In any high-rise fire, it is vitally important to understand everything there is to know about the area from which most operations will be originating – the core. This series of articles examines characteristics, features and oddities of core configurations and their performance during fires...
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Smoke towers. There are two basic types of smoke towers, commonly found in older high-rise buildings. One is where you walk from the floor through a door into a vestibule, then through another door into the exit stair (see Graphic D). In the vestibule there is an opening (or two) in the wall that may be covered with louvers/smoke dampers. The opening(s) can vary in size and the louvers may either be open all the time or may only open during a fire by an actuating device or manual operation. Open shafts with no louvers exist as well. The opening(s) lead directly into an adjacent smoke shaft (or two) that is designed to pull the smoke into it and away from fleeing tenants before they enter the stairwell itself. There may or may not be fans present to assist in ventilating the smoke. In theory, the smoke stays out of the exit stair while people evacuate from upper floors.
Graphic D. Interior smoke tower. Larger Image (PDF)
The other smoke tower (commonly referred to as the “Philadelphia Smoke-Proof Tower”) is the same thing except the vestibule is exposed directly to the outside, so no smoke shaft is required (see photo on page 76). As with the interior smoke towers, the opening may or may not be louvered. The objective is identical – keeping the smoke out of the stairwell.
Smoke towers have been proven to be very effective in preventing stair contamination in most instances involving tenant evacuation in fires. One major drawback is the fact that they may be used by the fire department as the attack stair, especially if it is closest to the fire; then the design becomes a significant impediment. If the standpipe (or hose cabinet) is located in the stairwell, both doors in the vestibule will have to be propped open, compromising the integrity of the exit stairs.
If the standpipe connection is located in the vestibule (in a hose cabinet or exposed standpipe), the design intent is to allow a fire attack to take place without opening the second door and compromising the exit stair. Unfortunately, aside from the impossible task of flaking out a 100- or 150-foot attack line in a vestibule the size of a closet, it is too dangerous to attack the fire from a connection that may be only a few feet away from the fire itself. The crew will be attempting to advance an attack line out of a chimney. The smoke shaft will be trying to pull the smoke into it, but that will also act as a vacuum in pulling the fire towards the vestibule (and stairwell). If the fire involves any appreciable area and amount of combustibles, this will be a fight that will likely not be won - especially if windows have failed and there is a fresh air supply feeding in from the opposite direction. The crew will take a terrible beating and no headway will be made. The attack will have to be abandoned and re-initiated from the other stairwell (which usually would not be a smoke tower). This will take considerable time and effort.
A type of exterior smoke tower commonly referred to as the “Philadelphia Smoke-Proof Tower.” The vestibule is exposed directly to the outside, so no smoke shaft is required.
One exception to this case would be where both exit stairs are smoke towers (see Graphic D), which can create a situation where a successful fire attack cannot be mounted from either (or both) stairs in serious fires. An exterior attack may be the only option if it is reachable from ladder streams. Otherwise, the stairs may have to be closed on the fire floor while the floor above is protected from the safety of the core (if possible, as with open floors/small floor plates) and allow the fire floor to consume all available combustibles, hoping that auto-exposure, curtain wall voids, privacy stairs, etc. are not allowing the fire to spread vertically. From a design perspective, smoke towers are intended as evacuation stairwells, NOT attack stairwells.
Remember that if there is a hose cabinet located in the vestibule, the doors will swing open the wrong way – facing toward the floor. If the fire is correctly attacked by connecting on the floor below, the cabinet door opens in the direction of the stairwell, thus impeding stretching a hand line into and up the stairwell to the fire floor. The door most likely will have to be “removed” with an axe or halligan tool. Also, note that with “Philadelphia Smoke Towers” being open to the outside, wind conditions will dictate their effectiveness! A strong wind can push the smoke back inside the building, negating their design and even worse, causing a wind-tunnel effect on the fire floor as air is being forced onto the fire floor from the exterior with the stair doors open.
Curtis S.D. Massey will present “The Art of 21st Century High-Rise Fire Department Operations,” with case studies involving “Rapid Ascent Teams” and recent major high-rise fires, at Firehouse World 2005 in San Diego, Jan. 31-Feb.4.