Normoxic Trimix Rebreather Training
What and Why?
Rebreather training comes in stages. You start at level one known as Mod 1
(Module 1 probably, I never asked). Mod 1 teaches you the basics of
rebreathering such as cleaning and maintaining it so it doesn't go wrong and
diving skills which contain, naturally enough, what to do if it does go wrong.
It is the OW and AOW of rebreather diving.
Once you have mod 1 you can go and dive and build up some experience of the
thing. My TDI card certified me to use air as a diluent (the basic gas in the
loop to which controlled amounts of Oxygen will be added), a maximum depth of
40 meters and decompression stops not exceeding 5 minutes.
Mod 2 is the short hand for the second level training option on a rebreather.
This includes much more serious decompression stops and the use of Normoxic
Trimix as a diluent.
If you want a discussion of Trimix follow the
Now it is always said that you don't chose the agency you choose the instructor
but there is only one agency that offers the course I wanted so the instructor
was the only choice. I was pointed to Martin Robson of
Eau2 who are based at Runnemead Divers.
Martin is a time served technical instructor with an international
training schedule and is right up the tree in the IANTD so he seemed a very
good choice. My advice was that he teaches technical skills rather than just
examines them. The web site also said they had taught just the course I wanted
in Lanzarote in the Canaries in the spring of last year.
Now those of you who dive the UK will know that getting blown out is a
feature of our diving. So booking a week off for a course and then sitting on
the dock watching the waves smash against the shore is bad news. Much of my
initial, mod 1, course was transported from Plymouth to Stoney Cove as the
weather took advantage of my natural tendency to seasickness to ruin the first
attempt. Lanzarote might be the Costa Club to some people but the relatively
benign climate and the fact that it is the peak of an undersea volcano, meaning
that you can have whatever depth you want by just swimming out further, make it
a very handy place for a deep water course.
Right Let's get on with the story
We had 20 Kilos of baggage allowance and Britannia kindly give you an extra 5
Kilos if you are a diver but Martin warned us to purchase another 10Kilos at
£35. Once I started packing this fell apart on me and I phoned for an extra 30
Kilos on top of that. I just about squeezed into 65 Kilos and a 5 Kilo cabin
baggage allowance. Once we were passed check-in the flight was quite
The Hotel is a strange place to English eyes. About 40 living room, bed room,
bath room apartments with a balcony gathered round a bar and a swimming pool.
We just had two as Martin is trying to provide a course at a reasonable cost.
Martin, Paul and Steve had one apartment and Danny, Emma and I had the other.
There is a zip-bed folded up in the bedroom but I just put the sheets, pillow
and blanket on the living room sofa. The room was already full of rebreathers
in various states of disassembly so to add the bed to the equation would have
We investigate the little self service shop over the road for breakfasty and
lunch shaped things and flagons of bottled water. We sleep OK although I am
not too keen on sharing the room with the with the fridge and Kareoke night at
the bar starting when I was planning on going to bed did give me emotional
problems but it didn't go on too late.
Next morning we piled into the van and headed off to the dive shop to pick up
the hired cylinders, weights and fill with Sofnoline. This was Deco-stop
Diving, now gone, in Costa Tequise and aside from one dodgy fill that we picked
up analysing they were cheerful and helpful even bringing stuff to us and
finding things to lend/hire as we progressively broke every bit of diving
equipment on the island.
Then it was off down to our dive site from the week. We are shore diving
because the place is suited to it. Remember we are on the top of a volcano
several hundred miles off the coast of West Africa. It rises from the seabed as
a volcano shaped cone so you can have virtually any depth you want by just
swimming out further. We have the steps on the jetty to enter and exit on and
we can dive on virtually any state of the tide.
Martin walked us out on the rocks to point out the salient features of the area
and, to cut a long story short, dropped the car keys. Now when you are climbing
over boulders with an average size of half a meter to a meter in most
directions this gives something small like car keys an opportunity to rattle
down a long way. In hind sight it was a serious problem solving, team building
exercise and the final solution of Steve upside down in one adjacent but
slightly larger hole poking a piece of rod we borrowed from the local dive shop
through into the hole the keys were in was a solution. The day was saved. Time
to kit up.
