NOT SO MANY YEARS AGO, diving while breathing anything other than air was available only to commercial and military divers.
Nitrox, or enriched air, was considered too dangerous for mainstream diving. It gained nicknames such as “devil gas”, and wasn’t available to the masses.
Using a third gas in the mixture was regarded as way too complicated for the average sports diver and was kept under wraps, reserved for professionals and shrouded in mystery.
This trilogy of gases called “trimix” contained helium, which, in those dark days, was almost impossible to obtain for sport-diving purposes.
How times have changed! Nitrox is currently regarded as possibly the safest of all the diving gases available, as long as the participant is trained and qualified in its use and understands its limits. The gas can be obtained in most places where there is diving to be had, and nowadays it’s as mainstream as social networking.
Trimix diving has enjoyed an increase in popularity, too. Divers who want to go deeper than the set recreational limits of 30-35m and keep a clear head without suffering the effects of narcosis while doing it are now spoiled for choice, because nearly all training agencies offer mixed-gas courses and qualifications in their ever-widening portfolios.
I qualified as an Advanced Trimix Diver to a maximum depth of 100m in 2003, and have conducted hundreds of dives well past the recreational limits since then.
It’s not something I do much these days, because I’m a photographer who enjoys the bright ambient light and longer photo opportunities found at shallower depths. However, it’s always good to keep my skills up to date, so I jumped at the opportunity of reviewing one of the many mixed-gas courses available.
I was invited to join Alun Evans, an easy-going Welshman with a larger-than-life personality who, along with his wife Moyra, owns and runs Elite Diving in Egypt’s Sharm el Sheikh. Elite offers diver training from multiple agencies, and is one of only a few British Sub-Aqua Club centres in the Sinai.
Alun can deliver the full range of BSAC technical programmes, and was putting Gareth Lince, one of his staff-members, through the Sport Mixed Gas course on his days off.
I joined them to play fly on the wall and gain an overview of what it was all about.

THE SPORT MIXED GAS COURSE is open to all BSAC Sports Divers (or equivalent) with a depth qualification to 35m and a minimum of 60 logged dives. You’ll also need to be an Advanced Nitrox Diver or Accelerated Decompression Procedures Diver (BSAC or equivalent), having the skills to decompress using high-oxygen-content nitrox mixes from 6m to the surface.
“The benefit of using gas mixes containing helium is controlling, to an extent, the effect of nitrogen narcosis,” said Alan as he kicked off the first session with Gareth.
“The narcotic effect of nitrogen becomes debilitating as depth increases. Controlling the narcotic effect of the nitrogen at depths greater than 30m reduces diminished awareness, therefore it’s deemed safer than diving deep while breathing just air.”
The classroom session continued, covering the theory of mixed-gas diving, including a brief history lesson. It surprised me to learn that US diver Sheck Exley had taught the first trimix courses to dedicated cave-divers as late as 1987, wreck-diver Billy Deans following up with the first recreational nitrox courses in the Florida Keys a few years later.
Alun also explained the limits of this particular BSAC qualification, which is the first step in mixed-gas training.
Divers using open-circuit equipment can expand their current skills and undertake dives to a maximum of 50m using the appropriate mixture of oxygen, helium and nitrogen, with oxygen percentages greater than or equal to 20% and helium less than or equal to 30%.
The rest of the session covered gas-analysis and calculating your personal Equivalent Narcotic Depth (END); decompression illness involving helium; thermal considerations and a reminder to maintain our personal skills.
After lunch there were more theory sessions. Alun discussed the equipment requirements, including decompression systems (sidemounted stage cylinders), twin-sets and regulators.
Ancillary equipment was next on the agenda, as the guys discussed their personal preferences on items such as reels and DSMBs, computers, dive-timers and slates, redundant masks, diver location devices and back-up dive-tables.
Gas analysis is an integral safety essential for all mixed-gas divers and this was covered in depth, with demonstrations on how to use the Analox ATA analyser for both trimix and nitrox mixes.
Kit arrangement followed. Gareth would be diving with a single nitrox stage cylinder placed following the standard, easy-to-remember practice of “lean mixture on the left, rich on the right”.
We finished the day by covering dive-planning using software programs such as Pro Planner, run-times, gas-management and redundancy. My head was in a spin, but Gareth seemed to be taking it all in, and was hungry for more.

ALUN HAD COVERED ALL the theory, and needed Gareth in the water to start learning the practical skills for this genre of diving, so it was with relief that we headed out in the sun to board our day-boat.
Gareth immediately got stuck into setting up his kit. He would dive with his own twin tank and wing arrangement, with the addition of a 12-litre stage tank clipped off on his left-hand side.
Hoses were routed on the twin back-mounted tanks to enable a streamlined configuration. Ancillary and redundant back-up items were positioned and clipped off for easy access, should the need arise.
We were ready for Alun’s briefing session as we sipped tea on the deck and the boat slowly chugged out along the coast.
Alun detailed the dive plan and the skills he was going to teach Gareth. There weren’t many – Gareth had already successfully completed the courses that lead to the mixed-gas diver component, and had the skills to dive with twins and stages. So this session would be about revisiting existing skills and adding a few more to his armoury.

