Bureaucrat hatching monstrosities (allegory)

  Federal rules and regulations
No more laughter left on earth
Blue Oyster Cult, "Monsters"

Monday, March 14, 2011

Perils in the Plane Privy

There are some news items that leave you incredulous. You read them and go *blink* *blink* whaaat? I call these "headscratchers". Judging by my baldness, I must have seen a lot of them.

The latest case of headscratching I saw is a report saying that all airlines operating in the US have discreetly removed the chemical oxygen generator from the toilets in their airplanes, because of a "hazard that could jeopardize flight safety". At least, that's what the FAA (Federal Aviation Administration) says in its Airworthiness Directive 2011-04-09.

An oxy... what?

A chemical oxygen generator
(Source: FAA)
Wait. What is a chemical oxygen generator? It's a small metallic cylinder, 10 inches (25 cm) long, that contains a chemical mix able to generate oxygen when heated. The main component of the mix is sodium chlorate (NaClO3) and iron powder. When a cabin pressure loss is detected, an overhead compartment containing face masks opens. When you, the passenger, pull on a mask, it releases a pin that fires a small percussion cap, igniting the mix. The heat decomposes the sodium chlorate and releases oxygen. Some of the oxygen goes into sustaining the combustion, and the excess flows into the masks, giving you 15 to 20 minutes of breath.

Since the metal cylinder can become as hot at 500 F (270 °C), you will smell an alarming yet normal burning odor. And since the canisters will be empty in 20 minutes, the pilots will be descending quickly to a breathable altitude.

Now, why are these things deemed dangerous in airplane lavatories? The FAA won't say. It even went so far as to secretly ask airlines to remove the generators from airplane toilets before making the directive public. Aren't you intrigued now? Don't you want to know what secret evil lurks in these live-saving cylinders?

Canisters of concern

Mix of NaClO3 and sugar burning
So let's see what we can dig out about sodium chlorate. It's a weed killer, it's toxic if ingested, and, if mixed with sugar, it can detonate (like gun powder). Aha! So the FAA is afraid that a terrorist will kill all the weeds on board! Either that, or they are afraid that they'll get sugar from their coffee and make a bomb.

The weed-killing threat would actually make more sense. The problem with sodium chlorate is that it's a lousy explosive. It has about half the explosive power of black powder, which is itself one tenth to one fifth of the power of TNT. And like black powder, it needs an enclosed container to explode, otherwise it burns like a sparkler.

Let's assume Al-Qaeda has found a suitably fanatical volunteer to blow up an airliner. Under the FAA oxygen generator scenario, the terrorist must go to the restroom, remove the generator from its brackets (with what tools?), saw open the cylinder (how?), scrape the chemical from the cylinder (don't lick your fingers, remember, it's toxic), pour it into a bottle or some other container (ideally, a sturdy pressure cooker). Then, he must mix in sugar (you'll need about 100 of these little paper packets), close the container, and light up some firing system (like an explosive cord fitting through the container.)

So all that Al-Qaeda has to do is to find somebody dumb enough to fall for their arguments, yet clever enough to execute such a scheme. I'm not saying it's impossible, I'm just saying that the talent pool of such gullible, suicidal MacGyvers must be quite shallow.

Accommodating attendants

(Source: Domino Sugar)
Assume that you can bring in the 200 grams of sugar, the container and the tools required for kludging up a sodium chlorate bomb. Why not bring 200 grams of high explosive and some weapons instead? Or does the FAA think that the crew will let an agitated passenger raid the galley and take all the sugar, then lend him a toolbox?

AIR ATTENDANT: Oh, my, you want the whole box of sugar packets from the galley? Sure! Help yourself. You do like a lot of sugar in your coffee, don't you?

TERRORIST: Yes, I like it very, very sweet. And, er, can I borrow a screwdriver?

AIR ATTENDANT: Certainly. Here you are. What for, if I may ask?

TERRORIST: It's for stirring all that sugar in the coffee. It gets a bit syrupy. Oh, and may I also borrow a hacksaw?


TERRORIST: For opening all these sugar packets.

AIR ATTENDANT: Of course. Fortunately, I always have one in my knitting bag. Here you go.

TERRORIST: Great. Can you help me carry all of that to the restroom? I'll grab my pressure cooker, my explosive cord and my lighter.

We might have hinted in another post that the TSA was less than 100% effective, but still, that's a lot of things to pass through those X-ray machines.

The more you think about it, the less credible the threat is. But that didn't stop the FAA from issuing a directive, and the airlines complied without a peep. Some foreign regulation outfits, such as the DGAC, the French civil aviation agency, even went so far as requiring their national airlines to obey this incomprehensible rule, even for planes that are never flying to the US. All of that to eliminate a risk that is vanishingly small.

But, you say, even if the risk is very small, why not eliminate it? It can't hurt, right?

Well, yes, it can hurt. It statistically will hurt.

Give me embarrassment or give me death!

Every year, 40 to 50 airliners suffer a rapid cabin depressurization. When that happens, the pilots bring the plane down to 10,000 ft or so. But from a cruise altitude of 35,000 ft (typical for a transatlantic or transpacific flight), this can take a good seven or eight minutes.

If you are in the loo at the time a depressurization occurs, you'll quickly get into hypoxia, better known as "getting dumb from lack of oxygen". Hypoxia is particularly sneaky because you don't realize you are losing your mental capabilities. Videos of volunteers subjected to a short hypoxia are quite hilarious and deeply embarrassing for said subjects, once they are back to breathing normal air. But stuck in the toilets, you won't get so lucky. Seven minutes is about twice as long as it takes to kill you. The crew has been instructed to check the lavatories in case of a depressurization. Pray that they are able to do so.

Next time you're in an airplane loo and you feel your ears popping, you might get lucky and remember to unlock the door before passing out. When you wake up, you'll be down on the aisle floor with your pants still down and a yellow mask on your reddening face, while nearby passengers try to stop young children from gawking.

And that, mind you, is the optimistic case.


  1. I'll have to sit on this for a while!

  2. Actually we,ve lost 2 airplanes due to oxygen generator fires. One was the Valujet 592 thst crashed with all aboard, the other was DC-10 in Chicago undergoing maintsinance. Exothermic reactions thst produce oxygen are a verry bad thing.

    Cover it with s jacket, pull the string, add paper towels and tampons, asnd you will get a blazing fire.

    Removing them isn't much of a risk, consdering a NSA study found that onboard automatic oxygen masks have never saved a life (as opposed to medical oxygen which has when passangers develop medical issues.) Also there are the afore mentioned oxygen cylinders available if some cannot be moved back to a seat (every row of seats typically has an extra mask- that why airlines must track Infants in arms.)

    Sorry to interject fact in this debate.

  3. Very interesting. Thank you for these facts. I tried to find the NSA study you quote, to no avail. Do you have a link?

    So, admitting that 1. oxygen generators are a fire hazard, and 2. They haven't saved anyone, shouldn't we then remove all of them? What good is it to simply remove the one in the toilet?

    Consider that there is about one airliner a week that suffers from depressurization. Are you saying that breathing oxygen at 35,000 feet is unnecessary? I don't understand how masks are deemed useless. Thoughts?

  4. And speaking of which...
    "A commercial flight from Phoenix to Sacramento this afternoon had to be diverted to an airport in Yuma due to rapid cabin decompression that may have been caused by a hole in the jet’s fuselage."