The View from the Porch Swing

FROM THE PORCH SWING

I DON’T HAVE AN ACCENT – BUT YOU MIGHT

If you spoke exactly the way I do, and if you always spoke clearly and slowly, and if I always listened with my full attention, I’d probably understand everything you say, every word. And understanding what you say, I’d have a better chance to understand your intent and underlying meaning, and be more likely to take an appropriate response. If I misunderstood what you said, I might do something inappropriate, maybe even non-compliant and/ or unsafe. And small differences in words can lead to these kinds of problems.

For example, the words “expired” and “expended” are quite similar. They start the same, go for about the same length, and end the same. Yet, they are also quite different in meaning.

Why you fly as a passenger on a commercial airline, you probably have to listen to a safety briefing at the start of each flight. “In the event of a sudden loss in cabin pressure, an overhead compartment will open up and drop an oxygen mask on you…”, or something like that. The flight attendant probably holds up a clear, plastic, flexible tube with a yellow cup and elastic strap on one end and explains how to use it. If one of those drops in your lap or on your head, or even just dangles enticingly in front of you, you are to put the cup over your face, the strap around your head, and breathe wonderful, life-giving oxygen.

Did you ever wonder what’s at the other end of that clear plastic tube? I used to think there were cylinders of gaseous oxygen up there above me, maybe one small one for each passenger, or maybe bigger ones with lots of tubes coming out of each. But that’s not how it works. At the hidden end of the tube is almost always a cylinder-shaped device that is NOT a gas-containing cylinder, but is a chemical oxygen generator. When triggered, chemicals inside the generator react, releasing large quantities of gaseous oxygen which gets forced through the tube to the passenger. As a by-product of the chemical reaction, a huge amount of heat is also created, so the chemical oxygen generators are usually surrounded by insulation up there in the ceiling of the airplane. After the release of the oxygen and heat, the device becomes inert, with all its potential dangers expended.

As a frequent flyer, I’m glad to know that I’ll get oxygen when I need it. However, over time, a small percentage of the chemical oxygen generators won’t work when triggered. If I’m on a plane with 200 passengers and only 99 per cent of the oxygen generators work, then there’s a chance that I’d be one of the two passengers without oxygen. I don’t really like those odds, when the outcome is that I might die of lack of oxygen. Fortunately, when the oxygen generators get too old, they expire, and get replaced with a fresh batch.

If asked to prepare a shipment of oxygen generators that can’t be used any longer, it might be important to know whether they are expended or expired. If they’re expended, there’s no capability to release oxygen and no capability to release heat, so they could be safely tossed loosely into boxes or bins and then moved. But, if they’re only expired, then a very large percentage of them could still release lots of oxygen and lots of heat, which risks a catastrophic fire, and so each individual one needs to be fitted with a cap to prevent accidental activation, and secured against