Stairwell Pressurisation Systems
Keeping stairwell escape and rescue routes free from smoke is an essential requirement for maintaining viable evacuation and firefighting options, even over longer periods of time.
There are different systems and strategies to meet the safety objective of keeping escape and rescue stairwell routes free from smoke. Different safety objectives may be defined to prevent smoke logging. Depending on the type and use of the building, it may be acceptable for some smoke in areas, others will have to be completely free from smoke.
Where it is not essential to keep a space entirely free from smoke, a purging system with pressure control may be used. This allows stairwells to remain mostly free from smoke. A pressure control unit is installed in combination with a roof light dome at the top of a stairwell. When a smoke detector detects a fire in the building, the dome will open and the fan is activated. The pressure control unit creates a minimum closed-door pressure of 15 Pa. The maximum door opening force must not exceed 100 N. Smoke entering the stairwell is diluted and purged. This method is only possible when the doors to the stairwell are not opened frequently.
Where space should be totally cleared, a pressurisation system is used to extract the smoke. This approach ensures that 2 m3/s flow through the open door and that the stairwell is kept free from smoke. A door-opening force for this system type must also not exceed 100 N.
In the event of a fire, the likelihood of smoke entering a Pressurised Stairwell is minimised if the stairwell is sufficiently airtight. The specified flow rate needed to ensure a correct level of pressurisation is achieved within the stairwell at design stage could require verification once constructed, as calculated flow rates may not fully account for the quality of construction. Air Tightness Solutions advises on and undertakes testing regimes in accordance with the design classifications detailed in BS EN 12101-6 to ensure that pressurised stairwells perform their primary role effectively.