IN THE WATER the first thing to do was a bubble-check, then to sort out buoyancy and trim. That done, we settled above a sandy seabed in around 5m.
Alun had already briefed Gareth on what was required for this dive, and had waterproof cards with the individual skills he wanted him to perform.
It was no surprise to see him produce the card that read “Remove mask and replace with spare mask“ first off the bat. Gareth’s wry smile behind his regulator told me that he had expected this too, and he went about the task with practiced ease.
In fact his spare mask was already in position around his neck, which made the transition a simple affair!
The next skills to perform were shut-down drills, first from a simulated freeflowing primary regulator, followed by a manifold shutdown. Once successfully completed, Gareth opened the manifold valve to put everything back to normal before moving onto stage-cylinder tasks.
The next card had Gareth removing his stage cylinder, ditching it on the seabed and swimming away before returning to retrieve and re-attach it.
The session moved on quickly as I kept my distance, watching the proceedings and nipping in with my camera only every now and then, trying not to be obtrusive or get in the way.
The guys covered out-of-gas responses for both primary and deco gas scenarios before Alun demonstrated some new skills to his knowledge-hungry student, including handing his stage cylinder off to Gareth both on the seabed and in mid-water.
We returned to the sand as the divers simulated the ascent phase of the dive. After deploying their DSMBs, they switched gases to their nitrox mixes and simulated decompression stops.
Alun produced the “out of deco gas” card, and offered to donate his regulator.
The last skill was for Gareth to slowly ascend in 1m increments without the help of his reel and DSMB.

DAY TWO MEANT DEEPER DIVES. We all kitted up in twins and stages for a dive on which to put everything learned so far into practice. This was to be to a maximum of 40m, but limiting ascent time to under 30 minutes.
On the way out, after analysing our gases Alun revisited the software-planning that had been calculated for the dive. He and Gareth sat on deck and discussed the dive-plan using a laptop, and Alun demonstrated how to visualise the planned dive.
Memories of my own trimix instructor and friend the late Keith Morris sitting on the back of a Weymouth dive charter came rushing back. He used to go into what was almost a catatonic trance as he conducted the entire dive in his head.
It’s a skill I am grateful to have been taught – it puts you in the right mindset and helps ensure that nothing gets overlooked.
I still use this skill on almost all my dives; it’s something from which we could all benefit.
Ras Mohammed national marine park offers spectacular and well-documented dive-sites, but few divers get to venture beyond the recreational depth limits here.
Today, however, we were going to conduct two training dives near a wall pulsing with brightly coloured soft corals and swarms of orange anthias, and we were going to do it with clear heads.
Thanks to the gases we were diving, narcosis wasn’t going to impair our enjoyment.
I’m sure that even with a clear head Gareth missed out on all this splendour as he concentrated on the tasks in hand, demonstrating gas shutdown and isolation skills.
At depth and as planned, we started to gain decompression penalties. It was soon time to start the ascent phase of our dive and conduct mandatory stops.
DSMBs were deployed as we ticked away the time under dancing light rays from the mid-day Egyptian sun.
During a lengthy surface interval, Gareth completed the last of his written assignments, and it was time for the final dive of the course. There would be no prompt cards on this straightforward deep trimix dive, with the student using all the skills at his disposal to safely complete a longer dive with more decompression and in-water time.
With fewer set tasks to perform, this dive saw Gareth enjoying the scenery, and the extended deco phase had us all drifting past the shallow brightly lit reefs, with plenty to see.
Back on the boat, it was “pat on the back” time as we headed to port and the promise of a few well-earned beers at Elite’s infamous watering hole, the Stella Bar.
This was the first BSAC course with which I had been involved. I enjoyed the simplicity of it all, and everything covered on the course was relevant, but it is basic – there
is a lot more to cover on the journey from open-water recreational diver to mixed-
gas diver.
The Sport Mixed Gas course is what it says, a mixed-gas qualification for sports divers who want to take their diving deeper than the recreational limits. But not to crazy depths.

The BSAC Sport Mixed Gas course is part of BSAC’s programme of technical diving, which also includes: Nitrox Open Circuit Diving, Accelerated Decompression Procedures, Mixed Gas Open Circuit Diving, Explorer Mixed Gas Diver and Advanced Mixed Gas Diver. Elite Diving offers the course as reviewed for £400 if booked in advance, including all kit, gas and boat dives. The manual and certification cost an extra £45. Elite Diving,