Sector

Ventilation and smoke control in an underground car park

A covered car park has to fulfil two distinct duties: continuous sanitary ventilation, which prevents the build-up of carbon monoxide from petrol vehicles and nitrogen dioxide from diesels, and smoke control in the event of fire. With mechanical ventilation, the air change requirement is usually met with 600 m³/h per parking bay (900 m³/h in the most demanding configurations) on high speed, and half that figure on normal low-speed operation. With natural ventilation, the high- and low-level openings represent a minimum of 6 dm² per vehicle. On the fire side, the installation must stay operational for at least one hour in hot smoke, which calls for fans whose temperature rating is declared to EN 12101-3.

Two duties, one installation

In most projects a single installation covers both duties: the fans are then necessarily smoke extraction rated, because the more demanding requirement dictates the equipment.

Sanitary ventilation and smoke control: different objectives
	Sanitary ventilation	Smoke control
Objective	Remove CO and NO₂ from vehicles	Remove smoke and heat from a fire
Operating regime	Continuous, two-speed	Occasional, released by the fire alarm system
Reference airflow	600 (to 900) m³/h per bay on high speed	Per smoke control sizing calculation
Equipment	Standard fans	EN 12101-3 rated fans, backed-up supply

Airflow rates and operating regimes

High speed (peak periods): of the order of 600 m³/h per parking bay, rising to 900 m³/h in the least favourable cases.
Low speed (normal operation): about half the figure above, which cuts energy use sharply outside traffic periods.
Natural ventilation: high- and low-level openings of at least 6 dm² per vehicle, distributed so the whole volume is swept.
Control: the switch to high speed is interlocked with CO detection, which avoids ventilating continuously at maximum airflow.

Carbon monoxide detection

CO detection is the brain of the installation: sensors distributed through the volume continuously measure the concentration and command the low-speed / high-speed changeover, and raise an alarm above a threshold. It is also a car park's main energy-saving lever, since maximum airflow is called for only when it is genuinely needed. The sensors must be calibrated periodically.

Ducted extraction or jet fans

Ducted network: extraction distributed through terminals, the classic solution, requiring clear height under the slab.
Jet fans: these remove much of the ductwork by pushing air towards the extraction points; they free up clear height, make circulation easier and give a more even sweep of the volume.
Air inlets: the entrance ramp, façade louvres or dedicated ducts — how they are sized determines how effective the extraction is.

Regulatory compliance in Morocco

Covered car parks fall within the scope of the fire and panic safety regulation enacted by Decree no. 2-14-499. The smoke control sizing, the rating of the fans and the interlocks with the fire alarm and control system must be confirmed with the project's approved inspection body and fire safety commission. Our dedicated guide sets out that regulatory framework in detail.

Frequently asked questions

What ventilation airflow does an underground car park need?

With mechanical ventilation, the air change requirement is usually met with an airflow of around 600 m³/h per parking bay on high speed, rising to 900 m³/h in the most demanding configurations, and about half that on normal low-speed operation. With natural ventilation, the high- and low-level openings must represent at least 6 dm² per vehicle.

Why does a covered car park need ventilation?

To prevent the build-up of harmful gases from vehicles: carbon monoxide (CO) from petrol engines and nitrogen dioxide (NO₂) from diesel engines. Sanitary ventilation runs continuously, at an airflow modulated by the concentration measured by the CO sensors. It is distinct from, but often combined with, the smoke control duty in the event of fire.

Which fans are needed for smoke control in a car park?

Fans whose temperature rating is declared to EN 12101-3, able to stay operational for at least one hour in hot smoke, with a backed-up electrical supply and an interlock to the fire alarm and control system. Where one installation covers both sanitary ventilation and smoke control, it is the smoke control requirement that dictates the equipment.

What are jet fans?

They are suspended fans that push air towards the extraction points, replacing all or part of the ductwork. They free up clear height under the slab, simplify the structure and give a more even sweep of the volume, for sanitary ventilation as well as for smoke control.

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