The code development groups have recognized that large groups of people cannot exit a stadium or arena in the time frames laid out for more standard occupancies, and that the standard exit width factors are not practical for these larger facilities. Both the model building codes and the Life Safety Code address these concerns by incorporating more performance-oriented design options. One such option allows the building design team to take advantage of a design concept referred to as smoke-protected assembly. This approach takes into account that by nature of design, large-assembly occupancies tend to have extensive unenclosed spaces that can create a reservoir for smoke and hot gases to fill, thus extending the available time to exit the facility before conditions in the space become untenable.
In order to fulfill the smoke-protected assembly provisions, the building design must first undergo a life-safety evaluation and then meet specific criteria for automatic sprinkler protection, smoke control and travel distance. Outdoor or retractable-roof facilities do not necessarily fulfill the smoke-protected assembly criteria. They, too, must be evaluated to confirm they meet the requirements.
The benefit of smoke-protected assembly design is that the required exit-width factors may be significantly reduced for large occupant loads. This reduction recognizes the large volumes of these spaces and associated greater available safe egress times than for typical occupancies. In lieu of using the standard 0.2 inches per person and 0.3 inches per person exit width factors for horizontal and vertical exit components, a smoke-protected assembly may use the values in the chart below, which is a recreation of Table 18.104.22.168 in the Life Safety Code.
The Life Safety Code and the International Building Code require that a life-safety evaluation be performed by a person acceptable to the authority having jurisdiction prior to the institution of the smoke-protected assembly concept. According to the Life Safety Code, the fire protection engineer's life-safety evaluation should include at a minimum an assessment of the following conditions and related appropriate safety measures.
1. Nature of the events and the participants and attendees
2. Access and egress movement, including crowd density
3. Medical emergencies
4. Fire hazards
5. Permanent and temporary structural systems
6. Severe weather conditions
8. Civil or other disturbances
9. Hazardous materials incidents within and near the facility
10. Relationships among facility management, event participants, emergency response agencies and others
A complete listing of items that should be included in this evaluation is included in Appendix A of the Life Safety Code. If the evaluation indicates that an acceptable level of risk is present, egress design using the smoke-protected assembly concept may proceed with the AHJ's approval.
Since the nature and types of performances taking place in stadiums and arenas constantly change, the life-safety evaluation should be periodically reviewed to ensure that all aspects of these dynamic occupancies are addressed.
Automatic Sprinkler Protection
Automatic sprinkler protection must be provided throughout the facility to fulfill the smoke-protected assembly criteria. The codes generally recognize that due to the heights of the bowl and seating areas of such facilities, a fire may not actuate the automatic sprinklers. To address this, designers may omit the installation of sprinklers in select areas where the ceiling height over the performance area is greater than 50 feet above the floor. Exceptions are also permitted in performance areas where the ceiling height is 50 feet or less and above the seating in the bowl, provided that an engineering analysis demonstrates that sprinklers would be ineffective.
One of the requirements of the smoke-protected assembly analysis is to evaluate movement of smoke through fire scenarios. The model building codes and Life Safety Code require that the building be designed such that exit paths remain tenable during the required emergency exiting period. (The Life Safety Code requires that the smoke layer be maintained a minimum of six feet above the highest floor of the means of egress, whereas the model building codes require that the smoke layer be maintained a minimum of 10 feet above the highest occupied level.)