The small amount of radioactive material in some smoke alarms is not a risk to health.
The ability of domestic smoke alarms to save life and property in house fires is well established. Some domestic smoke alarms use the radiation from a small amount of radioactive material to detect smoke or heat sources. The radiation dose to the occupants of a house from these smoke alarms is very small and does not pose a health risk. Due to the small amount of material used and the secure means of its encapsulation, these smoke alarms are completely safe under all normal conditions it may encounter, including during a fire.
How smoke alarms work
Smoke alarms that use radioactive material incorporated in an ionisation chamber are called 'ion chamber smoke alarms'. The application of a low-level electric voltage to the ionisation chamber which contains a radioactive source (Americium-241) causes a steady electric current to flow. Smoke or hot air entering the chamber changes the electric current level, triggering an alarm.
Australian smoke alarm standards
The Australian Standard AS3786:2015 Smoke alarms using scattered light, transmitted light or ionization requires domestic smoke alarms to be labelled with:
AS3786 also sets down various requirements for the radiation source itself including the type and activity of the source that can be used.
The CSIRO's ActivFire Scheme tests the ability of smoke alarms to detect smoke, in accordance with AS3786.
Radiation from natural sources is always present in the environment. It is in the food we eat, the air we breathe and the buildings we live in. This type of exposure is known as background radiation. Besides the radioactive materials that occur naturally in our environment, there are human-made radioactive materials. Americium-241 is one such material.
The dose rate from a domestic smoke alarm at a distance of one metre is less than one thousandth of that from background radiation, which in Australia is on average 1.5 millisievert per year. At greater distances, the dose rate is much lower. The dose rate to the hands when holding a smoke alarm is higher but is still less than one tenth that from background radiation. As the hands are very much less sensitive to radiation than internal organs and the time of exposure is likely to be only a few minutes per year, no significant radiation exposure would occur.
The radioactive source in a smoke alarm is extremely insoluble and, if swallowed, would not be absorbed into the body but would pass through the digestive system.
In a house fire, temperatures are unlikely to exceed 1200°C. While such a fire temperature might be sufficient to melt the source it would not be enough to vaporise it and create an inhalation hazard.
Individual (or small numbers of) smoke alarms can be safely disposed of in domestic rubbish. The amount of radioactive material in each smoke alarm is extremely small. From environmental and public health perspectives, the disposal of individual smoke alarms with domestic rubbish does not represent any risk.
When more than ten smoke alarms (or more particularly, the Americium-241 sources) are collected together for bulk disposal, they must be treated as radioactive waste, and the requirements of the National Health and Medical Research Council's Code of Practice for the Near-Surface Disposal of Radioactive Waste in Australia (1992) must be met. Contact your state or territory radiation control authority for advice.