PSDarchives.ascents

Ascents

7-30-02

Ascents

The issue of ascent rates must be looked at from many angles. Dr. Bennett
provided a very useful and well put scientific angle in Haldane Revisited
that all divers should be made privy too - particularly dive leaders and
those that write educational standards and procedures. I would like to
address the diver skill angle of safety stops and ascent rates. The safety
stop, as Dr. Bennett well explained is important for dropping "fast-tissue"
tensions. It also is important for decreasing the risk of making rapid
ascents in the last part of the ascent.
Can you relate to the following experience at any point in your dive career:
one minute your gauge reads somewhere between 15-10 feet and then seconds
later you are staring at the surface less than 2 feet away. "Wow, how did
that happen?"

We tell divers that they should make safety stops and perform 30 ft/min (9
m/min) ascent rates but are we teaching them how and making sure that they
can achieve them? We watch thousands of diver ascending annually with diver
certifications ranging from entry level to course director and I can tell
you that the answer to that question is a resounding "no." The medical
community is doing their part, but without diving educators and leaders to
make sure research findings are put in practice then we all fail.

Let us look just at the term 30 feet per minute. What does that mean? Can
you walk at a rate of 30 feet per minute accurately? How about a rate of 45
feet/min or 70 feet per minute? How can you measure that while doing it? Can
you tell when you are driving 45, 60, 60 mph without looking at your
speedometer? It is fine for scientists to say 30 feet per minute, but it is
not fine for dive instructors and leaders. We need to give divers a usable
term such as two seconds per foot. Ahhh, now they can ascend by counting two
seconds for every foot their hands move upwards on the anchor line, or they
can look at their gauges and count "one-one-thousand, two-one-thousand" for
every decreasing foot on the gauge during free ascents.

Never take what anyone says for face value. Go out and try it. Take a group
of divers. Put their hands behind their backs (to hide their watches) and
have them walk a length of 60 feet at "30 feet/min" and time them. Take
another group and tell them "two seconds a foot" and see what happens. The
divers in the latter group will go slower and be far closer to the rate we
are looking for. Play with this in the water and see what happens. Also
watch what happens when divers walk alone versus walking in a group. Peer
pressure can be a powerful force.
Having usable, measurable ascent rate terminology arises, no pun intended,
when divers do not have an ascent line. Any working dive guide will tell you
that few divers can competently stop and hang at any depth, let alone
shallow depths such as 15 feet. Why do so many divers end up popping up in
the last 15 feet? One answer is because they let go of the ascent line and
head for the boat after their safety stop. How many divers can perform a 2
second per foot ascent rate without a line? Not enough.

One of the main reasons for this is overweighting which starts in their
first dive classes and is allowed to continue throughout their diving life.
We teach already certified divers and we take an average of 6 lbs off these
students as the first step towards developing neutral buoyancy. In the last
two years we have seen a worsening overweighting problem and hear more often
that divers were taught to ascend by inflating their BCD. Sends shivers down
our spines. In the last year, for example, I have had at least thirty public
safety diver students tell me that "we are rescue divers so we were taught
to put lots of weight on so we can sink straight to the bottom." We are
seeing an increase in divers who are overweighting themselves by ten or more
lbs. That's scarier than a freshwater eel bumping you in zero visibility
water.

What does overweighting have to do with ascent rates and safety stops? It is
simple, every pound of lead is equal to about a pint of buoyancy. If you are
6 lbs over-weighted on the surface then you have to have 6 pints of air in
your BCD just to be neutral at the surface. By the time you reach ten feet
that air is compressing and you are dropping and you respond by adding more
air into your BCD, after possibly unconsciously taking in and holding a
large inhalation. By the time you reach 2 ATA (33 fsw) you have to have 12
pints of surface air in your BCD to compensate, and 18 pints at 3 ATA (66
fsw). This is in addition to the air you have to add for suit compression
caused by increased pressure at depth.

