Fire alarm changes and challenges

NFPA 72 continues to provide challenges and solutions to fire protection engineers and fire alarm designers

By Larry D. Rietz April 14, 2022


Learning Objectives

  • Understand what affects emergency communications system intelligibility and what should engineers understand to create intelligible designs.
  • Learn why are low-frequency tones required in sleeping occupancies and how can this requirement be difficult to comply with.
  • Know the code history of carbon monoxide detection and what recent research raises additional causes for concern about providing carbon monoxide detection.


In November 2021, the National Fire Protection Association released its 2022 edition of NFPA 72: National Fire Alarm and Signaling Code. First issued in 1993 as the “National Fire Alarm Code,” this is now the 10th edition of this installation standard.

NFPA 72 is one of the most widely accepted and applied installation standards in the world. While the individual details have consistently changed over the years, the guiding principle of NFPA 72 has remained the same. In the 1993 edition, NFPA 72 stated, “It is the intent of this code to establish the required levels of performance, extent of redundancy and quality of installation, but not the methods by which these requirements are to be achieved.”

The 2022 edition states, “This code establishes minimum required levels of performance, extent of redundancy and quality of installation but does not establish the only methods by which these requirements are to be achieved.”

The Technical Committees of NFPA 72, currently consisting of nine technical committees and one correlating committee, have attempted to hold true to these guiding principles of fire alarm system performance, redundancy and quality in the installation standards and guidelines that are contained within the document. The effort of these committees, now numbering over 300 individuals, constitutes thousands of hours of effort every three years in an attempt to update, modernize and clarify the requirements of the code.

In fact, many of the technical committee members involved in the 1993 edition are still actively participating some 29 years later. As with any consensus standard, some requirements are straight-forward and clear, while others remain hotly debated and tend to be consistently modified from edition-to-edition or remain somewhat confusing and challenging to the users interpreting the code. Intelligibility, low-frequency tones and carbon monoxide detection are not new issues or requirements in the code, but they continue to give code users difficulty with compliance and real-world application.

Figure 1: Diagram of components that affect an intelligible system design (diagram based on Designing Mass Notification Systems by Wayne D. Moore; modified with author’s permission). Courtesy: Jensen Hughes Inc.

Fire alarm intelligibility

Voice fire alarm systems have been in active use for more than 40 years. Over the past 10 years or so, there has been an influx of emergency communications systems from various manufacturers to meet the need of an increasing number of code requirements for voice systems. The word “intelligibility” was not even included in the 1993 edition of NFPA 72, although the inspection, testing and maintenance chapter referred to verifying the “voice clarity” of systems. By the 2022 edition, intelligibility is mentioned hundreds of times.

By definition, intelligibility is both a performance and quality aspect of the code. The code requires that voice signals are intelligible by being understandable, comprehensible and clear. This is regardless of whether the voice signal is a reproduction of a prerecorded message or synthesized message or a live voice signal produced through the use of a microphone, telephone handset or radio input. This requires various system components to work together.

The book “Designing Mass Notification Systems” by Wayne D. Moore, PE, includes some important items to note that may affect system intelligibility from a voice system perspective. It states, “First, you start with the audio source, which could be a person orally giving emergency instructions via a system microphone or may consist of a prerecorded message. If it is a prerecorded message, the quality of that recording, the media used to record the message and even the type of speaker recording the message (e.g., accent, male voice, female voice, etc.) will affect intelligibility. That audio source is then processed through the system’s electronics via line level (analog) or digital means and delivered to the amplifier(s). The amplifier then amplifies that signal and distributes it via individual circuits to the loudspeakers.”

Then you have the actual loudspeaker placement and selection of loudspeaker that has a large effect on how a listener interprets that message. An engineer or designer may have very little input into selection of the source and signal processing equipment. However, they should be able to have a large impact on the circuiting, placement and equipment selection of the loudspeakers. This is where a designer’s time should be focused in creating an intelligible design.

Although included in NFPA 72 since 2010, the creation of acoustically distinguishable space designations still continues to confuse many. Officially, an ADS is “an emergency communications system notification zone or subdivision thereof that might be an enclosed or otherwise physically defined space or that might be distinguished from other spaces because of different acoustical, environmental or use characteristics, such as reverberation time and ambient sound pressure level.”

