Calculating Occupant Load for Public Spaces
Businesses and building owners must ensure proper life safety measures are taken to protect customers and employees in the event of an emergency. One aspect involves calculating the occupant load of a public space. According to the National Fire Protection Association, the occupant load is the total number of persons who can occupy a building or a portion of the building at any one time. Emergencies can require the immediate evacuation of a building, particularly in the event of fire. If the facility is occupied by too many at once, the risk of injury or death increases dramatically. The 2018 International Building Code and International Fire Code outline the requirements for calculating and posting occupant load information in businesses and public spaces. Local building inspectors and fire inspectors can help determine the occupant load for business.
The first step in calculating occupant load is to determine the type of occupancy. Building occupancy classifications refer to categorizing structures based on their usage for the purpose of building and fire code enforcement. Occupancy types include assembly, business, educational, mercantile, storage and others. The code establishes a prescribed unit of area per person for each building classification and lists these as an occupant load factor. To calculate the occupant load, first calculate the area of the space by multiplying the length times the width, typically measured within the interior faces of the walls. For example, if a classroom measures 30 feet by 40 feet, the classroom has a total area of 1,200 square feet. Next, divide the total area by the established occupant load factor, which varies depending on the use of the space. This factor represents the amount of square footage per occupant. For a classroom, the code provides an occupant load factor of 20 net. It looks like this:
30’ X 40’ = 1200 sq.ft. divided by 20 = 60 max occupant load
The code provides the occupant load factor as either net or gross, depending on the specific classification. Gross floor area is measured within the inside surface of walls and includes all occupiable and non-occupiable spaces. Bathrooms, closets and mechanical rooms are included and not subtracted from the total floor area. Net floor area is based on actual occupied area. Non-occupiable spaces like hallways, bathrooms and closets are subtracted from the total floor area. Once the occupant load is calculated, it triggers additional life safety code requirements regarding means of egress and egress sizing, number of required emergency exit doors, types of exit doors and doorways, emergency and egress lighting, and exit access travel distances.
Establishing the occupancy classification and occupant load of a business and enforcing the code are essential to public safety. For instance, the Ghost Ship fire in Oakland, CA in 2016 killed 36 people. The fire broke out in a former warehouse that had been illegally converted into an artist collective with living spaces. A change of occupancy classification and occupant load would have triggered additional code requirements including a sprinkler system, fire alarm and additional emergency exits and exit passageways. These required changes would have reduced the risk of fire and saved the lives of all those who perished.
Fire inspectors are particularly concerned with assembly occupancies because the arrangement and density of the occupant load increases the potential for multiple fatalities and injuries in a fire emergency. An assembly occupancy is used for the gathering of more than 50 persons for purposes such as civic, social or religious functions, recreation, food and drink consumption or awaiting transportation. All assembly occupancies must have the occupant load posted on a sign near the exit door. This classification triggers the most stringent codes because life safety is paramount when groups of people gather.
Local fire inspectors are always available to visit businesses to discuss occupancy classifications, occupant load, and other fire and life safety issues. Your safety, and the safety of employees and customers, is always the primary concern.