Since this is the case, it is apparent that having a smoke alarm that can quickly and accurately detect smoldering fires, fires that produce the most smoke, is extremely important.
The majority of fatalities caused by fires are not from the flames, but from smoke inhalation, which is why most fire-related fatalities - nearly two-thirds - happen during the night while people sleep. The NFPA acknowledges the significant superiority of photoelectric smoke alarms over ionization alarms with regards to false alarm susceptibility. Ionization alarms are responsible for 97% of “nuisance alarms” – false alarms – and are thus much more likely to be disabled all together than other types of smoke alarms.During fast-flame fires, ionization alarms failed to provide sufficient egress time more frequently than photoelectric alarms failed to do so.During smoldering fires, ionization alarms failed to give sufficient egress time more frequently than photoelectric alarms failed to do so.The NFPA acknowledges that a well-designed photoelectric alarm will usually outperform ionization alarms in all fire situations, regardless of type and material. Ionization smoke alarms generally perform slightly faster (30-90 seconds) to fast flame fires – fires with flames which spread quickly – than photoelectric alarms.Photoelectric smoke alarms respond much faster (15 to 50 minutes faster) to smoldering fires – fires which move more slowly but produce the most smoke, the element of residential fires most responsible for fatalities – than ionization alarms.The findings from these studies and tests generally reveal the following: Key Differences Between Ionization and Photoelectric Smoke AlarmsĮntities such as the Underwriters Laboratories (UL), the National Fire Protection Association (NFPA), and others have conducted many studies in to determine key differences in performance between these two main types of smoke detectors. Other combinations add additional sensors, such as infrared, carbon monoxide, and heat sensors, to help accurately detect a real fire and decrease false alarms due to things like smoke from a toaster, steam from a shower, etc. Many combination smoke alarms join the ionization and photoelectric technologies in the hopes of increasing effectiveness. Combination Alarms: additionally, there are a variety of combination alarms.This reduction in light is detected by the alarm’s circuitry and triggers the alarm. When smoke particles partially block the light beam, the photosensitive device’s output is altered by the reduction in light. In this instance, though, the light beam is sent directly to the element. These alarms are also constructed with both a light source and a photosensitive element. Light obscuration: the other type of photoelectric alarms are designed around light obscuration.But when smoke particles from a fire enter into the beam’s path, the light beam hits the smoke particles and deflects into the photosensitive element, triggering the alarm. The beam is directed towards an area that cannot be detected by the photosensitive element. They possess both an LED light beam and a photosensitive element. Light scattering: most photoelectric smoke detectors operate on the principle of light scattering.Photoelectric smoke alarms are designed based on how smoke from a fire changes the intensity of light passing through the air:
The electronic circuitry within the plates senses this change in the chamber and, when a predetermined threshold is crossed, triggers the alarm. In the event of combustion, combustion particles enter into the ionization chamber, repeatedly colliding and combining with the ionized air molecules and decreasing their number. They consist of a chamber formed by two electrically charged plates and a radioactive material that ionizes the air moving between the plates.Įlectronic circuitry within the plates actively measures the ionization current created by this design.
Ionization smoke alarms are sophisticated in design. Ionization smoke alarms and photoelectric alarms rely on drastically different mechanisms to detect fires:
Understanding the difference between the two can help you make the best decision regarding the smoke alarms protecting your home or business. There are two main types of smoke alarms – ionization and photoelectric. The important role of well-placed, quality smoke alarms is easy to see. The majority of fire-related deaths occur at night while people sleep. According to the NFPA, there are over 354,000 residential fires a year, causing, on average, around 2,600 deaths and over 11,000 injuries.
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