In a recent post to Dave Farber’s Interesting People email list by Perry Metzger makes a number of good points about the current ban on carry-on liquids during air travel. I share many of his sentiments and encourage you to give it some critical thought as well.

First they came for the nail clippers, but I did not complain for I do not cut my finger nails. Now they’ve come for the shampoo bottles, but I did not complain for I do not wash my hair. What’s next? What will finally stop people in their tracks and make them realize this is all theater and utterly ridiculous? Lets cut the morons off at the pass, and discuss all the other common things you can destroy your favorite aircraft with. Bruce Schneier makes fun of such exercises as “movie plots”, and with good reason. Hollywood, here I come!

We’re stopping people from bringing on board wet things. What about dry things? Is baby powder safe? Well, perhaps it is if you check carefully that it is, in fact, baby powder. What if, though, it is mostly a container of potassium cyanide and a molar equivalent of a dry carboxylic acid? Just add water in the first class bathroom, and LOTS of hydrogen cyanide gas will evolve. If you’re particularly crazy, you could do things like impregnating material in your luggage with the needed components. Clearly, we can’t let anyone carry on containers of talc, and we have to keep them away from all aqueous liquids.

See the elderly gentleman with the cane? Perhaps it is not really an ordinary cane. The metal parts could be filled with (possibly sintered) aluminum and iron oxide. Thermit! Worse still, nothing in a detector will notice thermit, and trying to make a detector to find thermit is impractical. Maybe it is in the hollowed portions of your luggage handles! Maybe it is cleverly mixed into the metal in someone’s wheelchair! Who knows?

Also, we can never allow people to bring on laptop computers. It is far too easy to fill the interstices of the things with explosives — there is a lot of space inside them — or to rig the lithium ion batteries to start a very hot fire (that’s pretty trivial), or if you’re really clever, you can make a new case for the laptop that’s made of 100% explosive material instead of ordinary plastic. Fun!

No liquor on board any more, of course. You can open lots of little liquor bottles and set the booze on fire, and besides, see the dangers of letting people have fluids. Even if you let them have fluids, no cans of coke — you can make a can of coke into a shiv in a few minutes. No full sized bottles of course, since you can break ’em and use them as a sharp weapon, so no more champagne in first class either, let alone whiskey.

Then, lets consider books and magazines. Sure, they look innocent, but are they? For 150 years, chemists have known that if you take something with high cellulose content — cotton, or paper, or lots of other things — and you nitrate it (usually with a mixture of nitric and sulfuric acids), you get nitrocellulose, which looks vaguely like the original material you nitrated but which goes BOOM nicely. Nitrocellulose is the base of lots of explosives and propellants, including, I believe, modern “smokeless” gunpowder. It is dangerous stuff to work with, but you’re a terrorist, so why not. Make a bunch of nitrocellulose paper, print books on it, and take ’em on board. The irony of taking out an airplane with a Tom Clancy novel should make the effort worthwhile.

So, naturally, we have to get rid of books and magazines on board. That’s probably for the best, as people who read are dangerous.

And now for a small side note. It is, of course, commonly claimed that we have nitro explosive detectors at airports, but so far as I can tell they don’t work — students from labs I work in who make nitro and diazo compounds for perfectly legitimate reasons and have trace residues on their clothes have told me the machines never pick up a thing even though this is just what they’re supposed to find, possibly because they’re tuned all the way down not to scare all the people who take nitroglycerine pills for their angina.

Now, books aren’t the only things you could nitrate. Pants and shirts? Sure. It might take a lot of effort to get things just so or they will look wrong to the eye, but I bet you can do it. Clearly, we can’t allow people on planes wearing clothes. Nudity in the air will doubtless be welcomed by many as an icebreaker, having been deprived of their computers and all reading material for entertainment.

Then of course there is the question of people smuggling explosives on board in their body cavities, so in addition to nudity, you need body cavity searches. That will, I’m sure, provide additional airport entertainment. By the way, if you really don’t think a terrorist could smuggle enough explosives on board in their rectum to make a difference, you haven’t been following how people in prison store their shivs and heroin.

However, it isn’t entirely clear that even body cavity searches are enough. If we’re looking for a movie plot, why not just get a sympathetic surgeon to implant explosives into your abdomen! A small device that looks just like a pace maker could be the detonator, and with modern methods, you could do something like setting it off by rapping “shave and a haircut” on your own chest. You could really do this — and I’d like to see them catch that one.

So can someone tell me where the madness is going to end? My back of the envelope says about as many people die in the US every month in highway accidents than have died in all our domestic terrorist incidents in the last 50 years. Untold numbers of people in the US are eating themselves to death and dying of heart disease, diabetes, etc. — I think that number is something like 750,000 people a year? Even with all the terrorist bombings of planes over the years, it is still safer to travel by plane than it is to drive to the airport, and it is even safer to fly than to walk!

At some point, we’re going to have to accept that there is a difference between real security and Potemkin security (or Security Theater as Bruce Schneier likes to call it), and a difference between realistic threats and uninteresting threats. I’m happy that the police caught these folks even if their plot seems very sketchy, but could we please have some sense of proportion?