Suburban Firefighting: Carbon Monoxide Alarms

By Jerry Knapp
Carbon monoxide (CO) alarms are often our most misunderstood call. If you understand a few simple facts about CO, it makes your job much easier and more effective. There are really only three scenarios for us to operate in:
Most common: The occupants meet you at the door saying their CO detector went off. They may or may not have mild symptomsthe dog is running around in the house and the kids are excited to see the fire trucks. There may be low levels of CO in the house.
Most dangerous: The occupants are unconscious or wake up dead. This is an obvious rescue/recovery situation and an immediately dangerous to life and health (IDLH) environment for firefighters. Mask up and follow your procedures. Don’t forgetCO is flammable at 12.5-74 percent in air. This represents a level of 125,000-740,000 parts per million (ppm), which is really high, probably higher than your meter will read. There are high levels of CO in the house.
Most aggravating: The occupants say their detector went off. You look at it and it is flashing “B” for battery…dead battery. There are no levels of CO in the house.
Where does CO come from? The burning of most materials produces CO. Especially common sources are incomplete combustion or improperly vented boilers or hot water heaters; an improperly functioning stove; a car running in the garage; a charcoal grill near an open door or window (I’ve seen folks bring these into the kitchen due to bad weather); testing the snow blower in the basement or attached garage; a clothes dryer; space heater; and so forth.
Is CO lighter or heavier than air? It is about the same as air but it will get pushed around by air currents in the residence. The National Institute for Occupational Safety and Health (NIOSH) Pocket Guide to Chemical Hazards states CO is 0.97 percent as dense as air, making it very close to normal air but a slight bit lighter.
How dangerous is CO? It will obviously kill at high concentrations. If the occupant has been in the house for some time and just walked out of the house and does not have any symptoms, it is likely the CO concentration is low.
What does CO do when a person breathes it into their lungs? It rapidly binds with red blood cells and interferes with the ability of the blood to carry oxygen to all the cells in your body. Red blood cells and CO form carboxyhemoglobin in the blood, which is very stable and continues to inhibit oxygen perfusion in the victim. A reduced oxygen level causes headaches, nausea, vomiting, dizziness, fatigue, and ultimately unconsciousness and death.
The first step is to check the occupants for symptoms. If symptoms are present, evacuate them to fresh air. Emergency medical services (EMS) should provide oxygen and supportive care and evaluation if symptoms are present. If equipped to do so, determine the level of CO and oxygen in their blood to decide if transport is required.
The other concurrent first step is to question the occupants on details of the CO alarm. Below are some typical questions that will help you determine which mode you are in (most dangerous, most common, most aggravating).
Why did you call the fire department? This is a very broad question, but depending how it is answered, it often sets the stage for your actions. If the occupant says, “My detector was going off and I did not understand what it meant,” check the device; you maybe in the most aggravating mode. If he says, “The detector has been going off for a few hours and I have a headache,” you maybe in the most common mode.
Is anyone sick in the house? If so, what are their symptoms? How long have these people been in the house (and exposed to the CO)?  If they just entered the house five minutes ago after a day of ice fishing and now they are nauseous, two thoughts come to mind: The CO concentration in the house is really high (your meter should tell you this quickly), or they are sick from something else not CO-related. You need to sort this out through further questioning.
If there are symptoms present, continue your line of questioning. How long have they been in the house? Has the CO detector gone off before and for how long? Does the detector have a digital readout? What was that reading? If the detector is reading anything above background levels (9 ppm or greater) and they have headaches, it is likely they have a CO concentration in the house. Have you recently had any problems or repairs to your boiler, furnace, hot water heater, clothes dryer, etc.? These questions will help you find the potential source of the CO if it is present. 
What were you doing when the alarm went off? This is a great question so be prepared for some really stupid answers. Here is what I have heard:
“I was warming up the car in the garage.”
“I just sprayed room deodorizer on the detector.”
“I have been cooking all day and I think I burned a plastic container in the oven.

The black smoke coming out of the oven was probably a really good clue, along with the blob of the plastic remains hanging from the oven racks. This question, coupled with your evaluation of their lack of symptoms, usually puts the call to bed.

But always follow up with, “Did you open the windows and doors or turn on the attic fan to vent it out?”

Air monitoring is certainly required, but hold off if you can until you ask the important questions and others listed above. If there was CO in the house and occupants opened the windows, you may not find any. If they tell you they were having trouble with the boiler, you may want to send a crew to examine it. Often it will show signs of poor maintenance and performance, such as soot all over the vent stack or other signs.
It’s time to take your air monitoring instrument inside the home. But before you do, consider the following:
  • When was the instrument last calibrated? You are dealing with potentially lethal gas here, would be really nice if your instrument was in top-working order! Read the manufacturer’s directions that come with it. It will tell you how to properly maintain your particular instrument to ensure accurate readings.
  • Did you fresh-air calibrate it or were you standing near the exhaust pipe of the rig?
  • Move slowly through the house, giving the instrument time to detect the gas and provide you a reading or alarm. If you walk quickly through the area you are monitoring and the alarm sounds, was it sensing a high concentration when you walked in and just alarmed when you reached the second room, or was there something else?
What do the numbers on the monitor mean? There are no national standards for actions at different levels. According to an article in WNYF Magazine by Lieutenant Christopher Flatley (third issue, 2009), “Readings less than 9 ppm, evacuation is not required unless symptoms are present. Readings more than 9 ppm and symptoms present, recommend evacuation. Readings 100 ppm or more or symptoms present, mandatory evacuation.”
Generally, readings of 1-9 ppm are considered background levels. The Occupational Health and Safety Administration (OSHA) allows workers to remain for eight hours with 35 ppm in the workplace. But remember, this is for healthy workers; the very old, very young, sick, or infirm may be more susceptible.
With readings between 9 and 100 ppm, you need to do your detective work and make decisions based on symptoms and specific conditions at the scene. Although the numbers from experts vary, the following CO levels provide a relative value of risk.
  • 35 ppm is the time weighted average for workers
  • 200 ppm results in a headache if exposed for two to three hours
  • 400 ppm results in a headache if exposed for one to two hours
  • 1,500 ppm is an IDLH environment
  • 2,000 ppm causes death or irreversible damage in one hour
  • 3,200 ppm causes headache and dizziness in five to 10 minutes
Understanding these numbers will be helpful on the scene. But remember, the primary considerations that drive your decision making are the symptoms of the occupants and the safety of your members.
Your success and safety at the scene will be determined by how well you can assess and draw assumptions from the following: Symptoms (if any), the occupant’s answers to your questions, the occupancy’s meter reading, and your air monitoring results.
We know from experience that response to CO alarms is one part experience, one part art, and one part science. A lot of good detective work will really help out before you go dashing in with your meter.
Your standard operating guidelines (SOGs) will determine if you always call the utility company and whether you try to determine the source or simply always evacuate everyone on every call. 

This article not a complete summary of the hazards of CO, but rather an operational reminder and refresher for you of some important points. Always follow your SOGs and safety procedures for your department.


JERRY KNAPP is the assistant chief for the Rockland County (NY) Hazmat Team and a training officer at the Rockland County Fire Training Center in Pomona, New York. He is a 35-year veteran firefighter/EMT with the West Haverstraw (NY) Fire Department, has a degree in fire protection, and was a nationally registered paramedic. Knapp is the plans officer for the Directorate of Emergency Services at the United States Military Academy in West Point, New York.

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