Accueil » Resources » File: applying IT246
In IT 246 the rules relating to smoke control are detailed in the special provisions applicable to each type of establishment. The purpose of this instruction is to clarify the rules of execution of smoke control by proposing solutions which guarantee: the sheltering of smoke or smoke control of stairways, smoke control of horizontal circulations and smoke control of premises accessible to the public.
Natural draft smoke removal is achieved by using natural smoke vents and air inlets that are positioned to ensure proper sweeping of the area. These elements communicate directly with the outside or through conduits.
Smoke evacuation is provided by either:
The air supply is provided by either :
No opening shall be smaller than 20 centimeters.
In the case where the volume to be de-smoked is semi-buried and the air supply cannot be natural, then exceptionally mechanical air supplies can be used. They can only be associated with roof vents as a type of exhaust and the air velocity at the outlet is limited to 5 m/s.
Smoke extraction by mechanical draught is carried out by mechanical extractors as well as natural or mechanical air supplies distributed so as to ensure a sweep. In addition to the smoke sweeping, it is possible to add an overpressure to the spaces to be protected from smoke.
Smoke extraction and mechanical air supply are provided by vents connected to an extraction fan.
As previously stated, the air velocity at the air inlets should not exceed 5 m/s. They must also have a flow rate of approximately 0.6 times the extraction rate.
Supply air flow = 0.6 x exhaust air flow
Smoke extraction fans must comply with the NF EN 12101-3 standard and be CE marked. The fans must be able to withstand hot fumes of 400°C for 90 minutes. Fan sizing must take into account leakage and pressure drop losses.
For natural smoke ventilation, the following two rules must be respected by the ducts in order to solve the problems related to the generated pressure losses:
Vertical venting may not have more than two offsets with a maximum angle of 20 degrees.
Draglines, which are the horizontal floor connections of the exhaust ducts, shall be a maximum of 2 metres in length unless adequate flow is demonstrated. To justify this flow rate, a calculation must be made assuming that the flue gas temperature is 70°C, that the outside temperature is +15°C and that there is no wind.
Premises ≤ 1,000 sqmUseful surface of the smoke evacuations :
Premises > 1,000 sqm
The natural sweep of a stairwell is achieved by an evacuation device located :
Natural smoke extraction from stairways is a system independent of the facility’s fire safety system.
Stairway smoke removal installations are qualified in the NF S61-932 standard of July 2015. If natural smoke extraction is not possible, the staircase must be pressurized by a mechanical air supply and must be associated with the smoke extraction of the volume in direct contact.
The determination of the smoke clearing sections is defined in the technical instruction 246 (IT246)
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