Figure 2: Creating intelligible designs may mean providing nontraditional fire alarm loudspeakers to meet the needs for the space. Courtesy: Hyperspike

NFPA 72 Chapter 24 states that “occupiable areas” using voice evacuation messages shall incorporate ADS designations, meaning all parts of a building intended to have occupant notification need to be defined as ADS within any occupiable areas. A designer shall review all of the occupiable areas within a voice fire alarm system and designate areas that have similar acoustical, environmental and use characteristics to define the level of intelligibility that will be provided in each of those designations. Common occupiable spaces like corridors, reception areas, private offices, open-area office or cubical spaces, conference rooms and the like can be relatively easy to define and provide intelligible ADS designs.

A designer will have to spend much more time to create intelligible designs and/or alternate forms of signaling, in acoustically challenging spaces like large lobbies, atriums, airport terminals and concourses, workshops, factories, parking garages and similar spaces. Regardless of the specific type of space, the goal of ADS designations is for a designer to clearly designate the performance requirements of the voice system within the space under consideration.

The key for users of the code is to fully understand what NFPA 72 requires from an intelligibility standpoint. This may be quite different from how a designer would normally design a fire alarm system based solely on audibility. Additionally, it includes becoming familiar with defining the audibility requirements of all spaces including how sound moves through barriers like walls and doors, understanding how to define individual ADS designations, proper loudspeaker selection and being familiar with NFPA 72 Annex D, which can really assist in intelligibility commissioning efforts.

Although challenging, it is incumbent upon engineers to learn how to provide and explain their intelligible designs to the authority having jurisdiction. Designers need to understand how to measure intelligibility in both qualitative and quantitative ways, even though NFPA 72 does not currently require quantitative measurements of intelligibility unless required by the owner or AHJ.

Figure 3: Typical fire alarm system smoke sensor with low-frequency sounder base and low-frequency system loudspeaker in a hotel room. Courtesy: Jensen Hughes Inc.

Low-frequency fire alarm tones

In June 2007, the findings from two research studies were published by NFPA’s Fire Protection Research Foundation. These two studies, both performed by Victoria University in Australia, reviewed the waking effectiveness of various audible, visual and tactile devices. One study focused on waking individuals who were alcohol impaired, while the second study focused on adults who were hard of hearing.

Both studies found that a low-frequency audible alarm was significantly more effective in waking ability. The hard of hearing study stated, “a 520 Hz square wave T-3 [temporal three] sound was the single most effective signal, awakening 92% of hard of hearing participants when presented at or below 75 dBA for 30 seconds and awakening 100% at 95 dBA.” In contrast, the normal smoke alarm of 3,100 Hz frequency only awoke 56% of hard of hearing participants.

For the alcohol-impaired study, the low-frequency square wave sound signals “awoke 93% to 100% of participants at 75 dBA or less” while “the 3,100 Hz signal awoke only 61.5% of the moderately alcohol impaired participants.”

The results of these research studies were developed into new performance characteristics that were built into the 2010 edition of NFPA 72. The technical committee for Chapter 18 added a prescriptive requirement that all system-activated audible appliances used in sleeping areas must use a low-frequency 520 Hz square wave effective Jan. 1, 2014. The technical committee for Chapter 29 incorporated the same low-frequency signal requirement for residential protection with single- and multiple-station smoke alarms without an effective date, which meant the requirement was applicable when the 2010 edition was adopted in the particular jurisdiction.

The prescriptive requirements for low-frequency signals found in Chapters 18 and 24 apply to fire alarm system devices and appliances and are currently quite easy to comply with in various occupancies. Low-frequency listed notification appliances, sensor sounder bases, tone generators and amplifiers are readily available for commercial use. However, the low-frequency tone requirements found in Chapter 29 have proved to be troublesome to comply with for at least two reasons.

First, many sleeping room and guest room occupancies, like R-1 hotels/motels, I-1 assisted living/residential board and care facilities and similar facilities, only require the installation of a smoke alarm and building codes do not specifically require a fire alarm system device. The problem is that currently, there are no low-frequency smoke alarms that are commercially available. This means that compliance with Chapter 29 requirements is difficult or even impossible to meet without providing fire alarm system devices (see Figure 3).

