Air travelers embarking from most major airports in the U.S. this year may find themselves in a security line for one of two types of scanners: A backscatter X-ray unit (the gray and blue rectangular booth) or a millimeter wave unit (the gray cylindrical booth with clear windows).
Both units work by firing a beam of radiation at the person being scanned. An image of the radiation that bounces back is created and viewed by a Transportation Safety Administration worker in another room. For both units, the TSA worker in the side room cannot see the person being scanned and workers operating the machine cannot see the images. If a suspicious item appears on the scan, the person then undergoes a thorough pat-down.
The backscatter X-ray unit is the one generating the most questions. Dr. David J. Brenner, the Higgins Professor of Radiation Biophysics at Columbia University, recently answered x-ray scanner questions during a National Public Radio interview.
“[W]e know that X-rays can dam
age DNA in cells, and we know that X-rays can ultimately produce cancer. So the concern is about the possibility of inducing X-ray-induced cancer in one of the individuals who’s scanned,” Brenner said in the interview.
The TSA says that the amount of radiation a person absorbs during a backscatter X-ray scan is equivalent to the same amount a person is exposed to over a period of two minutes when flying in an airplane at cruise altitude.
CBS medical correspondent Dr. Jennifer Ashton reported that if 1 billion people a year go through an X-ray scanner, 10 additional cancer deaths – a fraction of one percent – would result each year.
The government estimates that each scan is the equivalent of one thousandth the amount of radiation in a chest X-ray. Some scientists, however, question the government’s figures.
Looking at the images produced by the scanner, Peter Rez of Arizona State Univeristy estimates that the true amount is closer to one one-hundredth or even one fiftieth of a chest X-ray dose. The probability of death, he said, was closer to one in 20 million. While that’s still a fraction of a percent, it is a higher risk than the risk of dying from a terrorist attack, which he put at one in 30 million.
Though the scanners could result in deaths, the risk is still far smaller than other risks, like the one in 500,000 risk of being struck by lightning in a given year.
Another group of scientists at the University of California, San Francisco, sent a letter to the President’s science and technology adviser arguing that the X-ray scanner poses a greater risk than medical X-rays and the radiation absorbed during a flight. In those two cases, the radiation is distributed evenly throughout the body, the doctors say. The radiation from the scanners, however, is embedded in the skin, resulting in a higher concentration of radiation in a given area.
Questions remain including how the X-ray scanners will affect frequent flyers (including businessmen and flight attendants who could go through security anywhere from 200 to 400 times a year), children, pregnant women and travelers with weakened immune systems. There is also a question of what could happen should a machine get stuck or fail, potentially blasting one point on a person’s body with excess X-ray radiation.
The good news about scanners: Millimeter wave scanners, which are also in use at airports around the country, use very far infrared waves, waves at the opposite end of the electromagnetic spectrum from the dangerous ionizing radiation of X-ray waves. X-rays are shorter waves that can penetrate the skin and alter DNA. Millimeter waves, by contrast, are longer waves that penetrate clothes but stop at the skin. The millimeter scan is akin to a heat lamp and is considered to be far safer than X-ray scanners.
The TSA plans to have 1,000 scanners in place at airports across the U.S. by the end of next year and as many as 1,800 in place by 2014 with the goal of making the scanners (or opting out) a mandatory part of security screening.
Passengers can elect to opt-out of either type of scan, but will be required to undergo a thorough pat-down, including an investigation of sensitive areas previously untouched by TSA workers. One website is calling for the day before Thanksgiving to be a national opt-out day, which would force the TSA to do more of the 1-2 minute involved pat-downs versus the 5-7 second body scan and could cause a significant security line logjam.
One Congressman, Ron Paul of Texas, is sponsoring legislation to fight the new scanning requirements, arguing that the examinations are a violation of the fourth amendment protecting U.S. citizens from unreasonable search and seizure.
In any case, as with any new technology prompting health questions, expect for some confusion among travelers facing the new screening devices and plan ahead. The busiest air travel day of the year just got busier.
