Context - Because of increased concern over terrorist attacks on aircraft, sensitive security scanners have been developed to screen passengers at airports more effectively.
Some of these scanners use X-rays, which is a type of radiation that can cause cancer and other health problems. Is their use safe for passengers and workers?
1. Introduction
Increased concerns for terrorist attacks has led to the development of new passenger screening methods.
Because of increased concern over terrorist attacks on aircraft, sensitive security scanners have been developed to screen passengers at airports more effectively. Some of these scanners use X-rays, which is a type of radiation that can cause cancer and other health problems. X-rays are one type of so-called “ionizing radiation”, which also include the radiation from radioactive materials. It is called “ionizing” because it has enough energy to knock out an electron from a molecule, turning it into an ion by giving it an electric charge. This can bring about chemical reactions that are potentially damaging to biological systems. When these reactions affect the genetic material of a cell, then there is the possibility of causing cancer. Everyone is exposed to background ionizing radiation from naturally-occurring radioactive rocks, from space, and from breathing in indoor radon. People also receive radiation from medical X-rays or if they are given radiotherapy in the treatment of cancer. The harmful effects of exposure to high doses of radiation are well known and are used to predict the likely risks to health of low doses, for which there are no experimental data. More...
2. What are the current guidelines for radiation protection?
Any procedure that exposes people to ionising radiation needs to be judged to do more good than harm, either to the individual or to society as a whole. The number of people exposed and the level of exposure need to be as low as reasonably achievable; and the dose received needs to be below a set limit.
Dose limits are different for medical and for non-medical applications, and also vary depending on circumstances. For the purpose of security screening, members of the public should receive no more than 1 millisievert of ionising radiation per year. This limit also applies to people who, because of their work, might be scanned frequently, such as air crews or couriers. More...
3. What are the technologies used in the proposed security scanners?
At present there are two types of X-ray scanners. One type (the backscatter technique) uses low energy X-rays that penetrate only the clothing and show up an image of the body and any objects concealed near the surface. The second technique (transmission) uses X-rays of considerably higher energy that go through the body, like in a medical image. This method can show objects swallowed or concealed inside the body.
Because ionising radiation is potentially harmful, manufacturers are responsible for fitting scanners with safety systems to avoid misuse and to ensure they remain safe even if there is a malfunction. More...
4. How is radiation exposure measured and assessed?
Frequent flyers and airline crews might be exposed to more radiation than the limits set for the general public
The best measure of the health risk from ionising radiation is the effective dose. This takes into consideration the type of radiation and the sensitivity of the body parts exposed. It is measured in Sieverts or millisieverts (thousandths of a Sievert).
A single scan delivers an effective dose of the order of a thousandth of a millisievert for the transmission technique, and about ten times less for the backscatter technique.
A frequent flyer, air crew or courier, who is scanned three times every working day would receive an annual dose of about 0.3 millisievert with the backscatter technique, which is below the limit set for the general public. However, if all the scans were done with the transmission technique, the annual dose would be close to 3 millisievert, which is too high and does not comply with radiation protection standards. More...
5. What are the health effects of exposure to ionizing radiation?
The very small doses of radiation from security scanners cannot cause any short-term tissue damage. High doses of ionising radiation have effects on the genetic material of cells, can cause cloudiness of the lens of the eye and increase the risk of cardiovascular disease and cerebrovascular disease. However, only the potential increase in cancer risk is relevant for the low doses considered here.
There is direct evidence that dose levels higher than 10 to 20 millisievert increase the risk of cancer in humans. The biological effects of doses from X-ray scanners are so low that they cannot be measured in experiments on animals or in cells grown in the laboratory. Therefore, the potential increase in cancer risk from security scanners cannot be estimated but is likely to be so low that it cannot be distinguished from the background risk due to other factors. Any increase in the number of cancer cases would be too small to show up in epidemiological studies, even if they involve large populations. More...
6. Conclusion: are X-ray security scanners safe?
Health risks are close to zero for individuals, but the risk cannot be ignored for populations.
The purpose of security screening using X-rays is to benefit society as a whole by improving aircraft security. While the additional risk to a single person being scanned is very close to zero, if screening is widespread and concerns a large part of the population, this vey small risk cannot be ignored at the population level. Estimates on the magnitude of any added risk are very uncertain and it is impossible to evaluate separately the effects on different groups of the population.
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