A carbon monoxide (CO) alarm is a time-weighted alarm. The way a time-weighted alarm works is by measuring the buildup of carbon monoxide in a house. For a person to begin feeling the effects of carbon monoxide poisoning, they would need to be exposed to a carbon monoxide level of 50 parts per million (PPM) for eight hours.

An alarm’s response time will vary depending on the level of carbon monoxide in the air. For example, an alarm will sound after three and a half hours of continuous exposure at a level of 50 PPM, but after only eight minutes of continuous exposure at a level of 400 PPM.

Levels of carbon monoxide exposure range from low to dangerous:

  • Low level: 50 PPM and less

  • Mid level: Between 51 PPM and 100 PPM

  • High level: Greater than 101 PPM if no one is experiencing symptoms

  • Dangerous level: Greater than 101 PPM if someone is experiencing symptoms

Carbon Monoxide Levels That Will Set Off Your Alarm

Carbon Monoxide Level    Alarm Response Time
40 PPM 10 hours
50 PPM 8 hours
70 PPM 1 to 4 hours
150 PPM 10 to 50 minutes
400 PPM 4 to 15 minutes

Carbon Monoxide Levels and Their Symptoms

IMPORTANT: If your carbon monoxide alarm sounds, or you suspect you are experiencing symptoms of carbon monoxide poisoning, you should immediately leave your home and call 9-1-1.

50 PPM None for healthy adults. According to the Occupational Safety & Health Administration (OSHA), this is the maximum allowable concentration for continuous exposure for healthy adults in any eight-hour period.
200 PPM Slight headache, fatigue, dizziness, and nausea after two to three hours.
400 PPM Frontal headaches with one to two hours. Life threatening after three hours.
800 PPM Dizziness, nausea, and convulsions within 45 minutes. Unconsciousness within two hours. Death within two to three hours.
1,600 PPM Headache, dizziness and nausea within 20 minutes. Death within one hour.

NOTE: For more information about your specific alarm, refer to your user’s manual.

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