Low levels of carbon monoxide will not set off UL listed CO alarms
You read the headline correctly. If you have a low level of carbon monoxide in your home, it’ll never set off your carbon monoxide alarm, and this is by design.
Carbon monoxide (CO) alarms keep people from dying; they don’t eliminate all health risks. Underwriters Laboratory standard UL2034 requires carbon monoxide alarms not to sound off when exposed to carbon monoxide levels under 30 parts per million (ppm). This means you could have a furnace with a CO reading of 25 ppm in the flue gas, and you could place the carbon monoxide alarm right inside the vent, and it would never go off.
Even at higher CO levels, UL-listed CO alarms might take a long time to sound off; long enough for you to start experiencing symptoms of carbon monoxide poisoning. Here are the current standards for key alarm thresholds:
- 70 ppm (parts per million): Must alarm between 60–240 minutes.
- 150 ppm: Must alarm between 10–50 minutes.
- 400 ppm: Must alarm between 4–15 minutes.
Does this mean low levels of carbon monoxide are safe? No. Low levels of carbon monoxide can cause chronic fatigue, palpitations, memory loss, and impaired decision-making (reference). If you have low levels of carbon monoxide in your home, something is wrong and needs to be further inspected.
What to do
For the best protection against low levels of carbon monoxide, buy a low-level carbon monoxide detector. This is a supplement, not a replacement, for the UL-listed CO alarm that is already required. For current CO alarm requirements for Minnesota residents, check out Minnesota requirements for CO Alarms.
