Smoke Detectors Ionization vs. Photoelectric

There are two different types of smoke detectors available for installation in your home, photoelectric detectors and ionization detectors. The type most commonly found in homes is the ionization type, as it is commonly available in most hardware and discount stores.

While both are effective, they each sense smoke differently. As a result, they detect different types of smoke better. In case you were wondering, there are two different types of smoke. There is a hazy, almost invisible smoke created by cleaner burning fires, such as grease fires or leaky furnaces. There is also the thick, noxious, cloudy smoke that comes from smoldering fires like fireplaces and burning upholstery.

The first type of smoke is best detected by ionization detectors, which are based on electrical sensitivity. The second type of smoke is best detected by photoelectric detectors, which work on the principle of the visibility of smoke. There are distinct advantages to each product.

There are two versions of photoelectric detectors, although both work on the same principle. The first type is activated when a light that is shining on a light-sensitive sensor is blocked by incoming smoke. Hence, you cannot see through smoke, and where there is smoke, there is fire.

The second type is activated when the light shining past the light-sensitive sensor is reflected onto the sensor by incoming smoke. Hence, you can see smoke and where there is smoke there is fire.

The ionization detector works a little differently. Each detector contains a small amount of radioactive material, which emits alpha and gamma radiation. The alpha radiation ionizes the air inside the smoke detector; this ionized air then conducts a current across a small gap. When smoke enters the detector, it lowers the conductivity of the air in the gap, thus setting off the alarm. The amount of radiation given off by a typical smoke detector is so miniscule; the detector is really quite safe.

When installing a smoke detector, avoid corners and the ends of hallways, known as dead-air spaces. Center your smoke detector on a ceiling, keeping it at least 6 inches away from any wall. If you have a wall-mounted unit, locate it one foot below the ceiling.

Keep your smoke detector away from drafts caused by vents, doors, and windows. The National Fire Code recommends that detectors be placed in any hallways leading to bedrooms and at the tops of stairwells. There should be at least one smoke detector on every level of your home, including the basement.

You should carefully vacuum your detectors and change the batteries at least once a year. Even if your home has a wired-in detector, you should have a battery-powered unit as a back up.

Your smoke detectors should be checked at least once a month. Pushing the test button only verifies that there is a power source present. It does not prove that the detector is capable of sensing smoke. To test your detector, hold a lit candle 6 inches below it. If the alarm does not sound, blow out the candle and let the smoke drift into the detector. If it still does not sound, check the power source.