Security Screening

Is it true that some walk-through scanners actually use x rays to screen people?

Yes, some of these are now being used in large international airports, such as Heathrow in London. There is very little radiation dose for a person passing through the scanner because the people running the scanners are not trying to see the detail of our "soft" tissues, as is done in medicine. They are looking for items that will stand out pretty easily.

According to the American National Standards Institute, in its standard N43.17-2002 "Radiation Safety for Personnel Security Screening Systems Using X-Rays," the maximum effective dose an individual could receive when walking through this scanner is 0.1 µSv (µSv is a unit of effective radiation dose). For some perspective on the level of this dose, the annual effective dose each of us receives from background radiation is about 3,600 µSv; the effective dose from one chest x ray is about 100 µSv. 

Is it safe for someone with a medical implant to go through the airport (or office-building) metal detectors?

There are two papers published in literature that discuss this. The more recent article, published by M. Niehaus and colleagues in 2001, discusses pacemakers and states: "In 103 patients who were monitored as they passed through typical metal detectors, security alarms invariably were activated. In none of the patients was the pacemaker function affected. It is therefore accepted practice to advise patients that while airport screening devices may detect the pacemaker, the device will not be adversely affected. Patients should carry their device identification card for the purpose of obtaining security clearance."

According to the articles' conclusions, patients can go through metal detectors without causing a pacemaker or cardioverter-defibrillator malfunction. For other types of implants, it may be best to ask your physician.

References
Niehaus M, Tebbenhohanns J. Electromagnetic interference in patients with implanted pacemakers or cardioverter-defibrillators. Heart 86:246–248; 2001.

Copperman Y, Zarfati D, Laniado S. The effect of metal detector gates on implanted permanent pacemakers. Pacing Clin Electrophysiol. 11:1386–1387; 1988.

I travel a lot (at least once or twice a week) and will continue to do so in the foreseeable future. Obviously, I have to go through the metal detector at least twice for each trip. What effect does this radiation exposure have on me in the long run?

The metal detector does not expose you to ionizing radiation, e.g., x rays; neither do the wands that are used for individual screening. Metal detectors operate by generating a low-intensity magnetic field that passes from one side of the detector to the other. If metal objects pass through that field, the magnetic field will induce a second field in the metal object. Since that second field is a disruption of the first field, the detector senses the change and sets off an alarm. Magnetic fields are a form of radiation, but they are called "nonionizing" radiation. This means that magnetic fields do not generate additional, damaging radiation the way that ionizing radiation (such as x rays) does. Magnetic fields below a certain intensity are considered to be safe in that they will not cause any biological damage to an individual. As a reference, MRI (magnetic resonance imaging) is considered safe and uses much higher magnetic field intensity than a metal detector. In summary, because of its nonionizing properties, the magnetic field generated in a metal detector will not cause harm to persons, even with routine and/or repeated scanning. 

I work for a major airline and will be required to spend eight hours a day near the new baggage x-ray machines (the big ones that I think are computerized tomography [CT] machines) that the Transportation Security Administration (TSA) uses. We have been given a handout saying that TSA has determined that the machines are not dangerous and that we do not need film badges. How can anyone say working near radiation is not dangerous if it is not monitored in any way?

Some of the newer x-ray machines used to scan checked luggage use CT technology, just like those used in medicine. The main difference between the two types of use (security at airports and medical diagnosis) is that the machines used in airports have more shielding to stop the scattered radiation (nearly the entire luggage belt is shielded; in medicine, the patient table is not shielded) and the baggage is subjected to lower doses because the image does not need to be as clear as it does for a patient.

Someone standing next to the unit in airports would receive little, if any, radiation exposure. Radiation emitted around a piece of equipment when it is operating is determined by the manufacturer and, sometimes, checked by the purchaser. A manufacturer must assure the equipment is operating within federal regulations that govern x-ray equipment, which in this case is 1.3 × 10^-7 C kg^-1 at 5 cm from the unit (Coulomb per kilogram [C kg^-1] is a unit of radiation exposure), though performance studies of the equipment indicate that the average exposure rate was about 2.1 × 10^-11 C kg^-1 per scan (NCRP Report 95). Purchasers can use the manufacturer's assurance and/or can perform their own surveys on the equipment. The dose to the luggage is very low and there is no detectable radiation outside the machines, according to one manufacturer.

What does it mean when my employer says the machines are safe because no "leakage" was found? What is leakage? I work around those big checked-luggage scanners, so what does leakage mean to me in terms of radiation exposure?

When we say "leakage," that simply means when the x-ray beam is on, the tube housing has some radiation coming through it. Actually, it always does and x-ray machine regulations limit the amount that can come through. So, in this case, "leakage" means someone was able to detect radiation being emitted through the tube housing at levels higher than what the regulations allow.

With that in mind, though, it does not mean that radiation was coming through the shielding around the unit. The scanners have shielding around them to make sure the x-ray beam cannot escape and expose people to unnecessary radiation. So even if radiation was leaking through the tube housing when the unit was on, it is unlikely it also went through the unit's shielding.

