What about dual-sensor alarms?
Dual sensor alarms incorporate both ionization and photoelectric sensors, so they seem like a great choice… but they might not be. A recent article in the ASHI Reporter by San Bruno home inspector Skip Walker, titled Silent Alarms; Deadly Differences, advocates the use of photoelectric smoke alarms over dual-sensor smoke alarms.
- – The perceived benefit of a dual-sensor smoke alarm is an increased response time to a fast flaming fire.
- – Ionization alarms are prone to nuisance tripping, which leads to disabling the smoke alarm.
- – In approximately 1/3 of all U.S. fire deaths, the smoke alarm was disabled.
- – There is no industry standard for sensitivity levels in dual-sensor smoke alarms; as long as the alarm sounds within the UL 217 requirements for single sensor alarms, the smoke alarm passes.
- – Dual-sensor smoke alarms can have the sensors adjusted to different sensitivity levels for the ionization and photoelectric sensors, provided one of the sensors goes off in a timely manner. This means that a dual-sensor alarm could theoretically have a non-functional ionization sensor, but as long as the photoelectric sensor makes the alarm sound, it meets UL 217 requirements.
- – When the ionization sensor is adjusted to go off quickly, the potential for nuisance alarms will go up, which increases the potential for the smoke alarm to be disabled.
- – When the ionization sensor is adjusted to take longer to go off, the perceived benefit of a faster response time to a fast flaming fire is diminished.
The International Association of Fire Fighters (IAFF) advocates the use of photoelectric smoke alarms, and in January of 2013, the American Society of Home Inspectors (ASHI) became the first home inspection organization to advocate the use of photoelectric smoke alarms.
If you’re curious about what type of smoke alarms you have in your own home, take the smoke alarm down and look at the back. Ionization alarms all contain a trace amount of a radioactive material, Americium 241. They’ll all have a warning about this on the back side. Click on any of the thumbnails below to see a blowup of the text on the back side of a smoke alarm, with the text indicating it’s an ionization alarm underlined.
The bottom line is that every home should be equipped with photoelectric smoke alarms.