Simultaneous Occupancy and NFPA 101®
Converging flows of occupants are sometimes overlooked.
NFPA Journal®, May/June 2008
I get asked many of the same questions, but there is one I hear quite often: Does NFPA 101®, Life Safety Code®, require the calculation of simultaneous occupancy? For example, if the floor of an office building has a separate conference room, should I consider that room when calculating the total occupancy of the floor? The answer is yes. Simultaneous occupancy is a condition involving the combined total occupant load of all the spaces found in a building. The Life Safety Code specifically requires that the occupant load of an assembly area in a building be added to the occupant loads of other spaces in the structure. Sections 220.127.116.11 and 18.104.22.168 of the Life Safety Code both read:
"Exits shall be sufficient for simultaneous occupancy of both the assembly occupancy and other parts of the building, except where the authority having jurisdiction determines that the conditions are such that simultaneous occupancy will not occur."
The Life Safety Code states that the available exit capacity must be adequate for the maximum number of people expected to occupy the building. If the authority having jurisdiction (AHJ) does not require exit capacity for simultaneous occupancy, he or she must be sure that the assembly areas will not all be occupied at the same time as other areas of the building. An example is an assembly room in a correctional occupancy, where the same population would be in the assembly room and other areas, but not at the same time. As we know, Mr. Murphy and his laws don’t always comply with the phrase "that will never happen."
The Life Safety Code also stresses simultaneous occupancy in the educational chapters, Sections 22.214.171.124 and 126.96.36.199. These sections address the combination of assembly uses with educational uses and again stress that, where they share means of egress such as corridors, the means of egress must be designed for the combined occupant loads of the educational and assembly spaces.
Another sometimes overlooked issue is the converging flows of occupants in, for example, a building with a basement that has stairs that also serve the upper floors. The concern is that occupants going down the stairs from the second floor will reach the door leading outside to the exit discharge concurrently with the occupants of the basement, who are going up the stairs. Section 188.8.131.52 of the Life Safety Code requires that the door exiting outside at grade level be wide enough to accommodate the combined occupant loads of both the second floor and the basement. Notice the Life Safety Code states the required, not the actual, capacity.
Where corridors or aisles converge to form a single egress path, the required egress capacity of the single egress path must be adequate for the combined required capacity of the converging paths. This is also required when aisle access ways converge with aisles.
Ensuring adequate egress capacity for all the occupants of a building or area is a basic requirement of the Life Safety Code, although egress capacity is generally more of an issue where assembly uses are involved. The Life Safety Code requires that the occupant load of all of the assembly uses be added to any other areas on that floor of a building, unless such spaces will never be used simultaneously.
Chip Carson, P.E., is owner and president of Carson Associates, Inc., in Warrenton, Virginia. He is also a member of NFPA’s Board of Directors.