Understanding fire alarm strobe requirements for optimal safety 

One would think that something as simple as fire alarm visible notification appliances would be easy to install correctly. However, that is not always the case.

Visible notification has been used for fire alarms since the 1980s. At first, the purpose was to locate them near exits to assist occupants in getting out of the building in case of a fire. However, that changed when the Americans with Disabilities Act (ADA) went into effect in 1990. Now the primary purpose for visible signals is to provide equal signaling for those who are deaf or hard of hearing.

At first, there was confusion about where strobes can be installed. The ADA didn’t allow strobes on the ceiling, since smoke could obscure a strobe light from view. They had to be 80 inches above the floor or 6 inches below the ceiling, whichever was lower. That is logical in a sleeping area, but not everywhere. The ADA also required a minimum of 75 candela in a 50-foot-by-50-foot area. So obviously, there were some conflicts with NFPA 72’s strobe light requirements. Since the ADA was amended in 2009, it now says to install them per NFPA 72.

Signal installation: NFPA 72 strobe requirements for location

The visible signaling requirements in Chapter 18 of NFPA 72 are reasonably easy to follow, but can be a little confusing. Remember that the building and fire codes dictate whether or not strobes are required. NFPA 72 tells us how to properly install required strobe lights. It allows strobes to be installed on either the ceiling up to a height of 30 feet, or the wall between 80 and 96 inches.

Personally, I prefer strobes on the ceiling because they are harder to obstruct. Think about an office with cubicles—strobe lights on the wall at 80–96 inches would be hard to see. Light would not always reflect into each cubicle. However, if they were placed on the ceiling, the light distribution would be much better.

Next, the fire alarm system designer must indicate the candela rating based on the area to be covered and the installed location. It is now a requirement to indicate the candela ratings on the fire alarm shop drawings.

However, many designers leave the selection of strobe lights up to the installation company. This is where I have seen a number of mistakes. Each strobe has a maximum coverage area based on the candela rating. I’m sure you have seen wall-mount strobes installed on the ceiling, and vice versa. Because the light pattern is different, it doesn’t meet code.

Fire alarm strobe: Common pitfalls and installation challenges

One difficulty is that you must be able to directly see each strobe light; however, direct viewing is only for corridor installations. Indirect viewing (reflected light from surfaces) is used everywhere else. NFPA 72 now allows using direct or indirect viewing in corridors. Using the indirect viewing method can possibly reduce the number of strobes that must be installed. For example, in a 40-foot-long corridor, using the direct viewing method would require a minimum of a 15-candela strobe within 15 feet of each corridor end, but with the indirect viewing method, one 60-candela strobe could be installed at the corridor’s midpoint. Both methods are acceptable.

Another problem area lies in placing strobes within a room. It is always a good idea to try to find out what the room will be used for before deciding how many are needed. You may be able to install just one, but based on what will be in the room, it may be necessary to install more than that.

Where you install the strobe light is also important. Say you have a 20-foot-by-20-foot room. According to Chapter 18, you could cover the entire room with one 15-candela strobe if it is installed at the halfway point of one of the walls. If you move it 5 feet over, the coverage area changes. 

Paragraph 18.5.5.5.4 states that if the strobe is not centered, you must measure the distance to the farthest wall or double the distance to the farthest adjacent wall, whichever is greater. In this example, if the strobe is moved 5 feet to one side, it would be 15 feet from the farthest adjacent wall. Double that, and you need a strobe to cover a 30-foot-by-30-foot room and a minimum of a 34-candela strobe to meet NFPA 72 requirements.

There are a number of other points that should be discussed, so I’ll cover those in March’s column.

Header image source: Jalen Hueser

Read part 2 >>