To maintain the smoke layer height above the exiting occupants, a mechanical smoke-control system is typically required for indoor facilities. (Note: Based on the analysis of smoke production in the fire scenarios, retractable-roof facilities may be required to use smoke-control systems. Additionally, because retractable roofs are generally not operated in all weather conditions, retractable-roof facilities must often be reviewed for smoke-control purposes as fixed-roof structures.) The design intent of the smoke-control system is to exhaust the volume of smoke produced so as to maintain the smoke layer at the minimum specified height above the occupants for at least the time required to completely evacuate the building.
Designers may choose between two methods of designing the smoke-control system. The more common method is to design the smoke-control system exhaust rate to match the smoke-production rate of the fire at the prescribed height. In theory, this method would allow the system to maintain the smoke layer at the design height indefinitely. An alternative method is to calculate the egress time for the entire facility and design the smoke-control system to maintain the design height for a period of time not less than the calculated egress time. To address the possibility of exits being obstructed and other unknown factors, a factor of safety of at least two should be used for these types of calculations.
Fire Alarm System
The codes require that large-assembly occupancies be provided with a fire detection and alarm system. If a mechanical smoke-control system is provided for the facility, it must be actuated by the fire alarm system upon sprinkler system initiation, activation of smoke or heat detectors or other approved means.
Evacuating tens of thousands of occupants in an alarm condition presents a hazard in itself. Recognizing this, the Life Safety Code permits a positive alarm-sequence response in accordance with NFPA 72 ? National Fire Alarm Code requirements. This type of system transmits an alarm signal to a constantly attended location?typically the security control room in the stadium or arena. Upon receipt of the alarm, security staff has 15 seconds to acknowledge it, which then initiates a 180-second alarm investigation period. This gives the security personnel an opportunity to evaluate the alarm. If the alarm is not acknowledged within the initial 15-seconds or the system is not reset within the 180-second investigation period, a general alarm to the occupants is initiated.
An approved voice alarm system and visual alarms must notify occupants of the hazard. Normally, the alarm system uses an approved public address system to provide audible notification to the bowl area and on the concourses. The use of the P.A. system allows the security staff to provide specific evacuation information, such as which exits may be obstructed as a result of the emergency situation. Visual alarms are typically interfaced with the facility scoreboards.
While the items noted above detail many of the general requirements relating to stadium and arena egress design, they are not all-inclusive. Each of the model codes includes provisions to permit the development of alternative methods as long as they achieve an equivalent level of safety. If alternate materials or methods are to be used, the security-design professional and the fire-protection and life-safety consultant must coordinate early in the design process.
Corey C. Weldon is a fire-protection engineering consultant for Rolf Jensen & Associates Inc. (www.rjagroup.com). W. Phillip Guy, P.E. is a licensed fire-protection engineer for Mustang Engineering (www.mustangeng.com).