Yael is worried about having enough air to breathe, but Don sets her mind at ease.   Y: Oh great! This weekend I have to go to another family reunion, where I'll be sharing a room with my seven-foot-tall body-building cousin Bertha. She's nice enough, but I keep worrying we'll run out of oxygen before morning.

D: Well, Yael, whenever you have these unreasonable fears--Y: --Unreasonable? What's unreasonable about suffocation?

D: Hang on, and let's work through this! Suppose you actually are stuck in an airtight space with Bertha.

Y: Okay.

D: Well, the rule of thumb is that if there's enough space to stand and stretch out, you're okay. The average body uses about 1100 gallons of air overnight, which is the amount enclosed in a room that's six by five, and about six feet high.

Y: Our hotel room will be bigger than that. But then again, Bertha does do a thousand nightly pushups.

D: Well, a body at rest does use a lot less oxygen than a body in motion. During the day, under normal conditions, you use about 3300 gallons of air, but when you exercise, you can require up to twenty gallons of air per minute.

Y: So I'm right to be concerned!

D: Sorry, Yael, but not when you stop to consider that airtight rooms are expensive and hard to come by. Even hospital isolation rooms aren't airtight. Instead, they're set up so the air pressure in them is lower than the air pressure in surrounding rooms, and this is enough to prevent germs from spreading.

Y: So basically, Bertha could do all the pushups she wanted to and I still wouldn't run out of air.

D: Yep. Breathe easy, you'll be fine.