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"Obesity and Diving" - David Colvard, M.D.
http://www.divingindepth.com/DesktopDefault.aspx?tabid=718&tabindex=34&DocumentID=4945
http://www.divingindepth.com/DesktopDefault.aspx?tabid=718&tabindex=34&DocumentID=4945
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Published Aug 30, 2007
Obesity is important in diving because of its relationship to fitness, the controversial risk
of decompression illness, fit of wetsuit and weights, and coexisting diseases such as
diabetes, hypertension and sleep apnea.
So, how can the obese dive more safely?
Let’s start with buoyancy and weight distribution.
Bonaire tech diver Andy Owens says, “It is harder to deal with buoyancy issues if you are
overweight from a body fat standpoint, thereby more buoyant, thereby needing more
lead, thereby needing more air in your BCD sometimes, which makes for higher risk of
uncontrolled ascent, and voila, higher DCS risk.
If you are fat, then you are probably going to need more air and are going to suck the
tank down most of the time, so training for proper air consumption is imperative. But, if
you need extra weight, then why not use heavier, higher capacity steel tanks? I would
much rather carry steel than lead.
When I was at 375 pounds and used a normal design BCD, I needed 36 pounds of lead to
be neutral. The benefit of a steel tank versus aluminum for a fat diver is that there is not
as huge a spread in buoyancy as the tank empties. A pressed LP steel 108 is 5 pounds
negative when full and a HP aluminum 80 is 2 pounds negative when full.”
So, if you are an average larger person needing 18 to 25 pounds of lead, then you have
more than enough room in your weighting to have plenty of weight to drop. In fact, if you
are large, then you are pretty buoyant, so dropping that much weight would be a disaster.
The better the weight is distributed between droppable and undroppable weight, the
better. Maybe a 50/50 split is reasonable.”
Duke University Medical Center Hyperbaric Medicine and Environmental Physiology Research
Associate Neal Pollock, PhD, comments:
“The problem with Andy’s strategy is the increase in non-ditchable, negatively buoyant
weight. This can be problematic. I encourage anyone who wishes to dive with a negatively
buoyant tank to check out this effect in a swimming pool.
Don only the tank and buoyancy compensator and then empty the buoyancy compensator
(as might be the case if the BCD failed during a dive). If kicking alone is not sufficient to
comfortably keep the head above water, then it may be a good idea to consider a less
negatively buoyant tank. Easily ditchable weight is much safer.
The reason I recommend the pool test is to make allowance for personal differences. Some
individuals might very well be able to manage the negative buoyancy of the tank with little
difficulty. If not, though, they should think carefully.
The 50/50 rule can sound good in theory, but the most important thing to me is practical
testing to really learn what you can and cannot handle before being in a situation when the
outcome could be direr.”
Obesity is important in diving because of its relationship to fitness, the controversial risk
of decompression illness, fit of wetsuit and weights, and coexisting diseases such as
diabetes, hypertension and sleep apnea.
So, how can the obese dive more safely?
Let’s start with buoyancy and weight distribution.
Bonaire tech diver Andy Owens says, “It is harder to deal with buoyancy issues if you are
overweight from a body fat standpoint, thereby more buoyant, thereby needing more
lead, thereby needing more air in your BCD sometimes, which makes for higher risk of
uncontrolled ascent, and voila, higher DCS risk.
If you are fat, then you are probably going to need more air and are going to suck the
tank down most of the time, so training for proper air consumption is imperative. But, if
you need extra weight, then why not use heavier, higher capacity steel tanks? I would
much rather carry steel than lead.
When I was at 375 pounds and used a normal design BCD, I needed 36 pounds of lead to
be neutral. The benefit of a steel tank versus aluminum for a fat diver is that there is not
as huge a spread in buoyancy as the tank empties. A pressed LP steel 108 is 5 pounds
negative when full and a HP aluminum 80 is 2 pounds negative when full.”
So, if you are an average larger person needing 18 to 25 pounds of lead, then you have
more than enough room in your weighting to have plenty of weight to drop. In fact, if you
are large, then you are pretty buoyant, so dropping that much weight would be a disaster.
The better the weight is distributed between droppable and undroppable weight, the
better. Maybe a 50/50 split is reasonable.”
Duke University Medical Center Hyperbaric Medicine and Environmental Physiology Research
Associate Neal Pollock, PhD, comments:
“The problem with Andy’s strategy is the increase in non-ditchable, negatively buoyant
weight. This can be problematic. I encourage anyone who wishes to dive with a negatively
buoyant tank to check out this effect in a swimming pool.
Don only the tank and buoyancy compensator and then empty the buoyancy compensator
(as might be the case if the BCD failed during a dive). If kicking alone is not sufficient to
comfortably keep the head above water, then it may be a good idea to consider a less
negatively buoyant tank. Easily ditchable weight is much safer.
The reason I recommend the pool test is to make allowance for personal differences. Some
individuals might very well be able to manage the negative buoyancy of the tank with little
difficulty. If not, though, they should think carefully.
The 50/50 rule can sound good in theory, but the most important thing to me is practical
testing to really learn what you can and cannot handle before being in a situation when the
outcome could be direr.”
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