After every major storm that causes extended power outages, the emergency rooms see a second wave: carbon monoxide poisoning. The pattern is consistent across hurricanes, ice storms, and extended blizzards — events that send households scrambling for any source of backup heat or power. The deaths that follow are not accidents. They are the predictable result of a specific misunderstanding about how carbon monoxide works and where it’s safe to run an engine.
This guide covers the hazard clearly so households running generators, camp stoves, or charcoal grills during emergencies don’t become part of that pattern.
What carbon monoxide is and why it’s dangerous
Carbon monoxide (CO) is a colorless, odorless gas produced whenever fuel burns incompletely. Gasoline engines, propane and natural gas appliances, charcoal, and wood fires all produce it. In open air, CO disperses and is harmless at typical concentrations. In enclosed or semi-enclosed spaces, it accumulates to dangerous levels with surprising speed.
The CDC’s carbon monoxide guidance describes CO as “the silent killer” precisely because it’s undetectable by smell or sight. Symptoms — headache, dizziness, weakness, nausea — resemble the flu and may not prompt the response of “get outside immediately” before they progress. At high concentrations, CO causes rapid loss of consciousness and death. It kills by displacing oxygen in the bloodstream: hemoglobin binds CO more tightly than oxygen, leaving cells starved of oxygen even as the lungs continue to move air.
The symptom pattern is particularly deceptive at night. People sleeping in a house with accumulating CO levels may never wake up.
The rule
CDC guidance on portable generators is straightforward:
Never use a generator, pressure washer, conventional space heater, charcoal grill, camp stove, or any gasoline, propane, natural gas, or charcoal-burning device inside your home, garage, basement, carport, or any enclosed or partially enclosed area.
The “partially enclosed” clause matters. A garage with the door fully open still accumulates CO to dangerous levels from a running generator. A covered porch with walls on three sides is a partially enclosed area. An open window near a running generator does not constitute adequate ventilation.
The required clearance is substantial: generators should be operated at least 20 feet from any window, door, or vent, with exhaust directed away from the home. This is not a guideline to approximate — it’s a safety threshold. The Consumer Product Safety Commission has worked with generator manufacturers to add CO shutoff sensors to newer models, but this feature doesn’t replace the outdoor placement rule.
The specific mistakes that cause deaths
Understanding the pattern helps households avoid it:
Running a generator in an attached garage. The most common scenario. Even with the garage door open, CO accumulates in the garage and migrates into the living space through the door between them. The garage is not outside.
Running a generator under a carport, porch, or awning. Overhead cover reflects exhaust back toward the building. This is not safe placement.
Running a generator near an open window or door. The intent is to allow fuel operation “with ventilation,” but typical residential openings provide nothing close to adequate dilution for engine exhaust. CO enters the house.
Using a charcoal grill or gas camp stove indoors for heat. Heating use — not just cooking use — is the context in which this occurs. When indoor temperatures drop below 50°F during an extended outage, the temptation to burn anything available becomes powerful. Charcoal grills produce carbon monoxide even while burning normally; the ventilation requirement for safe indoor use doesn’t exist in a typical home.
Running a generator in the basement or crawl space. These are fully enclosed spaces; CO concentrates almost immediately.
CO alarms: the detection layer
A CO alarm does not make indoor generator operation safe. No concentration of CO alarms makes any combustion source safe indoors. Alarms are the last-resort detection layer when a CO source exists in the building — not a license to bend the operational rules.
That said, every home should have CO alarms. The CPSC recommends at least one CO alarm on every level of the home and one outside sleeping areas. The critical requirement during power outages: alarms must be battery-operated or have battery backup, because a CO alarm that requires grid power to function is useless during exactly the scenario — extended outage — where it’s most needed.
Combination smoke/CO alarms are common and adequate for most homes. Standalone CO alarms can be placed closer to floor level, which matters because CO is approximately the same density as air and distributes throughout a space rather than rising like smoke. Many manufacturers recommend placing CO alarms at waist height or on nightstands in sleeping areas, but follow the manufacturer’s installation instructions for the specific unit.
Test CO alarms monthly and replace batteries annually. CO alarms also have a limited service life — typically five to seven years — after which the electrochemical sensor degrades. The manufacturing date is usually on the back of the unit.
If the CO alarm sounds
Get everyone out of the building immediately — including pets. Do not stop to investigate the source or grab belongings. Call 911 from outside.
Do not re-enter until emergency services have ventilated the building and confirmed it safe. Do not assume the alarm was a false positive and re-enter to check; the alarm sensor is responding to actual CO.
If household members report symptoms consistent with CO exposure — headache, dizziness, nausea, confusion — treat it as CO exposure and get out. Don’t wait for the alarm to sound if people feel sick.
Safe alternatives for heating during an outage
The generator/generator-for-heat scenario can be replaced with safer options:
Portable propane heaters rated for indoor use. Specific products — including the Mr. Heater Buddy-type units that are popular in emergency preparedness — are tested and certified for indoor use in adequately ventilated spaces. “Adequately ventilated” typically means a cracked window in the room. These units have oxygen depletion sensors (ODS) that shut off the heater if oxygen levels drop. Follow manufacturer guidance exactly; they are safer than generators indoors but not unconditionally safe in sealed spaces.
Wood-burning fireplace or stove. A functioning, maintained chimney-vented fireplace or wood stove is a legitimate emergency heat source with no CO indoor accumulation risk if operating correctly. Pellet stoves require electricity for their auger and fan; check whether your model has battery-backup capability before relying on it.
Passive retention. Concentrating household members in a single small room, using sleeping bags rated for the temperature, and hanging blankets over doorways to reduce the volume to be heated can maintain livable temperatures well below what the house thermostat would show. This doesn’t scale to multi-day subfreezing events, but it extends the window before other decisions must be made.
The core principle: any combustion source used for heat during an outage needs either an outdoor or chimney-vented exhaust path. There is no indoor-without-venting version of this that’s safe for sustained use.
FAQ
Can I run a generator in the garage with the door open?
No. An open garage door does not provide adequate ventilation for engine exhaust. CO accumulates in the garage and migrates into the living space through the interior door. Generator operation must be outdoors, at least 20 feet from any opening, with exhaust directed away from the house.
Does CO rise to the ceiling like smoke?
No. Carbon monoxide is approximately the same density as air and distributes throughout a space rather than stratifying. This is one reason sleeping people can be affected without warning signs like smoke near the floor.
How quickly can CO reach dangerous levels from a generator inside or near a building?
At typical generator operating levels, CO concentrations in an enclosed space can reach dangerous levels within minutes. The CDC has documented cases where CO reached potentially lethal concentrations in a home within two to five minutes of generator operation in an attached garage.
My CO alarm beeped once and stopped — should I be concerned?
Persistent, repeating alarm activation means get out. A single beep or chirp may indicate low battery — replace the battery immediately and test the alarm. If the unit is more than five to seven years old, replace it.