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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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A significant change in NFPA 72, The National Fire Alarm Signaling Code, became effective Jan. 1, 2014. That is the 520Hz low frequency audible fire alarm signal is required in certain sleeping areas of newly constructed spaces, such as hotel guest rooms and dormitory sleeping rooms.

What does this change mean for you, the installing life-safety contractor? The short answer is: It depends. And confusion regarding the wording in the 2010 and 2013 editions of NFPA 72 is partly to blame for the difficulty in providing a definitive answer. Let’s seek some clarity.

Chapter 18 Addresses Sleeping Areas

Section 18.4.5.3 of NFPA 72: 2010 requires that after Jan. 1, 2014, the low frequency audible fi re alarm signal be provided in areas to wake people sleeping in occupancies having a protected premises (building) fire alarm system. The Chapter 18 committee chose to apply the requirement to all sleeping areas — not just those where occupants have self-identified as having a hearing impairment. This was done intentionally for several reasons. For example, many people may not know they have a hearing impairment. In addition, the low frequency signal has proven very effective at waking children under the age of 10 and people with alcohol impairments.

In NFPA 72: 2013, the Chapter 18 text was changed slightly to clarify that the low frequency requirements were intended to “awaken” people who are sleeping only. The low frequency signal is not required in the hallway of a hotel or dormitory, but it is required in hotel guest rooms.

The low frequency tone benefits not only the hard of hearing, but also children, deep sleepers, and people impaired by alcohol or medications. The tone gives these individuals a higher chance of waking when a fi re occurs. In fact, studies have shown the low frequency signal is six to 10 times more effective at waking children, heavy sleepers and people with hearing loss than current high-pitched sounders, which operate at around 3kHz.

Specifically, the 520Hz low frequency signal is often required in the sleeping areas of these types of buildings:

  • Hotels/motels
  • College/university dormitories
  • Retirement/assisted-living facilities (without trained staff responsible for waking up patients)
  • Apartments/condominiums

As a result, any of these new buildings with sleeping areas will now need to include low frequency sounders as part of the fire and life-safety system. The requirement may extend to those that are upgrading or retrofitting existing fire and life-safety systems within those types of buildings.

What about sleeping accommodations in occupancies such as hospitals and detention or correctional facilities? These applications do not require low frequency sounders. In a hospital, a low frequency tone could unnecessarily awaken patients, which would be detrimental to their care. Instead, a standard audible fire alarm signal notifies staff members who will then awaken and relocate patients who are in danger. Regular, required fire drills prepare staff members in the case of an emergency.

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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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