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Carbon monoxide: symptoms and what to do

Emergency numbers differ by country. This page uses 911, the number for the United States and Canada. Many other countries use 112, 999, or another number. Find the number for your country.

Carbon monoxide (CO) is a gas you cannot see, smell, or taste. It can make people sick or kill them quickly. This page helps you spot the signs, act fast, and stop it from happening.

Do this now

  1. If an alarm sounds or you feel sick, get everyone outside to fresh air right away. Include pets.
  2. Call your local emergency number (911 in the United States and Canada, 112 across the European Union, 999 in the United Kingdom) from outside.
  3. Do not go back in until emergency services say it is safe.
  4. Stay outside and count everyone. Tell responders if anyone is missing.
  5. Get medical care for anyone with symptoms, even if they feel better outside.

Symptoms

Carbon monoxide poisoning can feel like the flu, but without a fever. Symptoms often come on gradually.

  • Headache
  • Dizziness or weakness
  • Nausea or vomiting
  • Chest pain or confusion
  • Shortness of breath

People who are asleep or have been drinking can be overcome without noticing any symptoms. If several people in the home feel sick at the same time, or feel better when they leave and worse when they return, suspect carbon monoxide.

... danger "Do not wait for symptoms to get worse" If an alarm sounds, treat it as real. Get out first, then call for help. Never assume it is a false alarm.

When the alarm goes off

A CO alarm is different from a smoke alarm. If yours sounds, do not open windows to try to fix the problem and do not stay to look for the cause. Open the door on your way out and leave.

Wait for emergency services or the gas utility to arrive. They will measure the air and find the source. Do not re-enter until they tell you it is safe.

Where it comes from

Carbon monoxide comes from burning fuel without enough air. Common sources include:

  • Portable generators
  • Charcoal and gas grills
  • Gas stoves and ovens used for heat
  • Furnaces, boilers, and water heaters that are faulty or blocked
  • Fireplaces and wood stoves with a blocked chimney
  • Cars and motorbikes running in a garage, even with the door open
  • Camp stoves and heaters used in tents or enclosed spaces

Generators and grills

Run a generator outdoors only, well away from doors, windows, and vents, with the exhaust pointed away from the building. The US Consumer Product Safety Commission advises at least 6 meters (20 feet) from the house. Never run one in a garage, basement, or shed.

Never use a charcoal or gas grill indoors or in a garage, and never burn charcoal inside a tent. Never heat a home with a gas oven.

Cars in garages

Never start a car in a closed or attached garage, and do not leave it running with the door open either. Fumes can seep into the home. Back the car out right away, and keep it outdoors while it warms up.

If you are stuck in snow, clear the exhaust pipe before you run the engine for heat, so fumes cannot back up into the car.

Prevent carbon monoxide poisoning

Prevention is simple and low cost. Do these things before you need them.

  • Install CO alarms on every level of your home and outside sleeping areas.
  • Test alarms monthly and replace them as the maker advises.
  • Have fuel burning appliances, chimneys, and vents checked by a qualified technician every year.
  • Keep vents and chimneys clear of snow, leaves, and nests.
  • Use only appliances made for indoor use, and follow the instructions.
  • Keep a battery or wind up flashlight and radio so you do not need candles or fuel heaters in an outage.

Rules for CO alarms vary by country and by region, and some places require them by law. Check with your local fire service or housing authority.

After exposure

Even a person who feels fine after fresh air may need care, because the gas can linger in the blood. Medical staff can test for it and give treatment such as oxygen.

Do not drive yourself if you feel unwell. Let responders take you, or have someone else drive.

... tip "Pregnant people, babies, and older adults" Children, older adults, pregnant people, and people with heart or lung conditions are more at risk. Tell medical staff if anyone in this group was exposed.

After a power outage or storm

Carbon monoxide poisoning rises after storms and outages, when people use generators and grills indoors. See power outage at home for safe ways to keep warm and cool. For storm specific advice, see hurricane.guide.