Fire and smoke ventilation in an underground car park

jet fan car park ventilation system - click for larger image CFD is being used increasingly to complement the engineering design of fire and smoke ventilation systems required to meet fire safety regulations. The use of CFD to simulate smoke removal during fires allows design strategies for ventilation to be investigated for different scenarios before construction and installation. In particular the response of key components of the smoke control system, such as powered exhaust ventilation fans, ceiling-mounted jet fans and smoke curtains, can be examined in terms of facilitating fire fighting operations and maintaining clear escape and access routes. 

The CFD code PHOENICS 3.4 has been used by Rucon B.V.Ventilatoran to investigate the performance of a fire-protection system in the event of a car fire in an underground car park. The fire-protection system in the car park comprises a smoke-exhaust ventilation system with a number of strategically-placed jet fans that transport the air-smoke mixture towards the extraction fans. The system is intended to ensure the safe escape of the occupants from the various car-park levels by maintaining any smoke layer above the heads of the people.

smoke concentration contours at a height of 1.7m - click for larger image The PHOENICS model simulated two levels of the car park and included such details as ceiling-mounted ventilators, extract fans, columns, dividing and external walls, ramps and other internal structures. The task was to predict fire and smoke movement in the underground car park for a number of ventilation designs. PHOENICS was used to simulate a car fire on the lower level by means of a time-dependent source of heat and smoke; thermal radiation was modelled by means of the computationally efficient and pragmatic IMMERSOL model. The final design for fire containment employed jet fans on the upper level to force air down towards an extract fan located on the lower level.

The PHOENICS INFORM facility was employed to specify via the pre-processor a smoke-dependent gas emissivity. In addition INFORM was used by Rucon to introduce their own formulae for computing the volumetric smoke concentration and estimates of the local visibility. The advantage of INFORM is that it obviates the need for user FORTRAN and recompilation, and it also enables easy and flexible interpretation of the solution fields in an engineering framework.

velocity vectors at a height of 1.7m - click for larger image The PHOENICS analysis allowed optimisation and verification of Rucon's ventilation strategy. Rucon commented "We have used CFD to prove that in the case of a car fire on the lower level, smoke does not progress to the upper level by use of the right ventilation system and strategy. The reason and the big advantage we have by using PHOENICS, is the fact that we can predict the movement of air and smoke in a car park before something is installed. We can make the airflow visible and understandable."