Consulting-Specifying Engineer - June 2008 - (Page 25)

The Las Vegas Retrofit Ordinance of 1981, which covers both smoke control and sprinklers, was enacted in response to these fires. Eleven of the 19 major features of the Retrofit Ordinance limit the production and spread of smoke in large buildings built after 1980. Because smoke control is difficult to retrofit into existing buildings, it only is required for hotels and casinos. Sprinkler systems were retrofitted within four years in the 38,000 hotel rooms existing at the time of these two fires. Codes and standards There are more than 137,000 hotel rooms in Las Vegas. More than 10,000 hotel rooms will be added to the standing inventory in 2008, and many large hotel/casinos are under construction or in the design stage. The 2007 permit valuation for Clark County, which includes Las Vegas and the Las Vegas strip, was a record $8 billion, and a number of current projects have multi-billion dollar budgets (see “Billion dollar babies,” page 26). Smoke control systems typically are required along the Las Vegas Strip for highrise hotel, condominium, or time-share towers taller than 55 ft; malls; atriums; arenas; underground buildings; and enclosed parking garages (see Figure 2). Smoke control systems also are required for low-rise buildings attached to high-rise buildings, unless there is a 3-hour fire- and smoke-rated separation between the buildings. Off-Strip buildings that require smoke control include office towers, hospitals, medical centers, institutional centers, and correctional facilities. Las Vegas smoke control systems must pass the rigorous design evaluation and testing procedures of the Building Division of the Clark County Dept. of Development Services. One challenge is posed by the shear number of requirements and specifications. There are 39 sections in the 2006 International Building Code (IBC) and an additional five sections in the 2006 Uniform Mechanical Code that impact smoke control systems. Many provisions are derived from NFPA Standard 92A, “Smoke Control Systems Utilizing Barriers and Pressure Differences.” The Clark County process The Clark County Dept. of Development Services usually becomes aware of the design Figure 1: Smoke control equipment included on the smoke control diagram typically includes a smoke exhaust fan (left) and a duct detector (right). Source all figures: Jim Arnold features of a hotel/casino at a pre-submittal meeting, which is required for all major projects. The actual project design may have been under development for many months by the date of the pre-submittal meeting. The smoke control design features are listed in a document called the Fire Protection Report, and may be further clarified in mechanical, architectural, and fire alarm drawings. The smoke control system often uses a combination of methods described in Section 909 of the IBC, including the passive method, Smoke control methods In modern Las Vegas high-rise hotels, condominiums, and time-shares, a “pressure sandwich” is used to contain and exhaust smoke from floors where there is a fire. A pressure sandwich is achieved with a combination of tightly sealed floor and wall construction and by exhausting the fire floor. A pressure differential of 0.05-in. water gauge between the fire floor and adjacent floors or smoke zones is sufficient to ensure no smoke leakage occurs from the fire area. The fire floor is under negative pressure from being exhausted, and the adjacent smoke-control zones are positively pressurized. Additional smoke control concepts that are codified in the International Building Code and used in modern high-rise Las Vegas hotels include the following provisions: • Positive pressurization of stairwells and elevator machine rooms to prevent smoke intrusion into these areas • Exhaust of smoke from the fire area to maintain a smoke-free layer for some distance above the floor (usually 10 ft) to allow personnel a safe exit path and also allow emergency responders a safe access path • Confinement of smoke to a single smoke zone using smoke-tight barrier construction and closure of openings in smoke barriers • Shutdown of normal ventilation equipment to deny oxygen to a fire and restrict smoke dispersion • Exhaust of hotel corridors (initiated by corridor smoke detectors) to prevent smoke introduction into neighboring guestrooms • The use of vestibules to maintain stair pressurization and corridor exhaust in highrise hotels while minimizing door opening forces • Shutdown of re-circulating fans if smoke is detected in their associated ducts to prevent the spread of smoke beyond the zone of origin • Early activation of smoke control to prevent flashover or backdraft conditions • Separation of exhaust outlets and fan inlets to prevent the re-introduction back into the building of exhausted smoke. Consulting-Specifying Engineer • JUNE 2008 25

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Consulting-Specifying Engineer - June 2008 Contents Viewpoint Letters News M/E Roundtable No Gambling Allowed on Smoke Control in Las Vegas Be Prepared: Hospital Protections for Catastrophic Events Ready for Retail Commissioning Documents: Necessary Evil Codes & Standards Codes & Standards Case Study Equipment Lifecycles New Products Advertiser Index Green Space

Consulting-Specifying Engineer - June 2008

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