Here is an interesting question that I just received from a colleague
concerning the breathing problems faced by scuba divers. The
errors concerning the causes of narcosis are obvious but what is
a better explanation of the phenomena?
Herb Gottlieb from New York City
(Where we always welcome correct explanations that can be understood
easily by most of our middle school students)
From: howard p lyon <aintlyin@juno.com>
In Science Links, vol. 14, page 45, there's a discussion of partial
pressures, some of which I'll quote here:
"Ordinary air is about 21 percent oxygen and 78 percent nitrogen. Under
water, each gas exerts its own pressure, independently of the other.
That means the compresed air that a diver breathes at 10 meters actually
has 42 percent of the total pressure due to oxygen alone. That's
approaching the danger leve. Much higher than 42 percent partial
pressure of oxygen, and the diver may go into convulsions. Prolonged
exposure to high concentrations of oxygen are dangerous. The solution is
to use less oxygen in the mixture of compressed gases that divers
breathe. Around 300 meters, the gas mixture may contain as little as 2
percent oxygen."
I surely do not understand the math here. Presumably at 10 meters the
total pressure is 2 atmospheres. But now 42 percent of that is oxygen.
At 300 meters the total pressure would be 31 atmospheres, and (using the
same math) the partial pressure would be over 600 percent oxygen. I
surely do not understand...
The hyperbaric oxygen therapy pictured on the same page using 100 percent
oxygen at elevated pressures apparently gets a partial pressure above 100
percent.
Please tell me what the writer is trying to say.
My brother, a former Navy Scuba diver (to an elementary degree) cannot
figure out what the book is trying to demonstrate.