Carbon Monoxide Alarms

By Frank C. Montagna

Here are some facts, operational procedures, and tips that you should know about carbon monoxide (CO) and responding to CO alarms.

  1. CO is absorbed via the lungs into the bloodstream, forming carboxyhemoglobin (COHb), which takes up space that should be filled by oxygen and prevents O2 present in the blood from being released to the cells. This dual effect results in tissue hypoxia, or oxygen starvation.
    • Symptoms can vary for similarly exposed people.
    • Small children have smaller body sizes and faster metabolism. The elderly often have preexisting medical problems. Both are more adversely affected by CO poisoning than normal, healthy adults are.
    • When a pregnant woman is exposed to CO, her unborn child will be more severely affected than will the mother. The fetus’ COHb level will continue to rise after the mother is removed to fresh air, reaching a COHb level higher than that reached by the mother.
  2. CO poisoning often is misdiagnosed because it manifests itself in many different ways.
    • Mild exposure (20 to 30 percent COHb in blood) mimics the flu or food poisoning.
    • Medium exposure (30 to 50 percent COHb in blood) causes drowsiness, confusion, loss of motor control, and slurred speech. Victims are mistaken for substance abusers.
    • Severe exposure (50 to 70 percent COHb in blood) quickly results in unconsciousness and death.
  3. A poorly maintained carbon-based fuel-burning appliance gives off excess CO; cold appliances give off more CO than when warmed up.
    • An improperly vented appliance will spill CO into the home.
    • A home should be operating at neutral pressure. However, if the home is tightly sealed, and if air is pulled or pushed out of it, a condition of negative pressure can be created within. This can occur if a strong wind blows over an unused chimney, creating a venturi effect and pulling air from the home. Flue gases are pulled down into the home through an active chimney, resulting in elevated CO levels.
  4. Find out why the CO alarm is sounding.
  5. Some older alarms had warning alarms, full alarms, low battery alarms, trouble alarms, and defective sensor alarms.
  6. Start taking readings at the entrance door.
    • You can’t investigate a CO alarm incident without a meter.
  7. If you can’t find the source of CO, consider that it may be coming from outside of the home or apartment or it might have cycled off.
    • Check the adjoining exposures and the apartments on top of and below where the CO alarm is sounding.
    • Was a car or truck parked near an open window or fresh air intake? Its exhaust might have caused the alarm to sound. If the vehicle subsequently left the scene, you will never find out what caused the alarm to sound.
    • A car, warming up in the garage can trigger the alarm. When it leaves, you will be left with a sounding alarm and no obvious source.
    • Ask questions about what was going on in the home before the alarm sounded.
  8. Of ten we respond to CO alarms and find no CO present in the home. All to frequently, this is written off as a defective alarm. This does not mean that there was no CO when the alarm sounded.
    • Some of the early CO alarms sounded for very low levels.
    • Consider that an intermittent source may have cause the alarm to sound and, by the time the fire department arrives, natural ventilation or the occupant’s venting might have cleared the home of CO.
  9. Don’t take CO alarm calls lightly.
    • Assume CO was the reason that the alarm sounded, and conduct a thorough investigation to find the source.
    • If you find CO present in dangerous amounts but can’t find the source, shut all sources of CO and ventilate the building.
    • If anyone is exhibiting symptoms, seek medical assistance.
The bottom line is, when you leave the scene, leave the occupants safe.

Frank C. Montagna, a 32-year veteran of the fire service, has been a battalion chief with FDNY for 15 years. He was an instructor at the FDNY Probationary Firefighters School, the officer in command of the FDNY Chauffeur Training School, and an adjunct lecturer at John Jay College in New York City. He is a member of the FDNY Chief’s Association and the author of Responding to Routine Emergencies (Fire Engineering, 1999) as well as a contributing editor to Fire Engineering magazine. Montagna has a bachelor’s degree in fire science and lectures on firefighting-related topics. You can view excerpts from his book at

No posts to display