Not All Smoke Alarms Created Equal

The study, which looked at more than 750 households in Washington State, found that nine months after a smoke alarm was installed, 20% of the ionized alarms did not function, compared to just 5% of the photoelectric alarms.  Researchers checked the same alarms six months later and found similar results.  The most common cause of a non-functioning alarm was the removal or disconnection of the battery.

Researchers found that ionization detectors were more prone to nuisance alarms, often caused by cooking. Nuisance alarms are the most cited reason by residents for removing or disconnecting an alarm battery. “Many fires in the house start in or around the kitchen, so we know that it is critical to have functioning smoke alarms on the first level, adjacent to the kitchen,” said Dr. Beth Mueller, the study principal investigator and epidemiologist at the HIPRC.  “Clearly, photoelectric detectors performed much better in this part of the house.” 

Alarms sold for home use in the U.S. are ionization, photoelectric, or combination designs. Photoelectric and ionization alarms operate differently.  While both detect particles from combustion, photoelectric alarms use optical sensors and are more sensitive to slow, smoldering conditions. Ionization alarms are responsive to flames by detecting particles from rapid combustion.

“The study results are significant,” said Dr. David Grossman, a pediatrician and study co-investigator who is now medical director for preventive care at Group Health in Seattle. “Though the U.S. has made great strides in getting these life-saving smoke alarms in people’s homes, we still have a long way to go to make sure that they remain operational.  Photoelectric alarms may be a key answer to providing longer term protection.”

The study appears in the April issue of the international journal Injury Prevention. Research was funded in part by the Centers for Disease Control and Prevention in Atlanta, and the King County Fire Chiefs’ Association. Harborview Injury Prevention & Research Center is affiliated with the University of Washington, and Harborview Medical Center in Seattle. It is one of the nation’s leading centers dedicated to injury prevention and trauma research.