AT THIS YEAR’S NFPA Conference & Expo, I gave a presentation on the changes to Chapter 24, “Emergency Communications Systems,” of the 2016 edition of NFPA 72®, National Fire Alarm and Signaling Code. An attendee asked why the code did not require that system designers omit speakers from any area equipped with a microphone, such as in the fire command center.
Among other things, the question provided an opening for me to discuss the nature of the code. Clearly, NFPA 72 requires all fire alarm systems to provide enough audible notification appliances to ensure the system will meet the audibility requirements of Chapter 18. The building codes state that the occupants must hear the alarm signals in all occupiable spaces. This would seem to require audible notification appliances in the fire command center. In addition, the code requires that the design of all voice systems provide intelligible messages—the occupants must clearly comprehend any voice messages.
Generally, the NFPA technical committees (TCs) developing codes and standards try to address most situations encountered in the field as those situations apply to their specific code or standard. However, the TCs simply cannot address all issues. In this case, the TCs expect that a specifically qualified individual will design the fire alarm system, and NFPA 72 defines the qualifications of both the system designer and the installer.
The questioner complained that any qualified design engineer of emergency voice/alarm communications systems (EVACS) should know that placing a speaker in the same general location as a microphone used for manual messaging will potentially distort the sound and produce an unintelligible message due to feedback from the speaker into the microphone—a common-sense design issue not addressed in the code. Someone in the audience suggested the questioner look at the Chapter 10 qualification requirements for system designers. In an actual installation, though, the building owner may not have a direct contract with the design engineer.
The questioner related his conversation with the design engineer, who said that since the code and the authority having jurisdiction (AHJ) required the speaker, the owner could not blame him for the subsequent problem caused by feedback. While the code requires audibility, this does not relieve the design engineer from the responsibility of knowing and understanding basic sound and communications principles. Using the common knowledge about sound systems, the designer would realize the potential for feedback and would omit the speaker in the fire command center. Other indicators would exist in the fire command center to alert those occupants of a fire. Furthermore, a qualified design engineer should know that a requirement in Chapter 18 allows the AHJ to permit the design engineer to reduce or eliminate audible signaling in certain situations where the system provides visible signaling in accordance with code requirements.
While NFPA 72 contains the minimum requirements for a reliable fire alarm system, it does not include all of the background and information that a fire alarm systems design engineer must know, understand, and use. A qualified fire alarm systems design engineer should know the code’s requirements and alternatives, know and understand basic acoustical principles, and should always apply common sense. The code provides guidance, but no one intended it to serve as a design manual.
WAYNE D. MOORE, P.E., FSFPE, is vice president at JENSEN HUGHES.