Deep Diving
For the purposes of restricting this discussion
the assumption has been made that no person reading this book for the first
time is contemplating diving beyond 30 metres. The ScotSAC Master Diver
training schedule and the Deep Diving Endorsement covers the planning and
execution of deep diving, including stage decompression, in more detail.
Deep diving is an emotive subject in diving circles. Some divers rather foolishly consider that the maximum depth that a diver has attained is a measure of his competence. A safe dive to a depth greater than that previously visited will add to the divers experience, but a risk/benefit assessment may show that the risks outweigh the benefits. Of course for many diving is an adventurous sport and one way of achieving that adventure is to dive deep. For others, who wish to experience as much of the ocean as possible, to dive deep is to explore a little more of the wonderful underwater realm.
However, deep diving is accompanied by extra dangers and the ScotSAC recognises the need for clear, sound advice for potential deep divers, but advice that is tempered by the need for caution.
It is difficult to define a deep dive. The risks
multiply rapidly as you dive deep. Shallow, no-stop diving is relatively safe,
but as depth and time underwater increases the chances of an incident rise.
·
The average club dive of 15 – 20m conducted properly is relatively
low risk.
·
Mid range dives 20 – 30m are fairly safe but long dive times in
this range can increase the degree of risk, particularly in the case of
repetitive dives.
·
Deep dives 30 – 40m need careful planning and will tend go close
to, or into decompression. With the advent of dive computers and accessibility
to increasingly sophisticated dive equipment this is a depth range where the
planning does not always match the standard necessary to meet the demands of
the dive.
·
Very deep dives in excess of 40m, which are regarded by most
divers as requiring careful planning and preparation.
An inexperienced trainee may feel that any dive beyond 15 metres is ‘deep’, whereas for an experienced diver 30 metres may not feel tremendously deep. However 30 metres is a good point to set the limit beyond which all diving should be regarded as deep.
There are increased risk
factors involved in deep diving and these must be clearly understood. These
factors will form a part of the Risk Assessment for the dive plan.
·
Cold
can dull the senses, impair dexterity, and lead to hypothermia, particularly
during long stage decompression stops where the diver remains relatively
stationary and inactive.
·
Low
visibility increases stress, impairs navigation, and
increases the chance of diver separation underwater.
·
Darkness
increases stress, impairs navigation, and increases the chance of diver
separation underwater.
·
Heavy
dive equipment increases drag and restricts mobility causing
fatigue.
·
Hard
work increases breathing rate, CO2 build
up, narcosis, fatigue, and the chances of DCS.
·
Increased
breathing resistance causes fatigue, CO2 build up,
anxiety and stress.
·
CO2
build up can increase breathing rate, narcosis, and the
probability of DCS.
·
Narcosis
impairs judgement and increases the probability of mistakes.
·
Increased
Gas Consumption leading to
running low on gas or running out altogether. Most rapid ascents are
caused by running out of gas, as are most missed decompression stops.
The risks of deep diving do not go away and are
not overcome by technology. A diver who wishes to go deep needs a high level of
training, experience, preparation and planning, as well as the correct
motivation and aptitude. These will help him to minimise the risks, but he will
still need to be aware of the risk.
Categories of Deep Diving
Diving in the 20-30 metre depth range is fairly safe under
“normal” conditions but if the dive lasts for long periods of time the diver
will come very near, or cross, the No-Stage-Decompression limit for that depth.
Dives in the high 20-metre zone needs to be carefully monitored.
Diving in the 30-40 metre depth range carries increased risk
and demands greater care and experience for most dives. These dives will go
very close to, or into, Stage Decompression and need to be planned and executed
with a high degree of care and discipline. These dives are not really suitable
for nervous or inexperienced divers. The dive planning for these dives is often
not as meticulous as the dive demands. Unexpected circumstances may easily turn
a planned no-stage decompression dive in this depth range into a stage
decompression dive.
Diving in the 40-50 metre depth range carries proportionally
greater risk and requires experience, discipline and very careful planning.
These dives will almost always result in some Stage Decompression and should
only be undertaken by ScotSAC Master Divers or Master Diver Candidates under
instruction. This is the kind of diving that should only be undertaken by a
small proportion of divers. Many divers do not wish to undertake dives to these
depths, nor are they competent to do so. To dive safely to these depths you
must be experienced, dive fit, well equipped, have the right back up and the
conditions have to be suitable.
Diving beyond 50 metres is not recommended on air
and is not recommended by the ScotSAC. Only divers with appropriate training and
experience using mixed gasses can dive safely to these depths.
