Compartmentation And Fire Barriers

An entire building or a large space can be divided into two or more separate spaces, each totally enclosed within a fire barrier envelope of floor/ceiling assemblies and walls. This compartmentation prevents the spread of fire, smoke, and heat beyond a restricted area of the building. Compartmentation protects the building's occupants and property by confining the fire, heat, smoke, and toxic gases to the area of their origin until the fire is extinguished or until it burns itself out completely. It stops the spread of fire by hot combustion gases. In row houses, fire-resistant walls separate dwellings. Compart-mentation is required between different types of functions within a building. Compartmentation is also used to provide areas of refuge for occupants and firefighters.

Building codes set maximum floor areas for various constructions and occupancies. Using sprinklers usually increases the limits on floor areas. Larger areas must be subdivided with fire-rated walls and doors. In one-story factories and warehouses where firewalls are not practical, incombustible curtain boards are hung from the roof to catch and contain rising hot gases. Self-opening roof vents in each compartment allow hot gases to escape before they can spread the fire. Doors of the roof vent are held closed against springs by a fusible link of a metal with a low melting point, which melts and releases the doors when heat builds up.

Fire barriers are fire-rated structural elements. They include wall, ceiling, or floor systems that prevent the

Fire Barrier Wall And Floor

spread of flame and heat through the use of fire-rated structural materials with fire-resistant (FR) ratings. Building codes limit the number of penetrations in a fire rated wall. Fire barriers can be divided into three types. Firewalls (Fig. 42-2) have the highest fire ratings and are usually part of the building shell. Fire separation walls are used to create fire-rated compartments within a building. The fire ratings of the third category, floor/ceiling assemblies, depend on the walls they surround.

Firewalls, also called party walls, are used for occu- X^f pancy separations. Firewalls provide continuous protection from the foundation of the building to the roof and to each exterior wall. They are built so that if one side of the wall falls, the other side would remain standing. Firewalls typically have three- to five-hour ratings. Firewalls are often used to subdivide a building into two separate types of construction. They are also used to separate one occupancy from another in a mixed-use building. Interior designers generally aren't involved in designing firewalls, but our work may involve possible penetrations. All openings in a firewall are limited to a certain percent of the wall's length, and must be protected by self-closing fire doors, fire-rated window assemblies, and fire and smoke dampers in air ducts.

Fire separation walls, which include tenant separation walls (demising walls), corridor walls, vertical shafts, and room separations, are more likely than firewalls to be added or changed during an interiors project. Tenant separation walls create fire-rated compart ments within a building that separate two tenants or dwelling units. They typically require one-hour ratings, depending on the occupancy and whether sprinklers are used. Interior designers often work with fire separation walls.

Corridor walls must have ratings of from one to two hours, depending upon how corridors are used, the occupancy, and whether sprinklers are used. Corridor walls that are used as exits must usually have a two-hour fire rating, and corridors used as exit accesses generally require one-hour ratings. We look at all the components of exits in more detail shortly. Typically, codes require that corridor walls be continuous from floor slab to floor slab, and that they penetrate suspended ceilings. Some corridor walls may also act as demising walls, and then the stricter requirements apply.

The walls that create vertical shaft enclosures for stairwells, elevators, and dumbwaiters are usually continuous from the bottom of the building to the underside of the roof deck. Stairs used as part of an exit have requirements for fire ratings, can have only limited penetrations, and may require that the enclosure be smoke-proof. Stair enclosures are required to have a one-hour fire rating for up to three stories, and two-hour ratings for four or more stories. Where stairs connect only two floors within a single occupancy, the space may be considered to be an atrium, and the enclosure restrictions may be less restrictive.

Most rooms within a space do not require fire rated walls. Where the contents of the room may be hazardous, however, codes may specify that they be separated from the rest of the building by a fire-rated wall. Construction costs are reduced if spaces with similar requirements, such as boiler rooms, furnace rooms, and large storage rooms, are located adjacent to one another.

Fire-rated floors and ceilings are rated as either floor/ceiling or roof/ceiling assemblies. The assembly consists of everything from the bottom of the ceiling material to the top of the floor or roof above. This includes all the ducts, piping, and wires between the finished ceiling and the finished floor above it. If you are adding a ceiling to a space, you need to determine the ratings of the surrounding walls and use the same rating at the ceiling.

Fire can spread quickly in concealed spaces over suspended ceilings, behind walls, within pipe chases, in attics, and under raised floors. Specify noncombustible materials in these and similar spaces. Automatic fire detection and suppression systems and oxygen deprivation systems can be used in concealed spaces. Fire stops and firewalls may be required to break up continuous concealed spaces.

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