Thursday Dive 1 - 23 meters 67 mins
Sorry. No in water shots. I don't even ask if I can take the camera on
training dives. Danny started well discovering that the boot was virtually
falling off his suit so he wasn't diving.
We ran down the slope and the flash cards started to make their appearance. I
have to agree that flashcards are a very good way to run a course like this but
being hit by a card saying 'Low O2' makes you have to react quickly and it soon
showed up the weaknesses in my disaster recovery drills. Back in the shallows
Martin laid out a line and we started eyes closed drills. Drop the bailout
cylinder and clip it to the line, continue up the line until patted on the head,
turn round and find your tank and clip it back on. Somebody had parked another
tank there but it wasn't clipped on so it wasn't mine.
Thursday Dive 2 - 7 meters 35 minutes
This was a six meter dive in full deep water kit. Danny had managed to hire a
wet suit and the tiniest pair of fins ever. Martin ran
him through some of our drills from the morning then set to run a line and
do some out of air style drills. There is a lot of swimming about with your
eyes shut and air sharing stuff. Now my TDI mod 1 course mostly concentrated
on managing problems yourself but here we were to learn the essentials of using
your buddy and being a buddy. Remember the amount of gas to bail out from 60m
is truly jaw dropping so the team carry enough to get one and a half divers
The drill evolved simulating an out of air by switching off the loop and onto
the bailout OC reg, swim to your buddy, locate and take his bailout and breathe
that. Switching to the OC reg means that Martin can spot you cheating and
taking a sneaky breath which, if you were on the rebreather would be impossible.
Thus dive must go down as the 'Fry Dive' as most of the drills were performed
in a cloud of immature fishlets.
Friday Dive 3 - 45 meters 96 minutes
Our first planned deco dive. 45m 20mins 27m for 2/31min, 18m 2/35min,
12m 2/38mins, and 6m 11/50mins. I switched up the setpoint too early and had a
quite nasty oxygen spike. What I should have done was stayed on 0.7 and let the
spike effect push me up towards the 1.3bar. At 45m we ran some drills involving
attaching and removing the bail out via the 'offboard' hose both to ourselves
and a buddy. The flash card made it's appearance again mid way through the
agreed drill. I'm still over weight and it was running me ragged so I trashed
my way through the whole Argon bottle and had to revert to using the wing. This
was new to me so I naturally made a pigs ear of it. Once we had completed the
deco Martin had some more drills.
Drill one. Switch to the bailout so Martin can see bubbles to know if we
are cheating then eyes shut start two divers at opposite ends of a line and
without breathing swim towards one another. On meeting locate their reg (clue:
it's in their mouth) and swap regs. Once you are on their reg you are allowed
to breathe. Next, eyes still closed, swap the bailout cylinders. Now I was quite
pleased to manage to identify that the way we swapped regs linked the hoses
through one another and I had to take the reg out to fix it and then hitch up
Steve's tank but Steve accused me of closing his dump valve and inflating his
suit. Strange. I know that I handled him very gently as I was worried about
dislodging his mask. However it occurs to me that a certain Robson was close on
the fray and Steve is trained by him. Not that I wish to make accusations, but
Steve, it wasn't me.
Drill two On the same line take your mask off and swim the line and at
the far end turn round and swim back. It was about half a kilometre each way I
think. I had heard that these cavers carry big reels and now I know. I hate
mask off drills. The one thing the PADI Tec Deep course instilled in me was
always carry a spare mask.
Saturday started with Danny tearing the neck seal of the hired drysuit. As Paul
had an ear discharge he wasn't diving and he is a big lad so they fetched his
suit and put Danny in that. Anybody who knows Danny will now realise that Paul
is not a little guy.