Deep diving demands a lot of equipment and the equipment should be of high quality.
·
A diver should always be comfortable with his dive
equipment. If the dive equipment feels uncomfortable and awkward it is probably
incorrectly set up.
·
The dive equipment should be set out in a logical
order, it should have:
Ø A
consistent layout, which is easily identified by another diver.
Ø A
consistent colour scheme, yellow octopus valves, high visibility pull dumps,
clearly visible weight release etc.
Ø A
consistent location, which is easily found by another diver.
·
The dive equipment should be easily accessible.
Ø By
feel in poor visibility or in a restricted space.
Ø By
your buddy in an emergency.
·
The diver should be familiar with the equipment
used in the dive.
Ø He
should practise with it in safe conditions before using it at depth. Can he
reach all of the equipment he needs? Can he use it safely? DSMBs can be a
source of confusion and stress if the diver is unfamiliar with their use. An unfamiliar safety aid can quickly become
a hazard.
Ø He
should know that it all works on the dive, not hope that it will work.
Ø It
will help with equipment configuration. Establishing the correct personal
configuration of dive equipment is usually the result of many hours of trial
and practise.
Do
not dive deep if you cannot:
·
Afford the right dive equipment.
·
Obtain the right dive equipment.
·
Cope physically with the dive equipment and diving
conditions.
·
Cope technically with the dive equipment and
diving conditions.
·
Cope psychologically with the dive equipment and
diving conditions.
Gas Supply
Gas is everything on any dive, running out of gas
is not an option. Most rapid ascents and missed decompression stops are due to
divers running out of, or being low on gas.
For deeper dives you must carry, on your person enough gas for all of the phases of your dive and enough to cover the unplanned events as well. You are further from the surface and will need more gas for the ascent, you may have decompression stops to carry out which cannot be missed, gas must be allowed for this. The planning needs to be much more comprehensive.
It is essential that anyone diving deep carry enough gas to complete the dive safely and cope with any foreseeable emergencies. We can learn from other areas in diving.
The Rule of Thirds gas management procedure
developed from cave diving and was later adopted by deep wreck divers. The
prolonged penetrations encountered on these dives called for very conservative
dive planning. It is simple to understand and use.
Use up to
1/3 of your gas on the way into the cave or wreck.
Use up to
1/3 of your gas for the return, exit, and journey back to the surface.
Use at least
1/3 of your gas as a reserve supply.
This was necessary because these divers were
operating in a physical overhead environment. They could not begin to ascend
until they had got out of the cave or wreck. Although we usually do not operate
in a physical overhead environment on our deep dives, decompression stops
create a ‘physiological ceiling’ that prevents immediate access to the surface.
We
can learn from the Rule of Thirds and should be aiming to finish deep dives
with at least 1/3 of the available gas supply intact. This should allow enough
gas for the ascent and the stops for the diver and his buddy in an emergency.
On
a deep dive the diver should leave the bottom with at least 50% of the gas
remaining.
These two rules cover almost all dives but it is
essential to check the gas calculations before the dive to confirm the plan.
The cylinder capacities and configuration cannot
be specified in a manual because they are dependant on the dive plan, the
diver’s breathing rate and the expected workload. Decisions about cylinders for
deep diving have to be made after the gas calculation phase of the dive
planning. Almost certainly a single cylinder will not be adequate for a most
deep dive.
Buoyancy
Many divers get very concerned about the weight of
the dive kit necessary for a deep dive and indeed the equipment does have a lot
of weight. It is, however, the overall buoyancy of the diver in the water that
is important and as the dive equipment gets heavier some weight can come off
the weighting system.
If this is not done the diver will be too heavy in
the water, which will increase fatigue stress and gas consumption, but more
importantly the diver’s B.C. may not be able to lift the fully kitted diver.
Big twin cylinder configurations need lots of lift
to cope with them. Many B.Cs used by club divers are hopelessly inadequate when
using multiple bottles; they rely on the inherent buoyancy of the dive suit to
help lift the weight. A 7mm wet suit loses 7kg of buoyancy at 40m due to
compression; a flooded membrane dry suit with a burst neck seal has no
buoyancy, in either case many B.Cs will not lift the diver without dropping his
weights. Dropping weights underwater makes a controlled ascent very difficult
on any dive, but particularly so on a dive where decompression stops are required.
Some BC jackets cannot lift a 12L cylinder with a
3L Pony with the diver’s normal weightbelt. Smaller B.Cs have less lift so the
problem is worse for women and the smaller diver.
