I have a titanium half-inch thick rod in the middle of my right femur, running from my hip to just above my knee and I have gone through airport metal detectors many, many times without ever having the detectors go off. The only conclusion I can reach is that the muscle and bone of my leg must serve to mask the metal rod. Perhaps someone with a steel plate in their head might have a similar type of masking occur. Of course a steel plate most likely would have nothing more than scalp covering it, so the density of the covering is much less and most likely would activate the detector.
I had been very concerned after the surgery that resulted in me getting a metal rod in my leg that I would be inconvenienced when I flew from that point on because security would always have to take the extra time to scan me by hand. My doctor had told me the metal rod wouldn’t make the detector go off but until I actually went through the detector for the first time I thought he was full of baloney. But he was right and there may be other cases like mine where metal in the body doesn’t necessarily make the detector go off.
“The truth does not make a good story; that’s why we have art.”
Your conclusion sounds reasonable, that the rod is well-enough hidden inside your body that it won’t make a detector go off.
If you are correct, though, that would raise an interesting possibility. I have heard of drug smugglers ingesting small bags of drugs to carry them through borders (and expelling them later.) Would it be possible for someone to build a small enough bomb or gun that they could ingest the parts in a plastic bag, expel them in the airplane toilet, and then use them for an attack? It seems far-fetched to me. Maybe I’ve seen too many Hollywood action movies.
As a result of an automobile accident several years ago, my wife has several metal pins holding her skull together. The first couple of years after the accident she was setting off every metal detector she went through (she had to carry a note from a doctor to get past security). After a while the detectors stopped beeping. Now she doesn’t even bother with the note when she travels. I suppose enough bone and tissue has grown around the pins to shield them from detection. That’s just a guess, though.
My girlfriend’s experiences (she has a metal rod in her back due to remedies for scoliosis) concur with Ursa Major’s. At first, she set off metal detectors all over. More recently, nothing.
“One more anal-probing, gyro, pyro, levitating, eco-plasm, alien anti-matter story and I’m gonna take out my gun and shoot somebody.”
– Fox Mulder
I got behind a guy in an airport one day and he set off the alarms. As they have a tendancy to do, no one else was allowed to pass until he cleared. “I have a steel plate in my head”, he said… “Yeah, right”, sez the security lady whipping out her wand. She starts at his feet and slowly works her way up to his neck. Nothing registered, so she starts on her way back down… “It’s in my head”, explains the man. “Unnnh hunnnh”, she says with sort of oh-brother sarcasm. She gets to his feet without finding the offending metal. “Would you mind stepping back through the metal detectors?”, she asked. Impatiently, the man explains, “I have a steel plate in my head!” All the while, pointing at his skull in an exaggerated motion. Reluctantly, she waves her magic wand up near his head and it beeps in recognition of metal… “Hey! You’ve got a steel plate in your head!”, she exclaims. “No shit, Sherlock.” says the exasperated man, “Can I go now?” Meanwhile, all of the people who have been backing up at security start applauding and some of them are yelling, “I’ve got a steel plate in my head, too! Yoo hoo. Miss. Steel plate; over here.” It was pretty funny. As I picked up my bag I said to the guy, “Man, that chick was dense.” To which he replied, “Actually, they’re all like that. Sometimes it takes me 15 or 20 minutes to clear security…”
I wonder if this is partly a case where 99% of the people who tell the guard they have plates in their heads are making feeble jokes, so it’s a surprise when someone who actually does comes through.
Also, if I understand correctly, the detector doesn’t say how many items it detected or where it is located. Therefore, it’s not enough to show that you have a plate in your head, the security people also have to make sure that you aren’t also carrying something else to make it go off. (E.g. an Uzi). This is especially difficult because this person can’t remove the steel plate causing the beep, so you would have to do a fairly thorough search for additional items in order to remove all doubt.
Metal detectors can also be set at different levels of sensitivity. It could be that the equipment has been set at a lower level if it was picking up too many false-positives. Our county courthouse has metal detectors (grrr, don’t even get me started) and they have the set to the highest possible level of detection. I walk right through airport detectors without setting them off while the courthouse detectors sound. The wand routine comes up with such dire threats to courthouse security as the metal eyelets on my boots and the metal pull tab on my zipper. Thank god those security guards are there to keep the world safe from my pants.
I am a nurse, and I used to work on a floor that did hip replacements. It was part of the whole protocol that the doctor gave three copies of a note about the steel hip to the patient on discharge, giving his name, number
etc and particulars about the stainless steel prosthesis. I dont know if these people set off metal detectors or not, but they were prepared for it. One was for the wallet, one for safe deposit and I guess one spare…
I have a steel plate in my arm from a rollerblading accident. I’ve never set off metal detectors. I guess I’ve got enough muscles to shield it from the rent-a-cops’ security.
