2707 COLBY AVE BASE FILE 2018-01-02 MF Import

Section 1807 (a) Scope. While a high-rise buildings can be defined in accordance with the special features just described, the UBC elects to define a high-rise buildings as one having floors used for human occupancy located more than 75 feet above the lowest level of fire department vehicle access. Most moderately large and larger cities have apparatus which can fight fires up to about 75 feet; thus, the fire can be fought from the exterior. Any fires above this height will require that they be fought internally. Also, in some circles, 75 feet is considered to be about the maximum height for a building which could be completely evacuated within a reasonable period of time. Thus, the fire department capability plus the time for evacuation of the occupants constitute the criteria used by the Uniform Building Code for defining a high-rise building. In Seismic Zones No 2, 3, & 4, an on -site secondary water supply shall be provided, with a supply of water equal to the hydraulically calculated sprinkler design demand plus 100 gallons per minute in addition to the total standpipe system for a duration of 30 minutes. As fires can and do break out as a result of earthquake damage to the various mechanical systems within a building, it is imperative that the reliability of the sprinkler system be such that any fires resulting can be automatically extinguished. Therefore, the code requires that the secondary on -site water supply be automatic so there is no time delay in the operation of the fire sprinkler system should a fire break out. 2. Modifications. Because the high-rise building is sprinklered, the UBC permits certain modifications of the code requirements, which are sometimes referred to as "trade-offs". The trade-offs in this case are considered to be justified on the basis that the sprinkler system, although a mechanical system, is highly reliable due to the provisions of Section 1807(c), which require supervision and also a secondary on -site supply of water. The provisions of this subsection were originally developed when the basic requirement for high-rise buildings was compartmentation and the installation of an automatic fire sprinkler system was considered to be an alternate to the basic requirement. Nonetheless, there are certain modifications of the code requirements permitted because of the installation of the automatic fire sprinkler system as follows: The reduction in the fire -resistive time periods of one hour from those outlined in Table No. 17-A for various components of the building as described in Item 1 are permitted. It will be noted that no reduction in fire -resistive protection for the structural frame is permitted. The code assumes that even with the reliability required by the code for the sprinkler system, a failure cannot be tolerated, and the structural integrity of the building must be maintained. The code prohibits the one -hour reduction in fire -resistive protection for exterior bearing and nonbearing walls whose fire -resistive rating has already been reduced in accordance with the exceptions contained in Section 1803(a) or 1903(a). If the reductions permitted in Subsection (m) were compounded with those permitted by the exception in Sections 1803(a) and 1903(a), it is conceivable that exterior bearing walls would be reduced to one -hour fire -resistive construction. This clearly is not the intent of the high-rise provisions. Although the probability that a significant fire would develop in a sprinklered high-rise building is low, the potential life risk is high due to the hundreds of people located on upper floors. Therefore, the intent is not to permit the fire -resistive rating of bearing walls to be reduced below that permitted by Sections 1803 and 1903. FAI