You will have seen more and more references
to ''Technical Diving'' on the pages of this magazine over the
past three years. When the term was first introduced its meaning
was unclear and undefined and, in the U.K. in particular, there
were many who declared that it brought nothing new, and that it
had been with us for a long time under a different guise. If its
meaning is a little clearer today, then it is because the said
activity has evolved and matured during this time, and it has
begun to take its place in the diving scene.
If we consider what we mean by ''Sport Diving'' or ''Recreational Diving'' then we can define it as the kind of diving that is contained within a broad sphere of activities that should be enjoyable, attainable, perhaps exciting and demanding, and surely safe. It has been the aim of the training organisations, such as the BSAC, to bring people to a reasonable level of competence in this activity, always bearing in mind that diving, when considered as a leisure activity, should not expose its participants to any unecessary risk.
Now, the degree of risk is often in inverse
proportion to the competence and experience of the diver. A further
period of training should improve competence, and reduce risks.
It is when the type of diving being practised
starts to present new problems that require new solutions, that
new techniques come to be evolved. The steady progress of diving
exploration is taking us beyond the more accessible inshore sites,
toward less accessible sites requiring a broader range of techniques
in order to maintain the required level of safety.
The training received by most divers has equipped
them to undertake air diving to the limit allowed by their qualification,
but in any case, not below 50m. For the vast majority of divers
this is more than they should ever need. But it is, as always,
the troublesome minority who have arrived at this limit and still
find the need to go further who have caused the ripples that have
resulted in the Technical Diving wave. This category of divers
found the ''amateur diver'' description a poor fit as their needs
led them to adopt techniques and equipment from the professional
and military sectors, and then to evolve their own.
For many, the need arose from the pursuit of
projects which slowly but surely took them outside the envelope
of normal sport diving and into a new area of risk which needed
a new set of solutions. This is the area which we also call ''Extended
Range Diving'' since it recognises the basic needs of being able
to go further, for longer, and in perhaps more extreme conditions.
It is this ''professional amateur'', professional in approach,
amateur in motivation, that forms the core of the Technical Diving
community.
What does it involve?
Technical Diving uses a range of special techniques and equipment to extend the safe operational range and the possibilities of the diver. A principle feature is the use of gas mixtures other than plain air to reduce problems associated with nitrogen (decompression and narcosis). Initially this means breathing a Nitrox mixture which has an increased level of oxygen, and a lower level of nitrogen than normal air (21% oxygen/79%nitrogen).
A further refinement is to further reduce the nitrogen content by replacing all or part of it with another inert gas (usually helium) to reduce the narcotic effect of the mixture during deep dives.
These mixtures can be breathed using conventional
SCUBA equipment, specially adapted SCUBA equipment, or rebreathers,
which recycle the mixture to make full use of the oxygen it contains
and to give longer duration.
Technical diving also considers carefully the
selection and suitability of all the diver's equipment for more
adventurous or extreme diving. Special equipment and accessories
have been developed with the aim of maintaining a high level of
safety while diving under more difficult conditions. The Technical
Diver leaves little to chance and aims always to be prepared for
any predictable emergency, usually by carrying the solution with
him. This is the direct opposite of the minimalist approach preached
in warm water recreational diving and should be understood as
having quite different objectives.
Techniques have been developed to ensure safe
diving during penetration of wrecks, deep into underground cave
systems and for diving under ice; a set of conditions grouped
under the description ''Overhead Environments''. Diving into a
situation where you cannot make a direct ascent to the surface
presents a host of additional problems and gives new urgency to
the problems of managing your gas supply. Once you go beyond the
reach of natural light you have to rely on the illumination you
can carry with you, and you have to concern yourself minutely
with the question of navigating your way in, and more importantly
out, of the cavity.
Other techniques have been evolved to allow
extended in-water decompression procedures to be carried out in
greater safety and with greater efficiency. Longer decompression
procedures can underline the need for improved thermal insulation,
beyond that required on normal dives.
The passage from normal sports diving to Technical
Diving does not commit you to running the full gamut of the possibilities
available. It allows you to acquire a few more tools and techniques
to make the kind of diving you intend to do safer and more satisfying.
The better understanding gained may make your normal air diving
safer and more interesting.
What are the advantages?
For most divers the passage into Technical
country starts with nitrox. The advantage we are looking for from
nitrox is longer no-stop times, or shorter decompression stops.
