Applicability of natural smoke extraction.
Natural smoke exhaust is the use of the buoyancy of the heat flow generated by the fire and the external wind force to exhaust the smoke to the outside through the external opening of the building to the smoke exhaust method, which is essentially the convection movement of hot smoke and outdoor cold air, and its power is the hot pressure generated by the fire heating indoor air and the outdoor wind pressure.
There are two ways to exhaust smoke naturally
1) Shaft smoke exhaust. The principle is to rely on the heat pressure generated during indoor fire and the wind pressure of outdoor air to form a "chimney effect" smoke exhaust. No energy is required, the equipment is simple;However, the shaft needs a smoke exhaust port and an air inlet, and the two ports need a larger cross-sectional area, otherwise the smoke exhaust effect is not good, and the construction area is more occupiedThe smoke exhaust effect is uneven;Applicability is limited.
2) Use the balcony, alcove or exterior window on the exterior wall of the building to provide easy to open for unorganized smoke exhaust. This smoke exhaust method does not require special equipment, has wide applicability, and can be combined with the original structure of the buildingThe disadvantage is that the smoke exhaust effect is not very stable due to the influence of outdoor wind direction, wind speed and the tightness or hot pressure of the building itself. As the smoke is discharged, the indoor pressure decreases, and when it is lower than the outdoor air pressure, the outdoor air flows into the room. This creates a convective movement between indoor smoke and outdoor air, known as thermobaric action.
Applicability of mechanical smoke extraction.
The mechanical smoke exhaust method is a way to use mechanical equipment to force air supply (or smoke exhaust) to remove the flue gas. Air supply and smoke exhaust can all be with the help of mechanical force, can also be one with the help of mechanical force, and the other with the help of natural ventilation or smoke exhaust, according to which, mechanical smoke exhaust is specifically divided into three ways.
1) Comprehensive ventilation and smoke exhaust mode: mechanical smoke exhaust for the fire room, and mechanical air supply for the corridor, staircase (elevator) front room and stairwell, control the air supply volume is slightly less than the smoke exhaust volume, and keep the fire room under negative pressure to prevent smoke from leaking out of the fire room
2) Mechanical air supply positive pressure smoke prevention mode: use a blower to send fresh air to the smoke-proof front room and stairwell, so that the pressure of these parts is relatively higher than that of the fire room, and the smoke of the fire room is discharged in a natural smoke exhaust mode through a special smoke exhaust port or external window;The use of mobile smoke extractors for positive pressure air supply is more frequent in the fire scene. The use of centrifugal fan to exhaust smoke, axial fan to supply air, in the fire room with the main engine (centrifugal fan) smoke exhaust, and at the same time to the corridor and stairwell front room with auxiliary machine (axial fan) to supply air, will speed up the smoke exhaust effect:
3) Mechanical negative pressure smoke exhaust method: use a smoke exhaust fan to exhaust the smoke in the fire room to the outside through the smoke exhaust port. It is required that the area of openable external windows on each floor shall not be less than 2% of the construction area of each floor, or a mechanical smoke exhaust system shall be set up in combination with an air conditioning system with air ducts. That is, if the farthest point in the premises is more than 30 meters from the nearest external window, a mechanical smoke extraction system must be installed.