When I discuss emergency communications systems (ECS) with other designers and installers, it seems there is always something they don’t know or misunderstand. I recently read about the Dunning-Kruger Effect, which describes what I was experiencing. This effect involves people overestimating their knowledge, skill or expertise. The most misunderstood area of these systems is communications.

NFPA 72, the National Fire Alarm and Signaling Code, covers all ECS in Chapter 24 and states in Section 24.2.3 that an ECS must communicate information about emergencies. The Annex A information for this section explains, “Emergency situations are not limited to fire, human-caused events, and natural hazards, but also include any situation that presents an immediate threat of injury, death, or property loss. Natural hazard emergencies include events that create a risk of injury, death, or property damage, such as flooding, wind, earthquakes, landslides, volcanic eruptions, or avalanches.”

Listen up!

To “communicate information,” the system must be able to reproduce prerecorded, synthesized or live (e.g., microphone, telephone handset or radio) messages with voice intelligibility throughout occupiable spaces.

As stated in the Annex A, “The term intelligible is intended to address only the communications channel and the acoustic environment. Intelligibility assumes that the talker or recorded voice message is in a language and using words known to the listener. It also assumes that the listener has normal hearing.”

NFPA 72 defines intelligibility as “the quality or condition of being intelligible.” It defines intelligible as “capable of being understood; comprehensible; clear.” 

We only use these terms in the code as they relate to voice communication. Obviously, if the message cannot be understood, it’s not helpful. 

Chapter 18 requires voice intelligibility and states in Section 18.4.12 that within “the acoustically distinguishable spaces (ADS) where voice intelligibility is required, voice communications systems shall reproduce prerecorded, synthesized, or live (e.g., microphone, telephone handset, and radio) messages with voice intelligibility.”

NFPA 72 does not require intelligibility in all spaces. Designers and authorities must address the question of where intelligible voice communication is needed when planning a system. 

Acoustically distinguishable spaces

An ADS is defined as an “emergency communications system notification zone, or subdivision thereof, that might be an enclosed or otherwise physically defined space, or that might be distinguished from other spaces because of different acoustical, environmental, or use characteristics, such as reverberation time and ambient sound pressure level.”

Varying effects in an ADS, such as wall configuration, ceiling height, etc., determine how many loudspeakers and what type they should be.

The ADSs must be determined by the system designer during the planning and design stage of all ECS. The designer must also identify whether each ADS requires voice intelligibility. The code is clear that unless specifically required by other governing laws, codes or standards, or by other parts of the code, intelligibility is not required in every ADS.

To ensure audibility, only qualitative measurements are needed. The code is clear in Section 18.4.12.5 that “Quantitative measurements shall not be required.” Although, as stated in the next section, they are permitted.

Now, if you only read Chapter 24, you would miss all the requirements and guidance in Chapter 18.

But to know how many loudspeakers are required in an ECS (either fire alarm or mass notification systems), you must understand acoustics and ADSs. You will need to know the wall, ceiling and floor finishes to determine the number and type of loudspeakers. A floor finish with carpeting absorbs sound, while tiles or cement reflect it.

As with non-ECSs, ambient sound also must be determined to ensure intelligibility. However, if the ambient sound level is 85 dBA or greater, meeting the pass/fail criteria for intelligibility might not be possible, and other means of communication might be necessary. So, for example, the space immediately surrounding a printing press or other high-noise machine might be designated as a separate ADS, and the design might call for some form of effective notification but not necessarily require the ability to have intelligible voice communications.

When it comes to ECSs, be careful. You may not know everything you need to know to have a code-compliant system. Don’t suffer from the Dunning-Kruger Effect.

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