Carbon monoxide responses are easy to treat like routine calls. Most of the time, we are dispatched for an alarm activation, a beeping detector, or a vague report of someone “not feeling well.” There is no smoke showing, no visible hazard, and no obvious emergency from the street. That is exactly what makes these calls dangerous. Carbon monoxide is odorless, tasteless, and colorless. It gives us very few warning signs until occupants become symptomatic or our meters tell us something is wrong.

Pre-Response: Set the Incident Up for Success

Dispatchers should instruct occupants to evacuate and leave the building as-is when safe to do so. One common mistake is allowing occupants to open every window and door before the fire department arrives. While their intention is understandable, it can make the investigation more difficult by releasing the accumulated gases before crews can locate the source. If occupants can safely leave without opening windows, shutting off appliances, or changing the environment, that gives firefighters a better chance of identifying the problem.

While responding, crews should begin building their investigation plan. CO is produced by incomplete combustion, so firefighters should start thinking about anything in or around the home that burns fuel or produces exhaust. Furnaces, water heaters, stoves, fireplaces, generators, vehicles, small engines, and blocked vents can all create a hazardous environment. Cold weather, power outages, recently started heating systems, attached garages, and exterior vents covered by snow or debris should immediately be on the radar. CO calls are investigations, and the best investigations start before the crew ever steps through the door.

The meter should also be prepared early. The most important tool on a CO call is the meter, but only if it is used correctly. Meters need time to work. They must pull in air, analyze the sample, and display the reading. Firefighters should turn meters on early, allow them to complete their self-check, and perform a fresh air zero in known clean air before entering the structure. This should not be done inside the building or near apparatus exhaust. 

Arrival and Initial Actions

On arrival, the first priority is occupant assessment. Occupants should be assessed for signs and symptoms of CO exposure, including headache, dizziness, nausea, weakness, confusion, shortness of breath, chest discomfort, or flu-like symptoms. Another red flag would be any symptoms that improve after leaving the structure. If anyone reports symptoms, an ambulance should be added, and SpCO monitoring should be utilized when available.

Crews should pay special attention to children and pets. Kids and pets can experience carbon monoxide symptoms before adults. Because children have faster metabolic rates and smaller bodies, they inhale more air relative to their size, causing oxygen-depleting toxins to build up much faster in their bloodstreams. Pets may also show signs before adults because they are often smaller as well. If the family says the dog was acting strange, the child was unusually tired, or multiple people in the home “just do not feel right,” take that information seriously.

Full PPE and SCBAs should be donned on all CO calls. These calls can change quickly. A false alarm may be a false alarm, but that decision should be based on investigation findings and meter readings. Depending on the department’s SOGs and the initial readings, crews may not need to be breathing air the entire time, but the SCBA should be on their back and ready.

Before entering, crews should confirm the 4-gas meter has been turned on, completed its self-check, and has been fresh air zeroed in a known clean environment. If the meter alarms during entry or investigation, crews should exit, mask up, and return to locate the problem.

Investigation: Meter Slowly and Search Methodically

Metering should be slow and deliberate. A quick walk-through with the meter held out in front of the firefighter is not an investigation. Meters need time to sample the atmosphere, process the information, and display an accurate reading. Crews should pause approximately 30 seconds in each area before moving on. If firefighters move too quickly, they can essentially outrun the meter and miss the hazard, only to later claim the building is clear.

Because carbon monoxide has a specific gravity very close to air, it mixes easily throughout the structure. It does not always rise or settle in a predictable way. Crews should check the entire building, not just the room where the detector was sounding. This includes all levels, attached garages, mechanical spaces, and possible exposure areas. While metering, remember one simple rule of thumb: once inside the structure, do not press buttons on the meter.

If crews arrive and windows are already open, they should consider that the readings may no longer reflect the original hazard. If the meter does not immediately show dangerous levels, closing windows and doors during the investigation may help recreate conditions and locate the source. This must be done with judgment. If the meter immediately shows a hazardous atmosphere, exit, mask up, and operate accordingly.

When investigating, start with the likely sources. The basement is a priority because it often contains mechanical equipment. Check the furnace, water heater, boiler, fireplaces, stoves, dryers, and any other fuel-burning appliances. Check attached garages for vehicles, generators, or small engines. Monitor near the ceiling, mid-level, and near the floor. Even though CO mixes with air, checking different levels helps ensure a more complete investigation and may reveal other hazards.

Crews should also inspect the home’s CO detector for age, dust, battery condition, and proper function. A bad detector does not automatically mean there is no problem, but it is part of the investigation. The detector is the reason we were called, and it should be evaluated just like any other piece of evidence on scene.

Do not forget the exterior. In a three-firefighter company, this is a good assignment for the engineer. Blocked or restricted exhaust vents are a common cause of CO issues, especially during snow events or cold weather. Walk the perimeter of the structure. Look for snow-covered vents, blocked appliance exhausts, damaged vent pipes, or items stored against the home that may interfere with ventilation. A fuel-burning appliance may be operating correctly but still create a CO problem if the exhaust is being pushed back into the home.

