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  • fire safety,
  • car park,
  • HVAC

Smoke control in car parks - to assist firefighting access

Designing a smoke control system to assist fire-fighting access (in accordance with clause 10 of BS7346-7) can be a challenge. However, with experience, sufficient knowledge of the physics involved and with the aid of CFD simulations this type of system can be designed and applied successfully. We have an extensive experience in designing and simulating this type of system and successfully completed many projects. The slider below contains a number of example projects. Further down we discuss the corresponding services we offer and how simulations can assist in getting approval.

Smoke control system to assist fire-fighting access

Thrust fans only
  • Car park ventilated by thrust fans and openings in the façade.
  • Reversible system based on wind direction.
  • Very uniform air flow.
  • The system provides 10 m visibility at 1.7 m height up to a point within 10 m of the fire.
Refurbishment with restricted options
  • The car park was refurbished with limited height available for equipment.
  • A short axial thrust fan was designed specifically for this car park.
  • A dedicated CFD was executed of the thrust fan to obtain a detailed flow pattern that could be applied in the simulation of the entire car park.
  • 3D CFD model accounts for a complex beam structure.
  • Access to the fire is created by creating sufficient speed next to the fire.
Full mechanical system
  • Full mechanical system composed of two extract shafts.
  • Three air supply points have been created.
  • The entrance is closed by a shutter.
  • Two smoke screens guide the incoming air flow.
  • Several ventilation zones with different switch for thrust fans and smoke screens are created with.
  • The system creates a very good access to the fire.
  • The temperature in the thrust fans is measured and as soon as the fan exceeds its temperature class it is switched off in the simulation (assumed to fail).
Natural ventilation
  • The car park is ventilated by holes in the ceiling and façade.
  • Air is guided by four smoke screens.
  • Two fire scenarios have been investigated.
  • Wind effects have been taken into account.
  • The CFD model accounts for the surroundings of the car park. This is important to accurately model the effect of wind on the ventilation of the car park.
  • The simulation results demonstrate that the natural ventilation system provides access to the fire for the fire-fighters.

In some situations car parks needs to be provided with a smoke control system to assist fire-fighting access. The amount of air required to make this type of system work is in most cases higher compared to standard smoke clearance systems (designed for 10 air changes per hour). In traditional designs the air flow is generated mechanically by means of exhaust fans and shafts. However, the air flow can also be generated in a hybrid manner by means of only thrust fans and sufficient openings in the façade. Thrust fans locally accelerate the air and a larger amount of air is set in motion through induction. The pressure acting on external vents create an air flow in and out of the car park. With a design consisting exclusively of thrust fans, space that would be required for (large) shafts is saved. However, sufficient external venting area must be present and the influence of wind must be considered.

Besides a sufficient amount of air, this must also be guided towards the fire ensuring sufficient velocity to prevent back layering of smoke along the ceiling. Additionally, there should not be any larger vortices that cause smoke to recirculate back to the air supplied. Designing such a system is complex and should be performed using CFD simulations.

In order to obtain approval from Building Control to install a smoke control system to assist fire-fighting access, the performance must always be verified by means of CFD simulations. The results are described in a report demonstrating that the fire-fighters will have 10 m visibility at 1.7 m height up to a point within 10 m of a fire in all cases. We have extensive experience in designing smoke control system to assist fire-fighting access. We know what is involved in this process, from optimization to technical limitations to associated regulations. We have successfully completed many of such projects in the United Kingdom, Ireland and other countries.