Symptoms
- Get everyone into fresh air, including pets.
- Call 911 from outside.
- Tell the medical team you suspect carbon monoxide, so they test for it.
| Severity | Common signs |
|---|---|
| Mild | Headache (the most common sign), dizziness, nausea, tiredness, shortness of breath on effort. |
| Moderate | Confusion, blurred vision, vomiting, chest pain, fast heartbeat, clumsiness. |
| Severe | Collapse, seizures, loss of consciousness, heart damage and death. |
Clues that point to carbon monoxide: several people or pets in the same place feel ill at once; symptoms improve when you are away and return when you come back; they are worse in the morning or when the heating is on.
Delayed and long-term effects
Some people seem to recover, then develop problems days or weeks later: memory loss, poor concentration, personality and mood changes, movement problems or depression. Doctors call these delayed neurological sequelae. Long-term, low-level exposure can also cause lasting headaches, fatigue and cognitive problems.
Feeling better is not the same as being well. Follow-up care matters.
How it is tested
The key test is a blood carboxyhemoglobin (COHb) level, taken from a vein or with a CO-oximeter. Timing is everything: COHb falls quickly once a person breathes fresh air or oxygen, so a normal result hours later does not rule out poisoning. A standard fingertip pulse oximeter cannot tell carbon monoxide from oxygen and may read normal even in serious poisoning.
- Non-smokers usually have a COHb below about 3%.
- Smokers commonly have higher background levels, up to around 10%.
- Readings must be interpreted alongside symptoms and the time since exposure.
How it is treated
The first treatment is high-flow 100% oxygen, which clears carbon monoxide from the blood much faster than ordinary air. In serious cases, including loss of consciousness, pregnancy, or neurological or heart symptoms, doctors may consider hyperbaric oxygen therapy in a pressurized chamber.
What CO levels mean
| Level | Reference |
|---|---|
| 9 ppm | US EPA outdoor air standard, 8-hour average. |
| 35 ppm | US EPA outdoor air standard, 1-hour average. |
| 50 ppm | OSHA workplace limit, 8-hour average. |
| 70 ppm | UL 2034 alarms must sound within 60–240 minutes. |
| 150 ppm | UL 2034 alarms must sound within 10–50 minutes. |
| 400 ppm | UL 2034 alarms must sound within 4–15 minutes. |
Sources: US EPA National Ambient Air Quality Standards; OSHA; UL 2034. Medical content to be reviewed by a physician before launch.