Photoelectric vs Ionization Smoke Detectors
Protect yourself from the devastating effects of fire with a monitored DSC Smoke Detector.
Smoke VS. Ionization Smoke Detectors
Is one type of smoke detector superior to the other? While customers don't typically ask this question there are some real differences in how these two types of smoke detectors work and in what detector is most appropriate for home use.
Photoelectric is typically the detector of choice for residential applications. Most residential fires are the result of smoldering household items, such as carpets, mattresses and furniture upholstery. These materials smolder before catching fire and generate smoke particles between the sizes of 0.3 microns and 10 microns. Photoelectric detectors react faster to smoke particles within this size range than do ionization detectors.
Photoelectric smoke detectors have a chamber that prevents light from entering but allows the smoke particles to enter. On the inside of the chamber, there is a photocell and light source. When the smoke particles enter the chamber, it causes the light to reflect into the photocell, triggering the photoelectric smoke circuit to respond.
Ionization detectors are more suitable in detecting fast-burning fires where there is little or no visible smoke at the initial stages of the fire. This type of detector has a quicker response time to fast-burning fires and can detect smoke particles between the sizes of 0.01 microns and 0.3 microns.
Lets take a look at how Ionization Smoke Detectors Work
On the inside of the unit, there is a chamber that has a very small amount (approximately 1/5,000 of a gram) of radioactive material that ionizes the air on the inside of the chamber. This allows a current to pass thorough the air in the chamber to two charged electrodes. When smoke particles enter the chamber, it decreases the conductance between electrodes. When the conductance drops to a certain predetermined level, the ionization smoke detector's circuit responds.
Whenever the word "radioactive" is used, alarms tend to go off in some people's minds. The chemical element used in ionization smoke detectors is americium-241. Am-241 emits alpha particles that are absorbed within a few centimeters of air within the detector and cannot penetrate a sheet of paper. The risk of radiation is essentially zero.
Photoelectric smoke detectors are not any better than ionization smoke detectors, or vice-versa. It's just a case of selecting the right detector for the right job. Regardless of how the smoke detector operates, UL requires that each smoke detector will detect both types of fires, but the response time of each detector will vary, depending on the type of fire.*