With so much gas in their BCDs think about what happens every time divers
rise or fall a little in the water column. If they rise six inches the air
expands causing them to become positively buoyant. They respond by dumping
air out of their BCDs, causing them to sink too far and fast, so they
reflexively take in a large breath and hit the power inflator. My mentor
Walt "Butch" Hendrick aptly named this the Great Compensation Chase. The
more air you have in your BCD, the faster and further you will rise and fall
with each change in body position. Hovering and slow free ascent rates
become a significant challenge, and in shallow water can be a near
impossibility for the average diver. In order to ascend at a 2 sec/ft rate
and hover it is necessary to remain neutrally buoyant continuously. Let us
see why this is so.

Place yourself in an over-weighted diver's fins at a 40 foot bottom. You may
have fifteen or so extra surface equivalent pints of air in your BCD as you
begin your free ascent. You raise your power inflator above your head and
hit the exhaust button. You raise your other arm to protect your head with
your hand, just like you were taught. You begin kicking. You keep on
kicking. After a few seconds of noticing significantly decreased visibility
you realize that your fin tips are kicking up the silt off the bottom. Many
of you can relate to this experience at least once can't you? Don't worry
you are, sadly, not alone.

Think about the obvious laws of physics. If you are negatively buoyant in a
vertical position and are not kicking then where are you going? Down. No two
blennies about it. So we all agree that if you are negatively buoyant you
must kick continuously to make an ascent and the moment you stop kicking you
will descend. The next question then is, is it possible to make a 2 sec/ft
free ascent while kicking continuously? I am going to say not likely, but
don't take my word for it, go to a pool, overweight by 6 lbs and try it.
Continuous kicking will cause a too fast ascent.

Now why do so many divers make negatively buoyant ascents? The reason is
they were allowed to overweight and they were taught ascent procedures that
made them negatively buoyant even if they were weighted neutrally. Try this.
Weight yourself neutrally. To do this, at the surface vent all the air out
of your BCD, cross your legs, stop moving, breathe normally, let your arms
hang down naturally, and you should be hanging with your scalp at the water
line. Descend by gently crossing your arms across your chest and tensing
your arm muscles, or by gently raising an arm out of the water and making a
slightly longer than normal exhalation. Once you are hanging vertically at
8-10 feet gently, slowly raise your arms above your head and see what
happens. Lo and behold you will sink. Try it again and this time hold your
gauge in one hand and your power inflator in the other. You should sink
earlier and a little faster. Putting weight above your center of gravity,
over your head, will make you negatively buoyant.

So think back to how you were taught to ascend? If you were neutral, then
just the act of raising one, or worse, two arms above your head will make
you negatively buoyant. Next we were taught to exhaust the air from our BCD
at the start and during our ascent to prevent a rapid rise from BCD air
volume expanding with decreased depth. If you had many pints of air to
compensate for overweighting then what has to happen if you vent that air?
You have to become negatively buoyant at a rate of 1 lb per pint of air
lost. Are divers taught how to vent just the right enough air to remain
neutral? Or are they taught to raise up both arms and vent? Answer
honestly. It is no wonder that more divers are reverting to adding air back
to their BCD to ascend - they literally cannot get off the bottom without
kicking.

The solution, as was taught to me by Hendrick is to start out neutral. Learn
how to plan dives and move efficiently throughout the dive so that you have
plenty of air left in your tank at the end of the dive (700-1,000 for sport
diving). Remember that if you drain your tank to 500 psi then you will have
to overweight yourself by at least 2-3 lbs just to compensate for the loss
of the air weight in your tank. You should not still be diving with so
little air for many reasons.