Saterday Dive Four - 52 meters 70 minutes
Fifty three meters and we are going to do a simulated total rebreather failure
of one diver and some added tricks like manually driving the unit and boosting
the ppO2 on deco. We made our way out and down and were put onto manual control
as expected. Then suddenly Danny is on his bail out reg and signalling UP with
urgency. I confess it took me a moment or two to realise that Martin had picked
him and we were combining two drills. Back the way we had come pushing in the
stops. Then came the signal to swap my bail out with Danny. He has,
simulatedly, breathed half his Trimix bailout and it is time for me to pass
over my more full tank. He takes my bailout reg and then I unship the tank and
pass it over. The diver with a problem gets the team's gas but each team member
needs to have gas in case he runs into his own problem. The rule is to breathe
half of what you have then swap. Once Danny is established on the new bailout
the simulation allows him to swap back on the loop or the low ppO2 of the
bailout (breathable at max depth) would keep him in the water forever (yes - we
do have the times for that on our slates). Then comes the DSMB drill. Heck my
DSMB has been out so many times it can virtually do it itself and Danny is the
same. The 90 seconds course standard is no problem. Then Steve gets told that
Danny needs another tank swap and the DSMBs certainly complicate matters.
We end up at 6m with an 18 minute stop to do and we are told to boost the
system to 1.4 bar. Martin is circulating noting numbers so the debrief will be
On the swim in I developed calf cramp so I cried out of the rescue drills. This
is the old routine we learnt at Rescue Diver to recover and dekit a
non-breathing diver at the surface doing AV as you take off the rebreather so a
boat crew etc. have a chance of pulling them out. I was annoyed with myself as
although I'm quite a bit older and a far weaker diver than the others I hadn't
missed anything up to then. However I was no longer a sensible person to be in
the water so it has to be.
Three days done. That's half way through the course. The news from home isn't
good. My son, my mother and my aunt who is visiting have locked themselves out.
I advise them to go for the cellar door window as it will be the cheapest to
fix. Cheap is a relative word here. **sigh**
Sunday Dive Five - 60 meters 94 minutes
This is the defining dive of the course. 60 meters planned depth. Not 61 Martin
is careful to point out. I have knocked off another two kilos and am diving the
suit on desqueeze and wing for buoyancy. It's like the old twinset. We are to
leave the rig on the low set point and drive the loop ppO2 to 1.3 from our
usual switch up point at about 30 meters. Martin also wants us to trade the
diluent inject hose to our offboard bail out so we use some of that to stretch
our diluent out and use more of the 7 litre tank as it is paid for. The descent
goes well but on hitting target depth, I put 59.2 meters on the Uwatec Dtimer
and 58 meters on the VR3, I get a cell error. I was annoyed. Put it in context.
I have a failure in the sensing part of my rebreather, one of the sensors is
reading 0.15 bar different from the others and my time to surface is about 40
Martin picks up that I should have done a more vigorous diluent flush but very
forgivingly puts me back on high setpoint and leaves me out of some of the
drills as I am in a real error mode. We do our stops back to 6m and here Martin
has us deploy the DSMBs and do a boost to 1.4bar ppO2. We stretch this stop and
then swim back. On reaching the steps I am showing just under 20bar of O2 and
the cramp has returned. I crawl back up the steps.
Sitting on the wall for a few minutes refreshes me enough to dekit. Martin and
the others arrive and talk is, amongst other things, of cell errors. Martin
starts to demonstrate a calibration check but runs my rig, now showing 15 bar,
right out of oxygen. At this point I discover my O2 SPG 'zeros' at 10 bar
displayed. This means I entered the water for a 60 meter dive with 90 bar of
O2, did all manner of O2 based drills and exited the water with 5 bar.
It's Monday morning. It's 19°C and I'm cold. I am also so looking forward
to not sharing my sleeping accommodation with a refrigerator.
Monday Dive Six - 53 meters 78 minutes
Monday we had to go back to the dive shop for fills and new Sofnoline and then
sat down to plan the dive. The idea was to find the Blue Hole at 18m and
dive through that. (Does every dive destination on earth have a place they call
the Blue Hole or is it just most?). The plan was to do an 18m search, find it,
down through it, out the bottom and then down to 52m, skills and the ascent.