By reducing the proportion of nitrogen in our breathing mixture
we will absorb less nitrogen during the dive and have less nitrogen
to eliminate during the ascent. For a given mixture we can calculate,
or read from a table, the Equivalent Air Depth (EAD). This is
the depth at which we would have the same PPN2 if we
were diving on air.Thus our no-stop limit at 30m using air and
the BSAC'88 table A is 20 minutes, but if we use EANx36 we will
have an EAD of 24m so we can extend it to 30 minutes.
Alternatively, if we want to spend 40 minutes
dive time at 30m on air we will need to make stops of 1 minute
at 9m, and 9 minutes at 6m. On EANx36 we would need only 1 minute
at 6m. (Note: this will only work for the first dive using current
BSAC'88 tables since the surface interval is carried out on air,
a different gas to that used during the dive).
A ''nitrox dive'' could be a dive carried out
almost entirely on air, perhaps in the 40-45m range, for which
air is quite suitable, with a nitrox mixture (probably between
50% and 80% oxygen, or even pure oxygen) used only during the
decompression stops. This will still give faster elimination of
nitrogen and shorter decompression times.
Another approach to improving your safety margin
is to dive on nitrox, but to treat it as air for decompression
purposes. To enjoy this benefit you breathe nitrox during the
dive or the decompression stops, or both, but use your usual air
decompression table or air dive computer to control your decompression
procedure.This is an approach which could have an appeal to the
more careful, older, less fit, or less frequent diver as it allows
you to keep comfortably within the recognised safety limits.
Should you have one of the latest generation
of nitrox dive computers then you can gain all the benefits of
reduced nitrogen intake due to the gas breathed, along with those
due to a possible multi-level dive profile. Before the dive you
enter into the computer the oxygen percentage of your gas mix
and the computer deduces the balance to be nitrogen, and calculates
the decompression requirement accordingly. Naturally, it will
work equally well for air diving. A nitrox computer has the added
advantage of tracking your oxygen exposure to ensure that you
do not exceed the recommended CNS toxicity limits.
It has been suggested that the use of nitrox
reduces the narcosis effect, but there is no scientific evidence
to support this. The solution to the narcosis problem is trimix,
which reduces the narcotic effect of nitrogen by replacing a part
of it with helium.
Another observation is that diving on nitrox
results in a lower consumption rate, since the diver enjoys a
higher PPO2 during the dive, but this has not yet been
demonstrated scientifically.
What are the problems?
While reducing the nitrogen content brings
some advantages; increasing the oxygen content introduces some
new problems. We have all learned that oxygen becomes toxic when
breathed at higher partial pressures, and that at 66m normal air
has reached the maximum recommended limit of 1.6 bar PPO2.
When we take the advised limit of 1.45 bar then we find that EANx32
has a maximum depth limit of 35m, EANx36 is limited to 30m, and
air to 59m. Clearly, nitrox is not a gas for deep diving.
An additional problem represented by oxygen
is that it can have a toxic effect on our Central Nervous System
if we are exposed to higher concentrations over longer periods.
For normal recreational dives the required exposures are longer
than we are likely to meet, but can be built up over a series
of dives. If we are diving to 30m on EANx36 (PPO2 =1.44)
then our maximum exposure should not exceed 120 minutes at that
depth, which would give us a number of other problems as well
(gas supply, decompression times, cooling). Over the course of
24 hours our time spent at this PPO2 should not exceed
180 minutes. These exposure times get substantially longer at
lower PPO2 levels.
Oxygen in high concentrations can also give
problems in its handling and use. Oxygen has the property of supporting
combustion, although it is not itself flammable. When it comes
into contact with certain substances, such as hydrocarbons at
high pressure, there is a risk of explosion. Any part of our diving
equipment which stands a chance of coming into direct contact
with high concentrations of oxygen must therefore be scrupulously
clean and free from any such contamination. The first candidate
is our diving cylinder which, along with its valve, must be cleaned
for oxygen use, known as 'in oxygen service', since the procedure
for filling it with nitrox could start by introducing a quantity
of pure oxygen into the cylinder. Our standard air regulator should
be suitable for use with nitrox mixtures containing up to 40%
oxygen, but if we wish to use it for higher concentrations, such
as decompression mixes, then this too must be cleaned for oxygen
use and never used with normal air.
What we need to do to go deeper is reduce the
oxygen content, to avoid toxicity problems, and reduce the nitrogen
content, to avoid narcosis problems. This usually means making
up the balance with helium. Now while helium helps considerably
with the narcosis problems of deep diving, it brings no decompresssion
advantage, and will even increase decompression times on shorter
recreational dive exposures. For deeper diving we can continue
to reduce the oxygen content, and replace all of the nitrogen
with helium, to give a mixture called Heliox. Unfortunately such
a Trimix or Heliox deep-diving mixture would have such a low oxygen
content that it would be unsafe at shallower depths.
