How It Works
There are two different types of smoke detectors that are used today. Both detectors get the same job done, however, they go about in different ways, specifically in the way they detect smoke, and the environments these detectors can be placed/used in.
The first smoke detector being discussed is used most commonly in public areas fit for larger domains. The Optical Smoke Detector, also referred to as a Photoelectric Type Device, uses a light source to detect smoke. The Infra-Red LED is a lens that shots a beam over a large area.1 If smoke is present in the room, it enters the optical chamber, having smoke particles scatter and sensor sets of the alarm. In very large areas where a smoke detector is placed, there are two optical detectors that send the straight line of infra-red beam from a sender to a receiver. Optical Smoke Detectors are less sensitive to false alarm fire, such as minor smoke from candles, cooking, steam, etc.2
The cheaper alternative smoke detector is the Ionization Smoke Detector. Like the Optical Smoke Detector, the Ionization Smoke Detector is able to sense smoke particles that are too small for the naked eye. Through alpha radiation, the ionization smoke detector passes through the air-filled space container, allowing flow of electrodes. However if any smoke gets inside the chamber and absorbs the alpha particles, it lowers the level of ionization, hurting the flow of electrodes, thus setting off the alarm. Unlike the Optical Smoke Detector, this model is very inexpensive and more commonly placed in individual homes rather than larger public areas.3
While the Ionization Smoke Detector was first discovered by a Swiss Company in the 1930s, their method of creating the ionization detector used too much power and radioactive material, being unrealistic to use in households. Pearsall’s team accidently discovered a more efficient and less expensive battery operated smoke detector. Though this invention, Pearsall noted, “It was a source of considerable satisfaction to learn that about then many instances throughout the country in which our devices were credited with saving lives, sometimes of whole families.”4
From the National Institute of Technology and Inventions, the released “Performance of Home Smoke Alarms: Analysis of the Response of Several Available Technologies in Residential Fire Settings” giving statistical evidence and analysis on smoke alarms and fire prevention. According to NIST, researchers state, “Consistent with prior findings, ionization type alarms provided somewhat better response to flaming fires than photoelectric alarms, and photoelectric alarms provided often considerably faster response to smoldering fires than ionization type alarms” However the downside to the ionization smoke detector is much more sensitive and sets off false alarm at times.5 In other words, photoelectric smoke detectors are quicker at detecting smaller smoldering fires, and ionization smoke detectors are quicker at alarming fast raging fires.
Please click the attached link below on a News Channel Report about the difference between the two different types of smoke detectors. The current video is unable to be streamed on this blog due to restrictions by the distributor.
- “Photoelectric Technology” U.S. Environmental Protection Agency (March 24, 2011) http://www.epa.gov/rpdweb00/sources/smoke_photo.html (accessed April 11, 2011). ↩
- FIREX, “Smoke Alarms” (2009) http://www.smokealarmdetectors.com/how-smoke-detector-works.html (accessed March 30, 2011). ↩
- “Ionization Technology” U.S. Environmental Protection Agency (March 24, 2011) http://www.epa.gov/rpdweb00/sources/smoke_ion.html (accessed April 11, 2011). ↩
- “Recipient Profiles.” Worcester Polytechnic Institute http://www.wpi.edu/offices/president/recipients.html (accessed April 11, 2011). ↩
- Bukowski, Richard W., Richard Peacock, Jason Averill, Thomas Cleary, Nelson Bryner, William Walton, Paul Reneke, and Erica Kuligowski. “Performance of Home Smoke Alarms: Analysis of Response of Several Available Technologies in Residential Fire Settings.” National Institute of Standards and Technology (December 2007) http://www.fire.nist.gov/bfrlpubs/fire07/PDF/f07063.pdf (accessed March 30, 2011). ↩
- NBC WESH CHANNEL 2, “Which Smoke Detector Works Best?” YouTube (July 16, 2009) http://www.youtube.com/watch?v=_IUzCEYETD8 (accessed April 11, 2011). ↩