Vertical Openings

Because the vertical spread of a fire through a building is the biggest problem, compartmentation requirements around vertical openings tend to be especially strict in order to prevent the convection of fire and combustion products through the building. Open vertical

Figure 42-3 Atrium fire protection.

shafts of any kind, including stairs, elevators, ductwork, and electrical wiring and piping chases, must be enclosed with fire-rated walls with self-closing fire-rated doors at each floor.

The only exception to the enclosure requirement for vertical shafts is a vertical atrium (Fig. 42-3). An atrium is defined in many codes as a roofed, occupied space that includes a floor opening or a series of floor openings connecting two or more stories. Atriums are often found in shopping arcades, hotels, and office buildings. Balconies around the atrium may be open to it, but surrounding rooms must be isolated from balconies and from the atrium by fire-rated walls. An exception is made for any three floors selected by the building's designer, so that lobby spaces on several floors can be continuous with the atrium.

Codes require a 1.8-meter (6 ft) deep curtain board (smoke barrier) at the opening to the atrium at each floor. Smoke detectors and motorized dampers in ducts are required. A building with an atrium must have sprinklers throughout. Sprinklers located 1.8 meters on center at the lobby level, the atrium floor level, and where office floors open to an atrium, create a water curtain. The frames for glazing at the perimeter of the atrium should be designed for thermal expansion so that they don't break their glass when they get hot, with sprinklers on the office side of the glazing. Fire-rated frames are listed for both heat resistance and water pressure from the hose stream. The atrium must be provided with fans with dampers that open and turn on automatically in case of fire to bring fresh air into the space at ground level and exhaust smoke at the ceiling level.

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