However on arriving on site I did my usual trick of kitting up early and
sitting on the dock chilling out so I missed the girl from Deep Stop Diving
warning Martin that there was a serious current running and they revised to
plan B. The dive was reasonably uneventful, it was the first time I had done
an ascent on OC where you have to vent the loop by flashing the mouthpiece open
over your head, but I scared myself slightly when the new even lower
weight me had a bit of a suit runaway and Martin grabbed me to re-establish
the stop depth. He now has me down to 9Kilos of lead plus the 7L steel stage.
When you consider that I finished my mod 1 course carrying 11.5Kilos in the
fresh water of Stoney Cove this is a serious drop.
We finished the dive by redoing the rescue scenario of unresponsive diver in
the water so dekit, ventilate and tow in.
I am so tired now. We have already done 7 hours and 20 minutes under the water
time plus swim outs and surface stuff. I would have passed on a couple of dives
by now if this had been a holiday. However this is the last day diving. We fly
at five tomorrow evening. Martin is trying to pace the theory side so that we
get tomorrow free(ish). Most people want to do something interesting but I will
settle for a veg out by the pool day.
Tuesday Dive Seven - 40 meters 60 minutes
I don't remember much about this one but it ended on the beach not at the pier
after a protracted manual control (solenoid jam open I think). I'm writing this
one up weeks later. The main thing I remember is how far it was from the exit
point to the van. Clearly the only way to do this sort of diving is from a
hard boat with a lift.
Now the bad news. "You haven't failed. You just
haven't passed yet."
Fair deal. I've been reducing the weight I carry all week and my buoyancy
control has gone from awful via bad to poor. Martin wants to see that sharpened
up quite a bit. Bad buoyancy control technical diving is messing about with the
most fundamental thing - how deep you are. You must have that under control
doing stops. Two more dives in the UK. There is a possibility of a south
coast trip or maybe Dorothea Quarry in North Wales.
Saterday Dive Eight - 46 meters - 59 minutes
Well here we are at Chepstow and the NDC for a weekend. I have a both good and
bad connections with Chepstow. Firstly that my daughter and granddaughter live
very close at hand so I can go and stay, which is fun, but also I had a very
bad experience here diving OC when on a trivial 30 meter dive I turned into
the gas guzzling monster who could not get enough gas through a TX50. I don't
want a repeat of that.
I am sharing Martin with two OC Trimix students who have some primary drills
to get through while I, certainly for the first dive, just need to do the
routine procedures. We cut an OC shaped table and, as I will be breathing a
richer mix I just check it is inside what I calculate.
There are some simple problems but I'm in my new Otter Britannic suit and it
just works. Weighting is right so buoyancy is right. Nice horizontal position
in the water. OK I admit to more than a bit of trepidation as we left the shot
at 46 meters and as my breathing rate climbed a bit I deliberately went round
the gauges and reassured myself I has lots of gas, spot on ppO2 and was OK.
Once we were underway it was pretty smooth. Martin made us stay an extra 5
minutes at 6 meters but it was warm and even sunny, just beginning to get
Sunday Dive Nine - 50 meters - 57 minutes
More of the same. OK this time I am to do manual oxygen control on the descent
and I spiked it a bit and fussed about but 1.4 isn't really a problem unless
you stay there and are doing a long dive. I was more worried about Martin
catching me out with a high ppO2.
The only complication was the we drifted under the pontoon while doing our 6m
stop. Well no. Martin pointed out we were finning which is naughty. We weren't
quite trimmed out and we were kicking slightly to stay level. Oh well. It must
have been better because he shook my hand and passed me with a set of strong
advice to practice the skills.
Overall a fantastic course. It has changed the way I dive the rebreather quite
fundamentally. It has sadly reaffirmed my feeling that I am actually not a very
skilful diver and I will have to make up for this with practice, practice,
practice. Still. If that means I need to spend more time in the water who am I
Finally all the left over pictures.
The ones I'm not sure which dive they go with. Including Steve's very soggy
scrubber - it still dived OK so we were quite surprised how much water came
out. Even some of me shot by Paul Porter. (Thanks Paul.)
The pictures can be accessed by clicking the thumbnail but they tend to be 900K+ files
Pictures by Nigel Hewitt and Paul Porter.
Thumbnails by Easy Thumbnails
by Nigel Hewitt