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If Oxygen Masks on Airlines Have Empty Bags, Where is the Oxygen Stored?

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If oxygen masks on airlines have empty bags, where is the oxygen stored?

C Stuart Hardwick:

Humans and airplanes both need oxygen, but high speed airliners operate much more efficiently at high altitudes where the air is thinner. The lack of oxygen doesn’t bother them because jet engines compress their intake air anyway, but above about 8000 feet, the lack of oxygen would start making passengers woozy, and at higher altitudes still, would be fatal.

That’s why airliners carry emergency oxygen. The cabin is normally pressurized to about 8000 feet, but if pressurization ever fails above about 14,000 feet, some passengers would be unable to absorb sufficient oxygen from the rarefied air and would grow faint, even ill—especially those who are old or infirm, and those accustomed to near-sea level pressure, which is a third of the global population.

We can tolerate much higher altitudes, though, if we have pure oxygen to breath instead of the 21 percent oxygen in ordinary air. Breathing supplemental oxygen, we can go up to about 35,000 feet (40,000 with a full face mask ensuring 100 percent undiluted oxygen). Much higher than that and we risk passing out or asphyxiation even with 100 percent oxygen. That’s why few airliners fly higher—passengers would need pressure suits or at least full face masks as backup life support. Were it not for that, planes would happily fly at 50,000, 60,000, or even 70,000 feet.

So ... to answer the question.

If you’ve ever gone scuba diving (or seen it on TV) you know that divers only get air when they draw a breath—their rig doesn’t just continually belch out air (unless the regulator is busted) because that would waste air.

That’s what the bag is for. The oxygen generator over your seat in an airliner does just continually belch out oxygen. There is no tank or regulator—just a canister containing chemical reactants which, once started, produce a continuous stream of oxygen until the reactants are used up (a few minutes, long enough to descend to thicker air).

The flimsy little bag is there to catch the stream of oxygen in between your breaths so it isn’t wasted. That’s it. It only inflates while you are exhaling, provided you are breathing slowly enough. That’s why it might not inflate (you might not give it a chance you panicky rascal).

This post originally appeared on Quora. Click here to view.

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Big Questions
Are There Number 1 Pencils?
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Almost every syllabus, teacher, and standardized test points to the ubiquitous No. 2 pencil, but are there other choices out there?

Of course! Pencil makers manufacture No. 1, 2, 2.5, 3, and 4 pencils—and sometimes other intermediate numbers. The higher the number, the harder the core and lighter the markings. (No. 1 pencils produce darker markings, which are sometimes preferred by people working in publishing.)

The current style of production is profiled after pencils developed in 1794 by Nicolas-Jacques Conté. Before Conté, pencil hardness varied from location to location and maker to maker. The earliest pencils were made by filling a wood shaft with raw graphite, leading to the need for a trade-wide recognized method of production.

Conté’s method involved mixing powdered graphite with finely ground clay; that mixture was shaped into a long cylinder and then baked in an oven. The proportion of clay versus graphite added to a mixture determines the hardness of the lead. Although the method may be agreed upon, the way various companies categorize and label pencils isn't.

Today, many U.S.  companies use a numbering system for general-purpose, writing pencils that specifies how hard the lead is. For graphic and artist pencils and for companies outside the U.S., systems get a little complicated, using a combination of numbers and letters known as the HB Graphite Scale.

"H" indicates hardness and "B" indicates blackness. Lowest on the scale is 9H, indicating a pencil with extremely hard lead that produces a light mark. On the opposite end of the scale, 9B represents a pencil with extremely soft lead that produces a dark mark. ("F" also indicates a pencil that sharpens to a fine point.) The middle of the scale shows the letters and numbers that correspond to everyday writing utensils: B = No. 1 pencils, HB = No. 2, F = No. 2½, H = No. 3, and 2H = No. 4 (although exact conversions depend on the brand).

So why are testing centers such sticklers about using only No. 2 pencils? They cooperate better with technology because early machines used the electrical conductivity of the lead to read the pencil marks. Early scanning-and-scoring machines couldn't detect marks made by harder pencils, so No. 3 and No. 4 pencils usually resulted in erroneous results. Softer pencils like No. 1s smudge, so they're just impractical to use. So No. 2 pencils became the industry standard.

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Big Questions
What Are Curlers Yelling About?
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Curling is a sport that prides itself on civility—in fact, one of its key tenets is known as the “Spirit of Curling,” a term that illustrates the respect that the athletes have for both their own teammates and their opponents. But if you’re one of the millions of people who get absorbed by the sport once every four years, you probably noticed one quirk that is decidedly uncivilized: the yelling.

Watch any curling match and you’ll hear skips—or captains—on both sides barking and shouting as the 42-pound stone rumbles down the ice. This isn’t trash talk; it’s strategy. And, of course, curlers have their own jargon, so while their screams won’t make a whole lot of sense to the uninitiated, they could decide whether or not a team will have a spot on the podium once these Olympics are over.

For instance, when you hear a skip shouting “Whoa!” it means he or she needs their teammates to stop sweeping. Shouting “Hard!” means the others need to start sweeping faster. If that’s still not getting the job done, yelling “Hurry hard!” will likely drive the point home: pick up the intensity and sweep with downward pressure. A "Clean!" yell means put a brush on the ice but apply no pressure. This will clear the ice so the stone can glide more easily.

There's no regulation for the shouts, though—curler Erika Brown says she shouts “Right off!” and “Whoa!” to get her teammates to stop sweeping. And when it's time for the team to start sweeping, you might hear "Yes!" or "Sweep!" or "Get on it!" The actual terminology isn't as important as how the phrase is shouted. Curling is a sport predicated on feel, and it’s often the volume and urgency in the skip’s voice (and what shade of red they’re turning) that’s the most important aspect of the shouting.

If you need any more reason to make curling your favorite winter sport, once all that yelling is over and a winner is declared, it's not uncommon for both teams to go out for a round of drinks afterwards (with the winners picking up the tab, obviously). Find out how you can pick up a brush and learn the ins and outs of curling with our beginner's guide.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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