Fixit: Carbon monoxide safety devices vary

Q How effective are carbon monoxide (CO) alarms seen in stores? What should I look for when buying a CO alarm?

A There are two types of devices. The terms "CO alarm" and "CO detector" (or CO monitor) are often used interchangeably, but the units are quite different.

CO alarms are designed to sound an alarm when CO levels become life-threatening. They do not provide information about chronic low-level exposures, which are known to be harmful.

A CO detector or monitor, on the other hand, will provide information about low levels, generally under 30 parts per million (ppm), and sound an alarm at life-threatening levels. (There is no standard for safe levels of CO in homes. The U.S. National Ambient Air Quality Standard for outdoor air is 9 ppm over eight hours.) Health authorities caution that long-term, low-level CO exposure should be avoided, especially by pregnant women, children and those with heart and lung disease. A CO detector/monitor also alerts occupants to a developing CO problem, so they can take steps to prevent a crisis.

CO detectors/monitors can be difficult to find; most retailers stock only CO alarms. That's because nine years ago Underwriters Lab (UL) changed the standard, turning away from monitoring and toward the less-sensitive alarm.

The change was spurred by a desire to reduce the number of nuisance calls to utilities and first responders. Some health authorities argued that the change would eliminate information about chronic low-level exposure.

Another reason for the wide use of CO alarms is a new Minnesota law that requires only minimum protection, installation of a CO alarm, in new construction. (The law will extend to existing housing next year.) But it doesn't preclude higher levels of protection.

When buying CO protection, remember that minimal protection is better than none at all. Then consider who's in your home and how much information you want. If your household contains pregnant women, infants, children, senior citizens, people with heart or respiratory problems, or if you want to be alerted to a developing CO problem, invest in a CO detector/monitor.

Several sites on the Internet sell the monitors, including the American Lung Association of Minnesota at www.healthhouse.org (1-800-586-4872).

If minimal protection is what you want, then buy a CO alarm. Look for one that meets the UL standard (usually indicated on the box), has a long-term warranty and can be self-tested and reset.

A basic, off-the-shelf CO alarm costs $20 to $50. The Lung Association's CO alarm sells for around $90 and its CO monitor, with a higher level of protection, sells for around $130, plus shipping and handling.

Whether you buy an alarm or a detector/monitor, it's a good idea to write the date on the device when you install it so you know to replace it in five years (or when recommended by the manufacturer).

Remember these are back-up devices and should not be relied upon exclusively. The first line of defense against CO is to make sure that all fuel-burning appliances operate properly, including water heaters. Have the heating system (including chimneys and flues) inspected each year.

Send your questions to Fixit in care of the Star Tribune, 425 Portland Av. S., Minneapolis, MN 55488, or call 612-673-9033, or e-mail fixit@startribune.com. Past columns are available at www.startribune.com/fixit. Sorry, Fixit cannot supply individual replies.