Marriott Marquis New York designed by John Portman. Image via Wikimedia Commons
A fundamental tenet of building codes at the time and today, including what’s in the Life Safety Code, is to compartmentalize buildings to prevent the effects of fire from spreading beyond the floor of origin, allowing occupants remote from the fire adequate time to evacuate. Atrium design scuttles that notion by opening up the building interior, allowing multiple floors to communicate amongst each other. This radical departure from conventional building design necessitated cooperation between the designers, code officials, and fire protection engineers to develop alternative means of compliance. As noted by Kathleen Almand, NFPA's vice president of Research, Data, and Analytics, in a recent blog she wrote to NFPA staff, “These alternative means included fire sprinklers, smoke management systems, and other features which are now common in fire safety design and code requirements in high-rise structures … (Portman’s) determination opened the door for a more scientific approach toward the development of fire safety design and building codes, which has been applied to other innovations in building design.”
The proliferation of atrium buildings in the 1970s and 1980s meant codes like the Life Safety Code needed to adapt so as to not hinder innovation, but still maintain the required level of safety for occupants. Requirements for atriums first appeared in the 1981 edition of the code as an exception to the requirement for the enclosure of floor openings. At the time, the requirements included:
- a minimum opening dimension of not less than 20 feet and an area of not less than 1000 square feet
- automatic sprinklers throughout the building
- an engineered smoke control system acceptable to the authority having jurisdiction (AHJ), with factors such as means of egress and smoke control of adjacent spaces considered
- separation from the remainder of the building by one-hour fire barriers or glass walls with closely spaced sprinklers, with an allowance for up to three stories open to the atrium
The 1981 edition included in Annex A prescriptive criteria for smoke removal systems, which were permitted in lieu of engineered smoke control systems. These criteria did not, however, take into consideration the anticipated fire size based on the actual fuel load, the time to egress based on the anticipated occupant load, or the physical building configuration. Fire and egress modeling was in its infancy in 1981, and the computing power needed to perform complex calculations was available only to a select few. It was a start, and it was based on the best information available at the time.
Times have changed. Today most of us carry around more computing power in our pockets than was carried into space on the first space shuttle. Fire protection engineers today have access to powerful computational fluid dynamics fire models that can predict fire and smoke spread in buildings based on the actual building configuration and fuel load. Egress models also continue to evolve and can be used to predict where building occupants will be when the effects of fire might potentially impact a specific area.
Because no two atrium building designs are the same, the 1988 edition of the Life Safety Code deleted the prescriptive smoke removal system criteria in favor of an engineered approach specific to the building design. In the 1997 edition, the minimum size requirements were removed, and an allowance for an unlimited number of stories to be open to the atrium was added based on a required engineering analysis. The engineering analysis was required to demonstrate that the building was designed to keep the smoke layer interface above the highest unprotected opening to adjoining spaces, or six feet (1.85 meters) above the highest floor level of exit access open to the atrium for a time period equal to 1.5 times the calculated egress time or 20 minutes, whichever was greater.
The Life Safety Code requirements for atriums haven’t changed much since the 1997 edition. Over the last 20 years, however, the tools to perform the required engineering analysis have matured, and the fire protection engineers who utilize them have gained invaluable experience. John Portman’s legacy will live on in every new atrium building. More importantly, perhaps, his legacy will also live on in the partnership between building designers, AHJs, and standards development organizations as codes like NFPA 101 continue to undergo revisions to promote, and not hinder, advancements in innovative building design.
Thanks for reading, and as always, stay safe.
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