Helium has two major disadvantages; it is horribly
expensive, and it cools you down faster than when breathing air.
Thus trimix and heliox diving bring additional problems of cooling,
which are further aggravated by the longer decompression times
involved.
As we can see, there is almost an optimum mixture
for each depth range, depending on how long you need to stay,
and the thermal factors. The well organised Technical Diver will
carry a travel mix suitable for breathing from the surface down
to a reasonable depth, and will then switch to a bottom mix, lower
in oxygen content, for the time at depth, and during the return
to the surface will have to switch back to the travel mix, with
the additional possibility of a decompression mix, with an even
higher oxygen content to give optimal nitrogen elimination, for
breathing during the shallower decompresssion stops,.
Just in case this sounds simple to some of
you, you may not have grasped the complexity of a dive which relies
on identifying and breathing from the correct regulator, attached
to the correct cylinder, for precise phases of the dive, while
always ensuring that you have enough of each of the required gases
available and in reserve for each phase.
The problem of carrying large amounts of gas
with you on a dive is a real one. The best solution is to use
the gas more efficiently, and that means to rebreathe it so that
the oxygen content is used more fully. A rebreather used with
normal air (21% oxygen) allows each breath to be recycled about
four times as only about 5% is used during the respiratory cycle.
A set fitted with a standard 10 litre cylinder would last about
as long as a twin 2 x 20 litre set on open circuit. Alternatively,
a much smaller cylinder can be carried, and if this is filled
with Nitrox, then even greater gas efficiency can be achieved.
Rebreathers therefore achieve major efficiencies in gas usage,
but have a high initial cost. They also demand far greater care
and attention, and considerable maintenance, compared with SCUBA.
We have mentioned in passing a number of commodities,
the gases and mixtures, which are not yet easily available, and
are all more expensive than compressed air. Dive centres equipped
to fill your dedicated nitrox cylinder with the appropriate mixture
are still few in number, and this will only change as a result
of increased demand. A fully-equipped mixed gas blending system
requires a major investment on the part of the filling station.
Alternative methods of providing the gas mixtures exist, but they
too are logistically more complex than simple air filling, and
this must be reflected in the cost. Nitrox is usually the result
of adding a prescribed amount of oxygen to air, and breathing
oxygen is a gas which is relatively easy to obtain and not unreasonable
in price. Once helium enters the scene then the price of a fill
escalates. A helium mix can cost as much as 20 times the price
of compressed air. But in a closed circuit mix rebreather the
amount of helium actually consumed is very low, making it economical
once more.
What training is available?
If you are already a diver, a BSAC Sport Diver,
CMAS 2 Star Diver or equivalent, with some additional experience
then you have the base required. If your qualification is higher
than this, then that can only give you an advantage. However,
in all cases there will be material to be covered which you have
not met before, as well as some useful revision of things which
you should remember from earlier training.
Where should you go for this training? If you
are a BSAC member, then you will soon be offered (end of 1995)
Skill Development Courses leading to BSAC Nitrox Diver and BSAC
Advanced Nitrox Diver. The Extended Range Diver course is also
in hand.
An alternative choice is to go to one of the
specialist agencies : IANTD (International Association of Nitrox
and Technical Divers), TDI (Technical Diving International), or
ANDI (American Nitrox Divers Inc.). They all offer a path starting
with nitrox diving and continuing through other Technical Diving
courses toward Trimix use, and eventually Rebreathers.
These are the early days of rebreather training
for amateurs and the specialists are now developing their training
courses. However, the pattern of first understanding how rebreathers
work in general terms, and then going on to learn how to use a
specific set, seems to have been adopted. Most of the rebreather
manufacturers have contracted with one or other of the specialist
agencies to supply the training for their equipment, and it will
often be packaged with the equipment cost since no sale will be
made to uncertified divers. Given the high cost of the equipment,
it is likely that courses will also be available for divers who
wish to qualify as users so that they can hire the equipment for
those special expeditions.
A good starting point would be ''An Introduction
to Technical Diving' by Rob Palmer, available from the Diver Bookshop,
£17.95.
If you are a travelling diver then it is worth
noting that CMAS (World Underwater Federation) should soon have
international equivalents available for a Basic Nitrox Diver and
an Advanced Nitrox Diver. This will allow their member organisations
(BSAC, TDI, IANTD, etc.) to apply for equivalents to their certificates
for issuing to their members. A degree of cross-recognition of
certificates will soon be in place between these organisations.
