Low Frequency Requirements Sound Confusing, But They’re Necessary

The wording of the 520 Hz 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.A significant change in NFPA 72, The National Fire Alarm Signaling Code, became effective January 1, 2014 – the 520 Hz low frequency audible fire alarm signal is required in all sleeping areas of newly constructed hotel guest rooms and dormitory sleeping rooms. What does this change mean for you? 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.

Chapter 18

Section of NFPA 72: 2010 requires that after January 1, 2014, the low frequency audible fire 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 slightly changed 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 fire occurs. In fact, studies have shown the low frequency signal is six to ten times more effective at waking children, heavy sleepers, and people with hearing loss than current high-pitched alarms, which operate at around 3 kilohertz.

Specifically, the 520 Hz low frequency signal is 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.

Chapter 24

Low frequency requirements have also been added to Chapter 24, which covers emergency communications systems, such as in-building fire EVAC systems and mass notification systems. Section requires a low frequency signal in sleeping areas to be followed by a voice message to communicate information to people who could be asleep, except in occupancies listed in 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 temp 3 audible alarm signal.

Section 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.

Chapter 29

Finally, low frequency requirements have been added to 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, 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.

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.

Beyond NFPA 72

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 the 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 not 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

Regarding Group R-1 and Group R-2 occupancies: It is very common to have a building fire alarm system with smoke alarms installed in the sleeping rooms of Group R-1 and R-2 occupancies. Section 907.2.9 of the 2012 IFC requires Group R-1 and R-2 occupancies to have a fire alarm system that activates the occupant notification system throughout all occupied areas of the building, including sleeping areas with dwelling units, by either pull stations or a sprinkler system. That means the low frequency signal (activated by the building fire alarm system) is required in all sleeping rooms.

Section of NFPA 72: 2013 exempts smoke alarms, installed in the sleeping rooms, from the low frequency signal requirement. In this application, there will be two different signals in the sleeping rooms:

1. Low frequency signal activated by the fire alarm system

2. The standard 3 Khz signal from the smoke alarm

Not every local jurisdiction has adopted the 2010 or 2013 version of NFPA 72, but an increasing number of jurisdictions have. Remember to follow manufacturer instructions, as well as your local building/code regulations, for the use and installation of any audible visible notification devices.


Overall, the takeaway is that each application must be evaluated on its own merits. Each application –hotel and motel guest rooms, dorms, and so on – requires a careful study to determine the suitability of systems to meet associated codes. It is not always one or the other; each application has its associated suitability versus code requirements.



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