When people are not wearing radiation dosimeters, there are a couple of other ways to find out if a machine is "leaking." One is the recognition that the images are not of the same quality as they should be. If the images are deteriorating significantly, it could mean many things, one of which is that not all of the radiation is getting to the luggage. Additionally, the manufacturer or contracted workers will do regular preventive maintenance on the unit, and if they work on the x-ray production portion of the unit, new surveys around the unit must be done to show that radiation protection controls still provide the necessary protection.

Would you recommend the frequency of radiation leakage measurement surveys in an airport environment for the screening equipment?

Every two to three years would be adequate if the machine is not opened for repair.  After it is serviced, a radiation survey is a must to ensure shielding and barriers have been repositioned correctly.

What type of instrument can I purchase to do radiation leakage checks on baggage x-ray screening machines?

It is likely you will need two types of equipment to do a leakage survey. The first is a Geiger-Mueller probe with a mica window (i.e., a pancake probe) because it would be the most sensitive to actually find the leakage radiation if there is any. The second is an x-ray calibrated (calibrated for the energy emitted by the baggage-screening equipment) ion chamber to measure actual dose or dose rate. In the United States, the Food and Drug Administration has regulatory authority over the manufacturers of radiation-producing equipment and has specified a leakage limit of 1.3 × 10^-7 C kg^-1 5 cm from the surface of the equipment (Coulomb per kilogram [C kg^-1] is a unit of radiation exposure).

With an airport baggage-screening machine, is it safe to line up bags in a continuous row, which doesn't allow the lead protection to be completely down when a bag is in the x-ray beam?

Judging by the experience of those who have measured radiation exposures around modern narrow-scanning-beam baggage security screening systems while they are continuously in operation, there is very little scatter from the piece of baggage being screened, so little, if any, radiation even makes it to the lead protection barrier.

I am pregnant and operate an x-ray machine at a courthouse, the type that scans items people carry in with them. Should I have any concerns? Should I continue working?

Baggage x-ray machines emit x rays just like medical x-ray machines except at much, much lower levels. The location of the operator is very well shielded and, really, exposes no one. It is safe to continue working while you're pregnant.

As a pregnant woman, does passing through airport security pose a risk to my baby?

Passing through an airport security portal does not pose a risk to a pregnant woman or her unborn child. The metal detector is not known to pose any health risk to individuals. The devices used to scan your carry-ons are very well shielded, so there is no risk from passing by those, either.

I reached into an airport x-ray screener that is used to see into our carry-on items. How much radiation exposure did I get?

There is nothing for you to worry about. Airport x-ray machines and similar x-ray machines used by federal and state agencies to screen briefcases and packages give much lower doses than x-ray machines in hospitals and medical clinics—almost immeasurable. They are designed this way because they do not have to see as much detail, are not designed for looking into very large objects, and are usually looking for things that really "stand out" on images (like metal).

In all likelihood, your hand was not in the actual beam, making your exposure much lower. Furthermore, the hands and feet are very radiation-tolerant relative to the rest of the body.

Does radiation from security screening devices, like those used in airports, affect the items that pass through them, such as baby bottles, food items, plants, electronic devices (cell phone), or drug products (like injectable nitroglycerin for a heart condition)?

The radiation exposure from these devices is too low to affect any items passing through (other than certain types of camera film, which can darken) even from repeated exposures. Additionally, in case you were wondering, there isn't any residual radiation in exposed materials after the exposure is complete either.

Does airport security x-ray screening have any effect on my pet?

The radiation exposure from these devices is too low to affect cats, dogs, birds, or other animals that need to be security-screened. If it is just the pet carrier that needs to be screened, you can put the carrier on the conveyor belt and walk or carry your pet through the metal detector portal instead of having the animal go through the x-ray unit.

Does radiation from a security screening device, like those used in airports, affect clothing if it passes through the screening a lot? I have a Gore-Tex^® jacket that gets screened quite a bit.

The amount of radiation to which the clothing, even the Gore-Tex jacket, is exposed is too small to degrade the materials. The manufacturers of these scanners indicate the radiation exposure to an item from one scan is about one-tenth the exposure we receive every day from naturally occurring radiation (commonly called background radiation).

Can I put my hand inside a screening x-ray machine to get an x ray to look for injury?

No, absolutely not. These systems are not designed for medical diagnosis and will not provide appropriate image detail or contrast. I would suspect that this would be illegal in most states. X rays of people should only be done with a doctor's order to do so.

If the airport security screener stops the conveyor to observe the x-ray image for a longer time, does that mean the item on the conveyer gets more radiation?

The scanners used for hand luggage at most airports take short single-shot images of items. The radiation is turned on for the same fixed amount of time for each item. The images are digital and held on the screen until the next coat, purse, or other item is processed. Thus, if the screeners choose to look at the images for an extended visual analysis, no additional radiation is used. If the item is removed from the scanner and put back onto the belt for a second time, however, it will then receive additional irradiation. In other words, these x-ray scanners are not "fluoroscopic" in nature, like the old machines from the mid-20^th century that were used to fit shoes, nor are they like angiographic or surgical x-ray machines. They are more similar to simple chest x rays, only performed using less radiation.

Ask the Experts is posting information using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.