Most carbon monoxide detectors on the market conform to UL2034 specifications. In the USA, these are:
- at 30ppm CO, the alarm must not activate for at least 8 hours
- at 70ppm CO, the alarm must not activate before 60 minutes but must activate before 240 minutes
- at 150ppm CO, the alarm must not activate before 10 minutes but must activate before 50 minutes
- at 400ppm CO, the point where “carbon monoxide can cause death after 2-3 hours” (more on this below), the alarm must not activate before 4 minutes but must activate before 15 minutes
Part of the reason UL2034 exists is to prevent “nuisance alarms”. This is misguided.
I think the alarm levels above are too high and too loose. The most common CO detectors sold in the United States just aren’t sensitive enough. Too many people die because they weren’t warned about CO safety and didn’t take appropriate steps to protect themselves.
European standards are a bit better:
- at 30ppm CO, the alarm must not activate for at least 120 minutes
- at 50ppm CO, the alarm must not activate before 60 minutes but must activate before 90 minutes
- at 100ppm CO, the alarm must not activate before 10 minutes but must activate before 40 minutes
- at 300ppm CO, the alarm must activate within 3 minutes
But you’re still not going to get a readout below 30ppm, and even then, you’ve been exposed to 30ppm of CO for at least 2 hours.
What if you want early detection below 30ppm? (Not necessarily an alarm for below 30ppm, but just a display indicating current CO levels?)
Then you need a more sensitive device, like the ones home inspectors carry with them when working in crawlspaces, boiler rooms, and other potentially dangerous areas.
After a bit of research on home inspector forums, I found the Sensorcon INS-2-CO1. I ordered it and have been using it for about 1.5 years now. It’s fantastic: any time the gas oven/gas range fires up and somebody forgets to turn on the exhaust fan, you can watch the Sensorcon 30 feet away tick up carbon monoxide levels pretty quickly. 5 minutes of gas can easily shoot you up to 9ppm. By this time we’ve usually turned on the range ventilation fan and aired out the room.
The Sensorcon device is expensive – around $150-$195 – but worth it. It’s a professional device, not a commodity. There are a few other brands recommended by home inspectors as well – check them out on home inspector forums.
I don’t trust that the cheap-o detectors that most people buy are going to go off in time to protect my family’s health, and I’m happy this gives me an early (silent) warning with an alarm at higher levels. The Sensorcon is definitely not the only CO detector in the house – I have one cheap-o First Alert alarm along with a couple of $113 Nest Protect smoke and carbon monoxide detectors – but it’s by far the most sensitive.
What are the effects of carbon monoxide exposure on the human body?
From research by Thomas H. Greiner, in a table published by Iowa State University:
9 ppm: The maximum allowable concentration for an 8-hour period in any year, EPA (ASHRAE). Polluted cities often reach and exceed 9 ppm, increasing incidence of congestive heart failure (Morris). Typical concentration after operation of unvented gas kitchen range (Tsongas).
15-20 ppm: Impaired performance in time discrimination (HbCO 2.0) Decrease in absolute exercise time (HbCO 2.5) Shortened time to angina response (HBCO 2.9) Vigilance decrement (HbCO 3.0) (World Health Org. 13).
27 ppm: 21 percent increase in cardiorespiratory complaints (Kurt, 1978)
[ At this point, standard alarms haven’t even notified you! ]
30 ppm: Earlier onset of exercise-induced angina (HbCO 4.96%) (WHO 13)
35 ppm: Maximum allowable outdoor concentration for one-hour period in any year, EPA (ASHRAE)
50 ppm: Maximum allowable 8-hours work place exposure, (OSHA). Most fire departments require use of self-contained breathing apparatus for exposures above 50 ppm. Preziosi et.al found chronic exposures produced significant morphologic changes in dogs, including brain pathology, heart pathology and abnormal EKG’s. Other researchers find higher concentrations needed. Minimum concentration for digital display to move from zero on some detectors with displays (Conversation with manufacturer).
75 ppm: Significant decrease in oxygen reserve available to the myocardium (HbCO 10%). Heavy smokers can reach HbCO of 10%.
100 ppm: U-L listed detectors must sound a full alarm within 90 minutes or less. Most alarm more quickly. Time to alarm varies with manufacturer, with some manufacturers electing to sound the alarm more quickly. Slight headache, tiredness, dizziness, nausea after several hours exposure. Causes morphologic damage to hearts and brains in dogs exposed 5 1/2 hours per day for eleven weeks (Lewey and Drabkin, quoted in Preziosi). Maximum concentration allowed from kitchen range ovens by many weatherization agencies (Tsongas).
200 ppm: Maximum recommended workplace exposure (NIOSH). U-L listed detectors must sound a full alarm within 35 minutes. Time to alarm varies with manufacturer, with some manufacturers electing to sound the alarm more quickly. Slight headache, tiredness, dizziness, nausea after 2-3 hours, might be life-threatening in long exposures (Bacharach). Abortions and lower birth rates in pigs (Carson).
400 ppm: U-L listed detectors must sound a full alarm within 15 minutes. Time to alarm varies with manufacturer, with some manufacturers electing to sound the alarm more quickly. Frontal headaches within 1-2 hours, life-threatening after 3 hours, maximum parts per million in flue gas under AGA test guidelines.
800 ppm: Dizziness, nausea and convulsions within 45 minutes. Unconsciousness within 2 hours. Death within 2-3 hours. Maximum air-free concentration from gas kitchen ranges (ANSI).
1600 ppm: Headache, dizziness and nausea within 20 minutes. Death within 1 hour. Smoldering wood fires, malfunctioning furnaces, water heaters, and kitchen ranges typically produce concentrations exceeding 1,600 ppm.
3200 ppm: Concentration inside charcoal grill (Greiner, single example). Headache, dizziness and nausea within 5-20 minutes. Quickly impaired thinking. Death within 30 minutes.
6400 ppm: Headache, dizziness and nausea within 1-2 minutes. Thinking impaired before response possible. Death within 10-15 minutes.
12,800 ppm: Death within 1-3 minutes.