Then, when it is time to ascend all you should have to do is get in a
vertical position and "think up" and you should slowly begin to rise at 2
sec/ft. If you have to kick then you are not neutral. There should be
minimal air in your BCD, especially if you are wearing only a thin wetsuit
and are not diving below 100 feet. As you ascend bring your power inflator
out forward at shoulder level and gently depress the exhaust button
periodically. If you find yourself having to kick to stay in place or rise
then you exhausted too much. You only want to vent enough air to keep you
neutral at your solar plexus level. The higher the power inflator, the more
air it will vent. If you vent just a few ounces too much you will become a
few ounces negatively buoyant and the Great Compensation Chase will begin,
although it will be manageable, as compared to errors in pint size volumes.

Practice hovering. At any point during the free ascent you or your buddy can
signal "stop." Stop for a few seconds and then continue with the ascent. It
is particularly important to play this game in depths at 15 feet or
shallower since that is where the greatest pressure changes occur.

Every diver should be capable of making 2 sec/ft ascents and hovering at any
depth even if they always dive with an ascent/descent line. Always have
practiced contingency plans. You cannot guarantee that you will always be
able to reach or find that line so be prepared to make free, slow ascents
and safety stops.

Being neutral from start to finish is the key. As one of course directors,
George Safirowski, frequently points out, too many of today's divers are so
unfamiliar with the feeling of being neutral because they always dive
overweighted, that they feel uncomfortable and even nervous when they are
properly weighted. They tell us that they feel out of control, they think
they are rising when they are not. It takes time to be comfortable with
feeling weightless, neutral, particularly if you have many hours negatively
buoyant hours underwater in addition to all the years of being negatively
buoyant on land.
Observe divers. Too many divers kick continuously as they progress forward
throughout their dive, and during the few times that they do stop to look at
something their hands and arms start sculling. Divers are not sharks, we
will not die if we stop kicking, but sadly many divers will rise or fall if
they stop kicking. They have learned to compensate for overweighting and
poor buoyancy skills by kicking and sculling. If you want to really learn
about this kicking compensation have an instructor take you in a pool and
remove your fins in the deep end. Without sculling your hands, work on
slowly rising and falling by just adjusting your body posture. If you gently
raise your arms you will fall slowly. If you gently take your arms out and
let your chest muscles relax "open" you will rise. Keep on breathing with
normal inhalations and slightly gentler, slower exhalations. Do not use your
lungs as elevators. Change your body posture and sometimes change your
breathing by an ounce or two and that should be all you need to rise, fall,
and stop. Practice hovering in a cross legged position, gently remove your
mask, breathe, gently don the mask, breathe, and then gently clear the mask
by exhaling just enough air to clear the mask not the pool (bubbles should
not escape from the mask). This drill will make you a far safer diver for
many different reasons.

Find an instructor who can move effortlessly and have that instructor trim
you out. In the first buoyancy control class I taught with Hendrick 15 years
ago I was amazed to learn that just the location of the weight on the belt
can make as much as a four pound difference. I watched him take ten or more
minutes per person, meticulously moving weight around on each student's belt
and then remove pounds just by getting the weight in the right place for
each person's body.

Make sure all your gear is secured to your body so that you and your gear
are one. When you move your gear should move with you at the same time in
the same way. Dangling gauges, octopuses are not only safety hazards, they
ruin good buoyancy control, which incidentally means far more than just
being able to hover and ascend slowly.

If your feet are positively buoyant then purchase ankle weights and adjust
the amount of lead shot to make your feet stay where ever you put them.
Hendrick, for example, has four pairs of ankle weights, with each pair
weighted for different exposure suits (wet suit socks, wet suit boots,
drysuits with thin socks, dry suit with thick booties).

Practice moving slowly and being neutral in the pool, teach your students to
do this if you are an instructor, and divers will have a fighting chance in
open water. Learn how to truly "be" in the water, and then hovering and 2
sec/ft ascents will become second nature. We greatly thank the scientists
for figuring out what we need to do to be safe, and we thank industry
leaders like those at DAN for communicating the information out to everyone.
It is up to us to figure out how to make sure all divers are capable of
performing these recommendations and standards.

Safe diving always,
Andrea Zaferes
Lifeguard Systems & RIPTIDE

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