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Radiation protection aspects in full-body scanners
- Especially at airports full-body scanners are increasingly used for security screening (passenger screening).
- There are passive and active scanners. Passive scanners detect natural radiation that is emitted by a person’s body and use it to locate objects worn or hidden on a person’s body. Active systems add artificial radiation to improve detection (backscatter technology).
- In 2010, the BfS conducted immission measurements on two active full-body scanners using millimetre wave technology in order to estimate the expected radiation exposure to screened individuals.
- According to the measurements, both systems give rise to low exposures to high-frequency electromagnetic fields. Health effects are not to be expected.
Full-body scanners can detect and locate forbidden objects concealed under a person’s clothing. In contrast to metal detectors used extensively at passenger airports, the new devices also respond to non-metallic objects such as explosives. In order to protect the privacy of screened individuals, latest generation devices do not show the operator any body images of the screened person but highlight suspicious body areas on a generic body image (matchstick figure). The security staff can then check the relevant body areas using other methods, for example a pat-down search.
According to the technology used, a basic distinction is made between the following types of devices:
active scanners / backscatter scanners
- with millimetre wave or terahertz radiation
- with X-rays
- passive scanners with millimetre wave or terahertz radiation.
Millimetre waves are high-frequency microwaves in the frequency range between 30 and 300 gigahertz. This range is followed by infrared radiation towards the direction of even higher frequencies in the electromagnetic spectrum. The frequency range from a few hundred to a few thousand gigahertz is also referred to as terahertz (THz) radiation (1 terahertz = 1000 gigahertz). Millimetre wave and terahertz radiation are non-ionising types of radiation. The human body itself emits radiation in these frequency ranges.
Passive scanners detect the radiation emitted by a person’s body and use it to locate objects worn on the body. As the body is not exposed to any additional radiation using the passive technology, health risks can be ruled out completely. From the radiation protection point of view, preference should therefore basically be given to passive systems.
Active systems add artificial radiation to improve detection (backscatter technology). The body is scanned point by point by the radiation and the detectors of the device. It is widely known that the frequency range starting from 10 gigahertz is basically suitable for that purpose. Higher frequencies allow higher resolution for the images produced.
Active scanners using X-rays
X-rays are ionising radiation that can directly damage human body cells. For this reason there is no safe threshold below which X-rays do not represent a health risk. The BfS rejects the application of X-ray-technology for full-body scanners for reasons of radiation protection. Its use is not justified because alternative methods without ionising radiation are available. Devices using ionising radiation are not listed as possible screening equipment to be deployed at EU airports in the Commission Implementing Regulation (EU) 1147/2011 concerning the basic standards on civil aviation security which entered into force in late 2011.
In 2010, the BfS conducted immission measurements on two active full-body scanners using backscatter technology in order to estimate the expected radiation exposure to screened individuals. Both systems use non-ionising radiation with frequencies directly below the frequency range usually referred to as "millimetre waves".
According to the measurements, both systems comply safely with internationally recommended general public exposure limits for the protection of human health. On account of the measured power flux densities and considering the exposure duration expected during operation, typical radiation exposure to the screened airline passengers can be estimated to be less than 0.0001 per cent for one of the systems and about 0.001 per cent of the recommended limit value for the other system.
Higher radiation exposures are possible
- when the transmitter antennas are approached in an atypical way
- when examinations are repeated within short time spans (a few seconds to minutes) and
- when a longer time is spent within the influence of devices in which the transmitter is permanently enabled. This was the case in one of the two tested devices.
For such unfavourable situations the radiation exposure resulting from one of the devices was estimated to be about 0.01 per cent and about 1 per cent of the limit value for the other.
The depth of penetration of non-ionising radiation into the human body in the frequency ranges used is small. At 10 gigahertz it is only a few millimetres and decreases with increasing frequency. The radiation does not reach deeper organs. However, the depth of penetration is sufficient to reach cells of the skin, of the peripheral blood circulation and of the peripheral nervous system. Damage to the cells can have local as well as systemic effects.
It is beyond dispute that non-ionising radiation absorbed by the body has thermal effects at sufficient intensity. The limit values recommended for the frequency range used by the devices are based on this thermal effect. There are a number of laboratory investigations on various cellular and subcellular endpoints for the microwave range up to about 10 gigahertz. However, the number of available investigations on higher frequencies is very low.
Research findingsshow / hide
Only a few working groups researched the effects of millimetre wave or terahertz radiation on cell culture systems. First to be mentioned in this context is the EU research programme "THz-Bridge". The effects on DNA and the distribution of chromosomes were examined in particular. No effects were found for exposure durations under an hour. For an exposure duration of at least two hours (not less) at 100 gigahertz, an Israeli working group described disturbances in the distribution of chromosomes in lymphocytes which are able to divide (Korenstein et al. 2008).
An investigation on a particular cell line in vitro indicated disturbances of the spindle apparatus, which is important for the distribution of chromosomes (Hintzsche et al. 2011). However, a departmental research project on human skin cells (fibroblasts and keratinocytes) commissioned by the BfS, found no indication of chromosomal damage at radiation exposures of 106, 380, and 2,520 gigahertz in the micronucleus assay and no indication of DNA damage in the COMET assay (Hintzsche et al. 2012, Hintzsche et al. 2013).
Assessmentshow / hide
The few results available from investigations on the frequency range of active full-body scanners using millimetre wave or terahertz radiation do not yet allow a final assessment from a radiation protection point of view.
The limit values recommended for this frequency range by the European Council and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) are based on few existing scientific studies. According to the recommended limits, the power flux density for the radiation exposure of the general population shall not exceed 10 watts per square metre (W/m²). Radiation exposures from the devices tested by the BfS in 2010 are significantly lower. It is only on this condition, that the use of full-body scanners is acceptable from a radiation protection point of view.
In accordance with the fundamental principles of radiation protection, unnecessary exposures should be avoided. From the radiation protection point of view preference should therefore basically be given to the use of passive systems.
Further research is needed
As there are still comparatively few data on biological effects in the millimetre wave and terahertz frequency ranges, the BfS has already commissioned investigations within the scope of departmental research and intends to go on doing so. Methods to determine exposure were investigated in the project Development and Application of Methods to Determine the Exposure to Non-ionising Radiation with Frequencies in the Terahertz Range.
Referencesshow / hide
- Avital Korenstein-Ilan, Alexander Barbul, Pini Hasin, Alon Eliran, Avraham Gover, Rafi Korenstein (2008): Terahertz Radiation Increases Genomic Instability in Human Lymphocytes. Radiation Research: Vol. 170, No. 2, pp. 224-234, doi: 10.1667/RR0944.1 (Abstract)
- Hintzsche H, Jastrow C, Kleine-Ostmann T, Stopper H, Schmid E, Schrader T (2011) Terahertz Radiation Induces Spindle Disturbances in Human-Hamster Hybrid Cells, Radiation Research: Vol 175, No 5, pp. 569-574 (Abstract)
- Hintzsche H, Jastrow C, Kleine-Ostmann T, Kärst U, Schrader T, Stopper H (2012), Terahertz Electromagnetic Fields (0.106 THz) do not induce manifest genomic damage in vitro, PLoS One, doi:10.1371 (Full text)
- Hintzsche H, Jastrow C, Heinen B, Baaske K, Kleine-Ostmann T, Schwerdtfeger M, Shakfa MK, Karst U, Koch M, Schrader T, Stopper H (2013), Terahertz Radiation at 0.380 THz and 2.520 THz Does Not Lead to DNA Damage in Skin Cells In Vitro. Radiat Res 179 (1): 38 – 45 (Abstract)
State of 2017.05.24