NFPA 1: Occupant load vs egress capacity, why these numbers are so important to our safety, #FireCodeFridays

Yesterday, NFPA's Nicole Comeau wrote a fantastic post about assembly occupancies, the dangers of crowds and the importance of enforcing fire and life safety codes at these venues. Thanks, Nicole!

Let's talk about the Code requirements behind this concept of occupant load. NFPA 1, Fire Code, is a valuable resource for fire marshals and AHJs when determining occupant load and the egress capacity of a space.  The direction provided by the fire Code helps prevent overcrowding and potential insufficient egress capacity. So, how exactly does a building determine its "occupant load" and why is it so important that these requirements are adhered to?

It is a basic concept of the Code that the means of egress system be sized to accommodate all people occupying a building. Sizing is accomplished by matching the occupant load of a floor with the calculated egress capacity of the egress components serving the floor.

Capacity = The number of people the egress system can accommodate safely during an emergency.

Occupant Load = The total number of persons that might occupy a building or portion thereof at any one time.

Per NFPA 1: The total capacity of the means of egress for any story, balcony, tier, or other occupied space shall be sufficient for the occupant load thereof. [101:]



Egress Capacity ≥ Occupant Load


The number of people or occupant load for which the means of egress system must provide egress capacity is calculated per the requirements set forth in NFPA 1 or otherwise determined. The occupant load is to reflect the maximum number of people anticipated to occupy the building rooms or spaces at any given time and under all probable situations. The occupant load is the maximum of either the calculated value OR the maximum probably number of people expected in the space. 

Egress capacity is calculated based upon the available width of egress components (doors, stairs, corridors, walkways, etc.)  Further requirements in Chapter 14 of NFPA 1 provide the details for calculating egress capacity of the space.

When the occupant load of a building or area exceeds what is was designed for, the egress capacity cannot accommodate the occupants safely and efficiently.  Queuing, bottle-necking, slow egress are all a results of improperly designed egress systems.

When all is said and done, it is critical that overcrowding be prevented and prohibited and that the fundamental concept of egress be upheld:

Egress Capacity ≥ Occupant Load

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Kristin Bigda
Technical Lead and Principal Fire Protection Engineer with a focus on building and life safety related content.

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