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Q:
On a recent liveaboard dive trip to the
South Pacific, I encountered some unusual
instructions regarding dive profiles. In the
briefing for the day’s first dive we were told the second
dive would involve a short swim-through at 90 feet.
Because of this, the divemaster wanted everyone to go
to 110 feet on the first dive — even though there was
nothing to see at that depth — for the sole purpose of
ensuring the day’s dives were progressively shallower.
Was there any good reason for this recommendation?
A:
The strategy you described (making an
unnecessarily deep dive first simply to maintain
a progressively shallower dive series) was
unwarranted. The additional inert-gas burden would
unnecessarily increase decompression risk. Diving to
appropriate depths for each dive and maintaining respect for
decompression limits are far more prudent.
While the concept of making progressively shallower
dives makes intuitive sense and is generally recommended,
evidence for any real benefit is difficult to find, and, even more
important, real-life conditions must be considered. Think about
a first dive following a layoff from diving. Arbitrarily applying a
deepest-dive-first rule would clearly be unwise.
Your thoughtfulness in asking questions is the most
promising for your long-term safety. Clear and critical
thinking should always be part of a dive kit. Divers should
remember that when they look at dive computer screens.
The box will never get DCS. The respect for decompression
limits I mentioned earlier is best achieved by adding
conservatism as inexpensive insurance against having a bad
day. Computers and general practice provide guidelines; we
have to bring the common sense.
—
Neal W. Pollock, Ph.D.
Q:
We are flying to Cook Island and will arrive
at 6 a.m. Some members of our group want to
dive right away, but others say we should wait
24
hours. I understand that being tired from flying may
be a risk factor, but is flying itself a risk?
A:
Unlike flying after diving, no clear nitrogen-
related problem exists with diving after flying.
However, there are some issues that warrant careful
consideration before diving soon after a flight. The more
time zones you cross, the more prudent it is to wait. Seldom
after lengthy trips are we well rested, optimally hydrated and
properly nourished. Fatigue can be an insidious risk factor.
When you arrive at your destination, honestly assess your
fitness at that time. Jet lag, stress, soreness and fatigue can
compromise safety. Muscle cramps and joint pain due to
recent air travel might even be mistaken for DCS if they are
first noticed after a dive. It is prudent to wait to dive until
you have fully recuperated from the trip and are mentally
and physically ready. Don’t let enthusiasm for diving lead
you to a potentially unwise choice.
—
Marty McCafferty, EMT-P, DMT
Q:
Now that I have decided to stop smoking, what
impact might smoking-cessation medications
have on my return to diving?
A:
The benefits of quitting smoking will generally
outweigh any side effects or complications from
drugs used to help you quit. According to the Mayo
Clinic, “Your health will benefit almost immediately if you
stop smoking. Just 20 minutes after your last cigarette, your
heart rate goes down. Twelve hours later, levels of carbon
monoxide, a toxic gas, in your blood return to normal. Your
lung function improves, and your circulation starts to get
better within three months. After a year, your risk of having
a heart attack drops by half. And after five to 15 years, your
stroke risk will be the same as that of a nonsmoker.”
Before quitting successfully, most smokers make several
STEPHEN FRINK