five students on the September course completed their self-study
requirements and arrived for the evening theory session at the shop in
Capalaba, Brisbane. I completed
the TDI Nitrox Diver course in June 1997 and have been using Nitrox ever
since. On this occasion, I sat
in on the course as Neil Harris delivered TDI’s online presentation,
complete with humorous anecdotes and good advice. Naturally, we covered oxygen toxicity, partial pressures and
nitrogen toxicity in some detail. The TDI course is very comprehensive and
also includes a few simple formulae, dive planning, blending and analysing
the theory session, Neil presented the various bits of equipment that are
used in Nitrox diving. Out came
the Nitrox computers, oxygen-cleaned cylinders, DIN valves, high performance
regulators and oxygen analysers. Since
most of the students had air computers, they would be able to dive these to
their deco limits and still have a safety margin due to the reduced nitrogen
in their breathing gas.
from the practical aspects of analysing your gas mix, filling in the tag on
your tank and the log sheets, the basic change to diving preparation is the
calculation of your Maximum Operating Depth (MOD) for the particular gas mix
in order to minimize the risk of oxygen toxicity.
To avoid errors, we use a simple table which shows the MOD for
various oxygen mixes at various partial pressures
depending on the circumstances. As
a very careful diver, I always use the recommended maximum partial
pressure of 1.4
planning using Nitrox can be made very simple.
The most common mixes that people use are 28%, 32%, 36% and 40%.
These allow you to dive to a maximum depth of 40, 34, 29 and 25
metres respectively. Since I
rarely dive below 30 metres, I generally ask for an EANx 36 mix and set my
depth alarm accordingly. Easy!
is a course which involves careful dive planning and the use of quality
gear. During the dives that
made up the practical part of the course, the students used 12 litre working
capacity (100 cu ft) oxygen-cleaned steel tanks with the distinctive green
and yellow Nitrox band. The tanks all have high pressure DIN valves so they can be
filled to their maximum working pressure of 230 Bar.
went along as a pleasure diver equipped with a 15 litre (120 cu ft) and two
12 litre (100 cu ft) steel tanks, all filled at the shop with EANx 36.
I also took my Poseidon Jetstream and Scubapro G250 Nitrox regulators
with analogue gauges attached. In addition, I wore a Nitrox computer on my
wrist pre-programmed with this gas mix. A depth alarm at 29 metres limits
the partial pressure of oxygen to a maximum of 1.4 Bar when using this mix.
As Bret Gilliam (TDI) says, this is not technical diving, just safe
Friday night, we met at Newport Waterways, Scarborough, and loaded our gear,
and two “G cylinders” of oxygen, on board “Big Cat Reality”. This is
a 25 metre, luxury live-aboard vessel which is available for charter to the
recreational scuba diving industry as an overnight dive vessel.
Big Cat Reality primarily provides a service on weekends, as a luxury
dive charter vessel with facilities to accommodate up to 24 divers and 7
crew including a K180 dive compressor, and rescue vessel.
She has the latest navigation equipment with a professional and
experienced crew. Big Cat Reality has a 10 metre beam which provides a large
stable dive platform. This is a
good thing because it was going to be windy!
Neil’s careful supervision, the students learnt how to calculate the
correct amount of pure oxygen to put in their tanks, so that it would end up
with the required mix when topped up with air. For example, how much oxygen do you add to a tank to get a 32% mix
when the previous dive left it with 70 Bar of EANx 36?
Sounds complicated! Once
again the ‘rocket science’ myth is removed by using a simple table to
arrive at the correct answer.
air from the on-board compressor was passed through a portable filter with
DIN fittings. When each tank was full, the diver analysed the mix, filled in
the tag and the log sheet with the pressure, gas mix and maximum operating
crossed Moreton Bay on Friday night and anchored in the shelter of
Tangalooma Wrecks on the west coast of Moreton Island.
At first light, we moved north to Curtin Artificial Reef for a dive
at high tide.
descended the anchor chain and located the Transfield Barge near the anchor.
A big Cobia came out of the hold and on to the sand. Inside the
barge, a 150mm Nudibranch was making its way across the sand! Over near the
north end of the wreck, a very large black stingray rested on the bottom.
Group went over to the tug Loevenstein, then explored the gravel barge
Estrella Del Mar then back to the Transfield Barge.
Mike and I did not have the URGQ Chart with us and had to
rely on memory to navigate from the sand carrier Centipede, to the yacht
Solace, to the tug Loevenstein, and into the
Etmore at 22 metres.
We then retraced our route back to the anchor.
it was a neap tide, there was not much water movement in the outgoing tide.
We were able to have a slow drift dive on Curtin Artificial Reef
after morning tea. Neil took us
on one of his guided drift tours and we had a lot of fun scooting in and out
of the wrecks. We started at
the southern end of the reef at the old tug Melbourne, then to
Barge 25, the
Transfield barge, the upside down Utah, and then stopped at the Bremer. The
students with reels practiced sending their safety sausages to the surface
to indicate our position. After
completing our drifting safety stop, Big Cat Reality was right there to pick
a superb lunch, we headed out to Flinders Reef, 5 kilometres off Cape
Moreton. The crew spotted some
large green turtles near the boat. During
the afternoon dive, you could hear the whale song underwater!
There were small cod, big Wobbegongs, and the usual abundance of reef
fish. The ‘no extraction’ policy is working. The marine critters are
really becoming abundant on this totally protected reef.
of the students was a bit heavy on the air consumption so I lent him my 120
cu ft tank for the night dive and then for the rest of the trip.
Neil spotted a big crayfish and a large male green turtle. He also
claims to have seen a Spanish Dancer as long as his forearm, pink in colour
with two pink shrimp on its back. He even got it to swim, magnificent!!! The
large parrot population is improving and we spotted a huge Wobbegong.
moved over to the sheltered anchorage at Yellow Patch and had a barbeque
dinner on board. Next morning, we anchored on the Cementco which was scuttled
in 1985 near Flinders Reef. We
swam around the outside of this upside down barge and peered into the
various holes underneath the hull reaching 26 metres.
Then we went for a little swim through the wreck where there were
quite a few baby cod. Hopefully
they will grow up!
second dive was at the northern end of Flinders Reef where we saw more
turtles, egg cowries, Nudibranchs, and a 3 foot long potato cod that was
not interested in leaving the cleaning station. We examined one of the new
permanent moorings before ascending to Big Cat.
lunch skipper James took us over to Smith Rock. We had a great time swimming
around the wreckage of the former Liberty ship Marietta Dal which hit Smith
Rock and sank in 1950. Those old Liberty ships were welded together and had
a bad habit of breaking in half! The
wreckage is strewn all over the place at about 12 metres.
We missed the bulldozers this time but saw a lot of interesting
country and a good mix of fish.
can tell who was diving on Nitrox on the way home from a trip.
The air divers are all asleep! The
future of diving is in Nitrox and ultimately in high-tech rebreathers.
We need to move away from the common alloy 88s with their unstamped K
valves to the new steel tanks which are 100s or 120s.
These can be oxygen cleaned and fitted with DIN valves rated to 232
bar. You can then take
advantage of the increased bottom times that are available when using
Nitrox, by using these bigger tanks.
students all demonstrated a high level of competence in their diving skills
and also had a great time doing it. They
were subsequently awarded their Nitrox Diver certificates.