Carbon Monoxide Alarm Considerations for Code Authorities

Carbon monoxide (CO) alarms play an important role in protecting people against carbon monoxide poisoning. Having a basic understanding of CO poisoning, CO alarms, how they are Listed, and how they are to be installed and maintained is an important for code authorities, especially those in jurisdictions where installation of CO alarms is required.

Carbon monoxide alarms typically have a CO sensor, control components and an alarm notification appliance. These CO devices may be either battery powered or connected to an DC or DC power source. Standby (battery) power is provided on all AC-powered CO alarms. CO alarms are intended for installation in occupancies with potential CO sources, such as fuel-burning appliances and attached vehicle garages, of residential occupancies, schools, dwelling units, recreational vehicles, mobile homes and recreational boats that have enclosed spaces and cockpit areas. A single station CO alarm works on its own, without connecting to other alarms. A multiple station CO alarm is a group of single alarms that can connect to each other. When one alarm sounds an alert, all connected alarms will sound.

CO alarms are Listed in the Single and Multiple Station Carbon Monoxide Alarms, UL product category (CZHF). These units are investigated in accordance with UL 2034, the Standard for Single and Multiple Station Carbon Monoxide Alarms. Listings are available for a variety of CO alarms, including single station, multiple station and alarms for travel and recreational vehicle use. Combination smoke and carbon monoxide alarms that comply with both smoke alarm and CO alarm requirements (UL 217 and UL 2034) are also Listed in this category.

The Listing, and the Listing Mark on the unit, indicate the application for which the unit has been investigated (e.g., single station carbon monoxide alarm, multiple station smoke alarm, also suitable as multiple station carbon monoxide alarm, etc.). Always look for the UL Signaling Listing Mark on the product.

CO is a colorless and odorless gas known as the “silent killer”. Studies have shown that the severity of CO poisoning is based on the amount of CO in one’s bloodstream. Symptoms may progress from a slight headache to nausea, dizziness, drowsiness, vomiting, collapse and ultimately death as carboxyhemoglobin (COHb) levels increase in the bloodstream and replace oxygen. The level of COHb in the bloodstream may increase slowly due to exposure to small amounts of CO or more quickly with higher CO levels. The UL 2034 Sensitivity Test is based on a 10% COHb level, which may be imperceptible or produce only a slight headache. Keep this in mind when a CO alarm activation is reported.

Listed CO alarms must pass several tests to establish they work well in different occupancies, locations and conditions. This means the alarms must respond within set times when exposed to different levels of CO. The higher the concentration of CO, the quicker an alarm must respond. Units are also tested to help ensure they don’t trigger alarms for low CO levels, such as those from traffic or normal use of a fuel burning appliance. They also cannot alarm when exposed to other vapors that may be present in a residence, such as methane and ammonia.

The CO alarm signal for has a four-tone pattern consisting of four spaced tones followed by a five-second silent period that repeats for at least four minutes. After four minutes, the five-second silent period is allowed to increase to 60 seconds. The alarm signal repeats until the alarm resets or until someone turns off the alarm. CO alarms may also have a visible alarm indicator. In comparison, UL 217, the Standard for Smoke Alarms, requires smoke alarms and combination smoke and CO alarms to generate a three-tone pattern when smoke is detected.

CO alarms should be installed, tested and maintained in accordance with their Listing and the manufacturer’s instructions. Activating the manual test switch on the unit will cause the audible and visible alarm indicators to activate. Newer CO alarms also produce an end-of-life signal that indicates when the device has reached the end of its useful life and should be replaced. This signal is distinct from CO and smoke alarm signals, but may be the same as other trouble signals, such as a low-battery signal.

Smoke alarms alert people in the building about a fire, so they can escape safely before the conditions become too dangerous. CO alarms tell people when there’s a dangerous level of carbon monoxide, so they know to act for safety.

For new construction, the model International Residential Code (IRC) requires Listed UL 2034 CO alarms to be installed outside of each separate sleeping area in the immediate vicinity of the bedrooms in dwelling units within which fuel-fired appliances are installed and in dwelling units with attached garages. Where more than one CO alarm is required for new construction, the IRC requires the alarms to be interconnected and permits wireless technology. State or local regulations may also require CO alarms to be installed in certain existing dwelling units. NFPA 72, the National Fire Alarm and Signaling Code, incorporates the requirements for CO alarms previously covered in NFPA 720. NFPA 72, Sections 17.12 and 29.7 include similar requirements for the installation of CO alarms, along with additional requirements for a distinctive alert tone, power supplies, installation, maintenance and testing.

If a CO alarm in your home sounds, immediately move to a fresh air location outdoors or by an open window or door. Make sure everyone inside the home is accounted for. Call your local emergency services, fire department or 9-1-1. Do not reenter the premises until the emergency services responders have given their permission. If a CO alarm reactivates within a 24-hour period, press the reset button, call emergency services and move to fresh air. Call a qualified technician to examine and/or turn off fuel burning appliances or other sources of combustion. It’s important to find the source of the CO and fix it properly.

Remember, an alarm shows that elevated levels of carbon monoxide are in your home. Some people can be exposed to dangerous levels of CO and not feel any symptoms. Whether or not you experience symptoms of CO poisoning, never ignore the alarm. In addition to installing CO alarms in the right places, the installer should follow the manufacturer’s instructions for power supplies, wiring and installation location.

CO alarms play an important role in protecting people against carbon monoxide poisoning. As a code authority, having a basic understanding of CO poisoning, CO alarms, how they are Listed, and how they are to be installed and maintained can help you better protect the citizens in your communities from this invisible killer.