Are airport scanners safe?

The new generation of airport safety scanners could pose a significant public health risk, according to leading scientists.

These ‘backscatter’ scanners, as they are officially known, are one of two types of full-body scanning machines being rolled out at airports across the US and the UK to reduce the threat of terrorists. The other type uses millimetre technology (radio waves) rather than X-rays.

They are known as ‘naked’ scanners because of the graphic image they give of the body. Both machines have sparked widespread privacy concerns. However, it is the backscatter devices which emit small doses of ionizing radiation that worries a group of scientists.

Four professors from the University of California (UCSF) – John Sedat, Professor Emeritus in Biochemistry and Biophysics, Marc Shuman, an internationally recognised cancer expert and David Agard and Robert Stroud, X-ray crystallographers and imaging experts – recently wrote to President Barack Obama’s Science and Technology adviser, John Holdren, about the potential serious health risks of the airport backscatter scanners.

Their main concern was that the safety of these devices has not been adequately demonstrated.

Considering the plans to rapidly implement these scanners as a primary screening step for all air-travel passengers, thereby exposing hundreds of millions of people to them, the scientists stressed the need for independent evaluations.

They voiced particular concern over the dosage of X-ray energy delivered by the backscatter devices to a scanned person’s skin.

They wrote: “These new devices operate at relatively low beam energies (28 keV). The majority of their energy is delivered to the skin and the underlying tissue. Thus, while the dose would be safe if it were distributed throughout the volume of the entire body, the dose to the skin may be dangerously high.”

The scientists believe the X-ray dosages from these machines have misleadingly been compared with cosmic-ray exposure, which we all encounter during air travel or chest X-rays.

They said: “Both the air travel cosmic-ray exposure and chest X-rays have much higher X-ray energies, and the health consequences are appropriately understood in terms of the whole body volume dose.

“In contrast, these new airport scanners are largely depositing their energy into the skin and immediately adjacent tissue, and since this is such a small fraction of body weight/volume, possibly by one to two orders of magnitude, the real dose to the skin now high.”

The letter also identifies vulnerable groups that may be at particular risk from such high skin doses, such as children, pregnant women, the elderly, and people with compromised immune systems such as HIV and cancer patients.

In addition, we could all be at risk if the machines malfunction. Any glitch in power at any point in the hardware or software that causes the device to stop could then deliver an intense radiation dose at a single spot on the skin, as no technology is perfect.

According to a recent posting on the White House’s Office of Science and Technology Policy webpage, the official response was an e-mail sent by Office director Holdren to the professors noting that the issue had been “studied extensively for many years by the Food and Drug Administration, Department of Health and Human Services and Department of Homeland Security.”

However, he conceded that the government needs to better explain the safety issues surrounding the backscatter scanners, and so asked representatives from the FDA and DHS to address the concerns raised in the letter.

The response concludes: “The potential health risks from a full-body screening with a general use X-ray security system are miniscule… we are confident that full-body X-ray security products and practices do not pose a significant risk to public health.”

However, this response does not satisfy Prof. Sedat. When he was interviewed, he called the reply “deeply flawed” and “double talk”, and said it didn’t answer any questions.

“Sadly, I have to say we still don’t have the information we need to decide what the dangers of this device are,” he commented, adding the group would make a full and formal reply to Holdren.

Other scientists remain equally unconvinced by the government’s response. David Brenner, who heads Columbia University’s Centre for Radiological Research, said in an interview: “I don’t think anybody would argue that point that the individual risk is small. But multiply that time by 700 million people (the number of people boarding planes at the moment) and that is the public health risk.”

He added that there is reason to believe the radiation dose delivered per scan is higher than the government says it is, based on calculations by Arizona State University researchers, published online on November 9, 2010, ahead of print in the peer-reviewed journal Radiation Protection and Dosimetry.

Although the estimated doses are still well below those associated with health effects, it is possible that certain groups, such as pilots and very frequent fliers, could reach the recommended annual radiation-dose limit. Brenner believes this will result in some cancers coming out of each year’s scanning operations.

Clearly, considerably more research is required on both types of scanners. In the meantime, what can be done for protection? In the US, travellers can still opt out of a full-body scan and receive a slightly more intrusive ‘pat-down’ as an alternative.

In the UK, restrictions have come into force that make it impossible to fly if one refuses to be subjected to a full-body scan. This mandatory screening is likely to be enforced in the US and other countries in the near future.

kathryn@maltanet.net