Second, the wording of the Chapter 29 requirements themselves lead some to believe that the requirement to provide low-frequency signals in sleeping areas is somehow subjective or even not necessary. For instance, in the 2019 edition, Section 29.5.10 states that notification appliances “provided in sleeping rooms and guest rooms for those with hearing loss shall comply” with the following two requirements “as applicable.”

The following two requirements are for notification to those with “mild to severe hearing loss” or “moderately severe to profound hearing loss.” Both of these sub-sections state that low-frequency signals shall be provided “where required by governing laws, codes or standards for people with hearing loss” and the Annex A explanatory information states the same.

An example of such a building code requirement would be the International Building Code Table 907. that requires a certain number of sleeping rooms in I-1 and R-1 occupancies to be provided with accessibility provisions like visual alarms. The challenge of providing a low-frequency signal arises when designing sleeping areas for so-called “normal hearing” occupants or for sleeping areas that are not required to be provided with specific accessible features.

It appears that the code is attempting to provide two options by dictating:

  • A low-frequency audible signal for those with mild to severe hearing loss.
  • Adding visual and tactile signaling for those with moderately severe to profound hearing loss.

The problem is that the definitive line between these two options is unclear in the language of the code because “severe” hearing loss is more significant than “moderately severe” hearing loss, creating two separate but overlapping requirements. And, in setting the floor of this requirement at “mild” hearing loss, is the code stating that those with no hearing loss or those who are alcohol-impaired are not to be addressed by the code, even though the studies that created these code requirements included these groups?

To help analyze this situation, some new research has been released. In August 2021, NFPA’s FPRF released the report entitled “Review of Alarm Technologies for Deaf and Hard of Hearing Populations.” This report states that it is “estimated that almost 1 out of 100 U.S. citizens over the age of 12 experience hearing loss classified as severe or profound hearing loss and more than 14 out of 100 U.S. citizens over the age of 12 experience hearing loss to some degree. Hearing loss is also more prevalent in older age.”

The report further states, “An important deficit of commonly used audible alarms is its inability to warn people who are deaf and to some extent also people who are hard of hearing. This effect is further enhanced when people are asleep.” Additionally, the National Institute on Deafness and Other Communication Disorders reports that “one in eight people in the United States (13%, or 30 million) aged 12 years or older has hearing loss in both ears, based on standard hearing examinations.”

While this information helps us better understand the seriousness of providing alarm signals that are effective in waking ability, it does not necessarily help us better understand whether low-frequency signals are required in all sleeping areas per the code. Based on the research we know that a low-frequency signal can significantly increase the waking effectiveness for all populations, including those who are alcohol-impaired and those with mild to severe hearing loss. And the lack of a commercially available low-frequency smoke alarm should not be an excuse for a designer or owner to refuse to install a device, nor an AHJ from enforcing the installation of a device that will actually wake up sleeping occupants.

The intent of the model building codes and NFPA 72 Chapter 29 requirements is that low-frequency signals shall be provided in every sleeping area, but until smoke alarm manufacturers can produce a compliant low-frequency smoke alarm, this issue will remain contentious.

Figure 4: Sampling of major carbon monoxide poisoning events in U.S. schools since 2012. Courtesy:

Carbon monoxide detection

The term carbon monoxide, commonly known as CO, is only mentioned once in the 1993 edition of NFPA 72, even though it was about that time that NFPA started to develop a standard on the installation and use of CO detectors. Originally published in 1998 as a recommended practice, in 2005 NFPA 720 became the Standard for the Installation of Carbon Monoxide Detection and Warning Equipment.

NFPA 720 was rewritten in 2009 and the standard began to look a lot like a miniature version of NFPA 72. In August 2015, the NFPA Standards Council voted to relocate the material within NFPA 720 into various chapters of NFPA 72. The 2015 edition of NFPA 720 was its last edition and as of the 2019 edition of NFPA 72, all requirements for CO detection is included therein.

However, despite all of this work by technical committees, there remain a few issues related to CO detector placement and installation requirements.

First, the most frequently asked question remains about where a CO detector is properly located when it is required. The location requirements for fire alarm system CO detection are found in Section 17.12 of the 2019 edition of NFPA 72 and the requirements, in many ways, mimic those of system smoke detectors. Section 17.12.1(1) specifically states CO detectors should be installed “on the ceiling.”

