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					                                                                                                           Fact Sheet 6


Radioactivity in Domestic Smoke Alarms
Introduction
Smoke alarms are important safety devices, because of their       3. The identity and amount of radioactive material in the
obvious potential to save lives and property. There are two           source.
types of smoke alarm commonly available. One type uses
the radiation from a small amount of radioactive material to      AS3786 also sets down various requirements for the radia-
detect smoke or heat sources. These are the most popular          tion source itself including the type and activity of the
type, because they are inexpensive and sensitive to a wider       source that can be used.
range of fire conditions. The other type does not contain ra-
dioactive material – it uses a photoelectric sensor to detect
the change in light level caused by smoke.                        The CSIRO's ActivFire Scheme tests the ability of
                                                                  smoke alarms to detect smoke, in accordance with
This Fact Sheet is intended primarily for those who may be        AS3786.
unsure whether or not to use this important safety device
because of their concerns about the use of radioactive mate-
rial in smoke alarms. Due to the small amount of material
                                                                  Radiation Safety
used and the secure means of its encapsulation, these smoke
                                                                  Radiation from natural sources is always present in the en-
alarms are completely safe under all normal conditions it
                                                                  vironment. It comes from cosmic radiation and radioactive
may encounter, including during a fire.
                                                                  materials in the ground, building materials, food, water, the
                                                                  atmosphere and even our own bodies. We are continuously
Operation                                                         and unavoidably exposed to this background radiation.

Smoke alarms that use radioactive material incorporated           Besides the radioactive materials that occur naturally in our
in an ionization chamber are called “ion chamber smoke            environment, there are man-made radioactive materials.
alarms”. Americium-241 is the radioactive material used           Americium-241 is one such material. In a smoke alarm,
and it emits alpha particles and low energy gamma rays.           the radiation source comprises americium-241 dioxide in a
The alpha particles are absorbed within the alarm, while          gold matrix covered by a silver foil. The foil is thin enough
most of the gamma rays escape. The radiation health con-          to allow the alpha particles to escape into the ionization
sequences of this are discussed later.                            chamber. The alpha particles travel only a few centimetres
                                                                  in air before they are absorbed and hence will not escape
The alpha particles collide with the air in the ionization        from the smoke alarm. They do not have sufficient energy
chamber to produce charged particles called ions. A low-          even to penetrate the dead layer of human skin, which is
level electric voltage is applied to the chamber to collect       approximately 70 micrometres thick.
these ions, causing a steady electric current to flow. Smoke
or hot air entering the chamber changes the rate of ioniza-       The gamma ray dose rate from a domestic smoke alarm at
tion and, therefore, the electric current level, which triggers   a distance of one metre is less than one thousandth of that
an alarm.                                                         from background radiation, which in Australia is on average
                                                                  1.5 millisievert per year. At greater distances, the dose rate
Alarm Requirements                                                is much lower.

The Australian Standard AS3786-1993 Smoke Alarms , as             The dose rate to the hands when holding a smoke alarm
amended, requires domestic smoke                                  would be higher but would still be less than one tenth that
alarms to be labelled with:                                       from background radiation. As the hands are very much
                                                                  less sensitive to radiation than internal organs and the time
1. The words “WARNING –                                           of exposure is likely to less than a few hours per year, no
   RADIOACTIVE MATERIAL”                                          significant radiation exposure would occur.
   or equivalent;
                                                                  The radioactive source in a smoke alarm is extremely
2. The radiation warning (trefoil)                                insoluble and, if swallowed, would not be absorbed into the
    symbol (right); and                                           body but would pass through the digestive system.
In a house fire, temperatures are unlikely to exceed 1200°C.      When more than ten smoke alarms (or more particularly,
While such a fire temperature might be sufficient to melt the      the americium 241 sources) are collected together for bulk
source it would not be enough to vaporise it and create an in-   disposal however, they must be treated as radioactive waste,
halation hazard. Hence, there would be no inhalation hazard      and the requirements of the National Health and Medical
during the fire or afterwards.                                    Research Council’s Code of Practice for the Near-Surface
                                                                 Disposal of Radioactive Waste in Australia (1992) must
Safe Disposal                                                    be met. Contact your State or Territory radiation control
                                                                 authority for advice.
In its November 2001 statement, the Radiation Health Com-
mittee recommended that the preferred method of disposal         Conclusions
for individual or small numbers of smoke alarms is to include
them in the domestic rubbish. The Committee considered           •    The small amount of radioactive material that is used in
this action acceptable because:                                       these alarms is not a health hazard.
1. The amount of radioactive material in each smoke alarm
   is extremely small and, from environmental and public         •    The radiation dose to the occupants of a house from a
   health perspectives, the disposal of individual smoke              domestic smoke alarm is minute compared to natural
   alarms with domestic rubbish does not represent any                background radiation.
   hazard;
                                                                 •    Individual (or small numbers of) smoke alarms can be
2. The radioactive material is securely bound in a metal foil         safely disposed of in domestic rubbish.
   within the smoke alarm; and
                                                                 •    The ability of domestic smoke alarms to save life and
3. The amount of naturally-occurring alpha-emitting                   property has been shown in many house fires.
   radioactivity in normal soils is equivalent to a dozen or
   more smoke alarms in every cubic metre. The dispersal
   of smoke alarms, even in large numbers, through refuse        References
   land-fill sites is therefore not significant in comparison.
                                                                 1.   AS 3786-1993: Smoke alarms, as amended; Standards
                                                                      Australia, PO Box 1055, Strathfield NSW 2135.


                                                                 2. Sievert is a unit of radiation dose and estimates the ef-
                                                                    fect that radiation exposure has on people. (Note: 1,000
                                                                    millisievert = 1 sievert).




 © Australian Radiation Protection and Nuclear Safety Agency                 619 Lower Plenty Road, Yallambie VIC 3085, AUSTRALIA
 Email: info@arpansa.gov.au                                                                                 Web: www.arpansa.gov.au
 Telephone: +61 3 9433 2211                                                                                     Fax: + 61 3 9432 1835

				
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