Carbon Monoxide: The Invisible Life Safety Risk
Dr. Rodger Reiswig, SET, PMSFPE
Carbon monoxide (CO) is nothing new to our world. CO has been around since the dawn of time. What has changed is our awareness of its effects on the body, as well as how it’s being used in construction today to build more energy efficient buildings. The fire and life safety community has realized that CO plays a role in life safety and, in many cases, is not directly associated with fire.
CO is a byproduct of incomplete combustion. It could be found from any fuel burning appliance, or as NFPA 72, The National Fire and Signaling Code for 2025 defines it, as a “permanently installed carbon monoxide source.” The fuel source could be, for example, wood, coal, oil, propane natural gas, etc. Another potential producer of carbon monoxide is an automobile, generator, or construction equipment.
As our buildings have become more efficient and do not promote fresh air exchanges, the need for awareness and alerting occupants of carbon monoxide poisoning is very important.
In almost all occupancy classifications, carbon monoxide detectors will be required when a permanently installed carbon monoxide source is installed within a building or has an attached parking structure.
According to the Centers for Disease Control and Prevention’s website, www.cdc.gov/co, “The most common symptoms of CO poisoning are headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. CO symptoms are often described as “flu-like.” If you breathe in a lot of CO, it can make you pass out or kill you. People who are sleeping, drunk, or under the influence of other substances can die from CO poisoning before they are aware they have symptoms.”
NFPA 72, 2025 states in section 17.14.1 that “Carbon monoxide detectors are required in the following locations.
(1) On the ceiling or on the wall with the top of the detector within 12 in. (300 mm) of the ceiling, where installed in the same room as the permanently installed carbon monoxide source
(2) Centrally located in every HVAC zone of the areas required by laws, codes, or standards
(3) Outside of each separate sleeping area, guest room, and guest suite within 21 ft (6.4 m) of any door to a sleeping room, with the distance measured along a path of travel
(4) Other locations where required by applicable laws, codes, or standards
(5) In accordance with the manufacturer’s published instructions”
Research from the Fire Protection Research Foundation has shown that carbon monoxide can quickly and easily migrate throughout a building. And because of this a large amount of carbon monoxide detectors are not required. Further, CO detectors are unlike smoke or heat detectors in that they do not have a spacing requirement or are listed by a laboratory for spacing by dimensions. Because of this, NFPA 72 created minimum requirements for the placement of these detectors.
When selecting a carbon monoxide detector, it is important to ensure that the device meets the requirements of NFPA 72, 2025 section 17.14.2*. This section states that “Carbon monoxide detectors shall meet the following requirements:
(1) Carbon monoxide detectors shall be listed in accordance with applicable standards.
(2) Carbon monoxide detectors shall be set to respond to the sensitivity limits specified in UL 2034, Single and Multiple Station Carbon Monoxide Alarms.”
For the notification of the presence of carbon monoxide, NFPA 72, 2025 states that the notification signal needs to be what the industry refers to as “modified temporal four pattern.” The language for the requirement is found in section 18.4.3.2 of NFPA 72, 2025.
“Where an audible signal is required, the carbon monoxide signal shall be a four-pulse temporal pattern and comply with the following:
(1) Signals shall be a pattern consisting of four cycles of 100 milliseconds ± 10 percent “on” and 100 milliseconds ± 10 percent “off,” followed by 5 seconds ± 10 percent “off,” as demonstrated in Figure 18.4.3.2.
(2) After the initial 4 minutes of the carbon monoxide signal, the 5-second “off” time shall be permitted to be changed to 60 seconds ± 10 percent.
(3) The alarm signal shall be repeated in compliance with 18.4.3.2(1) and 18.4.3.2(2) until the alarm resets or the alarm signal is manually silenced.”
Carbon monoxide detection plays a critical and increasingly central role in modern life safety strategies. As buildings become more energy efficient and air exchange is reduced, the risk posed by CO exposure grows quieter and more dangerous. Because it is odorless, tasteless, and invisible, carbon monoxide gives no warning until its effects are already underway. That reality places a greater responsibility on designers, installers, and life safety professionals to ensure detection systems are properly specified, placed, and maintained in accordance with current codes and standards. By understanding the requirements outlined in NFPA 72 and applying them thoughtfully, the industry can continue to reduce preventable injuries and deaths and fulfill its core mission: protecting lives through awareness, technology, and proactive design.
