Consulting-Specifying Engineer - August 2007 - (Page 51) (Continued from page 40) independent pressurization control system in order to achieve reasonable control of smoke and allow safe passage to occupants. Architects and contractors who are involved in hoistway design and construction must make the elevator hoistway an airtight structure in compliance with Construction Standards Institute (CSI) elevator shaft construction standards so that during fire a positive pressure is automatically kept at 0.05 in. W.G. The pressurization sensing controls should take into consideration the piston effect due to the car movement inside the elevator. In addition, the building’s HVAC system should not seriously interfere with this positive pressurization system for the elevator hoistway and elevator lobbies. Case history The report, “Building Standards,” by V.R. Bush, P.E., published information on the MGM Grand Hotel fire in Las Vegas in February 1981. This report said that smoke and gases, which raced up the hotel elevator hoistway, were trapped at the top of the hoistway due to failure of an automatic vent damper to open. With the pressure buildup, smoke diverted into the 26th floor and then out into the corridors. The features that contributed to the spread of fire and smoke through the building were: 1. No elevator hoistway pressurization. 2. No elevators lobby areas pressurization. 3. No stairwell pressurization. 4. Inadequate sealing between the elevator hoistway doors and the door framing at the lobbies, which allowed smoke from the hoistway to enter and escape into the hotel corridors and stairwells. Use of elevators during fires Smoke control in elevator hoistway, elevator lobbies and stairways must be controlled by a UL 864 listed alarm system meeting the requirements of NFPA 72. Elevator cartop electrical components should be enclosed in a NEMA 4 enclosure to resist water that may drip on top of the car, during the fire extinguishing. Evacuation of passengers from elevators shall comply with ASME A17.4 “Guide for Emergency Evacuation of Passengers from Elevators,” 1999. Elevator hoistways should be mechanically pressurized with outside air when activated by any manual or automatic alarm-initiating device or fire sprinkler water flow, to maintain a positive pressure of 0.05-in. W.G. An elevator hoistway pressurization system should not have fire or smoke dampers. A pressurization fan must be provided with a smoke detector wired to the fire alarm system. Pressurization ductwork system connecting the pressurization air handling unit to the hoistway penetration shall be enclosed in a 2-hour fire resistive enclosure. Turning off the hoistway pressurization system should only be controlled by trained firemen. Smoke venting of a hoistway to the outdoors is prohibited. The elevator hoistway’s pressurization systems should be independent from other systems. Because this article only deals with elevator issues, no further discussion is extended to cover the elevator lobby and the stairwells pressurization. Elevator systems designs often are determined by the architects who request a layout and specifications from the elevator manufacturer representatives. In this instance, the architect will eliminate the mechanical engineer’s participation in the elevator design, and the important considerations for proper HVAC design of machine rooms and shaftways also will be left out. It is important that the elevator system designer coordinates with the mechanical engineer, as well as with the fire protection and electrical engineers to ensure the integration of all environmental and safety requirements for the elevator system. When all of the design elements are properly considered, the operation of one of the most important public elements of the building will work efficiently and reliably. References: 1. International Building Code, 2006 Edition, Section 9.4, Elevators. 2. “Vertical Exiting,” NFPA Journal, J. Brooks Semple, June 1993. 3. ASME A17.4, “Guide for Emergency Evacuation of Passengers From Elevators,” 1999. 4. Elevator World Research Site, “Lighting up the Shaftway” by Edward Donoghue, Dec. 2005. 5. Smoke Control – High Rise Buildings – City of Denver. Denver Fire Dept., July 2003. 6. “Emergency Preparedness,” Elevator World, Roger Howkins, Dec. 2000. 7. ASME A17.1, “ The Safety Code for Elevators and Escalators,” 2005. Vision Fire & Security has a new identity. Solutions for: Life Safety. Business Continuity. Security. For more information on our name change visit www.xtralis.com Input #227 at csemag.com/quickResponse Consulting-Specifying Engineer • AUGUST, 2007 51 http://www.xtralis.com http://www.xtralis.com http://csemag.com/quickResponse
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