High-Rise Fire Alarm Systems

By Wayne D. Moore | Jun 15, 2005
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Delayed notification is a major factor of fire-related deaths in the United States. In most cases, the building occupants did not hear the audible alarms in the building or failed to understand the voice message instructions proved by the fire alarm voice communication system. Many contractors already understand the audibility requirements of the National Fire Alarm Code. Contractors may have experienced a delayed opening of a building they worked on due to a deficiency in the fire alarm system audibility measurements. The code states in the Annex that “notification appliances be sufficient in quantity, audibility, intelligibility, and visibility so as to reliably convey the intended information to the intended building occupants in a fire emergency.”

NFPA 72-2002, National Fire Alarm Code, offers very specific requirements defining two “operating modes” of notification: Public Mode and Private Mode. NFPA 72-2002 defines these as follows:

°Private Operating Mode: Audible or visible signaling only to those persons directly concerned with the implementation and direction of emergency action initiation and procedure in the area protected by the fire alarm system.

°Public Operating Mode: Audible or visible signaling to occupants or inhabitants of the area protected by the fire alarm -system.

In most fire alarm system installations, the code will require you to use the public operating mode. The operating mode will define the audibility sound levels you must achieve throughout the building.

Section states “to ensure that audible public mode signals are clearly heard, ... they shall 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 1.5 m (5 ft) above the floor in the occupiable area, using the A-weighted scale (dBA).”

This means when you take the sound levels, you must set your sound level meter to the A-weighted scale. Sometimes the ambient sound level persists at an unusually high level, such as loud music playing throughout a nightclub. In this situation, the code allows a fire alarm system to stop or reduce the ambient noise level and use the reduced sound levels as the base measuring point. The system should contain relays that, when a fire occurs, would disconnect the power to the amplifiers of the music system.

NFPA 72-2002, section states in part that when a contractor uses audible-notification appliances for private mode operation, they “shall have a sound level of not less than 45 dBA at 3 m (10 ft.) or more than 120 dBA at the minimum hearing distance from the audible appliance.”

To ensure those served by the private-mode audible-notification appliances can clearly hear them, these appliances “shall 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 1.5 m (5 ft) above the floor in the occupiable area, using the A-weighted scale (dBA)” on the sound level meter.

Private mode signaling serves many specific occupancies or part occupancies. Examples of private-mode applications include hospitals or nursing homes where the fire alarm system would notify the staff so they could provide evacuation assistance to the bedridden patients.

When you install a high-rise fire alarm voice communication system, you must consider the intelligibility of the messages transmitted over the speakers.

NFPA 72-2002 states in section, “emergency voice/alarm communications systems shall be capable of the reproduction of prerecorded, synthesized, or live (e.g., microphone, telephone handset, and radio) messages with voice intelligibility.”

As used in the National Fire Alarm Code, the terms intelligibility and intelligible apply to voice communications systems intended to reproduce human speech. When a person can clearly distinguish and understand human speech reproduced by such a system, the system provides intelligible communications. Satisfactory intelligibility requires adequate audibility and adequate clarity meaning, “freedom from distortion of all kinds.”

Unfortunately, the code does not specify a required method to measure intelligibility. Some manufacturers of fire alarm systems do have measuring instruments available. Because of the numerous variables affecting intelligibility, most fire authorities still rely on their own personal ability to hear and understand the message clearly.

Contractors will find that meeting the audibility and intelligibility requirements of the code will usually require the installation of additional notification appliances. All too often, this discovery comes after the contractor thought the fire alarm installation was completed. This can lead to delays in the building owner receiving an occupancy permit, which may lower your image in the eyes of the owner and significantly reduce your chances for repeat work.

You need to understand these issues and ask the right questions to ensure a smooth installation and acceptance test. EC

MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a co-editor of the current National Fire Alarm Code Handbook. Moore is a principal with Hughes Associates Inc. at the Warwick, R.I., office.


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]





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