Understanding the Core

Curtis S.D. Massey examines characteristics, features and oddities of core configurations and their performance during fires, including stack effect.


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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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, including stack effect. It is written based on office buildings with two primary exit stairwells – the most common configuration in properties with small to medium-sized floor plates.

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Be extremely careful when lifting a load with a power spreader. The arc of the arms as they open can push the load instead of lift it. Lift a little, then crib, reposition the spreader and lift some more. A little at a time is preferred to maintain stability.

Types of core designs. There are numerous types of cores – center, side, end, dual and multiple (see Graphic A). Virtually any configuration you can imagine exists, although the majority of modern office buildings utilize a center core design. Note that two of the drawbacks to center core design evolve from the fact that if there is an open hallway encircling the core, there will be a “wraparound effect” that will have to be addressed. Not unlike fighting fire in an attic with a mansard roof, you can push the fire one way and have it wrap around you in the opposite direction. Attacking a core area fire from one stairwell can allow the attack team to possibly push the fire all the way around the core back to their point of entry, as with a dog chasing its tail. Attacking the fire from both stairs can cause the crews to push the fire toward each other with opposing hoselines (the crew possessing the bigger line wins the battle!). Obviously, this can prove very dangerous.

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Graphic B. The 3 most basic types of core stairwells. (PDF)

What is contained within the core? The core contains the primary building services that allow the building to function, including methods of moving people. You can find risers, chases, shafts and rooms for water (fresh and waste), electricity, ventilation, natural gas, liquid fuel and communications. You may also find trash chutes, mail chutes, mail conveyors and dumbwaiters (the last two are sometimes found near, but not in, the core). Restrooms, storage areas, load-bearing structural components, elevators and exit stairwells comprise the remainder of the core area.

In some tall buildings, the core can take up to 30% of the total floor area at the base of the building, due to vertical transportation demands. Examples include:

  • Aon Center (Chicago) – 82 stories/30%
  • Empire State Building (New York City) – 102 stories/30%
  • John Hancock Center (Chicago) 100 stories/25%

Types of stairwell configurations. You can find three primary types of stairs in modern office buildings within the core: U-return, scissor and straight-run (see Graphic B). U-return stairs stay in their given area as they ascend, reversing their direction at the mid-point between floors, but always discharging at the same point on each floor (for example, the north stairwell stays on the north side of the core). Scissor stairs discharge at opposite sides of the core on alternate floors (for example, the stairwell that originates on the north side of floor 1 will discharge next on the south side of floor 2). Straight-run stairs go directly from one side of the core to the opposite side of the floor above and terminate there.

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Graphic C. Proper stairwell labeling. Larger Image (PDF)

Beware of improperly labeled stairs! I have seen scissor stairs labeled north/south and east/west on the interior of the shaft. The shaft has to be labeled in a non-directional fashion (such as A-B or 1-2), since every other floor the stair is discharging on the opposite side of the core – facing the other direction. Stairs should always be properly labeled for firefighters (yet rarely are), giving the floor number, shaft designation, whether there is fire department roof access and ideally what street and direction you are facing (see Graphic C). This is vitally important to interior operations and the command post. The next re-entry floor, or exit floor, also should be noted, primarily for the tenants. Preferably, the signage should be on the wall adjacent to the stairwell door opposite the hinge side, not on the back of the door, which moves.

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