Fire Alarm 411: A Fire Alarm System Installation, Part 2

This column is the second part of a sample installation that I began in the January 2025 issue. The idea is to take the framework for understanding fire alarm rules and regulations outlined in my first 8 columns and make it practical – using our sample building to illustrate how to determine which codes apply.

To recap, our example building is a 200,000 sq. ft. (18,600 sq m)  mixed-use building in Plano, Texas, with the following floors (with heights):

• 1st floor: a bank, restaurants, and shops - 20 ft (6 m)
• 2nd floor: offices - 13 ft (4 m)
• 3rd floor: offices - 13 ft (4 m)
• 4th floor: residential condos - 13 ft (4 m)
• 5th floor: hotel - 13 ft (4 m)

Group B Occupancies

Plano uses the 2021 editions of the International Building Code (IBC) and the International Fire Code (IFC). Picking up where I left off, we’re ready to assess the “What” code requirements for Group B “Business” occupancy areas.

Group B fire alarm requirements can be found in IFC 907.2.2. This section is similar to the 907.2.1 requirements for Group A “Assembly” occupancies but has an added condition for multiple floors.

For one-story buildings, the threshold to require a manual fire alarm system is 500 people; however, if there is at least one floor above or below a floor where you can exit directly out on the same level, the threshold becomes 100 people on those other floors combined.

Ideally, you can find the engineer’s occupant load calculation on the drawings. If not, use the building code to quickly estimate the occupant load. For B occupancies, IBC 1004.5 requires at least 150 sq ft (14 sq m) per person. As noted last time, factors like egress width can lower this number.

Next, we need to figure out which parts of the building are classified as Group B. The office areas are obvious. Perhaps less obvious is the bank. IBC 304.1 tells us that the business classification applies to any occupancy used for office, professional, or service-type transactions. It then lists several examples that you might not expect to be in Group B – like barber shops, car washes, car dealership showrooms, research and testing laboratories, and martial arts studios.

Let’s say the bank is 4,000 sq ft (1,200 sq m). That could have an occupant load of up to 27 people. Combined, the two floors of offices encompass 80,000 sq ft (7,400 sq m), so we can estimate roughly 534 people for the office floors. That gives us a total Group B occupant load of 561 people.

The threshold for a Group B fire alarm is 500 people on the first floor or 100 people on another floor. We’re well past that limit. Even if everyone was on the first floor, IFC 907.2.2 would require a fire alarm system; therefore, the Group B rules in IFC 907.2.2 mandate a manual fire alarm system in our example building. Just like the Group A rules in IFC 907.2.1, we’re exempted from installing pull stations since the building is sprinkled.

How to Determine Occupant Load

Before proceeding to the next occupancy classification (in the next installment of this column in May), here’s a quick tutorial on occupant load calculations in mixed-use buildings. First, determine the total occupant load. Once you know the total occupant load, you can figure out which sections’ rules apply.

With a few exceptions, most jurisdictions apply the total occupant load to each occupancy classification. That means the most restrictive requirements will always apply.

Put another way, if any occupancy group in IFC 907.2 would require a fire alarm or a voice evacuation system using the total occupant load, then those rules apply. The same goes for sprinklers, etc.

Imagine a warehouse with a substantial amount of office space on the second floor. If the Group B space exceeds 15,000 sq ft (1400 sq m) – 100 people at 150 sq ft (14 sq m) per person – then the Group B requirements for a fire alarm system kick in. That means they would also apply to the Group S warehouse on the first floor, not just the Group B offices upstairs. This is one reason you don’t see a lot of warehouses with upstairs offices.

As another example, imagine a one-story building with a 200-occupant assembly area and a 400-occupant business area. The Group A area is below the 300-person threshold and the Group B area is below the 500-person threshold; however, the combined occupant load of 600 exceeds the thresholds for both groups and thus would require a fire alarm system.

Similarly, if the assembly portion had 800 occupants, that wouldn’t by itself require voice evacuation; however, when combined with the 400 business occupants, the 1,200-occupant total crosses the Group A voice evacuation threshold. The building would require speakers throughout.

Hopefully, this is starting to make sense. In the next edition of this column, I’ll continue the basic occupancy rules with the Groups M, R-1, and R-2 requirements before proceeding to introduce the rules for high-rise buildings.