Ionization smoke detectors were one of the most widely used smoke alarm systems in Germany until the 1990s. While the intensity of use in Germany has declined significantly due to various factors and fire protection is now more optical smoke detectors used, counts the ionization smoke detector, among others in the United States or Australia, continues to be the most widely used smoke detection systems and also in other countries Use.
What are ionization smoke detectors and how do they work?
Ionization smoke detectors – often also referred to as ionization detectors or, for short, as I-detectors – are smoke detectors which detect smoke or fire particles using an ionization current.
For this purpose, a radioactive substance is used, which is usually placed on a support as a radiator foil and fixed in the housing of the smoke detector. The radiator foil emits radiation which ionizes the air in the smoke detector. Using an electrical voltage creates a so-called ionization whose size is changed upon entry of smoke particles or fire aerosols. Using an evaluation, this leads directly to the alarm triggering.
The structure of the ionization smoke detectors differs above all through this electronics as well as through the used measuring chambers and reference ranges, which are needed for the detection of the ionization current. The radioactive substance is usually the chemical element americium, which is also used in other areas as a source of ionizing radiation and is used here with activities of about 15 to 40 kilobecquerels. Older ionization smoke detectors can also be equipped with Radium 226.
The radioactive material is installed in the ionization smoke detector in a precious metal foil and also integrated into a plastic housing. As a rule, there is no risk of radiation because the radiation range in air is a few centimeters and in body tissue at fractions of a millimeter. The outer skin layers can therefore not be penetrated.
However, a serious health risk can occur if the radioactive material is absorbed.
What are the advantages and disadvantages of ionization detectors?
In comparison with other smoke detection systems, such as thermo-optical smoke detectors or photo-optical smoke detectors, it can be seen that the ionization smoke detector can be classified as particularly reliable and fast and triggers relatively few false alarms.
The disadvantages of the ionization smoke detector arise from the radioactive material used. Although the radiation is safe, as long as the housing is intact, due to the numerous provisions and requirements, these smoke detectors are rarely used in Germany, mostly in commercial buildings in extremely hazardous areas. Because the ionization smoke detector responds quickly to fires with an open flame as well as liquid fires and reports even small smoke particles and is therefore very well suited in this area.
Smoldering fires, however, recognize this smoke detection system less well.
Depending on the manufacturer, an ionization smoke detector can be used for between ten and 15 years. Since the system contains radioactive substances, the device – unlike optical detectors – must be checked every ten years by an expert for leaks. The maintenance of the detector must be approved.
Are ionization smoke detectors prohibited?
Ionization smoke detectors are generally permitted in Germany as a fire protection reporting system, whereby a general ban applies to private households throughout Germany. Both the acquisition, handling and maintenance as well as the disposal of the detectors in the so-called Radiation Protection Ordinance ( StrlSchV ) is regulated. This states that the handling of equipment and devices containing radioactive components must be approved.
With the ionization detectors, only one exception is made if they are type-approved. This approval is granted in Germany by the Federal Office for Radiation Protection and various requirements must be met – for example, that the radioactive components are shrouded safe and tight and the tightness is maintained even in case of fire. The activity of the substance, mostly americium-241, must not exceed a certain value of kilobecquerel.
For example, while ionization smoke detectors may be disposed of with household waste in the United States, they must be returned to the payee or a collection agency in Germany after approval has been obtained. If there is a fire or if the building is demolished, all ionization smoke detectors must be removed by the requirements. If this can not be ensured, the entire building rubble must be disposed of as hazardous waste.