Should I get involved?
Just answer these simple questions :
1. Do you feel the need to lengthen the no-stop times of your dives in the 20-35m range?
2. Do you regularly do dives with long decompressions in the 20-35m range?
3. Do you feel a need to increase your safety margin beyond that which you practise currently?
4. Do you accept that you will probably have to dedicate one or two cylinders and one or two regulators for
nitrox-only use?
5. Are you ready to accept strict maximum depth limits on your dives?
6. Do you accept the need for some additional specialised training, whatever your current level?
7. Do your long term aims include silent, bubble-free, constant buoyancy diving?
If you answered 'yes' to at least three of these questions, then it is time you started considering taking the first steps.
If you answered 'yes' to 5 or 6 questions, then you have probably already started, or are about to.
Whatever you decide now, we are bound to see a continuing evolution in the techniques and possibilities offered
by new diving technologies, and there will always be new developments to convince you that the time has come to take a step forward.
It is generally accepted that breathing Nitrox mixtures on open circuit SCUBA equipment may not give you the
result you need for some of the more serious diving projects. However, it provides a valuable bridge from sport diving techniques and disciplines to the more advanced techniques and stricter disciplines required for trimix and rebreather diving. Although considered a major step today, Nitrox will probably come to be considered a standard recreational diving gas within a few years.
What are the objectives?
Although the immediate objective is to benefit
from the advantages offered by nitrox, in all its applications,
the main attraction in following the Technical Diving path is
to make the leap to rebreather technology.
The attractions of the rebreather probably
outweigh for most of us any trifling problems such as cost. The
first rebreathers to be offered to the non-commercial, non-military
diver will seem to be highly priced, but will surely come down
in price as they gain in popularity. Prices quoted today range
from £5000 to £10000 for different specifications. But
if you count the cost of a fully rigged technical diver's kit
it too soon achieves horrific proportions. And don't forget the
real economies in gas cost per dive that are possible with the
rebreather. But most of all, consider the advantages of a relatively
light-weight and compact set which gives you silent, bubble-free,
constant buoyancy diving, the dream of every photographer and
marine biologist.
Although the cost of specialised rebreather
training will probably be part of the package in most cases, it
is a real factor for would-be rebreather divers. Adequate familiarity
with the equipment needs at least a week of training before the
proud new owner, or renter, can be let loose with the equipment.
In summary, the objectives of Technical Diver
Training should be to give the diver a wider range of techniques
and knowledge so that the right choices and decisions can be made
for each dive, with never a need to compromise on safety. The
techniques and disciplines acquired should not encourage the diver
to undertake greater risks, but rather to reduce the risk through
a more thorough approach to planning and executing a dive.
Although the activity places a heavy emphasis
on equipment and technology, none of this will be of any use if
the diver does not first accept the need to approach it with the
right attitude. Do not expect the passage to Technical Diving
to be an easy one; it is intended to make you careful, responsible,
thorough, fastidious, and aware of your new limits. You will find
yourself more often at the limits of our knowledge on diving physiology;
the more experts you meet, the more often you will hear the reply
''We don't know, yet.''
Take care when exploring the frontiers, it is all too easy to stray from the beaten path.
Some definitions.
ANDI : American Nitrox Divers Inc.
CMAS : Confédération Mondiale des Activités Subaquatiques - World Underwater
Federation.
EAD : Equivalent
Air depth.
Heliox : A
breathing gas mixture containing oxygen and helium
IANTD : International
Association of Nitrox and Technical Divers. (IANTD UK, 42 Marsh
Road, Thatcham, Berks RG13 3QR.
Nitrox : Also
know as 'oxygen-enriched air', 'Safe-Air' (registered to ANDI),
EANx (Enriched Air Nitrox). A gas mixture containing nitrogen
and oxygen, where the oxygen content exceeds that of normal air
(21%). Generally expressed as Nitrox XX, or EANxXX, where XX indicates
the percentage of oxygen in the mixture.
PPO2 :
partial pressure of oxygen in the mixture breathed. BSAC recommended
limit for this is 1.40 bar for in water use. Overall recommended
limit by all agencies is 1.6 bar
PPN2 : partial pressure of nitrogen in the mixture breathed.
TDI : Technical Diving International. (TDI Europe, Unit 7, Elliott Road, West
Howe Industrial Estate, Bournemouth, Dorset. BH11 8JX, U.K.
Trimix : A breathing gas mixture containing oxygen, nitrogen, and helium.
or 