John Bantin samples a course for divers who want to use nitrox gas to go beyond the usual depth limits of 30-50m
I took a few shots of Rob Palmer swimming along the almost-inverted deck. The others scrambled about in search of souvenirs; Colona IV had gone down laden with all the personal effects of her crew.
By now I had used about half of my air supply. Roberto appeared with a PADI dive-log. "They're not meant to go below 40m!" I mused as I photographed him posing with it, sporting a cheeky grin.
He then found and waved "his" spanners. This had become a routine cabaret act for Roberto each time he visited Colona IV. He never brought the tools up; he just liked to know they were still there. It was his way of establishing that no one else had trespassed on his territory.
Meanwhile Karim Hilal, our host and director of Technical Diving International (Egypt), had picked up a rather nice vase.
Organised by Diver's Lodge, the Red Sea's leading technical diving centre, this last dive of my week was also the ultimate one for divers who had just completed the TDI Extended Range course.
This covers descents beyond the 30-50m depth limits normally associated with leisure diving. It deals with dive planning, advanced oxygen tracking, pressure, the physiology of deep diving, stress-related subjects, and the philosophy of total equipment redundancy - doubling up on every item of equipment to avoid facing disaster should a malfunction occur. With deep diving, there is no escape route to the surface.
Although Rob had an octopus rigged to the second of his tanks of air which I might have used to prolong my time on the wreck, I preferred not to get involved with too many party tricks involving another diver at that depth.
The last frame of film shot, I went over to the bottom of the reef and made my way up to 33m. Here it was safe to switch to the colour- coded regulator of my own second tank, filled with nitrox 36. I had just under 50 bar of ordinary air left; but at this point, safely on to my second tank, there was no longer any sense of urgency in our ascent.
In fact, as Rob and I dawdled upwards, the others caught up with us. Their bottom time was only a few minutes longer than ours, but they were into much longer decompression-stop times. Switching to nitrox 50 (in the stage tanks slung across their chests) at 18m enabled them to reduce the duration of each stop needed.
Because my buddy also had an octopus-rig on his stage tank, I chose to swap from my nitrox 36 to his nitrox 50 as soon as it was safe to do so, although this was not strictly necessary in my case.
I was sticking to the decompression requirements of my air computer. However, reducing the levels of nitrogen inhaled at this time increased the nitrogen pressure gradient in my body, flushing out what I had previously absorbed all the sooner.
We each put up delayed deployment surface marker buoys and dangled from them. This is a technique familiar to many British divers, but I was amused to see one of the extended-range course divers making something of a hash of it, letting out too much line from her reel, allowing her buoy to collapse at the surface, and getting the line tangled with the reef. Roberto, her instructor, came to her rescue. The whole dive had taken around one hour.
Extended-range diving was not the only course with which I was involved at Diver's Lodge. Although, like many diver readers, I have dived in undersea caverns and entered wrecks, I also chose to do a TDI Overhead Environment course.
Like the extended-range course, the OHE one consists of classroom work, a theory exam and practical evaluation. Who better to teach it than well-known cave diver, director of the Bahamas Blue Holes Foundation, and co-founder of TDI, my buddy Rob Palmer?
The theory part all made good sense, including the group's catchphrase: "Get it wrong and you're dead!"
We studied the limits of the conditions for which we were being trained: 40m maximum depth, with-in the available light; the rules regarding air supplies (one third for the journey in, one third for the journey out, and one third kept in reserve); and the prohibition on passing through any constriction too narrow to accommodate two divers side by side.
We learned about different sorts of caverns and caves, common dangers, and environmental hazards like silt caused by mud, sand or clay. We mastered the additional vocabulary of signals needed by a cavern diver, and were told about the specialised equipment required, such as different kinds of guidelines and reels, and about line protocol.
Because many fatalities in this category of diving have been associated with the absence of a properly belayed guideline, line-laying is an essential part of an OHE diver's skills.
One of our first exercises was to belay a line from our winder reels around an area of seashore near the classroom. It took me only a minute to "expertly" lay out about 50m of line using the "placements", "wraps" and "tie-offs" I had learned previously. We were then asked to find our way along the line - blindfolded!
It was at this point that I wished I had not positioned my line between rocks along the edge of a crumbling cliff. It seemed to take forever to find my way hesitantly to where I had left the reel, untie it and wind my way back along the line.
Next we did the same thing under water, belaying our line over the outside of a conveniently sited wreck before finding our way along it "in the dark". It was easy to follow one's own route but things became more exciting when we were asked to do the same thing with a line laid by somebody else.
Then we repeated the exercise while sharing an air supply, practising finning skills so as not to stir up any sediment. Next we made a more complicated dive, this time inside a wreck.
We had studied the theories on stress, its causes, how to recognise it and how to cope with it. I don't know if this helped under water, but am sure it would have deterred any uncertain candidates before things proceeded too far.
Other common causes of accidents relating to overhead environments include failure to carry appropriate light sources or observe depth limits, ineffective gas management and lack of proper training. The course proved to be a lot of fun. Learn to be a "reel" diver first!
A third programme which would interest most divers is the TDI Rebreather course. This is also offered at Diver's Lodge, along with the other TDI advanced diving courses (there are seven in all).
Semi-closed-circuit rebreathers (SCRs) are the logical development of the use of nitrox. They allow you to use it in the most efficient way possible, rebreathing it and taking full advantage of the oxygen contained within it. This allows a diver with a rebreather to carry relatively small cylinders of breathing gas.
There has been a lot of misinformation about rebreather technology in print. SCRs are not about going deeper for longer. A diver still needs to pay attention to decompression requirements; but by using high levels of oxygen in the nitrox mix, and staying within safe depth limits, he can be as safe from decompression illness as possible.
The course explains what to do if things go wrong, and how to recognise the symptoms of a malfunction. The Draeger Atlantis 1, the only SCR available to sport divers at the time of writing, is used, complete with conventional open-circuit scuba as a safety back-up.
SCRs give perfect buoyancy control irrespective of changing lung volumes caused by reathing. This can be a great advantage, but it means learning a different way of conducting oneself underwater. SCRs produce far fewer bubbles than open-circuit apparatus, where one exhales mighty curtains of air into the water. Absence of bubbles is helpful when trying to get close to wildlife, especially mammals which interpret exhaled air as a sign of aggression.
Another benefit of SCRs is found in cold water. Not only are the units disinclined to freeze and free-flow, but because the diver is breathing gas at normal body temperature, which is also warmed by the exothermic reaction of the CO2 scrubber unit, his body core is kept from cooling.
This cannot be said for divers filling their lungs with every breath from an open-circuit regulator supply, cooled dramatically by the effect of the huge pressure drop as it leaves an already cold scuba cylinder. SCR divers stay warm in cold conditions.
They also need to know how to maintain their units. It is all quite simple: do a course. The only prerequisite is to have a nitrox diver certification.
