NFPA members and AHJs can use the Technical Questions tab to post queries on NFPA 72.

Author(s): Wayne Moore. Published on May 1, 2015.

WHEN WE DESIGN audible signaling appliances for a new system, we rarely question what type of appliance we plan to use. For example, if we design an in-building fire emergency voice/alarm communications system (EVACS), then we will choose speakers as the audible appliance. If we design a non-voice system, we might choose horns for the audible alarm appliance.

However, every so often an issue arises when we design audible appliances for a new fire alarm system that leads us to question if we made the right choice. Such a question recently appeared on the NFPA LinkedIn Forum, accompanied by a number of interesting responses.

Essentially, the question asked if NFPA 72®, National Fire Alarm and Signaling Code, allows the use of two different audible appliances in the same building. For a fire alarm system upgrade, the designer wanted to use horns or horn/strobes in half the building, while leaving bells or bell/strobes in the other half. We’ll assume the building serves a single occupancy.

At first look, we might conclude that such a design does not make sense. A number of operational issues come to mind. First, how do the signals interconnect to operate efficiently as one system? Second, how much training will the owner provide to ensure all occupants know that the sounding of both bells and horns indicates a fire alarm in the building? And how will the system synchronize the differing signals?

Chapter 18 first requires the synchronization of the standard evacuation signal within a notification zone. As the Annex for the chapter states, in A. “The Code does not require that all audible notification appliances within a building be of the same type. However, a mixture of different types of audible notification appliances within a space is not the desired method. [My emphasis added.] Audible notification appliances that convey a similar audible signal are preferred. For example, a space that uses mechanical horns and bells might not be desirable. A space that is provided with mechanical horns and electronic horns with similar audible signal output is preferred.

“However, the cost of replacing all existing appliances to match new appliances can impose substantial economic impact where other methods can be used to avoid occupant confusion of signals and signal content. Examples of other methods used to avoid confusion include, but are not limited to, training of occupants, signage, consistent use of temporal code signal pattern, and fire drills….”

It is apparent the Technical Committee thought about the issue and has provided reasonable guidance. But a concern still exists as to whether visitors to the building would understand which sound constitutes an alarm signal.

NFPA 101®, Life Safety Code®, states in Section that “audible alarm notification appliances shall produce signals that are distinctive from audible signals used for other purposes in a given building.” The commentary in part states that “…the manner of sounding alarms should be standardized to obtain uniformity throughout as large a geographic area as practicable, so that people moving from one location to another will not be misled or confused by differences in the manner of sounding alarms.” Two hotel fires in the late 1970s support this concern; survivors reported that they thought the noise made by the alarm system was either a telephone or alarm clocks ringing.

It would appear that we must answer the Forum question with a “Yes, but…,” but in my opinion the “but” outweighs the “yes.” Designers and installers need to understand that notifying the occupants to take action without hesitation remains the ultimate goal of a fire alarm system, and adding anything into the mix to cause confusion is very unwise.

WAYNE D. MOORE, P.E., FSFPE, is vice president at JENSEN HUGHES.