Smoke Detector Comparison

There are two types to consider when making a smoke detector comparison. One is photoelectric and the other is ionization. Additionally, instead of individual units that operate separately from others, new home detection systems offer integrated intercommunication wireless devices that trip all detectors when one alarm sounds. Also, any system can be set up as an optical smoke detector that will send a signal to set off a system-wide fire alarm and possibly initiate a fire-depression feature like ceiling sprinklers or a kitchen exhaust hood suppression device. This type system is normally installed in an industrial, commercial or a large residential building like an apartment complex.

Photoelectric

Photoelectric devices emit a light beam that, when blocked by the presence of smoke, sound an alarm. This takes place when the smoke present at the location of the detector reduces the amount of light traveling to a photocell to sound the alarm. Without the smoke present, an LED (light-emitting diode) produces a constant beam of light above the photocell maintaining a constant connection. This type is a popular choice because smoke emanating from behind bedroom or other living space walls will easily trip a photoelectric smoke detector that is placed on a ceiling since smoke rises quickly. Heat detector-based devices measure a certain temperature before sounding even though smoke may be present.

Ionization

Ionization detectors employ a small amount of radiation in the form of a really tiny particle of americium-241. There are two plates separated by about a centimeter of space where one is charged positively by a battery and the other, negatively. The americium  releases alpha particles that ionize the oxygen and nitrogen present in the air inside the detector chamber while knocking electrons off air atoms. Positively charged nitrogen and oxygen particles become attached to the negative plate while the electrons are attached to the positive plate. An alarm is triggered when smoke enters the chamber neutralizing the ions keeping them from reaching the plate. The loss in a steady current is what sets off the alarm.

Which One to Choose

Both types of detector designs make effective smoke alarms. All detectors have to pass certification tests operated by the Underwriters Laboratory, a third party reference certifying product safety and compliance. An ionization device is better suited to detect a flaming fire where a photoelectric device can detect smoldering fires more effectively. An ionization alarm is less expensive but when placed near kitchens has a tendency to sound frequently in the course of a normal day’s cooking activity. Ionization detectors will sound an alarm when the battery is failing--a useful feature to warn homeowners it is time for a change. A photoelectric detector can have a back-up battery allowing for continued operation but must be tested for battery life. Ionization devices can be found in many commercial kitchens since these can be set to a certain level that allows normal kitchen operations. Photoelectric devices are popular in residential settings.

Wireless devices alert all occupants in a building when one alarm sounds thus providing an instant alert to everyone that danger is imminent.