cave diving and the nss - bei Swiss-Cave-Diving

CAVE DIVING COMMUNICATIONS 5
Chapter Two
SOUND SIGNALS
There are some real problems with using sound for communication
in underwater caves. In close quarters, the noise of
reverberating exhaust bubbles can tend to overwhelm any other
sound. The walls, floors and ceilings can alternately absorb or
distort meaningful signals past recognition. And while water conducts
sound waves more efficiently than air does, sound is still
quickly lost in convoluted passageways. High flow will have the
same effect as wind, and literally sweep the sounds away.
Even such a simple open-water attention-getting device as
banging on a tank poses problems in a cave environment. For
starters, cave divers don't ordinarily carry the big macho samurai
dive swords favored by ocean ninja divers, which they use to hit
the tanks. Our lightweight forearm knives, or even tiny plastic line
cutters, may not be heavy enough to produce a good quality tone,
and other typical cave-diving implements such as primary lightheads,
backup lights, reels, dive computers, or video cameras, are
not generally designed with that kind of deliberate abuse in mind.
But it's certainly possible that you might be able to let your
buddy know that you want his attention by banging on your tank.
(If you're really clever you might even be able to tap out Morse
Code messages to each other.) The problem is that—assuming
that you've managed to overcome all the obstacles with sound
transmission listed above—distance and direction to a sound
source are extremely difficult to determine underwater. Although
you may be able to hear your buddy, you may not be able to find
him unless you can see his light; and if you can see his light, then
you can probably see his light signal. It has been generally conceded
that the superiority of light signals for attracting a fellow cave
diver's attention makes audio signals for the most part run a very
poor second.
However, while you may not
choose to try to communicate messages
to your buddies with audible
signals, sounds can definitely convey
important, useful information.
For example, the countdown alarm
on a digital dive watch may be the
sump diver's only method of keeping
track of his bottom time in a particularly nasty, no-visibility sump.
Under certain conditions it may be possible to pause occasionally
as you swim and, ceiling conditions permitting, listen for air leaks
from your equipment. The percolation of your buddy's exhaust
bubbles or whine of his scooter will advise you that they are both
operational. And a "singing" regulator will assure you of its user's
proximity (although not necessarily of the state of its repair). The
audible warning signals of "sonic regulators," on the other hand,
which are activated at low tank pressures, are obviously of dubious
value in most cave-diving scenarios.
It's not true that you can't ever understand talking through a
regulator underwater. Profanity comes across astonishingly well.
And there are a few cave-diving buddy teams around who seem to
be so completely attuned to each other that they are able to comprehend
some clearly enunciated commands that are shouted—or
perhaps it's hissed—at each other.
But for the most part, with our current technology talking is
simply not a viable form of communication underwater. And it's an
even less viable form in "air" pockets. We have a suspected instance
of a couple of open-water divers succumbing to the foul air
in a cavern air pocket: it is thought that they might have drowned
as a result of having lost consciousness
while in the air pocket with their
regulators out of their mouths. If an
air pocket is large enough, you can
certainly "surface" for a quick conference,
but you are very strongly
urged to breathe only from your own
air supply. You you are cautioned to
treat all standing air pockets and
abandoned decompression troughs
as potentially poisonous.