Egress Challenges Related to Assembly Spaces Located at the Top of High Rise Buildings

The best views of the urban landscape are often from the top floors of the area's high rise buildings. This real estate has become sought after for restaurants, multi purpose rooms, large corporate meeting areas and even tourist attractions. Assembly spaces such as these, located on the top floors of high rise buildings combine the hazards of high occupant density with the egress concerns of high rise buildings, creating challenges in egress design as well as facility operators. This blog will review how NFPA 101, Life Safety Code provides guidance on mitigating these challenges effectively. 

What is an assembly space?

When 50 or more individuals can gather in a space for uses such as entertainment, eating, drinking, or deliberation, the area is considered an assembly occupancy. This type of use may involve dense occupant loads, ten times that of a business occupancy and more than ten times as dense as residential occupancies. The occupants of assembly spaces are often first-time visitors who are unfamiliar with the location and availability of egress.

When is a building considered a high rise?

Any building containing an occupied floor which is more than 75ft above the lowest level of fire department vehicle access, would be considered a high rise building. The 75 ft value corresponds with the highest level most common fire department aerial apparatus can reach. Total evacuation of these buildings can take anywhere from tens of minutes to hours depending on their size.

Design considerations

In the United States, new high rise buildings must incorporate fire protection of the structural elements. This is typically accomplished with the use of non-combustible or limited combustible construction (Type I & Type II). The building must also be protected throughout with an approved automatic fire sprinkler system, class I standpipe system and voice communications fire alarm system. All vertical exit enclosures in high rise buildings must be designed as smoke proof enclosures. Additionally, the entire building requires emergency/standby power as well as an emergency command center. 

In the case of an assembly space, located on the top floor of a high rise building, the occupant load of the assembly space will drive the means of egress requirements for the entire building. The table below shows how the number of required exits increases as the occupant load increases. Even a medium size assembly dining room or bar may require three exits, which continue to the level of exit discharge. This can take up valuable real estate in the building all the way to the ground floor as shown in the building section below.

Table 1: Minimum Number of Exist (NFPA 101 7.4)

Figure 1: Minimum number of exits example (NFPA 101 Handbook)

Depending on the type of assembly space, the main entrance/exit may need to be sized to accommodate ½, or even ⅔rds of the occupant load. After considering the number of exits, exit sizing, and the need for exit remoteness (required distance between exits) the inclusion of the assembly space on the upper floors can drastically impact the egress requirements.

Although elevators may not count as a means of egress, consideration may be given to their use in evacuating occupants in immediate danger. The design of the elevator enclosure as well as system functions may depend on if this use is by emergency personnel, staff or building occupants.

Facility operators considerations

Once a building is constructed and occupied, the facility management team is often tasked with ensuring an adequate level of safety is maintained. For assembly spaces in high rise buildings good facility management involves a comprehensive emergency action plan (EAP). At a minimum this includes how emergencies are reported, the response to emergencies by staff and occupants, and the evacuation procedures for all types of emergencies.

Emergencies may be detected automatically, in the case of a fire event, or may be reported to or witnessed by staff, which is often the case in medical emergencies. The EAP will detail the response including if/when first responders are notified and how staff shall direct occupants. Should evacuation be necessary the EAP provides guidance on when zoned evacuation is appropriate, where occupants are directed away from an emergency to lower floors, or if a full building evacuation is necessary. If equipped with elevators designed for evacuation, the EAP will recommend when their use is appropriate. For more complex incidents the emergency command center will be staffed to provide additional resources and command/control. Due to the complex nature of the EAP, regular drills for all types of emergencies are required to ensure proficiency.        

In existing high rise buildings, the addition of assembly space may be possible if the Authority Having Jurisdiction (AHJ) is willing to establish a maximum occupant load based on the capacity of the means of egress. It is often the facility management team's responsibility to ensure the occupant load is kept below that level for any events conducted in the space and that appropriate egress is maintained.

Summary

The combination of densely packed occupants, unfamiliar with their egress, located above the level of fire department aerial apparatus in buildings which may take over an hour to fully evacuate present challenges for both designers and facility managers. The Life Safety Code requires many features which increase the level of safety in these occupancies. When these requirements are combined with good facility operations practices, assembly spaces at the top of high rise buildings can safely provide breathtaking views for occupants to enjoy.