Shostack + Friends Blog Archive


Speaking of Hot Knives, Butter

It seems that Zylon “bulletproof” vests are not nearly as effective as Kevlar ones, and the Justice department may pull funding for purchasing them. (All the press releases and reports are at the DOJ site.) They are, however, more effective than not wearing a vest.

I am routinely outraged here by poor technology decisions that apply to the public. Let me be clear that this is equally outrageous. People working in the public interest (including cops and firefighters) deserve to have great, well-tested, effective safety gear. I don’t know if the breakdown here is the same sort of breakdown that leads to things like CAPPS or zippo-banning. But I suspect they’re related, and maybe there’s common cause to be made there between libertarians and police?

See also the New York Times, “A Common Police Vest Fails the Bulletproof Test.”

(As an aside, one of the problems with blog display formats is that you read my latest writings first, where logically, this should come after the Robertson Lies post, so that the title makes sense.)

2 comments on "Speaking of Hot Knives, Butter"

  • Wow. An example of how a news article can be completely uninformative. It provides no numbers on failure rate in action, or even a rough estimate of how many lives are saved from using vests. How frequent are the “close quarter gunfights” mentioned by NYPD spokesperson? The article mentions that the new vests are lighter and more comfortable: the former could increase overall ability and the latter makes some one more likely to wear a vest at all.
    Finally, we don’t even know “what they knew and when they knew it” to evaluate whether it was indeed a poor technology decision. Witness this delightfully unclear sentence: “The Justice Department, which began studying Zylon vests in 2003, found in earlier tests that the material deteriorated quickly, particularly when exposed to light, heat and moisture.”[emph. mine] How long have they been in the market? Who did the original tests? I could read the study if I were curious, but the article is very frustrating.

  • John LaRue says:

    What seems strange to me is that I heard the critical flaw here is that Xylon breaks down over time when exposed to a certain combination of heat + moisture; at least, that is the rumor. On its own in ideal conditions, it should retain its strength.
    Unless I am missing something, it looks to me like the error is a design problem with the vest itself and not the Xylon — I mean, can’t you laminate the material or seal it somehow inside the vest so that the Xylon is isolated?
    Anyways, the worst part (and I agree with everything you’ve said), is just that apparently the manufacturers were aware of this problem. Most of the info I have gathered just came from random sessions of NPR.

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