Fire regulations, do you know how it affects your ventilation system?

Do you know the requirements established by the CTE DB SI, Safety in case of fire related to stairs? Next, we explain how the regulations affect both protected stairs and specially protected stairs (the regulations do not affect unprotected stairs) and the important role played by ventilation.

Applicable regulations for protected stairs

We talk about a protected stair when its uninterrupted route (from the start of the stair to its outlet) constitutes a safe area in case of fire, so that its occupants can remain in it for a certain time. Regarding safety in case of fire (for usage safety, the basic document of the CTE DB SU should be consulted), the CTE establishes that the area of the stair must be protected from smoke by following one of the two following solutions:

• Through natural ventilation via operable windows or openings that open to the outside. The usable ventilation area must be at least 1 m² per floor.

• Through ventilation by the arrangement of two autonomous ducts for the intake and exhaust of air of 50 cm²/m3 of room per floor (air intake and exhaust). If the ducts have a rectangular section, the relationship between the sides must not exceed 4. The grilles must have equal surface area and the same relationship between their sides as the duct. The air intake grilles must be no more than 1 m from the ground. The exhaust grilles will be located facing the aforementioned and their bottom must, at least, be 1.80 m from the ground.

Applicable regulations for specially protected stairs

We talk about a specially protected stair when it meets the conditions of a protected stair and also has an independent vestibule at each of its accesses. If the stair opens to the outside, the independent vestibules can be omitted.

Applicable regulations for independent vestibules

We talk about an independent vestibule when it is an area exclusively used for circulation, which offers a greater guarantee of compartmentalization against fires and communicates only with areas to be separated, with floor toilets and with elevators. Just like the stairs (protected and unprotected), they must provide protection against smoke.

Pressure differences

The standard EN 12101-6:2005 establishes all the information and requirements for the design of systems intended to limit the propagation of smoke through pressure differentials. If positive pressure is maintained in the protected spaces, we talk about pressurization. If the hot gases of the affected area are eliminated to a pressure lower than that of the adjacent protected area, we talk about depressurization.

The aim is to determine a pressure gradient that ensures maximum pressure in the protected evacuation areas and progressively decreases the pressure level in areas away from the evacuation routes. The airflow velocity through the open door between a pressurized area and the occupied area must not be less than 0.75 m/s.

It should be noted that the supply of outdoor air pushed into the interior of the building must be arranged so that said air cannot be contaminated by smoke from the fire. To blow outdoor air into a pressurized space, mechanical fans will be used, properly located and of construction characteristics that ensure correct protection against fire.