Dive
Equipment
Second
Regulator / Octopus an essential item. Carrying out shared
ascents with a single regulator at depth is fraught with difficulties. A shared
ascent with an Octopus is far easier and should be the method of choice. If you
are carrying a pony regulator and an octopus on the main cylinder hang the Pony
regulator around your neck, if you lose your main cylinder you need access to
your Pony regulator immediately.
Mask
essential to see instruments and the environment. It would be
advisable to wear the mask strap under the hood to prevent the mask being dislodged.
If the mask is broken or lost the diver will find it very difficult to find the
shot line, control the ascent, and manage any stops required because he will
not be able to read his instruments. This is an occasion when the buddy system
can be a lifesaver. The ‘Technical Diving’ practice of carrying a spare mask on
a dive makes sense in this situation.
Hood
& Gloves are
necessary to combat the cold. Deep dives are usually colder and often longer,
cold reduces a diver’s mobility and dexterity long before hypothermia becomes a
contributing factor.
Knives
/ Scissors are
useful for cutting lines and nets, good scissors can be used one handed which
is an advantage. Whatever is carried it must be accessible, the large knife
strapped to your leg may not be of any use if it is rusty or blunt; or if you
cannot reach it when you need it. You should carry a couple of knives in case
you lose one and at least one mounted on the arm or chest for easy access.
Torches
are necessary for
reading instruments in dark conditions. They are also useful for staying in
contact with your buddy, seeing what you are diving on, and signalling to the
dive boat when on the surface. Unfortunately dive torches fail and flood at the
most inopportune times and a spare torch, even a small one, is necessary.
Computers
/ Dive Timers / Watch / Decompression Tables computer batteries do fail, usually during a dive when
they are using power. A second computer with a similar algorithm would be
ideal. A dive timer/watch & depth gauge and decompression tables can be
used, but using them when suffering narcosis can be difficult so pre-planning
is important.
If your computer fails and you are near
decompression ascend quickly and safely to 9m wait a couple of minutes, go up
to 6m and wait 3 or 4 minutes, then go to 3m and wait there until you have used
up almost all of your air. Leave a little for suit Stab jacket inflation on the
surface.
It is recommended to carry your dive plan on a
slate during the dive.
DSMB
and Reels the reel can be used as a distance line off the
shot line, for penetration into wrecks or caves. The DSMB (preferably
self-sealing) and Reel can be used if you cannot get back to the shot line to
help to control the ascent. The reel should have a line at least 1½ times the depth
to which you are diving or planning to deploy it from. A DSMB needs practise or
it can go horribly wrong. A DSMB is also useful for signalling to the dive boat
when on the surface.
A
Slate & Pencil can
be used to record the dive plan and run time, instead of trying to remember it.
It can also be useful when signals are not enough to communicate with your
buddy. Remember that writing when suffering narcosis can be next to useless at
times.
Surface
Location Aids Flags, whistles, air horns, EPIRBs, etc. can be
useful for signalling to the dive boat when on the surface or to locate divers
who have drifted from their expected surfacing location.
Thermal
Protection Dry suits, although not essential, are preferable
for deep dives in our waters. Wet suits compress and lose thermal insulation.
Deep dives can involve long decompression hangs and cold can be a major
consideration.
Thinsulate undersuits are preferable to
traditional woolly bears because they retain more of their insulation if they
get wet.
A diver who is warm is physically and
psychologically better prepared to meet the demands of the dive.
It should be apparent that deep diving requires a considerable amount of planning, organisation, equipment, and support. The planning and execution of a deep dive will be far more meticulous and demanding than a ‘normal’ shallower club dive.
While the Buddy System is still valid a deep diver
in a buddy pair should aim to be as self sufficient as possible. The buddy
system is useful for monitoring each other for signs of narcosis and stress;
and to help if a diver becomes entangled, but the ability of a buddy to do all
you would want and expect on a shallow dive decreases as the task loading
increases at depth.
Obviously both divers in the buddy pair should be
suitably experienced, built up and equipped for the deep dive.
Deep diving as a group of three divers in not
recommended, if a diver encounters a problem and one diver lends assistance the
remaining diver effectively becomes a solo diver. The attention of the other
two divers will be fully, and correctly, on managing the incident and not
looking after the third buddy. It is also very difficult for three divers to
remain in contact in conditions of low visibility or strong currents.
Preparation and execution of a deep dive can be a
complex and time consuming affair. Before the day of the dive the divers should
have planned and carried out the gas consumption calculations, the
decompression requirements, the dive profile, the personnel required in and out
of the water, the equipment considerations, and carried out an appropriate risk
assessment of the dive.
