How to Respond When a CO Alarm Sounds and You Are Not the Heating Tech

Why this matters

Painters, cleaners, plumbers, flooring crews and handymen spend whole days inside other people's houses in heating season, often alone, often with the homeowner at work. When a carbon monoxide (CO) alarm goes off, the person standing under it is usually not the one who knows anything about furnaces, and the two instincts that kick in are both wrong: press the button to make it stop and keep working, or start hunting for the cause. CO has no smell, its early symptoms feel like a cold or a long day breathing paint, and it impairs the judgment you need to decide what to do about it. The right response for anyone who is not a combustion tech is short, fixed, and the same every time.

The exposure science, meter use and the heating-side response are owned by another card: see related, Carbon Monoxide Testing + Response Reference. This card is for the person who has none of that equipment.

Read the alarm in two seconds

Before anything else, know what you are hearing, because the next step depends on it.

• Four beeps, a pause, four beeps is the standard CO alarm pattern. That is an alarm. Go to step 1.
• Three beeps, a pause, three beeps is the standard smoke pattern. Treat it as a possible fire: everyone out, 911 from outside.
• A single chirp, repeating about once a minute is a low battery or an end-of-life signal, not an alarm, and it is a different card: see related, The CO Alarm End-of-Life Signal and How Long a Sensor Lasts.
• A combination smoke and CO unit with a voice or a display usually tells you which it is. Believe it.

If you cannot tell which pattern it is, treat it as an alarm. Guessing low is the expensive mistake.

Why the alarm is not exaggerating

Residential CO alarms listed to UL 2034 are deliberately built to stay quiet at low levels and sound only after an exposure has built up. In substance, the standard requires the alarm to sound within 60 to 240 minutes at 70 ppm, within 10 to 50 minutes at 150 ppm, and within 4 to 15 minutes at 400 ppm; check the current edition. Two things follow for a tech standing under one:

• By the time it sounds, you have already been breathing it. The alarm is answering accumulated exposure, so a sounding alarm and a headache that started an hour ago are the same event, not two coincidences.
• It is not a hair-trigger device. Unlike a smoke alarm in a steamy hallway, a CO alarm has few everyday nuisance causes. Treating it as a nuisance is how people get hurt.

The steps

1. Get everyone out now, including yourself, and do not stop to fix anything. Tell everyone in the house to leave: your crew, the homeowner if present, children, anyone asleep upstairs. Carry or lead people who cannot move fast. Do not stop to open windows, look at the furnace, gather tools or finish a cut; the minutes you spend inside are the exposure you are trying to end, and a house left as found helps the responders find the source. A pet that comes when called comes with you; one that hides is reported to the firefighters, not searched for.

2. Do not silence it and stay. Pressing the button on a sounding CO alarm may quiet it for a few minutes, and the CO is still there. A quiet alarm in a room that still holds CO is worse than a loud one, because it removes the only warning. If you hit the button while heading for the door by reflex, keep heading for the door.

3. Call 911 from outside, in fresh air. Not from the hallway, not from the garage with the door shut, not from inside the van parked against an open garage. Tell the dispatcher, in this order: a CO alarm is sounding; the address; how many people were inside and that they are out; anyone with symptoms (headache, dizziness, nausea, confusion, unusual tiredness) and how long they have had them; anyone or any animal still inside; and any fuel-burning appliance or engine you know is running. The fire department meters the house and, in many areas, the gas utility also responds to CO calls; the dispatcher sends whoever your area sends.

4. If your own engine-driven equipment is running, say so first. A gasoline pressure washer near an open garage door, a propane floor buffer, a portable generator, a gas-powered concrete saw: these are among the most common CO sources a field crew creates, and they are yours. If the kill switch is on your direct path out, stop the engine as you pass. Do not go back in for it. Tell the dispatcher it may be the source. See related, Carbon Monoxide From Your Own Tools.

5. Get anyone with symptoms looked at. CO poisoning is treated by getting the person onto clean air or oxygen, and it is assessed by a measurement, not by how the person feels. The responding crew can usually check, and a person who had symptoms should be seen even if they feel better outside. Headache is the most common early sign and the easiest to dismiss on a painting job.

