Answer to Question #5211 Submitted to "Ask the Experts"

Q

I work for the TSA (Transportation Security Administration). It claims the amount of radiation emitted from the machines is roughly what we would receive from typical environmental background radiation. What would the effects from this "usual dose" spread out over eight hours times a five-day work week be compared to, let's say, your typical low-dose x ray on an arm.

We've had our dosimeter badges removed after a study conducted by NIOSH (National Institute for Occupational Safety and Health) said there are almost no emissions. I know the machine is actively scanning about 80% of the time and, frankly, the lead curtains are heavily worn. On several occasions customs agents have had their equipment in a tizzy just passing PAST the x-ray machine, not even through it. I would assume this indicated leakage. When you can easily see through certain thicknesses of metal objects, I doubt it is such a small dose.

The person who maintains the equipment on contract just happens to be the same guy who certifies it is producing proper emissions amounts. Would this not be a conflict of interest on his or his company's part as a radiation compliance inspector?

A

The federal law (Title 21 of the Code of Federal Regulations, Section 1020.40) requires "all x-ray systems designed primarily for the inspection of carry-on baggage at airline, railroad, and bus terminals, and in similar facilities" to have a radiation "Emission Limit." The "Radiation emitted from the . . . x-ray system shall not exceed an exposure of 0.5 milliroentgen in one hour at any point five centimeters outside the external surface." You may well ask, "What does that mean?"
The average person in the United States gets about 365 milliroentgens a year from natural and medical x-ray exposure, including exposure to natural radon gas in the air. This is about 1 milliroentgen a day.

If you stood 5 centimeters (about two inches) from the side of the x-ray system your skin would get about 0.5 milliroentgen every hour; thus standing still there for eight hours your skin would get 4 milliroentgens a day and 20 milliroentgens a week. Notice, I said your skin.

I said your skin, because the x rays used in baggage scanning are close to the same kind (energy) as the x rays used to x ray people at a doctor's office. For one chest x ray, at the doctor's office, the body's dose is usually 8 milliroentgens while the skin's dose could be about 24 milliroentgens. This is because the x rays are of such a low energy that a lot of the x rays are stopped by your skin. Bones stop almost all the x rays and, thus, show up easily on the x-ray film.

Also, as you move away from the x-ray system, your skin being the closest to the machine, the radiation emitted from the system also drops off quickly, just like the heat from a fire is much less intense as you move away from the fire.

So, if you work a few feet away from the x-ray system, the emitted radiation should be a very small percent of the limit of 0.5 milliroentgen in one hour.

Concerning "the lead curtains are heavily worn. On several occasions customs agents have had their equipment in a tizzy just passing PAST the x-ray machine, not even through it." It may be that there is leakage of radiation above the limits. However, detecting this with the customs agent's equipment really depends upon the sensitivity of his/her radiation detection equipment. If they have a microR (microroentgen) meter (one-thousandth of a milliroentgen is a microR) the equipment will certainly be registering (be in a tizzy) when the radiation emitted is even around 10 to 20 microR per hour (or 0.010 to 0.020 milliroentgen in one hour), which is two to four percent of the regulatory limit. Also, contamination or "pancake" radiation detectors have the same kind of response as microR meters. If you suspect that the x-ray system's shielding has been compromised, by wear or other means, you should ask your management for a survey of the device by a qualified expert. A certified health physicist (CHP) is such an expert. The Food and Drug Administration has such experts, your state may also hire such experts, and a local hospital that uses x-ray machines should have a person qualified to measure the system's emitted radiation, to assure that the emitted radiation is within the regulatory limits.

Concerning "The person who maintains the equipment on contract just happens to be the same guy who certifies it is producing proper emissions amounts. Would this not be a conflict of interest on his or his company's part as a radiation compliance inspector?" I think this is not a conflict of interest because if the maintainer finds that the radiation levels are too high, he/she now has the perfect reason to charge a fee to replace parts, repair the unit, or replace the entire system with a new unit. Thus, it may be in his/her best interest to measure radiation levels that are too high.

John P. Hageman, MS, CHP