However, Section makes it clear that stand-alone CO alarms and CO detectors can be located “on the wall, ceiling or other location as specified in the manufacturer’s published instructions.” It is unclear why the allowance of wall-mounted system CO detectors is only found in Chapter 29. The additional location guidance found in Chapters 17 and 29 and Annex A points to a more performance-based approach to the location of CO detectors and alarms and presents a challenge to engineers that can require additional research and time to create a proper design.

Second, despite the increase in CO detection laws and codes, at both a national and local level, the NFPA and the Centers for Disease Control and Prevention report that CO poisoning incidents continue to occur at a fairly consistent rate. The CDC reports that every year at least 400 people die in the U.S. from accidental CO poisoning, with approximately 20,000 people visiting the emergency department each year. Other sources report annual emergency room visits at twice or even three times that amount. And up to 25% of these poisoning incidents take place in public occupancies, many of which currently have no CO detection requirements.

Recently, this was further confirmed after one mother, Nikki James Zellner, experienced the CO poisoning of her two young children, ages 4 and 3, in February 2020 at their Virginia preschool. Her difficult experience led her to become a researcher and advocate for change and she founded Carbon Monoxide Safe Schools in partnership with the National Carbon Monoxide Awareness Association.

Zellner stated that, “carbon monoxide exposures and poisonings are happening in U.S. schools and daycares more often than we know. It is impacting a greater number of occupants, stemming from a wider variety of sources, spreaders and situations.”

In June 2021, Zellner’s organization released a report documenting some 200 instances of carbon monoxide exposures in U.S. schools and daycares from 2004 to 2021 in which at least 2,400 children, teachers, school staff and community members were injured. In the data complied, 47.5% of those incidents occurred due to noninstalled fuel burning systems like vehicles, propane or fuel-powered cleaning equipment or other similar sources. This data challenges the effectiveness of national ordinances because almost all codes and laws only address CO detection where fuel-burning systems are installed or are permanent features of an occupancy.

To add to this, some recent NFPA FPRF reports have raised additional questions about CO. A February 2015 report entitled “Carbon Monoxide Diffusion through Porous Walls: A Critical Review of Literature and Incidents” included a sobering finding. It stated, “Our analysis and review independently confirms that CO can diffuse through porous walls [including gypsum board and other porous wall types] at a fast rate and that the phenomena may merit consideration in life safety standards.”

The February 2021 report entitled “Carbon Monoxide Detection and Alarm Requirements: Literature Review” highlighted the abundance of various inconsistent state and national regulations across the range of occupancies both new and existing. It noted the “limitations” and “shortcomings” in the available data around CO incidents. And it emphasized the short-term and long-term effects of CO poisoning, including the fact that there are “serious and permanent consequences” such as “neuropsychological and cardiovascular complications.”

While the installation standards of NFPA 72 and CO legislation have come a long way in recent years to address concerns, it appears there may be a long way to go to fully address the CO risks encountered in various occupancies and ultimately to reduce CO poisoning injuries and deaths. Building codes need to fully address these risks and dictate when CO detection is required to meet these ongoing and serious risks. Very recently, the NFPA FPRF acknowledged this need by prioritizing several future research projects related to CO poisoning. In the meantime, it may behoove engineers to become familiar with the content of published research in an attempt to provide more comprehensive performance-based designs.

Fire alarm codes and standards

After decades of work, analysis, revision and clarification, NFPA 72 remains a well-respected and solid foundation on which engineers and designers around the world base their designs to protect life and property from the dangers experienced in our built environment. Despite constant changes to the code, challenges remain to address on-going concerns.

Diligent engineers will benefit themselves and their facilities by seeking answers to any questions they have from reliable sources and by being up to date on these requirements. It is also important that engineers and designers provide continuing feedback into the code improvement process so that code challenges can be more fully addressed in the future.



Larry D. Rietz
Author Bio: Larry D. Rietz is global service line leader, fire detection and alarm at Jensen Hughes Inc. He is a fire alarm and emergency communications system designer, author and instructor with more than 27 years of fire alarm industry experience.