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Information Sheet No. 8

Reviewed August 2009

This publication can be downloaded as a PDF (94 kB)

Domestic Smoke Alarms

There are two forms of inexpensive domestic smoke alarms sold in New Zealand:

1. ionisation smoke alarms, and
2. photoelectric smoke alarms.

Ionisation smoke alarms contain a radioactive source (americium-241) while photoelectric smoke alarms contain a light-sensitive cell.

The amount of americium-241 contained in a domestic ionisation alarm is very small, typically 37 kBq (kilobecquerels) or 1 microcurie.

To place this in context:

• One smoke alarm has a radioactive content equivalent to that naturally present from potassium-40 in ten human bodies.
• One smoke alarm has a radioactive content equivalent to that naturally occurring in 0.08 cubic metres of soil.
• The average New Zealand brick house has a radioactive content equivalent to that contained in 300 - 400 smoke alarms.

Any health risk associated with the use of the small americium-241 sources in smoke detectors is negligible.  The external radiation from the detector makes a very small addition to the naturally occurring background level, and this small addition is much less than variations in the natural background levels from place to place.  There is no credible risk from ingestion because:

• The radioactive source is securely sealed within the ionisation chamber of the alarm, and cannot fall out or be accidentally removed.  Removal requires a dedicated effort.
• The form of americium-241 used is a non-dispersible foil.  Even if swallowed, the material would pass through the body with a calculated maximum absorption of one percent or less.

The importation and use of radioactive substances is controlled in all developed countries, including New Zealand.  This is achieved under the provisions of the Radiation Protection Act 1965 and the Radiation Protection Regulations 1982.  The general approach to the importation of radioactive substances is to control and monitor importations, and subsequent use and disposal unless such substances are exempted by regulation.  Smoke alarms are an exempt item within the current regulations.  This is consistent with current international exemption guidelines.

The recommended method of disposal of smoke alarms is by means of conventional refuse collection and subsequent landfill.  The reasons for this include:

• Random disposal within household refuse results in random distribution within a large landfill site.  The net increase in radioactive content per cubic metre of landfill is negligible.
• If the radioactive source is left within the ionisation chamber of the smoke alarms it ensures effective long-term storage.
• The americium-241 foil is not water soluble and therefore even after long-term breakdown of the smoke alarm it will not contaminate water tables with leachate.

For further information, contact:

National Radiation Laboratory
P O Box 25099
Christchurch
New Zealand

Phone:

+ 64 3 366 5059

Fax:

+ 64 3 366 1156

Internet:

http://www.nrl.moh.govt.nz

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