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Lowdown on Latest Low Frequency Requirements

The wording of the 520Hz signal requirement in NFPA 72: 2010 and 2013 has caused some confusion. In general, low frequency sounders take the place of standard sounders in commercial sleeping spaces. However, there’s far more to know about the newly enacted requirement.



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Frequency Changes in Chapters 24, 29

Low frequency requirements have also been added to NFPA 72 Chapter 24, which covers emergency communications systems, such as in-building fire EVAC systems and mass notification systems (also see MNS features in this issue). Section 24.4.2.4.2 requires a low frequency signal in sleeping areas to be followed by a voice message to communicate information to people who may be asleep, except in occupancies listed in 24.4.2.4.3. The reason for this provision is to comply with the NFPA 72 and UL 864 requirement for the voice evacuation message to be preceded by two cycles of the Temporal Three audible alarm signal.

Section 24.4.2.4.3 does not require a low frequency signal in occupancies where the voice system is used to communicate to occupants who are awake. For example, in a hospital, the voice message is used to notify staff members who are already awake. The staff will then respond to the appropriate location in the hospital to carry out their duties, which could include waking and relocating patients in potential danger.

Finally, low frequency requirements have been added to NFPA 72 Chapter 29. The scope of this chapter covers all occupancies that are required to install smoke alarms or household fire alarm systems. In accordance with 29.3.8 and 29.3.8.1, the low frequency signal is required in sleeping areas for people with mild-to-severe hearing loss where required by governing laws, codes or standards, as well as where provided voluntarily for people with hearing loss.

The basic purpose of a fire alarm system is to alert all occupants in the building. It’s important to point out that the requirements in NFPA 72 and section 907.2 of the IFC do not apply retroactively to existing systems.

To summarize the NFPA 72 low frequency requirements, Chapter 18 and Chapter 29 have different scopes. Chapter 18 requires the low frequency signal in all sleeping areas to wake people sleeping in occupancies having a protected premises fire alarm system. Unlike Chapter 18, Chapter 29 does not require the low frequency signal in all sleeping areas. Instead, Chapter 29 requires the low frequency signal in areas to wake up people with mild-to-severe hearing loss only. Also the scope of Chapter 29 covers occupancies where smoke alarms and household fire alarm systems are installed.

Other Bodies Weigh in as Well

Low frequency requirements go beyond the reach of NFPA 72. In response to the NFPA 72 changes for low frequency smoke and fire alarms in sleeping rooms, the 2012 International Fire Code (IFC)/International Building Code (IBC) indirectly requires a low frequency signal in certain occupancies because the 2010 edition of NFPA 72 is referenced in Chapter 80 of the IFC and Chapter 35 of the IBC.

Section 907.2 in the 2012 edition of the IFC/IBC requires a fire alarm system to be installed in new buildings in accordance with NFPA 72 and provide occupant notification in accordance with section 907.5. Section 907.5 requires the activation of a fire alarm system to send a signal to the control unit and then provide occupant notification throughout all occupied areas of the building, including both common and tenant spaces. Common spaces are corridors, lobbies or meeting rooms. Tenant spaces are dwelling units within apartment buildings, guest rooms of hotels or dormitory sleeping rooms.

The basic purpose of a fire alarm system is to alert all occupants in the building. It’s important to point out that the requirements in NFPA 72 and section 907.2 of the IFC do not apply retroactively to existing systems.

This translates to providing low frequency sounders in sleeping units in newly constructed Group R-1 hotels and motels, as well as in R-2 colleges, universities and apartment buildings where there is a protective premise fire alarm system in the building. There are two exceptions to the Group R-1 requirement:

  1. A manual fire alarm system is not required in buildings more than two stories in height where all individual sleeping units have an exit directly to the public way, egress court, or yard
  2. Permits the fire alarm system to be activated by a sprinkler system and provide occupant notification

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Article Topics
Fire/Life Safety · Carbon Monoxide · NFPA 72 · All Topics
Carbon Monoxide


By Tom minerich on May 21, 2014

Very informative

By Dan Gauvin on May 19, 2014

Good article

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