Page 54 - AlertDiver_Spring2013

Q:Recently I’ve seen many reports of
downdraft currents on various online forums
accompanied by debates about the best
method for escaping them. Do any of DAN’s experts
have an opinion or advice?
A:As you will probably appreciate, there is no formal
body of research addressing this specific question.
The appropriate response and the degree of
vigor required will be influenced by the depth, strength
and volume of the downdraft, the distance from the eddy
line (the edge of the draft), the topography, visibility, risk
of entanglement or entrapment, the bulk of the diving
equipment worn, the strength, power, buoyancy control,
skill, decompression status (or obligation) of the diver and
potentially other factors. What seems like a simple question
quickly becomes impractical to study in a safe, controlled
and still meaningful manner.
Even without quantification of the actual effort required,
the question can be addressed conceptually. The priority
is maintaining control — particularly vertical control — to
avoid serious buoyancy and/or gas-space issues that could
make the situation worse. Getting negative, hugging the
reef and climbing out rock by rock might be workable if
the strength and size of the current flow required it and
the topography allowed it. The advantage of this approach
is control. The diver is unlikely to have serious shifts in
buoyancy or of gas in sensitive spaces (primarily the middle
ears and lungs) when control is maintained.
Again, depending on the conditions, swimming
perpendicular to the flow could be effective. An advantage
of this may be a reasonable degree of control, with minimal
need for fast changes in buoyant state or risk to sensitive
gas spaces. Choosing to increase buoyancy probably
represents the greatest risk of all. While it may be necessary
in extreme situations, it is also possible that it could result
in an overcorrection and the subsequent hazards of an
uncontrolled ascent, the latter resulting in an elevated risk of
barotrauma and decompression illness.
My fundamental recommendation is that divers think in
advance and be prepared with a continuum of responses from
which to choose and, when appropriate, to shift between.
The progression of the graded response would be as follows:
a mild downdraft could be ignored; a little more strength
would prompt horizontal swimming to move out of the
affected zone (with minimal or no addition of air to the BCD);
even more strength or an uncomfortably large downdraft
flow zone would prompt grabbing the wall for stability and,
possibly, climbing out. A minor amount of gas might be
added to the BCD at the hanging-onto-the-wall point, but not
as a primary part of the solution. Adding too much positive
buoyancy could create a situation more dangerous than the
initial hazard. It could pull the diver off the wall, precipitate a
runaway ascent or make what could otherwise be a mild case
of entanglement extremely problematic.
Mental practice is an important way to improve skills and
responsiveness. A critical part of this effort is to remember
that every event has its own idiosyncrasies. Having multiple
options and the physical skills and calm demeanor to employ
them in a thoughtful, progressive manner will provide the
best protection.
—Neal W. Pollock, Ph.D.
RESEARCH, EDUCATION & MEDICINE // F R O M T H E M E D I C A L L I N E
52 | SPRING 2013
Dealing with Downdraft Currents
DAN® medics answer your questions about dive medicine.
B y t h e D A N M e d i c a l A N D R E S E A R C H S t a f f
STEPHEN FRINK