Smoke Detector Program

Similarities:

Both Ion (Ionization) and Photo (Photoelectric) smoke alarms respond to combustion particles given off by developing fires. Both have to pass the SAME fire tests by Underwriters Laboratories Inc. (UL). Both are designed to give adequate warning in case of fire, whether a fire starts slowly and smolders, or bursts into flames quickly and spreads rapidly.

Differences:

Ion and Photo sensing chambers use different methods to detect smoke. The differences between them are pretty technical, so let's start with a simple analogy: Think of wrist watches. Some are digital, some have dials with hands. Both tell time, but they use different methods. Same idea with ion and photo smoke alarms.

Ionization: Ion smoke alarms react to changes in ionized particles, and are somewhat better at detecting flaming fires. Flaming fires spread quickly, "consuming" or burning materials in their path rapidly. Examples include paper burning in a wastebasket or stove-top grease fires. According to a recent study released by the U.S. Consumer Product Safety Commission, 94% of reported home fires were categorized as flaming fires.

Photoelectric: Photo smoke alarms react to how smoke affects light, are somewhat better at detecting smoldering fires. These fires can smolder for hours before bursting into flames. Examples include cigarettes burning in couches or bedding.

It's impossible to say one sensor -- photo or ion -- is universally better at detecting all types of fires. Why? Because both sensors are designed to respond to combustion particles produced by smoldering or flaming fires, and because fires themselves are different. The combustion particles produced will vary depending on what starts the fire (matches, electrical fire, etc.) and what burns (paper, fabric, wood).

If a lit cigarette drops directly onto a couch, it is more likely to start a smoldering fire. If that same cigarette drops onto a newspaper on the couch, the resulting fire may be more characterized by flames than smoldering smoke.

Major testing under the National Bureau of Standards sponsorship confirmed either type of smoke alarm will give adequate warning in either type of fire. And remember, both have to pass the SAME fire tests by Underwriters Laboratories Inc. (UL).

The most important factor in protecting your family is having the recommended number of working smoke alarms installed in the proper locations. It is recommended you install both photo and ion smoke alarms in your home, or choose dual sensor smoke alarms which feature both sensors in one unit.

One of the major problems with smoke detectors, is that the owner removes the batteries due to false alarms. An ionizing detector is more likely to false alarm in the presence of sudden heat, such as the opening of an oven. A photoelectric detector is more likely to false alarm in the presence of a wood burning stove. Selecting the proper detector for the proper location will help reduce the odds of a false alarm. 

A recent report by the Consumer Product Safety Commission (CPSC) estimates that 94% of typical household fires are flaming fires. However, since you can't be sure what type of fire might start in your home, consider installing both ionization and photoelectric smoke alarms on every level of your home, and near every sleeping area.