Underwriters Laboratories

Carbon monoxide (CO) is a poisonous gas that kills approximately 500 people in the United States alone every year. Consumer products like a stove or water heater that emit CO kill about 200 people of that number. You cannot hear, taste, see or smell carbon monoxide, giving it the nickname the "silent killer," because it sneaks up on its victims and can take lives without warning.

CO is a byproduct of incomplete combustion. CO sources can include malfunctioning appliances such as furnaces, stoves, ovens and water heaters that operate by burning fossil fuels such as natural or liquefied petroleum (LP). When malfunctioning appliances are not adequately ventilated, the amount of CO in the air may rise to a level that can cause illness or even death.

Additional sources of CO include vehicle exhaust, blocked chimney flues, fuel-burning cooking appliances used for heating purposes, and charcoal grills used in a home, tent, camper, garage or other unventilated areas.

When victims inhale CO, the toxic gas enters the bloodstream and replaces the oxygen molecules found on the critical blood component hemoglobin, depriving the heart and brain of the oxygen necessary to function.

The following symptoms are related to carbon monoxide poisoning and should be discussed with all members of the household:

• Mild exposure -- Flu-like symptoms including slight headache, nausea, vomiting and fatigue
• Medium exposure -- Severe throbbing headache, drowsiness, confusion and fast heart rate
• Extreme exposure -- Unconsciousness, convulsions, cardiorespiratory failure and death

In many cases of reported CO poisoning, victims are aware they are not well, but they become so disoriented that they are unable to save themselves by either exiting the building or calling for assistance. Young children and household pets are typically the first affected.

CO alarms are intended to trigger at carbon monoxide levels below those that cause a loss of ability to react to the danger of CO exposures.

CO poisoning victims may initially suffer flu-like symptoms including nausea, fatigue, headaches, dizziness, confusion and breathing difficulty. CO poisoning often causes a victim's blood pressure to rise, turning the victim's skin a pink or red cast.

Have your fuel-burning appliances inspected by a qualified technician at least once a year. A qualified technician should have practical knowledge of the operation, installation and proper ventilation of fossil-fuel-burning devices; carry the applicable insurance; be bonded; and be licensed to perform heating, ventilation and air conditioning (HVAC) work in your area.

Be alert to these danger signs that indicate a potential CO problem:

• Streaks of carbon or soot around the service door of your fuel-burning appliances
• The absence of a draft in your chimney (indicating blockage)
• Excessive rusting on flue pipes or appliance jackets
• Moisture collecting on windows and walls of furnace rooms
• Fallen soot from the fireplace
• Small amounts of water leaking from the base of the chimney, vent or flue pipe
• Damaged or discolored bricks atop the chimney
• Rust on the portion of the vent pipe visible from outside your home

Also, recognize that CO poisoning may be the cause when family members suffer from flu-like symptoms that do not disappear but improve when they leave home for extended periods of time.

The most important steps are preventive. Have a qualified service professional inspect your fuel-burning appliances at least once a year. Install UL Listed CO alarms outside of sleeping areas and near all fuel-burning appliances.

Other precautions include:

• Avoid using charcoal grills inside a home, tent, camper, or in an unventilated garage.
• Do not allow vehicle exhaust fumes to enter the home.
• Make sure all fuel-burning appliances are properly ventilated.

Rather than looking for specific features, look for the UL Mark with the adjacent phrase "Single Station Carbon Monoxide Alarm."

UL Listed CO alarms are designed to detect elevated levels of CO and sound an alarm to alert you and your family of a potential poisoning risk. Although CO indicator cards and other devices on the market are also intended to detect elevated levels of CO, most are not designed with an audible alarm. The presence of an audible alarm is significant especially while you and your loved ones are asleep.

UL Listed CO alarms are required to have a manually operated alarm reset/silence button that will allow you to silence the alarm signal. If elevated levels of CO continue to exist, the alarm will sound again in six minutes.

UL evaluates and Lists CO alarms intended for use in recreational vehicles (RVs) and areas such as garages or attics where dampness, humidity and temperatures aren't as controlled as in the living space of the home. CO alarms used in these areas comply with additional requirements designed to address the special conditions often present in these environments.

UL also evaluates CO travel alarms. These devices are equipped with a mounting bracket for temporary mounting only.

UL Listed CO alarms intended for use in these environments are marked accordingly near the UL Listing Mark.

Although they may look and sound similar, CO alarms and smoke alarms are designed and intended to detect two distinct hazards. Therefore, to help protect your family from both hazards, it is important to install both UL Listed CO alarms and UL Listed smoke detectors.

Follow the installation instructions found in the manufacturer's use and care booklet that accompanies the product. Proper installation is an important factor in receiving optimal performance. It is important to follow these instructions step by step in their entirety.

CO alarms need to be tested regularly and cleaned as indicated in the manufacturer's use and care booklet. If the unit operates off a battery, test the detector weekly and replace the battery at least once a year.

Read the manufacturer's use and care booklet for installation and maintenance guidelines. Keep these instructions on file for future reference.

If your unit operates off a battery, do not remove it for any length of time unless to change it. Like any appliance or power tool, a CO alarm cannot work unless it has a functioning power source.

When UL evaluates samples of residential CO alarms, consideration is made that your home may contain moderate levels of cleaning chemicals and other substances. UL 2034, the Standard for Safety of Single and Multiple Station Carbon Monoxide Alarms, UL engineers and technicians use to test residential carbon monoxide alarms, includes exposure tests to normal concentrations of methane, butane, heptane, ethyl acetate (nail polish remover), isopropyl alcohol (rubbing alcohol), carbon dioxide and propane; all of these are gases typically found in a home.

You should, however, keep these chemicals away from your CO alarms. Low exposure over an extended period of time could damage the sensing device and cause it to sound a false alarm.

Immediately operate the reset/silence button and call emergency services (fire department or 911).

Move outside or open a window to allow fresh air to enter. Check to make sure that everyone in your household is present. Do not re-enter the premises nor move away from the open door or window until the emergency services have arrived, the premises have been sufficiently ventilated, and your CO alarm remains in its normal condition.

If your CO alarm reactivates within a 24-hour period, operate the reset button, call your emergency services and move to fresh air. Call a qualified technician to examine and/or turn off your fuel-burning appliances or other sources of combustion. If your RV, car or truck is idling in an attached garage, turn off the engine. Although the problem may appear to be temporarily solved, it's crucial that the source of CO is determined and appropriate repairs are made.

Remember that an alarm indicates elevated levels of CO in your home. CO is called the "silent killer" because it cannot be seen or smelled. Some people can be exposed to dangerous levels of CO and not feel any symptoms. Regardless of whether you feel symptoms, never ignore the sounding of a CO alarm.