Grivory Knives Invisible to Metal Detectors: Should Security Guards Worry?

Undetectable weapons passing through metal detectors have long been a bugaboo of the security industry. 3D printing experiments notwithstanding, usable non-metallic firearms are still a pipe dream for the average criminal. “Plastic Glocks” caused a flurry of panic in the late 80s – the Austrian manufacturer developed a gun significant parts of which were made using non-ferrous polymer; although the barrel, slide and other parts were still made of metal, public perception soon distorted the gun into a plastic weapon that was undetectable by metal detectors. This version of the Glock was notably portrayed in Die Hard II. However, the fears of a plastic gun were found to be largely baseless – as already mentioned, the real weapon at the base of the controversy had a number of metal parts, and security checkpoints equipped with metal detectors had little trouble finding them.

Cold weapons are a different story. Lacking moving parts and the need to contain exploding propellant, these are much easier to make from non-metallic materials. “Grivory” is one such material.

Grivory is the most common trade name of a polymer called Polyphthalamide, which is a synthetic resin related to nylon. It exhibits heat resistance and hardness that make it a suitable replacement for metal in a number of roles, such as high-temp car parts.

Grivory has found a some use in knife manufacture, as well. Cold Steel, a California-based maker of edged weapons, uses it in a number of their lines. Mostly, the material goes into knife handles, because it’s light and strong, but some knives have Grivory blades as well. Most of these are fixed-blade knives, meaning they can’t be folded and the blade extends into the handle.

The questions with Grivory knoves are whether they are truly undetectable, and whether they constitute dangerous weapons.

There is a popular perception that all knives are required to have metal parts to make them detectable by security. This is comforting but false in any meaningful sense.

As you might expect, many jurisdictions ban the manufacture or sale of undetectable weapons – for example, the California Penal Code section 12001.1.(a) bans the manufacture or import of any “undetectable knife,” defined as “a knife or other instrument with or without a handguard that is capable of ready use as a stabbing weapon that may inflict great bodily injury or death that is commercially manufactured to be used as a weapon and is not detectable by a metal detector or magnetometer, either handheld or otherwise, that is set at standard calibration.”

However, we were easily able to find fixed-blade Grivory knives for sale online that only had one metal part – a loop similar to a keychain ring. This ring can be removed with hardly any effort, making the knife truly invisible to metal detectors, which is exactly how this product was advertised (and yes, they ship to California).

The performance of Grivory blades is another question. For what it’s worth, these knives aren’t known for their strength or ability to hold an edge – some users report tips breaking off while cutting boxes, while another called them “as dangerous as a credit card.” Sharpening them is a dicey proposition, with some users saying it can’t be done, while others recommend doing it carefully with a file or sandpaper. Knife aficionados report that Grivory and other polymers are fairly useless when it comes to cutting, although they are somewhat effective at stabbing.

All told, a Grivory knife can cause some injury, but is fairly ineffective and brittle as a combat weapon – your baton or night stick has much better reach and can, in most cases, do way more damage.

Not coincidentally, Grivory knives (and other non-metallic knives) don’t appear to have great appeal among criminals, especially since their properties are useless when it comes to bypassing X-ray scanners. Law enforcement practice hasn’t seen many criminal uses of these knives in routine civilian life – it appears that they are simply not used that often to commit crimes.

In conclusion, it’s true that you can buy undetectable, non-metallic knives for fairly cheap, and smuggle them through metal detectors. However, as a security guard, your chance of running across one of them is very low, and you should be more concerned about other weapons that are frequently used to commit crimes – such as good old metal firearms.

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