Carbon Monoxide After a Power Cut: The Symptoms Look Like Heat Illness

If a carbon monoxide alarm sounds, or several people in a building feel ill at the same time, get everybody outside into fresh air and call 911 from outside. Do not go back in to check anything.

The CDC lists the symptoms of carbon monoxide poisoning as “headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion.”

Now read the CDC’s list of what happens when the body gets too hot: muscle cramping, heavy sweating, shortness of breath, dizziness, headache, weakness, and nausea.

Those are nearly the same list. And in Arizona the two situations arrive together — the power goes out in a monsoon storm in August, the house heats up, somebody starts a generator, and every symptom that follows has two possible explanations and one of them is odourless.

First, the number that prevents all of it

The CDC’s instruction is specific, and it is further than almost anybody puts a generator:

“Never use a generator, pressure washer, or any gasoline-powered engine inside your home, basement, or garage or less than 20 feet from any window, door, or vent.”

Twenty feet, and from any window, door or vent — not twenty feet from the wall. A generator just outside the back door, in an open garage, under a carport, on a covered patio, or in the lee of the house out of the rain is inside the distance that matters.

The rain is the reason people get this wrong. A generator started during a storm gets put somewhere sheltered, and sheltered is another word for enclosed.

Why you cannot rely on noticing

CDC describes CO as “an odorless, colorless gas that can cause sudden illness and death if inhaled”, and elsewhere as a gas that “kills without warning.”

And then the sentence that should decide how seriously anybody takes the twenty feet:

“People who are sleeping, drunk, or under the influence of other substances can die from CO poisoning before they have symptoms.”

Before they have symptoms. So the plan of “we would notice and get out” does not work for the people most at risk, and the hours when a generator runs all night are exactly the hours everybody in the house is asleep.

This is why the detector is not optional, and CDC says where to put it: “Install battery-operated or battery back-up CO detectors near every sleeping area in your home.”

Battery or battery back-up, which matters more here than it sounds — a mains-only detector is asleep during the power cut that created the hazard.

How common is it

CDC: more than 400 Americans die each year from unintentional CO poisoning not linked to fires, and more than 100,000 visit an emergency department.

Hold both of those numbers together. The deaths are rare enough that most people never meet one. The emergency department visits are common enough that this is an ordinary presentation rather than an exotic one — which is the case for a detector rather than against it.

Telling it apart from heat illness, and the honest answer

You mostly cannot, from symptoms. That is the point of this page, and pretending otherwise would be worse than saying it.

What does distinguish them is not how anybody feels. It is circumstance:

Is anything burning fuel? A generator, a charcoal grill, a gas range used for heat, a car running in a garage, a camping lantern or stove indoors. CDC names all of these as CO sources.

Is more than one person affected? A gas fills a space, so it reaches everybody in the space. Two people with a headache at the same time in the same room is a different event from one person with a headache — and heat illness does not usually arrive simultaneously in a group that is sitting still indoors.

Are the pets unwell too? Same reasoning, and animals are often affected first.

Did it improve when somebody went outside? That is information worth telling the dispatcher.

What to do

If an alarm sounds, or you suspect CO: everybody outside, into fresh air, now. Do not stop to open windows, turn things off, or find the source. Call 911 from outside, and do not go back in.

We want that done before anybody is certain, because certainty in this situation arrives too late to be useful. That is our instruction rather than a quotation, and it is the whole of what we would ask of anybody in a house with a running generator and a headache.

Call 911 for anybody who is confused, drowsy, unresponsive, having chest pain, seizing, or who cannot be roused. And for anybody who was asleep in the building, regardless of how they seem once they are outside.

Come to an emergency room for headache, dizziness, nausea or weakness where a combustion source was running — even if it has settled in the fresh air. CO poisoning is measurable with a blood test, and an emergency department is where that happens, which is the reason to come in rather than to wait and see how the evening goes.

Our emergency rooms are open every hour of every day and are walk-in, with a full laboratory in the building. Go to the nearest one, and if another emergency department is closer, that one is the right answer tonight.

If you are unsure which of the two this is, treat it as an emergency — that is the correct response to both of them.

Questions people actually ask

The generator is outside, so we are fine? Outside is not the test. Twenty feet from any window, door or vent is the test, and a generator under a carport or just beyond the back door usually is not.

Can I run it in the garage with the door open? No. CDC names the garage explicitly, and an open door does not make a garage outdoors.

We have no detector and the shops are shut. Then the twenty feet matters more, nobody sleeps in a room near where it is running, and if anybody develops a headache the generator goes off and everybody goes outside. Get a detector with battery back-up before the next storm.

It is 110 degrees and the power is out. What are we supposed to do? Get cool somewhere else — that has its own page, and a few hours of air conditioning somewhere public genuinely helps. Do not solve a heat problem with a combustion problem.

Everybody has a headache and the generator has been running since last night. Outside, now, all of you, and call 911 from outside. Do not wait to see whether it passes.

Could it be heat rather than carbon monoxide? It could be either, and both are emergencies. Get out of the building and into fresh air, which is right for both, and call.

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Twenty feet from any window, door or vent, a detector with battery back-up near every sleeping area, and everybody outside before anybody is sure. Both of our emergency rooms are open 24 hours a day, every day of the year — walk in, no appointment and no referral. Find your nearest emergency room →

Related reading: heat exhaustion or heat stroke · where to cool down when the house will not

Sources

13. About Heat and Your Health — Centers for Disease Control and Prevention. https://www.cdc.gov/heat-health/about/index.html
36. What to Do to Protect Yourself During a Power Outage — Centers for Disease Control and Prevention. https://www.cdc.gov/natural-disasters/response/what-to-do-protect-yourself-during-a-power-outage.html
37. About Carbon Monoxide Poisoning — Centers for Disease Control and Prevention. https://www.cdc.gov/carbon-monoxide/about/index.html

This article is general information, not a diagnosis. If you are unsure, come in — this list is not exhaustive and you are not expected to tell carbon monoxide from heat illness yourself. If it might be an emergency, treat it as one and call 911.