Exiting is one of the most critical requirements of building codes. It comprises three main categories:. exit access, exit, and exit discharge (Figure 11.3).
Arrangement of exits is specified by code. They should be located as far apart from one another as possible so that if one is blocked in an emergency, the other(s) can still be reached. The code states that when two or more exits are required, they must be placed a distance apart equal to and not less than one-half the length of the longest diagonal dimension within the building or area to be served, as measured in a straight line between the exits. This is known as the half-diagonal rule and is shown diagram-matically in Figure 11.4).
The codes limit the length of travel distance from within a single space to an exit-access corridor. This is defined as the maximum distance and cannot exceed 200 feet (61 m) in an unsprinklered building and 250 feet (76.25 m) in a sprinklered building (Figure 11.5). There are exceptions to the rule, such as when the last portion of the travel distance is entirely within a 1-hour-rated exit corridor. Basically, codes classify travel distances into two types: The first relates to the length of travel distance from within a single space to the exit-access corridor (also known as the common path of travel), and the second
regulates the length of travel distance from anywhere in a building to the floor or building's exit. Typically, however, if the travel distance within a tenant space exceeds 75 feet (22.9m), an additional exit is required, even if it is not required by the occupant load.
Codes usually allow a room to have a single exit through an adjoining or intervening room, provided that it affords a direct and unobstructed means of travel to an exit corridor or other exit and as long as the total stipulated maximum travel distances are not exceeded. Exiting is not permitted through kitchens, storerooms, rest rooms, closets, or spaces used for similar purposes. Codes normally categorize foyers, lobbies, and reception rooms constructed as required for corridors with a one-hour-rated wall as intervening rooms, thereby allowing them to be used for exit purposes.
Typically, corridor construction must be of 1-hour fire-resistive construction when serving an occupant load of 10 or more in R-1 and I occupancies and when serving an occupant load of 30 or more in other occupancies. The 1-hour-rated corridors must extend through the ceiling to the rated floor or roof above unless the ceiling of the entire story is 1-hour-rated. Where a duct penetrates a fire-rated corridor, a fire damper that closes automatically upon detection of heat or smoke so as to restrict the passage of flame must be provided.
There are different types of stairs including straight run, curved, winder, spiral, scissor, etc. Exit stairs should be wide enough to allow for two people to descend side by side with no sudden decrease in width along the path of travel. Stairs must also adhere to specific code and accessibility requirements and be constructed in a manner and using materials consistent with the construction type of the building. Typically, new stairs are required to have a minimum width of 44 inches, an 11-inch tread depth, and a maximum riser height of 7 inches (Figure 11.6). Handrails and guardrails are likewise regulated.
Escalators and moving walkways, like elevators, are not usually allowed as a means of egress and should not be taken into account as such in egress calculations, although there may be some exceptions, in which case they must be provided with standby power and must comply with emergency operation and signaling-device requirements.
Requirements for residential exiting (individual dwelling units and single-family houses) are not as strict as for commercial occupancies. Codes typically have a subclassification specifically for dwelling units. The International Residential Code (IRC) is specifically designed for one- and two-family houses. The designer must verify which code is applicable to a particular project.
The IRC requires at least one regulated exterior door per residence with minimum dimensions of 30 inches x 80 inches. Bedrooms located on upper floors typically require an emergency means of egress for these areas—which can usually be an operable window as long as it is not more than 44 inches from the floor. Stair and ramp dimensions are also regulated but are not as strict as those for commercial use. One handrail is normally required in residential stairs and ramps.
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