Can You Hear It Now?

By Wayne D. Moore | Dec 15, 2012




You’re reading an older article from ELECTRICAL CONTRACTOR. Some information, such as code-related information, may be outdated. Find the most up-to-date content in our latest issues.

We all know the guy in the Verizon Wireless ads moving around with his cell phone, asking: “Can you hear me now?”

The same scenario can happen every time you install a fire alarm system. Building and fire codes require that the people in all occupied spaces of the building are able to hear the alarm signals. Chapter 18 of NFPA 72 2013, the National Fire Alarm and Signaling Code, addresses all of the requirements for both audible and visible notification appliances used to initiate and direct evacuation or relocation of the building occupants.

The code, by itself, does not require evacuation. However, it does require all alarm notification signals to meet audibility requirements so that the occupants can hear the alarm signal and can take whatever appropriate action the building’s fire management plan requires. The code also requires that, when the building fire management plan prompts the occupants to evacuate the building, the appliances must operate using the National Standard Evacuation Signal consisting of a three-pulse temporal pattern. The pattern operates as follows:

  1. On phase lasting 0.5 second at ±10 percent
  2. Off phase lasting 0.5 second at ±10 percent for three successive “on” periods
  3. Off phase lasting 1.5 seconds at ±10 percent

The authority having jurisdiction (AHJ) can approve the continued use of an existing evacuation signaling scheme other than the national standard if one already exists.

Chapter 18 contains all of the installation requirements for notification appliances, or as stated in the code, it “establishes the means, methods, and performance requirements of notification appliances and systems.”

Section specifically addresses “Appliances intended for use in special environments, such as outdoors versus indoors, high or low temperatures, high humidity, dusty conditions, and hazardous locations, or where subject to tampering, shall be listed for the intended application.”

And, in all commercial/industrial/institutional (CII) market applications, the code requires the installing contractor to provide mechanical protection for appliances that may become subject to physical damage (such as from a forklift or stock-retrieval system in a warehouse). And this protection must obtain a listing for use with the device. Such a listing must specifically make note if the protection in any way affects the notification appliance’s field performance. The manufacturer must provide information on proper use of the mechanical protection.

As a professional contractor, you already know that the circuit conductors cannot physically support any electrical device you install. This rule most certainly applies to notification appliances, as well.

Because the code requires the fire alarm system control unit to monitor the integrity of notification appliance circuits, the control unit must provide terminals, leads or addressable communication to ensure the monitoring of the circuit’s integrity to the appliance. Some contractors have falsely thought that the monitoring of integrity requirement meant that the fire alarm system control unit monitored the operational integrity of every notification appliance. As the code explains in Annex A, “It should be noted that monitoring the integrity of the installation conductors and their connection to an appliance does not guarantee the integrity of the appliance or that it is operational. Appliances can be damaged and become inoperable or a circuit can be overloaded, resulting in failure when the appliances are called upon to work. Presently, only testing can establish the integrity of an appliance.”

In addition to properly installing the notification appliances, you also must follow the requirements for ensuring audibility of the notification appliances. You must ensure intelligibility if your appliances consist of speakers reproducing the sound of a human voice. First, determine which mode of signaling the particular application will require you to provide.

The code recognizes two modes of signaling: public mode and private mode. For CII occupancies, public mode will predominate. However, institutions, such as hospitals, will also use private mode.

Public mode requires that signals “have a sound level at least 15 dB above the average ambient sound level or 5 dB above the maximum sound level having a duration of at least 60 seconds, whichever is greater, measured 5 ft. (1.5 m) above the floor in the area required to be served by the system using the A-weighted scale (dBA).”

Private mode requires signals to “have a sound level at least 10 dB above the average ambient sound level or 5 dB above the maximum sound level having a duration of at least 60 seconds, whichever is greater, measured 5 ft. (1.5 m) above the floor in the area required to be served by the system using the A-weighted scale (dBA).”

Some exceptions to these requirements include circumstances where the fire alarm system design has included visible signaling. In such a case, the AHJ may approve reduced sound levels or the total elimination of audible signaling. And the code allows audible notification appliances installed in elevator cars and restrooms to use the audibility criteria for private mode signaling.

When you install fire alarm systems in CII buildings, you will encounter some areas that possess a high ambient noise level. Your first inclination might be to ensure your audible notification appliances produce louder sounds than the ambient noise. Although this tactic might prove appropriate in some circumstances, the code advises using a visible appliance for notification when there is a sound level greater than 105 dBA. This method ensures you do not exceed the OSHA maximum sound pressure limit of 120 dBA. In fact, the code requires that the total sound pressure level, with all of the notification appliances operating, does not exceed 110 dBA.

Additionally, the code permits the fire alarm system to stop or reduce the ambient noise—such as loud music from a band—to allow the notification appliance sound levels to then meet the audibility requirements for the space. The code states in Section that “a system arranged to stop or reduce ambient noise shall be permitted to produce a sound level at least 10 dB above the reduced average ambient sound level or 5 dB above the maximum sound level having a duration of at least 60 seconds after reduction of the ambient noise level, whichever is greater, measured 5 ft. (1.5 m) above the floor, using the A-weighted scale (dBA).”

The code further requires the addition of visible appliances to the area where the fire alarm system has stopped or reduced the ambient noise levels.

More stringent requirements exist for CII buildings where the occupants will be sleeping. In these cases, sleeping areas, must have “a sound level of at least 15 dB above the average ambient sound level or 5 dB above the maximum sound level having a duration of at least 60 seconds or a sound level of at least 75 dBA, whichever is greater, measured at the pillow level.” If barriers such as doors, curtains or retractable partitions separate the pillow and the notification appliance, you must take the sound pressure level measurement with the barrier in place—e.g., with the door closed.

Recent research has shown that a frequency of 520 Hz will more effectively awaken occupants who are asleep. The research has included the very young, the very old, and people under the influence of alcohol. Based on that research, the technical committee responsible for Chapter 18 added the requirement that where “audible appliances are provided to produce signals for sleeping areas, they shall produce a low frequency alarm signal that complies with the following:

  1. “The alarm signal shall be a square wave or provide equivalent awakening ability.
  2. “The wave shall have a fundamental frequency of 520 Hz ± 10 percent.”

This requirement will take effect in January 2014. The delay is deliberate to allow manufacturers time to develop the appliance for code compliance.

As you can see, you must very carefully review the design, layout and installation of audible notification appliances to avoid surprises at the end of the project when you take sound pressure level measurements. When someone asks if the occupants can hear the alarm, you want to confidently reply, “Yes!”

About The Author

MOORE, a licensed fire protection engineer, was a principal member and chair of NFPA 72, Chapter 24, NFPA 909 and NFPA 914. He is president of the Fire Protection Alliance in Jamestown, R.I. Reach him at [email protected]





featured Video


New from Lutron: Lumaris tape light

Want an easier way to do tunable white tape light?


Related Articles