive development stage.

After the flashover occurs, the combustibles in the room are fully burned, the room temperature rises sharply, and the temperature can reach 800–1000 ℃. Under the action of fire and wind pressure, the flame and high-temperature flue gas will pour out from the doors, windows, holes, etc. of the room, and spread rapidly in the horizontal direction along the corridor and ceiling. At the same time, due to the effect of the chimney effect, the fire will pass through the vertical direction. Tube wells, shared spaces, etc. spread to upper floors.

The descending stage of an indoor fire

In the later stage of the full-scale development of the fire, with the reduction of the number of combustibles in the room, the fire burns slowly, the burning intensity weakens, and the temperature gradually drops. When it drops to 80% of its maximum value, the fire enters the extinguishing stage. The room temperature then dropped significantly until the indoor and outdoor temperatures reached equilibrium and the fire was completely extinguished. Photoelectric smoke alarm detector is a good way to prevent indoor fire.