Editing Smoke detector (section)

=== Ionization === <!-- [[Ionization smoke detector]] redirects here. -->
[[File:Smoke-engineerguy.ogv|thumb|A video overview of how an ionization smoke detector works]]
[[File:smokealarm.JPG|thumb|Inside a basic ionization smoke detector. The black, round structure at the right is the ionization chamber. The white, round structure at the upper left is the [[piezoelectricity|piezoelectric]] horn that produces the alarm sound.]]
[[File:Americium-241.jpg|thumb|An americium container from a smoke detector]]

An '''ionization smoke detector''' uses a [[radioisotope]], typically [[americium-241]], to ionize air; a difference due to smoke is detected and an alarm is generated. Ionization detectors are more sensitive to the flaming stage of fires than optical detectors, while optical detectors are more sensitive to fires in the early smouldering stage.<ref name="ionizaton">Fleming, Jay. [https://www.scribd.com/doc/14390291/Smoke-Detector-Technology-Research-Chief-Jay-Fleming "Smoke Detector Technology Research"] {{webarchive|url=https://web.archive.org/web/20160420071735/https://www.scribd.com/doc/14390291/Smoke-Detector-Technology-Research-Chief-Jay-Fleming|date=2016-04-20}}, retrieved 2011-11-07.</ref>

The smoke detector has two [[ionization chamber]]s, one open to the air, and a reference chamber which does not allow the entry of particles. The radioactive source emits [[alpha particle]]s into both chambers, which [[ionizes]] some air [[molecule]]s. There is a [[potential difference]] (voltage) between pairs of [[electrode]]s in the chambers; the [[electrical charge]] on the [[ion]]s allows an [[electric current]] to flow. The currents in both chambers should be the same as they are equally affected by air pressure, temperature, and the ageing of the source. If any smoke particles enter the open chamber, some of the ions will attach to the particles and not be available to carry the current in that chamber. An electronic circuit detects that a current difference has developed between the open and sealed chambers, and sounds the alarm.<ref>{{cite book |last1=Cote |first1=Arthur |title=Principles of fire protection |last2=Bugbee |first2=Percy |publisher=National Fire Protection Association |year=1988 |isbn=0-87765-345-3 |location=Quincy, Massachusetts |page=249 |chapter=Ionization smoke detectors}}</ref> The circuitry also monitors the battery used to supply or back up power. It sounds an intermittent warning when it nears exhaustion. A user-operated test button simulates an imbalance between the ionization chambers and sounds the alarm if and only if the power supply, electronics, and alarm device are functional. The current drawn by an ionization smoke detector is low enough for a small battery used as a sole or backup power supply to be able to provide power for years without the need for external wiring.

Ionization smoke detectors are usually less expensive to manufacture than optical detectors. Ionization detectors may be more prone than photoelectric detectors to false alarms triggered by non-hazardous events,<ref>Residential Smoke Alarm Performance, Thomas Cleary, Building and Fire Research Laboratory, National Institute of Standards and Technology, UL Smoke and Fire Dynamics Seminar. November, 2007.</ref><ref name="NIST">{{cite web|title=Performance of Home Smoke Alarms Analysis of the Response of Several Available Technologies in Residential Fire Settings|url=http://www.fire.nist.gov/bfrlpubs/fire07/art063.html|work=Bukowski, Cleary et al|url-status=live|archive-url=https://web.archive.org/web/20100822192559/http://www.fire.nist.gov/bfrlpubs/fire07/art063.html|archive-date=2010-08-22}}</ref> and are much slower to respond to typical house fires.{{Citation needed|reason=At least one source not mentioned in the article indicates that most house fires are fast burning "flaming" kind, and the only thing saying something like this claim that this is the typical (rather than some or many types of) house fire that I found in the citations (many of which are dead links) was only one quote in a magazine article.|date=July 2024}}

==== Radiation ====
[[File:Americium button hd.jpg|thumb|A 141 [[nanogram|ng]] speck of [[Americium dioxide|americium-241 dioxide]] on a coin-sized aluminum button<ref>{{cite magazine |last1=Bettenhausen |first1=Craig |title=Chemistry in Pictures: Americium the beautiful |magazine=[[Chemical & Engineering News]] |date=July 7, 2021 |url=https://cen.acs.org/materials/Chemistry-Pictures-Americium-beautiful/99/web/2021/07 |access-date=11 June 2023 |publisher=[[American Chemical Society]] |issn=0009-2347}}</ref>]]
[[Americium-241]] is an [[Alpha decay|alpha emitter]] with a [[half-life]] of 432.6 years.<ref>{{Cite web |title=NuDat 3.0 database |url=https://www.nndc.bnl.gov/nudat3/ |website=NNDC.BNL.gov |publisher=[[Brookhaven National Laboratory]] |access-date=24 September 2022 }}</ref> Alpha particle radiation, as opposed to [[Beta decay|beta]] (electron) and [[Gamma ray|gamma]] (electromagnetic) radiation, is used for two reasons: the alpha particles can ionize enough air to make a detectable current; and they have low penetrative power, meaning they will be stopped, safely, by the air or the plastic shell of the smoke detector. During the alpha decay, {{SimpleNuclide|Americium|241}} emits [[gamma radiation]], but it is low-energy and therefore not considered a significant contributor to human exposure.<ref group=Note name=Note01/><ref group=Note name=Note02/><ref group=Note name=Note03/>

