Stair pressurisation system
A pressurisation system is intended to prevent smoke leaking through closed doors into stairs by injecting clean air into the stairwell. The intent is to have the highest pressure in the stairwell and a reducing pressure in the accommodation area to facilitate pedestrian escape route and firefighting access. Since the publication of the relevant standard, EN 12101-6, familiarity has increased along with understanding of pressurisation systems. However, there are some aspects of the standard which are not taken into account. Eg selecting the correct class of pressurisation and recognizing the purpose of the system.
The standard describes six differential pressure systems based on their function, ranging from facilitating a safe evacuation in the fire affected area only through to keeping firefighting access smoke free while evacuation takes place.
Class A system: For means of escape: The design conditions are based on the assumption that the building will not be evacuated unless it is directly threatened by fire. The level of compartment means that it is normally safe for the occupants to remain inside the building.
Class B system: For means of escape and firefighting: This pressure system may be used to minimise the possibility of serious smoke contamination during evacuation and while fire fighters are extinguishing the fire.
Class C system: For means of escape via simultaneous evacuation: These systems are designed for all of the occupants of the building to be evacuated when the fire alarm is activated.
Class D system: For means of escape. Risk to personnel that are sleeping: These systems are designed for buildings where the occupants may be sleeping.
Class E system: For means of escape via evacuation in phases: These systems are installed in buildings where evacuation is carried out in stages or phases.
Class F system: Fire protection system and escape means: These pressure systems are used to minimise the possibility of serious smoke contamination of staircases used by fire fighters at the same time that the building is being evacuated.