Narrow Band Signaling: A Clearer Option for Emergency Notification

08/01/2005


Needing to be heard is not always about making a lot of noise, but making the right noise. In 2002, the National Fire Alarm Code (NFPA 72) recognized the need for clear audible messages by including a new audible signaling requirement for optional use on fire systems. Called "narrow band signaling" this technology was designed as a cost-effective method for making emergency messages heard in high-noise factories and other industrial areas.

It works by reducing the number of audible appliances needed in noisy environments by issuing signals and voice messages at pre-determined frequencies that ride above the average ambient noise.

In addition, since narrow band signaling systems can be designed to be fully compliant with OSHA and NFPA requirements, the technology makes it possible to provide audible notification communications to areas where it was not feasible under the previous NFPA code.

How narrow band signaling works

The narrow band method is based on the fact that noise at one frequency range does not mask sound signals at other frequency ranges. Consequently, this new signaling method uses narrow (1/3) octave bands instead of broadband dBA to measure sound levels and ensure alarm signals exceed background noise by at least 10 dB in one of the octave bands.

Covered under section 7.4.5.1 in NFPA 72 (2002), this technology is also specifically cited as an alternative for conventional dBA methods. As a result, narrow band signaling can provide daily paging as well as emergency alarm signaling and voice messaging to noisy work areas that cannot be suitably supported by traditional communication systems. This is because many conventional dBA methods may not be feasible due to the number of speakers and the total wattage required to meet NFPA code requirements.

For instance, to meet the 15 dBA above ambient requirement in a 200 ft. × 400 ft. protected area with conventional speaker systems, cluster speakers would have to be spaced in a grid pattern every 28 ft. This would require an incredibly cost-prohibitive usage of 98 clusters utilizing 392 speakers at 5,880 watts.

In comparison, the narrow band method used within the same application would require far less speakers and power.

Another advantage to narrow band signaling is its ability to be customized or tailored so the audio message can rise above different noise levels. This is a particularly useful benefit to factories and plants that operate different machinery at varying noise levels throughout their facilities.

A wise choice

Combined with voice alarm and paging systems, narrow band signaling technologies not only offer ready compliance with strict regulations, but can also improve employee safety by supplying enhanced communications capabilities during emergencies as well as normal daily operations.

Conventional

Narrow Band

Ambient Noise

94 dBA

83 dB @ 2,000-Hz band

Code - 3 dBA

107 dB @ 10 ft.

105 dBA @ 10 ft., 2,000 Hz

Cluster Spacing

28 ft.

Zero ft.

Total Clusters

98 (392 speakers)

15 (60 Speakers)

Total Watts

5,880

900



Benefits of mass notification

Clear, audible messaging in loud environments

Allows notification communication to areas where it was not feasible under previous NFPA code

Can provide daily paging as well as emergency alarm signaling and voice messaging



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