Design Alternatives to the Enclosed Elevator Lobby: Fire and Smoke Safety Solutions
Another problem that is commonly cited with the lobby fire and smoke barrier solution is the amount of floor space that it requires to execute. Instead of setting aside dead space on every floor for an enclosed elevator lobby, architects could use that space to add one more hotel room or hospital room to the floorplan, or create larger condos generating more revenue for the owner from essentially the same footprint.
Over the years, new products, systems, and design techniques have been developed giving architects more tools to create fire and smoke barriers than the basic construction materials used to build self-contained boxes around the elevator doors. There are now code-compliant alternatives to the enclosed elevator lobby enabling architects to meet fire and life safety code requirements with a much smaller intrusion on the building's floorplate. In response to the dynamic construction environment and new practices and tools available, the codes have evolved to identify instances when an enclosed elevator lobby is no longer necessary and to allow architects to implement fire and smoke containment solutions that are equal to or superior to the enclosed elevator lobby of long ago. IBC 2009 specifically identifies seven exceptions to the enclosed elevator lobby mandated by Section 708.14.1 (IBC 2012 713.14.1) and an allowance for alternative means and modes.
A swing door mounted at an elevator opening and held open with a magnetic hold meets the fire and smoke partition code requirements, but can be susceptible to tenant tampering and have an undesirable aesthetic effect in the space.
Photo courtesy of Smoke Guard, Inc.
Exception 1: Ground Floor of a Building with Automatic Sprinklers
Exception one applies to buildings where the ground floor is equipped throughout with automatic sprinklers. When the ground floor is protected with automatic sprinklers, enclosed elevator lobbies on the ground floor are not necessary to meet fire and life safety codes. Most new buildings will incorporate automatic sprinklers throughout the building and will qualify for this ground floor exception.
Exception 2: No Elevator Shaft
In buildings where the elevator is not enclosed in an elevator shaft, there is no requirement for an enclosed elevator lobby to separate the shaft from the rest of the floor. Elevators entirely within a hotel atrium are a common application of this provision.
Exception 3: The Additional Door Option
Another way to avoid designing an enclosed elevator lobby onto each floor is to specify that a gasketed swing door be mounted directly at the elevator opening and held open with a magnetic hold device. The IBC refers to this door as an "additional door" and as long as it carries an S rating (smoke rating), is equipped with a closer, the device that pulls the door closed when the magnetic hold-open releases, is "openable from the elevator car side without the use of a key, tool, knowledge, or special effort", and is tested in accordance with UL 1784 for air leakage, this swing door solution readily meets the fire and smoke barrier code requirements for the space. In the event of a fire, the magnetic hold-open releases and the swing doors close over the elevator opening. The gasketing along the jamb of the door assembly fills in the space between the swing door and the door frame, creating a seal to block smoke from trespassing onto the floor. A drop seal is mounted to the door undercut to prevent smoke migration at the sill.
While this solution is much more space friendly than creating an enclosed elevator lobby on each floor, there are a few concerns that should be considered before mounting swing doors to the elevators in your designs. Swing doors closed over the elevator door can impede firefighter access to the area and creates a visible barrier between a firefighter riding the elevator and an occupant waiting on the floor. Additionally, swing doors are often wedged open by tenants or inadvertently blocked by furnishings on the floor. If they are unable to properly close, they are useless as a smoke barrier.
Exception 4: Sprinkler Trade-Off
Buildings less than 75 feet in height that have sprinklers installed throughout, do not need to isolate the elevator shaft from the rest of the building. Healthcare facilities (I-2) have other special requirements defined in Section 407 regarding protection from smoke migration. I-3 occupancies (confinement facilities and prisons) and buildings more than 75 feet in height cannot apply this exception.
Exception 5: Sprinklers and Smoke Partitions
Where a building is equipped with an automatic sprinkler system, the fire and smoke partition required at the elevator shaft can be reduced to smoke partition construction, which means that the assembly can be rated for smoke protection only and no longer needs a fire rating. Additionally, the opening protective, or door, in a smoke partition needs only to be rated in accordance with UL 1784. Since the building code requires that all high rise buildings have automatic sprinkler systems, many high rises can take advantage of this exception.
Exception 6: Elevator Shaft Pressurization
The IBC recognizes that elevator shaft pressurization can be used to separate the elevator shaft from the rest of the building in lieu of enclosed elevator lobbies. Elevator shaft pressurization contains smoke migration by using fans to inject large quantities of air into the elevator shaft in order to create a positive pressure environment in which smoke can not enter the hoistway or move freely from floor to floor. Section 707.14.2 describes all requirements that must be met by the elevator shaft pressurization system.
Successfully maintaining a positive pressure environment can be a very effective solution for smoke containment-even keeping smoke confined in the office suite or condo where the fire originated and out of egress pathways. Unfortunately, there are many obstacles to maintaining a positive pressure environment in an elevator shaft. Shaft pressurization systems are complex electrical and mechanical systems. Floor loading designs must consider their impact as well. One challenge is the fact that the elevator doors leak considerable amounts of air from the shaft onto each floor, causing the shaft to lose pressure continually. Designs must consider fans large enough to overcome leakage and emergency generators to power them.
It is important to evaluate the plausibility of a pressurized system on a project by project basis. Enclosed elevator lobbies and swing doors mounted in front of elevator doors can be used for fire and smoke protection in buildings of any height. While pressurization is not limited by building height, engineering considerations indicate that effective elevator shaft pressurization can only occur in low/mid-rise and some high rise buildings. The size of the shaft and the number of cars in the shaft are among the factors that will determine how many floors can be effectively and economically pressurized.