Remember to investigate exposures as well. In apartments, townhomes, and other attached occupancies, this means checking adjoining units — not just to the left and right, but also above and below. CO can travel through shared walls, utility chases, HVAC systems, attic spaces, basements, and other common voids. Expand the investigation until the affected area is identified, the entire exposure concern has been addressed, or meter readings confirm there are no signs of CO in the adjoining spaces.

If a Source Is Found

If CO is detected, the crew should attempt to identify and secure the source. If the source is an appliance, it should be shut down or isolated if possible. This may include shutting off a furnace, water heater, stove, fireplace, generator, or vehicle. If the source involves a generator or vehicle, make sure it is moved or shut down in a way that prevents continued exposure.

The utility provider should be contacted when appropriate, especially when CO is detected and the source involves gas appliances or cannot be confidently identified. The fire department should attempt to remain on scene until the utility company arrives when applicable. The officer in charge and the utility representative should determine when the structure is safe to occupy.

Ventilation is required when readings are elevated. A practical action level is anything above 9 ppm. Natural ventilation is preferred when possible. Open windows and doors to allow the structure to clear. If fans are needed, use battery-powered or electric fans. Do not use gas-powered positive pressure fans for CO ventilation because they can introduce exhaust into the environment you are trying to make safe.

After ventilation, close all openings to the structure and allow the building to sit for a few minutes. Then recheck the structure with the meter. If CO is detected again, crews should consider the possibility of an additional source, an improperly secured source, or an incorrectly identified source. Ventilation without re-monitoring is an incomplete investigation. During the second monitoring, crews should confirm that readings have dropped to the department’s accepted threshold and remain there after ventilation has been completed and the structure has been returned to normal conditions.

If No Source Is Found

If CO is suspected but not detected, crews should not immediately dismiss the call. A zero reading does not always mean there is absolutely no gas present. It means the meter is not detecting CO above its threshold. That distinction matters when speaking with occupants.

When no source is found, firefighters should continue the investigation methodically. Check all levels of the home. Recheck the mechanical room, attached garage, fireplace, stove, and exterior vents. Consider whether the building was ventilated before arrival. Consider whether an appliance was running earlier but has since shut down. Consider whether a vehicle was recently running in the garage. Consider whether a generator had been operating but was moved or turned off before arrival.

If the cause is unclear or the reliability of the detector is questionable, the occupants should be advised to contact a certified technician to evaluate the appliances, detector, and air quality. If there is any doubt, the utility company should be requested or consulted. It is better to slow the call down than to leave occupants in a potentially unsafe environment.

Be accurate with occupants. Do not overpromise. A better explanation is, “Our meters are not detecting hazardous levels at this time,” rather than, “There is nothing in the house.”

Re-Occupancy

Re-occupancy should not be treated casually. Occupants should not return until the cause has been identified and secured, or the alarm has been confirmed false. The structure should be ventilated to below the department’s accepted threshold. All detectors should be reset and functioning properly.

Occupants should be educated about CO hazards, detector maintenance, and the importance of calling 911 again if the alarm reactivates or symptoms return. They should understand that CO is invisible and that symptoms may be vague. They should also understand their responsibility to maintain working CO detectors and have appliances serviced when needed.

If the cause is uncertain, the safest answer is to involve the utility company or a certified technician before normal occupancy resumes. The officer in charge should not feel pressured to declare a building safe when the investigation does not support that decision. We have a responsibility to make a reasonable determination based on our equipment, our findings, our SOGs, and the resources available to us.

Documentation

Documentation is the final piece of a quality CO response. The fire report should clearly describe the actions taken, the meter readings found, the areas checked, the suspected or confirmed source, whether the utility company was contacted, how the structure was ventilated, and what information was provided to the occupants before leaving.

The report should include initial readings, readings during the investigation, readings after ventilation, and the location where those readings were found. If the detector was checked, document its condition. If the utility company was requested, document that. If occupants were advised to contact a certified technician, document that.

Good documentation protects the officer in charge, and the department. It also shows that the call was handled as a real emergency, not a nuisance alarm.

Carbon monoxide calls require discipline. They are not fast calls. They are not “just alarms.” They are investigations into an invisible hazard that can injure or kill occupants and responders. The best practice is simple: slow down, wear your SCBA, use the meter correctly, search for the source, ventilate when needed, confirm the atmosphere is safe, educate the occupants, and document what you did. The danger may be invisible, but our response to it should be deliberate, professional, and thorough.

-       Cole Kleinwolterink is a member of the Waukee Fire Department, Granger Fire Department, and Fire Science instructor at Des Moines Area Community College. Feel free to reach out to him at kleinwolterinkc@gmail.com with any questions, comments or inquiries.