For many years, fire departments have had to contend with multi-floor tenants who possess internal staircases that allow for quick and efficient travel of employees between floors rather than wasting precious time waiting for an elevator cab to come by. This increases worker productivity...
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For many years, fire departments have had to contend with multi-floor tenants who possess internal staircases that allow for quick and efficient travel of employees between floors rather than wasting precious time waiting for an elevator cab to come by. This increases worker productivity. Firefighters, however, know that these stairs (commonly referred to as "privacy," "convenience," "tenant" or "access" stairs) are as convenient for the fire as they are for the tenants.
Fire, heat and smoke can travel vertically through this floor penetration very quickly and easily. Even in sprinklered buildings, there can be multiple floors of water, heat and smoke damage. They can be straight-run, U-return or spiral stair configurations (see the photos above). They can be open or enclosed, although most are open for efficiency and aesthetics. Some have fire dampers or even fire curtains that drop down if the floor's alarm is activated or a detection device at that location trips, but these are the exception rather than the rule.
With modern, state-of-the-art high-rises, the building's fire alarm computer takes over during a fire and activates certain fire protection and safety features. It can recall elevators to the lobby or recall level, activate stairwell and possibly elevator shaft pressurization fans, release stairwell door locks, activate the alarm notification system for both the tenants (strobes, horns, etc.) and the central monitoring agency, and send a signal to the heating, ventilating, and air conditioning (HVAC) system, which then performs certain functions. The HVAC system will either shut down the fans to the fire floor, while possibly pressurizing floors above and below, or it may go into "smoke purge" while pressurizing the floors above and below the floor of alarm (no return/full supply — utilizing fresh outside air as "make-up air" on the supply side).
Two very important things can occur during alarm sequence that must be considered, both of which can affect firefighter safety. For instance, if the fire originates near the bottom of an open internal access/tenant staircase that serves three floors (e.g., floors 28 to 30), the smoke can drift up and initially trip the detector on the floor at the top of the staircase (floor 30), two floors above the fire (see Graphic 1). The first-due engine is riding around on building inspections and is only a block away when the call comes in. The members arrive in less than one minute, rush into the building and check the alarm panel. It reads floor 30 as the alarm floor. They hop in the elevator to head upstairs two floors below the "fire floor" as per standard operating procedures (SOPs) and they arrive at the actual fire floor on 28, with the fire nearby. In a non-sprinklered building, this could prove to be quite dangerous if the crew cannot quickly get the cab doors shut and move back down to a lower floor to regroup. Of course, by now, other detectors would have tripped on the true fire floor, but they may not be aware of it without direct communication with security or engineering personnel in the lobby (which is doubtful).
Fooling the Computer
Another thing that can happen is that the smoke can drift up and set the first detector off on the floor above the fire (see Graphic 2) and get the HVAC system activating the smoke purge on the wrong floor — having been fooled by the stairwell. The computer thinks that the fire is on 29, when in fact it is on 28. The system then begins pressurizing the floors above and below the alarm floor (28 and 30). Unbeknownst to the fire crews, the supply fans are forcing large volumes of fresh air onto the fire floor, feeding the fire plenty of oxygen. Not good.