Synonym: the word you use in place of a word you can’t spell.
A number of posters have mentioned that they have “enough shielding” around metal body parts to screen the metal from the metal detector.
I don’t think this can be the principle at work here. Consider: if I wanted to smuggle weapons onto a plane, and flesh/bone surrounding metal prevented the metal detector from working, I could simply wrap my weapons up in a steak. (I haven’t tried this, and I have no plans to, but I really hope it doesn’t work…)
I don’t know how metal detectors work, but I’d guess that they probably deal in some form of electromagnetism, which would likely make them most sensitive to ferric metals (which titanium, for one, is not) which are the ones used in guns anyway.
My limited experience with airport metal detectors would lead me to believe that they vary enourmously in their sensitivity. Some trips through the detector have taken five minutes while I ditch my keys, my shoes, my Altoids, my film, my coat, etc. Other times, wearing the same coat, shoes, etc, I breeze right through.
The observation that metal body parts set off the airport detectors initially, then stop doing it as they age could be explained partly by the variation in metal detector sensitivity, but possibly also through improving technology. Perhaps newer metal detectors can tell the difference between several small pieces of metal (like bone pins or bobby pins) and a big chunk of metal (like a gun). The metal body parts used to set off the old detectors, but don’t fool the newer ones.
I’d love to see a followup here by an EE or a metal-detector designer, who might be able to translate the EM physics into English.
Wow, talk about stamping out ignorance. Sure would be nice to get a definitive answer from a metal detector manufacturer or such.
I think I agree more with Lagged2Death. The metal detectors are primarily looking for steel, not titanium. Also, sensitivity levels differ. Perhaps the airport security levels were adjusted since the first few times people set them off?
I recall metal detectors working basicaly this way. in a outer ring an AC current is applied, which causes a magnetic field. a inner ring doesn’t ‘feel’ the field because it is places in a way that the net magnetic field is cancled or electronically compansated for. if a ferous metal is close enough to the magnetic field, it will develope it own electric charge and its own electric field - that is the field the inner ring uses to detect the metal (as current is induced in it. Aluminm based metals can be detected if the detector is tuned for it (the magnetic field will be opposite).
Also the orinatation of the metal makes a great diffrence.
Well I’m not a metal detector designer, but I am double-E and I’ve built the little metal detectors you use to find coins at the beach and I know how these work. I can’t say that airport security metal detectors work with identical principles… OK enough disclaimers…
Usually the metal detectors require some reasonable ferromagnetic metal content (typically iron), which is why many aluminum and titanium alloys don’t always set them off. Surgical steel has a high nickel content, but some iron, so I suspect it’s marginal, depending on the sensitivity of the equipment settings.
The basic principle of the ones I built was that you have a coil of fine wire in a loop. The coil is a part of an oscillator which is designed to change frequency easily with changes in the inductance of the coil. The inductance of the coil changes when ferromagnetic metals enter the field…
This is the same mechanism used by most modern street light controllers and parking lot security gates, by the way.
Also, titanium and aluminum don’t make good materials for building handguns. Too brittle and too prone to heat distortion. Ceramic is the material of choice for today’s discerning terrorists (so I’ve heard).
I think the answer is in the size of the prosthesis. They are looking for guns mainly. If your prosthesis is not as big as a small gun then the detector will probably not detect it.
Sometimes stamping out ignorance can be easier than you think.
I have a new hip. Can’t wait to check out the detectors. This could be fun.
Nope. That’s not likely to be the same phenomenon. For one thing, the human body is not much better as a ferromagnetic core than plain 'ole air and secondly, a human at street level is too far away from the ballast (the coil part) of the sodium vapor lamps to have any effect.
However, I have seen (and have demonstrated it myself), when a neon light is flickering and refusing to go on solid, if you put your hand up near the bulb, the light comes on. This may be some capacitive effect that either moves some of the gas around in the bulb or boost the efficiency of the ballast somehow… I’m not really sure. Anyhow, since I know this phenomenon to be real, I’m not completely ready to dismiss the street light phenomenon.
I think this is unlikely as the titanium rod in my leg is 1/2 inch in diameter and 18 inches long, the volume of which would be more metal than the metal in probably many large handguns.
I think it is related to either the non-ferous idea or because it is masked by being covered by bone and muscle tissue. Also, I don’t think it is a sensor sensitivity issue as I have NEVER had any kind of detector go off by walking through it.
“The truth does not make a good story; that’s why we have art.”
The street light detector is a magnetic detector. Like the one I worked on many years ago to detect submarines.It detects the change in the earths magnetic field due to the magnetic field of the submarine. It’s called magnetic anomally detection.
I’m not sure how magnetic titanium is. It would not detect ceramic at all. My hip is stainless steel. Not very magnetic. It would probably still affect the detector that I used to work on though.since it only has to disrupt the magnetic field.
