Bringing NFPA 72 520 Hz into Focus

ask-the-expertAsk the Expert with Wayne D. Moore

Hughes Associates, headquartered in Baltimore, Maryland, is a fire protection engineering and code-consulting firm with regional offices throughout the world. Wayne D. Moore, P.E., FSFPE, F.NSPE, CFPS, SET, is principal and vice president for Hughes. He is also chairman of the National Fire Alarm and Signaling Code® (NFPA 72: 2013) Emergency Communications Systems (Chapter 24) Technical Committee and vice chairman of the RI Professional Engineering Licensing Board. Moore is the 2009 recipient of the NFPA Standards Medal and the 2012 Recipient of the AFAA Lifetime Achievement Award. Both through Hughes and his association work, Moore has been actively involved in life safety system audibility, including how it pertains to the new low-frequency 520 Hz requirement.

What is the significance of the 520 Hz requirement in the 2010 and 2013 editions of NFPA 72 that becomes effective Jan. 1, 2014?

The reason for the change in the code is research performed by Bruck and Thomas in Australia.* In over a decade of research, they found that the 520 Hz square wave signal was the most effective in waking all individuals. With children and young adults, the low-frequency signal is 6 to 10 times more effective than the current high-frequency signal. In adults with hearing loss, it was found to be more than seven times as effective as the standard high-frequency (~3,000 Hz) tone used in most audible appliances today.

“Installing different signals in different parts of the building is unnecessary when a 520 Hz sounder will get everyone’s attention.”

Wayne D. Moore, Principal and Vice President, Hughes Associates

This research prompted the technical committees to review which areas they felt should be changed, and then they focused on the use of the low-frequency signal in areas intended for sleeping. The discussion in Chapter 18 of NFPA 72: 2013 states that low-frequency audible appliances are not required in hallways, lobbies or other “tenantless” areas.

The use of these 520 Hz appliances does not preclude the use of other devices such as bed shakers. But it was clear from the early research that strobe lights were relatively ineffective in waking hard-of-hearing individuals.

What prompted the need for the research?

The research was done to prove the waking effectiveness of alarm signals. It goes back to when a fire department in Michigan first discovered that standard smoke alarms were not waking sleeping children. They put together a video on this, and it went viral. Concurrently, Australia began to research why people were not awakening from the fire alarm signal.

This brings me back to when I first got in the business. The standard horn device had a low-frequency output. When those were replaced in an existing system with the newer (at the time) low-current, high-frequency horns, people began to complain that they couldn’t hear them as well. At the time, I wasn’t sure what was causing the problem. They both measured 85 db at 10 feet. But the frequency was the issue, not the output of the sound. That’s what the research sponsored by the NFPA Research Foundation proved.

Is the 520 Hz criteria covered in any other chapters?

Yes, it appears in Chapters 18, 24 and 29. The effective date for the appliances given in Chapter 18 is not allowed in Emergency Communications Systems. Chapter 24 specifically requires that “in occupancies where sleeping accommodations are provided and the voice message is intended to communicate information to those who could be asleep, a low frequency tone that complies with 18.4.5 shall be used.”

The Annex to the requirement states the reason behind the committee wanting immediate compliance: “The effective date listed in Chapter 18 for using a low frequency signal has not been allowed in because voice systems are easily adapted to comply, whereas the requirements of 18.4.5 also apply to stand-alone tone signaling appliances.”

Additionally, Chapter 24 does not require the 520 Hz signal where the voice communication system notifies occupants who are awake in occupancies where sleeping accommodations are provided. The committee felt that in occupancies such as healthcare or detention and correction where personnel in charge are notified, then there was no reason to require the low-frequency signal. By notifying the staff in these occupancies, they could awaken individuals and relocate them as necessary.

NFPA 72: 2013 is not enforced in any jurisdiction specifically yet, but it is the latest technological information we have available to us that we should be using for design.

Wayne D. Moore, Principal and Vice President, Hughes Associates

How do you approach a design for the hearing impaired?

Among the people at risk of not waking to an auditory smoke alarm are the more than 34.5 million people in the U.S. who are hard of hearing. Given the aging of America, this number will continue to grow. My goal is to produce a universal design that will alert all occupants.

A recent acquaintance, who is deaf and blind, has quoted Myrlie Evers-Williams, who reportedly has stated, “Let us act on the idea that everyone is included.” What this means to me is to use whatever available technology exists to ensure the fire alarm system design will alert everyone in a building. Obviously, the Code requirements not-withstanding, any designer should be aware of the occupants expected in a building and whether or not there are sleeping accommodations.

If we are aware that the occupants in a sleeping situation could have mild to severe hearing loss, the code requires us to address the situation. Our design goals center around ensuring that the fire alarm signals are heard by everyone. We have also added tactile devices such as bed shakers or pillow shakers to a design. Obviously, in the hotel example, the Americans with Disabilities Act (ADA) requires that a certain number of rooms be made accessible for those with hearing loss, and that would be required in any design.

What brought about the 520 Hz expansion for all sleeping areas from the 2010 to the 2013 edition of NFPA 72?

Initially, the technical committees addressed the hearing impaired, but it did not make sense to limit the requirement. Another common sense design that has yet to appear in the code: to not intermingle signals or try to make sense of which signal is which in a building. If it applies for everyone, then we should keep them all the same. From an installation cost point of view, it’s the same: Why should I supply two different kinds of audible signals when one will do the same thing?

As we get older, we lose the high end of our hearing spectrum, and that’s the high frequency. A 520 Hz signal encompasses universal design.

How does the new 520 Hz requirement translate to your designs for these areas?

Anyone designing systems today really needs to pay attention to the current code requirements. Many people would argue that, for example, NFPA 72: 2013 is not enforced in any jurisdiction specifically yet, but it is the latest technological information we have available to us that we should be using for design. Sometimes that presents an issue with authorities having jurisdiction because it may require more or less than a previous code. Legally, you’d be advised to follow the most recent technical document available when conducting your work. We not only follow the latest editions of the code in our designs, but also take advantage of any new research that gives insight in order to provide more universal designs to our clients.

What are the challenges in real-time applications and installations?

There are two major challenges as they relate to universal design. The first is a general lack of understanding of the problem and the fact that for the hearing impaired, at least, it is addressed in the National Fire Alarm and Signaling Code®.

The second challenge is to better understand how audibility of the alarm signals is impacted and to adjust the design to ensure audibility at the code-required level. In many cases, owners and installers have a difficult time understanding why there seems to be too many notification appliances. Ensuring audibility is not an option. We’ll have to use the 520 HZ square signal soon for all systems, not just Fire Emergency Voice/Alarm Communications Systems.

How well are the current technologies accommodating the code requirements?

When a non-voice system is designed, it is now relatively easy to obtain horns or speakers. They’re available from System Sensor, which can provide the 520 Hz square signal. It makes sense to use the low-frequency signal throughout most occupancies with the exception of healthcare where awakening a patient may be detrimental to the patient.

There are challenges to accommodate everyone. This fact alone requires any designer to work closely with the owner or operator of a building to fully understand the occupants’ needs and with manufacturers to determine what is available to meet those needs.


*Reducing Fire Deaths in Older Adults: Optimizing the Smoke Alarm Signal Research Project.

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