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more like normal topside breathing than open-circuit
breathing is. It’s so similar to normal breathing, in fact,
that it felt very strange to do it underwater.
Elegant Design
A rebreather’s hoses, mouthpiece and counterlungs are
known as the loop. The beauty of recreational rebreathers
is their ability to make sure the gas in the loop is always
optimized for breathability. They do this automatically,
detecting the percentage of oxygen in the circulating gas,
accounting for depth and adding oxygen or air to the
mix as needed. A canister of carbon-dioxide-absorbing
scrubber removes CO2 from the gas. All this delivers two
primary benefits to recreational divers: long dive times
and the quiet absence of bubbles.
Rebreathers combine stunningly complex components
with very simple, yet brilliantly implemented ones. On
the complex side, the battery of the unit I used can get
30 hours out of a charge, has its own onboard computer
(which stores dive-log data and decompression status
separate from the unit’s main computer) and even houses
LEDs and a speaker that broadcast distress signals if
the computer detects any problems. On the simple side,
rebreathers’ mushroom valves are a pair of thin, rubbery
discs that sit within the hoses on either side of the diver’s
mouth. When the diver inhales, the valve on the side
of the freshly scrubbed and properly oxygenated gas is
pulled open, while the one leading toward the scrubber is
pushed closed. When you exhale, the flexible discs blow
the other way. These two thin discs are all it takes to keep
the air moving through the loop in the right direction.
A recreational rebreather is so thoroughly automated
that I had some initial trepidation about trusting my
life to a computer. “You do it every time you fly,”
pointed out my instructor, Georgia Hausserman, who
was a pilot. I also appreciated the perspective offered
by another grinning rebreather diver, who said, “Think
of it this way — who would you rather have making
these calculations: Richard Pyle and Bill Stone or
YOU?” Perhaps most reassuring was a comment made
by another diver: “Don’t think of your rebreather’s
computer as a PC; think of it as a calculator.” That
worked for me; I’ve wanted to throw my laptop out of
a window more than a few times, but I’ve never had a
calculator tell me two plus two equals five.
Checklists Save Lives
Learning to use a checklist and conduct a prebreathe (a
five-minute test breathe of a rebreather before diving)
are essential parts of becoming a rebreather diver.
Georgia had seen a man become hypoxic on the surface
and nearly die just a few weeks earlier. He had failed
to reconnect his oxygen after a predive problem that
required him to disassemble and reassemble his unit. If
he had done any number of things, including starting his
checklist over from the beginning, conducting a proper
prebreathe or checking his display, he wouldn’t have
come within inches of his life while trying to put on fins
in three feet of water. Fortunately, bystanders noticed
he wasn’t moving, pulled him out and saved his life. The
man had been arguing that checklists don’t work the
previous evening at dinner.
Amazing Experiences
When I asked Georgia about her own transition into
rebreather diving, she told me she was dragged kicking
and screaming but that she now dives more with her
rebreather than she ever did with open-circuit scuba.
When I asked her why, she said, “Because I expect to have
amazing experiences.” One such experience involved an
eight-foot hammerhead, which swam up behind her and
passed within a few feet. Another involved a whitetip reef
shark that circled her three times, while a second whitetip
cruised in from out of nowhere to make a close pass.
I’ve only logged a few rebreather dives so far, but I’ve
had some memorable interactions, too. A big mutton
snapper and I watched each other closely as it swam
toward me, gazing intently, before veering off mere
inches from my face. Early in my training before I had
figured out how to maintain the right amount of gas in
my loop, I was watching some jawfish dance above their
burrows. Every time I had to vent gas from the loop
they shied downward into their holes. When I managed
STEPHEN FRINK