The amount of elemental americium-241 in ionization smoke detectors is small enough to be exempt from the regulations applied to larger deployments. A smoke detector contains about {{convert|37|kBq|abbr=on|lk=on}} of radioactive element americium-241 ({{SimpleNuclide|Americium|241}}), corresponding to about 0.3&nbsp;μg of the isotope.<ref>{{cite web | url = http://media.cns-snc.ca/pdf_doc/ecc/smoke_am241.pdf | title = Smoke detectors and americium-241 fact sheet | publisher = Canadian Nuclear Society | access-date = 2009-08-31 | url-status = live | archive-url = https://web.archive.org/web/20110706173242/http://media.cns-snc.ca/pdf_doc/ecc/smoke_am241.pdf | archive-date = 2011-07-06 }}</ref><ref>{{cite web|url=http://www.atsdr.cdc.gov/toxprofiles/tp156.pdf|format=PDF; 2.1MiB|title=Toxicological Profile for Americium|first=Julie Louise|last=Gerberding|publisher=[[United States Department of Health and Human Services]]/[[Agency for Toxic Substances and Disease Registry]]|access-date=2009-08-29|date=April 2004|url-status=live|archive-url=https://web.archive.org/web/20090906112953/http://www.atsdr.cdc.gov/toxprofiles/tp156.pdf|archive-date=2009-09-06}}</ref> This provides sufficient ion current to detect smoke while producing a very low level of radiation outside the device. Some Russian-made smoke detectors, most notably the RID-6m and IDF-1m models, contain a small amount of plutonium (18&nbsp;MBq), rather than the typical {{SimpleNuclide|Americium|241}} source, in the form of reactor-grade {{SimpleNuclide|Plutonium|239}} mixed with titanium dioxide onto a cylindrical alumina surface.<ref>{{Cite web |date=2017-02-07|title=Analysis of Soviet smoke detector plutonium|url=https://carlwillis.wordpress.com/2017/02/07/analysis-of-soviet-smoke-detector-plutonium/|access-date=2021-12-23|website=Special Nuclear Material|language=en}}</ref>

The amount of americium-241 contained in ionizing smoke detectors does not represent a significant radiological hazard.<ref>{{cite web |title=Backgrounder on Smoke Detectors |url=https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/smoke-detectors.html |website=NRC Library |publisher=U.S. [[Nuclear Regulatory Commission]] |access-date=24 September 2022}}</ref> If the americium is left in the ionization chamber of the alarm, the radiological risk is insignificant because the chamber acts as a shield to the alpha radiation. A person would have to open the sealed chamber and ingest or inhale the americium for the dose to be comparable to [[Background radiation#Natural background radiation|natural background radiation]]. The radiation risk of exposure to an ionizing smoke detector operating normally is much smaller than natural background radiation.

==== Disposal ====
Disposal regulations and recommendations for ionization smoke detectors vary from region to region. The government of New South Wales, Australia considers it safe to discard up to 10 ionization smoke detectors in a batch with domestic rubbish.<ref name="FireRescueNSWDisposal">{{cite web |date=26 November 2012 |title=Safe disposal of smoke alarms – Fire and Rescue NSW |url=http://www.fire.nsw.gov.au/page.php?id=704 |url-status=live |archive-url=https://web.archive.org/web/20130420103030/https://fire.nsw.gov.au/page.php?id=704 |archive-date=20 April 2013 |access-date=2013-06-26 |publisher=New South Wales Government |language=en |publication-place=Australia}}</ref> The U.S. [[United States Environmental Protection Agency|EPA]] considers ionizing smoke detectors safe to dispose with household trash.<ref>{{cite web |title=Americium in Ionization Smoke Detectors |url=https://www.epa.gov/radtown/americium-ionization-smoke-detectors |website=RadTown |date=27 November 2018 |publisher=[[United States Environmental Protection Agency|EPA]] |access-date=24 September 2022}}</ref> Alternatively, smoke detectors can be returned to the manufacturer.<ref name="EPADisposal">{{cite web |url=http://www.epa.gov/radiation/sources/smoke_dispose.html |title=Disposing of Smoke Detectors &#124; Radiation Protection &#124; US EPA |date=27 June 2012 |publisher=[[United States Environmental Protection Agency|EPA]] |access-date=2013-06-26 |url-status=live |archive-url=https://web.archive.org/web/20130602015411/http://www.epa.gov/radiation/sources/smoke_dispose.html |archive-date=2 June 2013 }}</ref>