Fire fighting operations - high rise buildings:

Inlets that allow the fire service to supplement to water to the sprinklers and to the fire mains are useful additions to the measures that assist fire fighting.

When fire fighting operations are being undertaken, doors to the fire fighting staircase are bound to be held open (by hose) so either ventilation or pressurisation must be provided to stop the stairs becoming smoke logged. Elements of a pressurisation system are automatic opening vents on each floor.                                         

These open to keep the area where the fire has started close to ambient pressure so that a pressure difference can be maintained to the staircase (the staircase being at a slightly higher pressure).  The vents also allow a continued through-flow of air when doors are open for fire fighting.  If the vents do not open or are obstructed because new internal partitions have been constructed, for example, then the space where the fire is will become pressurised, losing the pressure difference between it and the staircase and the through-flow of air when the door is open will not take place allowing smoke to enter the stairs.  Vents are normally required on at least  two faces of  the building  to  allow for  positive  wind pressures on one face of the building.