Smoke Detectors

Smoke Detectors containing radioactive materials

We are often asked about radioactivity in smoke detectors. We have not researched this topic in detail. An internet search turns up a lot of information, but some of it is garbage. In particular take any statements about "low radiation hazard" with a pinch of salt, for the reasons we explore here as well as in the rest of this site.

These devices are probably not a problem unless they burn, in which case the Americium would be released in particulate form - an inhalation hazard. The dangers of this kind of exposure have been massively neglected by the risk agencies. [Rose Tilly has, in addition, raised concerns about gamma radiation from smoke detectors which need further investigation. Her 1997 article is reproduced below].

We do not advise anyone to remove existing smoke alarms. It seems obvious that so long as the so-called ionising detectors are sited sensibly - not close to where anyone will be in close proximity for appreciable periods - they have a far greater chance of saving lives than of damaging health.
If in doubt use the [unfortunately more expensive] photo-electric type.
If you have or decide to fit the ionising type (we use them) don't mess with them. When they are no longer needed or stop working DO NOT DISPOSE OF THEM IN ANY WAY THAT ENTAILS INCINERATION. Under European Union law they are classified as Waste Electrical and Electronic Equipment (WEEE)). Ask your local authority how to dispose of WEEE responsibly.

The radioactivity in ionising detectors is a film coated with Americium 241, a relatively long-lived and very active alpha emitter (half life 458 years, 1167 million Bq per milligram). Internet sources suggest smoke alarms each contain 30,000 Bq.

These characteristics of Americium 241 make it a long lasting source of alpha disintegrations which ionise the air in the vicinity of the film, thus increasing its electrical conductivity. If smoke particles are present the conductivity changes; this triggers the alarm.
Don't worry about the alpha radiations - they have such a short range in air that they will not penetrate beyond the casing of the detector.

Which type is better?

Ionisation detectors (i.e. those containing Americium 241) are more sensitive to tiny particles of combustion that can't be seen or smelled - those emitted by flaming fires.
Photoelectric detectors are more sensitive to the large particles of combustion emitted by smouldering fires.
The difference between the two types is generally not critical, since the difference in response time is only a matter of seconds.
Early in the growth of most home fires detectable amounts of both large and small smoke particles are produced, so either an ionisation or a photoelectric detector will meet most needs.

Rose Tilly's article Radioactive Smoke Detectors (from Green Events July/ August 1997)

Household smoke detectors, often as many as fifty, are displayed on rails in supermarkets, department stores and hardware shops. They look harmless enough and the Home Office and Fire Brigade widely promote their use in the home but what is not mentioned is the fact that ionising detectors contain a fission by-product of the nuclear industry.

Text books state that Americium 241 is used in smoke detectors yet Americium 241 is ranked 14th out of 236 radioactive materials in level of radiotoxicity and is noted to cause cancer. But is the radio-nuclide contained in smoke detectors actually Americium 241? When a scintillation meter is run over a smoke detector, gamma radiation is recorded at up to 500 counts per second (1). Americium 241 is mainly an alpha emitter which represents 85% of its radioactive output. Gamma emission comprise only 8%.

The authorities cannot explain this phenomenon. Is there another isotope contained in smoke detectors of which we are unaware?

A department store in Bournemouth displays a notice over a line of 70 ionising smoke detectors bearing the legend "Ideal for Nurseries." Ask department store managers, however, if they are aware they are selling a consumer product containing a radioactive fission product from the nuclear industry and they won't believe it until they see gamma radioactivity being registered on a scintillation meter.

Smoke detectors are nice little earners - millions are sold world-wide every year. Manufacturers are quick to defend their product. "Levels are no more than background radiation" is the common response. Yet background radiation levels register no more than 5-10 cps.

The National Radiological Protection Board states the Government is revising legislation relating to smoke detectors. EC legislation states smoke detectors should state the radioisotope used in smoke detectors and give the energy. Go into any hardware store, however, and no such information is shown. In any case it would mean very little to the public who as usual are kept in the dark. If legislation included the statement that a fission by-product of the nuclear industry which will emit gamma radioactivity up to 30,254,000 CPS every 24 hours for over 400 years (Americium 241 has a half life of 432 years (2)), then it is likely that sales of ionising smoke detectors would be drastically reduced.

What will Environmental Health Officers do about the situation? Nothing whatsoever. "We are satisfied that smoke detectors conform to British Standards" is the general comment. But what about the public? Don't they have a right to know that smoke detectors are radioactive? No comment. A letter to Mr R Clifford of the Radioactive Substances Division of the Department of the Environment asking why government leaflets advertising smoke detectors fail to mention they emit gamma radiation has gone unanswered.

In the event of a fire, firemen would be at risk when the plastic housing melts and the fission by-product released to the atmosphere. The Fire Brigade Union is concerned about the risk to fire men attending fires in factories and offices where up to 200 may be installed. Smoke detectors also pose a risk to air-crew. Thousands of smoke detectors containing a gamma emitting fission product have been installed in the metal ceilings of toilet cabins just a matter of inches from the toilet user's head. This means that passengers and air crew standing in front of the mirror receive 400-500 counts per second gamma radiation. This is in addition to increased radioactivity at high altitudes. Airline managements, however, were not informed about radioactivity when purchasing smoke detectors in bulk for their airlines. Now, having spent thousands of pounds purchasing and installing the devices they are unwilling to replace them.

Black and Decker is the only supplier who investigated radioactivity in smoke detectors when the matter was brought to their attention and in 1992 the company ceased to market them.

Many specialists agree that even low level radiation can damage cells so why should smoke detectors containing fission products continue to be manufactured when the risks are so high to factory staff encasing the fission product in a supposedly protective foil, assemblers installing the fission material in smoke detectors and the public and aircrew who will be continuously exposed to gamma radioactivity?

There is an equally effective alternative to gamma emitting smoke detectors. Optical smoke detectors cost 7.50 against 5.50 for radioactive smoke detector, so the Public have a choice albeit slightly more expensive. A small price to pay for a gamma free environment.


1 ... 500 cps ... LLRC has not been able to reproduce this finding. Our instruments showed 12 times natural background holding the instrument 1 inch from the smoke detector, whereas Rose Tilly is reporting 50 times or more. The possibility of impure sources in her smoke detector(s) should be investigated. We found a clear gamma line at 60keV (36%), which is what you'd expect from Am 241; there's a weak gamma line at 26 keV (2.5%) as well.
This note was written in 1997. More recently we have checked using much more sensitive equipment and we still have not been able to reproduce Rose Tilly's finding. In 2007 we wrote to the appropriate authorities to ask if they were aware of any smoke detectors which emit gamma radiation in the amounts she reports. We have no record of a reply.

2 This should be half life of 458 years


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