Get to the launch site
or shore site early, last minute rushing about increases the chances of
mistakes. Assess the weather conditions and the condition of the divers; is it
still a good idea to carry on with the dive? This is, in effect another risk
assessment of the dive plan in light of the conditions.
Carefully assemble the equipment and load the
boats, if used, logically to allow you to access equipment, as you need it. The
shot line will be going in first and must be readily at hand.
Drive out to the site carefully. Thrashing over waves will bounce the divers and the kit around. The divers may get injured, or stressed and anxious. The equipment may get damaged. Neither is good before a dive of any sort.
Locate the site and drop in the shot line. The first pair of divers can kit up, take your time and do it methodically. Do not allow yourself to become rushed or mistakes may happen. Confirm the dive plan and go through a careful buddy check. Log the pre-dive details with the Dive Marshal; while you are doing this, the safety diver can be getting organised. Ensure that the Dive Marshall is aware of and fully understands the dive plan.
The dive.
Enter the water when
told to do so and quickly get to the shot line. If you have a problem getting
onto the shot line do not waste gas trying to swim to it, get the boat to pick
you up and put you back on the shot line. If you have used a lot of gas on the
surface you may have to re-plan or abort the dive.
Quickly check that you are both OK and start the descent. Take care not to pull hard on the shot line, swim down it. Give ascending divers the right of way; you have more gas and less decompression penalties. Check that you are both OK and happy a couple of times during the descent. It is good practice to check your own equipment and your buddy’s at a suitably shallow depth (e.g. 6m) before proceeding down to depth.
At the bottom of the shot line check your cylinder pressures and check again that you are both OK. Check the area around the shot line for landmarks and set off on your dive.
During the dive you must carefully monitor your buddy; your depth, time, cylinder pressure and navigation and check these against your dive plan, check out your buddy regularly for signs of narcosis, stress, unease, as well as gas consumption. You should always know what point of your dive plan you are at during the dive.
As the bottom time is coming to an end you should be back beside the shot line. If you are not, do not waste time looking for it, send up a DSMB and prepare for the ascent. Take account of you depth and possible currents. Check you are both OK and begin the ascent, during the ascent do not pull hard on the shot line.
At the first decompression stop hold onto the line or clip a short line onto the shot line and hang from that. Gentle swimming promotes circulation and may help to reduce the chances of DCS, hard exercise promotes the chances of DCS. If you do not need to use any spare cylinders at the decompression stop leave them for others divers.
When you surface signal that you are OK and come off the shot line. There may be other divers in the water and the boat handler will not want to get too close.
If you are diving from a RIB take off your weights and pass them into the boat, take off your BC and get the boat handler or dive marshal to lift them into the boat. Climb in and help to store your kit out of the way.
If it is a Hard-boat try to pass as much kit up into the boat before you climb the ladder. This will depend on the system the skipper uses, but if you are offered a rope to pull your kit on board take it. Hard work and at the end of a deep dive and could bring on DCS.
Record your dive details with the Dive Marshal then RELAX, try to stay as warm as possible, drink some isotonic fluids and if you have been using Nitrox during the dive, or to decompress, continue to breathe it on the boat. The higher Oxygen content and the increased Partial Pressure gradient of Nitrogen will aid off gassing.
The divers should try to avoid pulling up and recovering the shot line. This can prove to be hard work and can be increase the chances of DCS. Let the Boat handlers and Dive Marshal take care of the shot line. Putting a DSMB on the shot line when it is still on the bottom can help with lifting it, but care must be taken not to lift it off the bottom accidentally in doing so.
Avoid flying or driving to
altitude immediately after a deep dive.
Debrief the divers and analyse anything that could be done better next time. Every dive should be viewed as a potential learning experience. Complete your logbook and monitor your health for the next 24 hours. Sit back and relax and enjoy the memory of another successful dive.
If there were any problems you should be able to report them openly without fear of recrimination, the important thing is that learning takes place. If it is regarded as an incident then it should be recorded and an incident form completed and returned to the BDO and ScotSAC Headquarters.
Some of the Added risks and dangers of deep diving have been identified here. Remember that the risks increase in proportion to the depth. Diving beyond 30m can be executed safely and enjoyed, but only by those divers with sufficient experience, knowledge, and understanding to do so.
Deep diving is a challenging area of our sport but one that requires a high practical level of expertise and the ability to plan dives in meticulous detail. To learn more about the planning and execution of deep dives the ScotSAC recommends that divers complete the ScotSAC Deep Diving Endorsement