Smoke alarms

You should always have a working smoke alarm in your home – it could save your life.

The New Zealand Fire Service website has advice on choosing, installing and maintaining smoke alarms. Ideally, you should have a smoke alarm in each living room, bedroom and hallway.

Types of smoke alarm

There are two main types of smoke alarm.

  • Photoelectric smoke alarms detect smoke when it affects the light levels in a sensor chamber.
  • Ionisation smoke alarms detect smoke when the particles block the stream of ions (electrically charged particles) in a sensor chamber.

The New Zealand Fire Service recommends people only install photoelectric smoke alarms. They are better at detecting different kinds of fire.

Radiation and ionisation smoke alarms

Ionisation smoke alarms contain a radioactive source called americium-241. The americium releases ions into a sensor chamber. When the flow of ions is interrupted (by smoke particles), the smoke alarm goes off.

The amount of americium in the smoke alarm is very small. You’d need 300–400 smoke alarms to get the same radioactivity as the average brick house.

Exposure to radiation

The radiation from the americium is almost totally absorbed inside the smoke alarm. Only a small amount gets out – less than 0.01% of what you get from natural sources, such as cosmic rays and the radioactivity in soil.

Risk of poisoning

There is no risk of poisoning from your smoke alarm.

The americium is bonded to a metal foil. Even if you did swallow it, you would only absorb a tiny amount of radioactivity. And the foil is sealed inside a metal chamber inside the alarm. It cannot fall out or be removed by accident.

If the alarm is fire-damaged

If you do have a house fire and your smoke alarm is burnt, there’s no danger of radioactive smoke.

The metal foil containing the americium-241 has been tested thoroughly. It can withstand heating to over 800°C for more than 30 minutes, without any release of radioactivity. This is a much more severe test than most house fires.

Disposing of old smoke alarms

When your smoke alarm fails, you can put it out in your normal rubbish disposal.

On average, a cubic metre of New Zealand soil is about as radioactive as 13 smoke alarms. Disposing of smoke alarms in a landfill doesn’t really change the landfill’s overall radioactivity.

In fact, the natural radioactivity of domestic rubbish is less than that of soil. Even if every household threw out several smoke alarms a year, the average radioactivity in landfills would still be lower than in most New Zealand soils.

Transporting smoke alarms

You can send smoke alarms in the mail or transport them by any means within New Zealand. The amount of radioactive material in the alarms is so small that the rules for transporting hazardous materials don’t apply.

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