6. Call the homeowner from outside, after 911. Tell them what sounded, that everyone is out, that the fire department is on the way, and that you will not re-enter until the fire department says the house is safe. Do not speculate about the cause on the phone.

7. Do not go back in, reset it, or resume work until the fire department releases the house. The responders measure, ventilate and look for the source. They may shut off an appliance or the gas to it and leave a notice that it must not be used until a qualified heating contractor checks it. Their release lets people back inside; it does not mean the appliance is fixed. Your work resumes when the house has been released and the source has been shut off or found to be absent. Before it does, check the CO alarm that sounded: it is back on its base or plugged in, not left hushed, and it sounds on its test button. If responders took it down or it shows a fault, the house has no CO alarm there, and the homeowner is told that in writing before anyone sleeps in it. If you cannot heat the house to work in it, or the job depends on that appliance, that is a schedule conversation with the customer, not a reason to restart it.

8. Leave the diagnosis to the fire service and a combustion tech, and write down what you saw. You are a witness, not the investigator. Write down the time the alarm sounded, which alarm, where everyone was, who had symptoms, any equipment of yours that was running, what appliances you noticed operating, and what the responders said and did. That record is useful to the heating contractor who comes next, and it is the shop's account of the day.

Worked example: the painter and the second-floor alarm

A two-person painting crew is working in a two-story house in January. The homeowner left for work at 8:00 and the furnace is running. Around 10:30 the lead painter notices a headache and puts it down to the primer. At 11:20 the combination smoke and CO alarm in the upstairs hallway starts sounding four beeps and a pause. The helper is in the back bedroom with a roller; the homeowner's cat is somewhere in the house.

What the lead does:

• 11:20. Recognizes four beeps, shouts to the helper to drop the roller and come out, and goes down the stairs with the helper behind. No window opened, no look at the furnace, no reflex press of the button. The cat does not appear.
• 11:21. On the front lawn, calls 911: "Carbon monoxide alarm sounding at this address. Two of us were inside, both out now. I've had a headache since about ten-thirty. Nobody else is home. There's a cat still inside. The gas furnace is running. We weren't running any engines." The crew's only power tool was a corded electric sprayer, so step 4 does not apply, and saying so plainly saves the responders a question.
• 11:24. Calls the homeowner: what sounded, everyone out, fire department coming, nobody going back in.
• 11:31. The fire department arrives, meters the house, and finds elevated CO, highest near the basement furnace. They shut the furnace off at its gas valve, ventilate, and leave a notice that the furnace is not to be used until a heating contractor inspects it. The cat is found under a bed and carried out. The responding crew checks the lead painter for CO exposure and tells him to get seen if his headache continues.
• 12:15. The fire department releases the house for entry. The furnace stays off.

Does the crew go back to painting at 12:15? The house is released and the source is off, so step 7's two conditions are met. But the house now has no heat in January, the homeowner has to arrange the heating contractor, and the lead's headache has not fully cleared. The lead calls the office, the office calls the homeowner, and the crew packs up for the day rather than working in a cooling house. That is a business decision the release allows; it is not one the release makes for them.

The lead's written record covers the time the alarm sounded, which alarm, the two people and the cat, the headache since 10:30, no engines in use, the furnace running at the time, and the fire department's readings, shutoff and notice as they described them. The office attaches it to the job.

What would change the response

• Your own engine was the likely source. If the crew had been running a gasoline pressure washer on the driveway with the garage door open, the response is the same up to the 911 call, and the record says plainly that it was running, where, and for how long. The shop then has its own practice to fix.
• Someone refuses to leave. An elderly homeowner who will not go is not a reason for you to stay inside with them. Tell them clearly, leave, and tell the dispatcher someone is inside and refusing. Firefighters are equipped to go in; you are not.
• The alarm stops on its own before you are out. Keep going. A CO alarm that falls silent has not confirmed the air is clean; it may have been hushed, lost power, or reached the end of an alarm cycle.
• You are the heating tech after all. Then you work from the combustion card with a meter, and this card does not apply to you.

References

• UL 2034, Standard for Single and Multiple Station Carbon Monoxide Alarms (alarm response times)
• Your local fire department and gas utility guidance on CO calls
• See related: Carbon Monoxide Testing + Response Reference
• See related: Why Every Trade Owes the Life-Safety Devices in a House