The main functions for the natural removal of smoke and heat are as follows:
- Ventilate areas with a risk of fire by exhausting gases through the roof envelope
- Prevent or delay the spread of fire
- Protect the building outfit and equipment
- Reduce thermal effects on the building construction during fire
- Lower losses caused by fire
Spontaneous ventilation equipment is intended for building into the roof envelope; it serves for the creation of a smoke-free layer above the floor during a fire. Under normal operating conditions, it may also serve for lighting the buildings with the possibility of day ventilation. It meets all the regulations and requirements for improving conditions for the safe escape and rescue of people, animals and property protection; it makes possible to eliminate fire in a stage of fire development.
They are tested for reliability, strength and fire resistance by a state testing body; they obtained a certificate for use during fire safety ventilation.
The calculated aerodynamic area of smoke exhaustion, which is the main valve parameter, can be increased by using a spoiler for all types of spontaneous exhaustion equipment.
Description of a building fire without spontaneous ventilation equipment
From the point of view of fire, smoke starts to evolve toward the room ceiling as in a stove with a disconnected chimney. With the increasing intensity of the fire, the volume of suffocating smoke starts to increase from the ceiling; the level of a smoke-free layer starts lowering. The hot smoke (up to 9000C) transfers heat to the roof construction; the steel elements of the building and fittings become soft at a temperature of 4500C and lose their strength. Different temperatures cause tensions in concrete. There is a risk that the building will collapse. Oxygen, which supports burning, exhausts gradually and insufficient combustion occurs that produces more smoke and flammable gases. These gases are heated to a high temperature and accumulate under the ceiling. When the window glass breaks or fresh air enters the building in another way, the “over flash” effect occurs. Gases ignite suddenly and a horizontal flame several meters long flashes through the broken windows. It is more difficult to localize such a fire and the fire brigade units are deployed rather from the outside.
Description of a building fire without spontaneous ventilation equipment
Smoke begins to evolve from the place of the fire. Sensors detect the fire and the spontaneous ventilation equipment opens. Fresh air flows through the ventilation openings and the fire burns. People being evacuated can see the escape route. The bearing constructions are cooled by flowing air and smoke rises through the flaps outside.
The deployed fire squad units can localize the fire more easily and extinguish the centre of the fire.
The function of the flaps deteriorates during inversion and in strong winds.
