The difference between “Then and Now” in Technical Diving

By Michael Thomas

“Have you got a light, guys?”

Many years ago, surfacing from a cave or sump dive and hearing the cry “have you got a light, guys?” was not uncommon. Diving light failure happened a fair bit, as lighting was not as reliable or bright as we have now. A team member’s light was either out or producing lumens not much better than a glow worm in a jam jar! Not really a problem if you are back at the entrance to the cave, but more of a problem if you have surfaced beyond a sump inside the cave. 

Sitting at my desk, passing the time in Coronavirus lockdown, I started thinking about the equipment and techniques we used back in the 90s compared to what we use now. Was it all the bad old days? Did the skills we developed then and problems we had to overcome put us in a better place for dealing with modern long exposure technical diving on rebreathers and mixed gas today? The list of differences is long and would be very tedious to the reader. I’ve chosen eight subjects to compare that have had major changes since my diving life started in 1987. 

Deep Air 

This is the one old school technique every diver today knows is a bad thing — the skill set that really needs to be in the diving dustbin. A breathing gas at depths below 30m gives increasing narcosis and increasing PP02. Both of these are bad, and combined with increased work of breathing, increasing gas density, and C02, it really does not have much to offer. 

So why did we use it as a deep gas? 

Firstly, it was readily available and cheap. Oxygen and nitrox were not easy to get for divers, let alone helium. Plus, so few divers within the sports diving and fledgling technical diving world knew how to produce decompression tables for helium. So, for most, air was the only option for inquisitive divers that wanted to explore deeper. Exploration is a powerful driving force for some. 

Now you also need to consider the attitudes of the time: going deep was deemed cool. It proved something to your peers. This was an attitude that killed many and the rest of us just got lucky. But what did we learn from deep air diving? The TDI standards of today are based on sensible diving limits learnt the hard way by many, and I, being one of the lucky ones who survived, can teach with first-hand experience about what narcosis and gas density are all about. Deep Air: just don’t do it. 


This gas, with a combination of Oxygen, Helium and Nitrogen, has become the go-to gas for deeper diving on open circuit and now, more commonly, on rebreathers. With the correct gas mixture for the planned depth, low narcosis, low work of breathing and gas density are achieved. Today, many dive computers can compute for any gas mixture and your mobile phone contains gas mixing and decompression planning apps. The understanding behind the Decompression theory is at an all-time high, with multiple papers and blogs explaining the current thinking. 

If we go back to the mid-1990s, trimix diving was very different. 

We were still at the point of hiding nitrox cylinders to get them on dive boats. The primary agencies of the time, BSAC and PADI, had declared nitrox a devil gas that would kill everyone, and both the US Navy and British Navy said recreational/technical divers did not have the knowledge or backup to use trimix safely. However, we persevered. A few brave divers took the plunge, resulting in some success and also tragedy, but we carried on. Bill Hamilton would supply trimix diving tables to technical diving expeditions for a price, and eventually, Sheck Exley released a decompression planning software program called Dr X. Other notable divers followed suit around the same time and technical diving agencies were born, producing trimix manuals complete with decompression tables. 

Now, our knowledge then was very different from today. When I did my open circuit trimix course in 1997, the general consensus was the need to get off the helium as deep as possible on the way up. Our lack of understanding about how helium reacts led us to believe the lighter gas, helium, would cause decompression illness if we stayed on it at shallow depths. We did some gas switches to air at around 50m after 85m trimix dives! Now, during deep CCR dives, the diver will stay on the helium in the loop all the way to the surface. 

Another big change is the use of dive computers, either in open circuit mode or real-time monitoring of your CCR, with divers carrying a backup computer to give the all-important decompression information. 

Now back in the 90s, we had pockets full of laminated decompression tables for the planned depth and time. We also had multiple variations of depth and time, such as deeper and longer and shorter bailout tables if you missed the wreck or had a problem on the descent. The time and depth were either recorded on bottom timers or divers would use a standard air computer and just bend the air computer on surfacing. More than once, I remember dive partners surrounded by decompression tables on decompression stops, as the homemade laminated tables fell apart and alarming air dive computers in a bucket of water on the dive deck to muffle the sound.

Independents Doubles 

A twin set is now a fairly common and basic entry requirement into the technical diving world. In Europe, the standard is generally a 12l (cylinder size may vary elsewhere) steel set with an isolation manifold fitted. Regulators with longhose on the right, a single pressure gauge to the left and primary donate being the preferred option. A backplate and wing making up the complete system. Most divers preferring a Hogarthian system, keeping it clean and simple. 

Back in the 90s, a lot of twin sets were independent cylinders with no manifold at all, either banded together with traditional stainless bands as you see now, or using temporary cam bands to join two cylinders together. In the early years, most independent twinsets had two right-handed cylinder valves, giving you no chance to shut down the left-hand cylinder. It took a while for the technical diving community, especially in Europe, to start thinking about shutdowns and using a left-handed valve on the left cylinder. Being able to shut down the gas supply on your own at that time was not high on the list of things-to-do. Eventually, manifolds started to become more popular, and finally, manifolds with an isolation valve became the norm, making diving safer and divers more skilled. 

Fixed Sidemount 

I started sidemount diving in 1992. The day I started cave diving, I was loaned a 1980s style sidemount harness. The cylinders were clamped at a single point, about a quarter of the way down the cylinder. We had different size clamps for different size cylinders. The cylinder and clamp was then threaded onto the harness belt loop along with the weight needed to dive. Regulators were then attached to cylinders. We had standard length high-pressure hoses wrapped around the first stage and valve, held down with bungee loops. The diver then had to lay the sidemount harness out on the ground, complete with cylinders, then step over it and pick it all up to get it onto their waist! With large cylinders, help was generally needed. The harness had no built-in buoyancy, so a modified open water BCD was used and worn over the top of the harness. When diving this system, back pain on long dives was very common, as the entire weight of the harness, cylinders, and lead rested on your lower back, pushing the diver into shallow V shape. 

Compared to todayʼs modern sidemount harness choices, some of which are superb, with built-in BCDs, weight running down the spine and the ability to attach cylinders after the harness is on, the harness we started with is a world away. Sidemount diving is easy and enjoyable now, once you have the modern harness set up correctly. The techniques we developed have been ever-evolving. But gas management, rule of thirds and balancing cylinder pressure was done from the early years. 


Having good lighting is one simple yet expensive way to improve the overall dive experience. From caves to wrecks, ocean dives to photography, lighting can make or break the dive. The other thing Iʼve learnt over many years of diving is if you donʼt want a dive light to fail during the dive, leave it at home safely in storage and make sure you have a backup light. Iʼve seen lights fail in every conceivable way, from floods to cable breaks and blown bulbs. 

Modern lighting is generally very good now, with LED bulbs, high lumen output and battery technology thatʼs improved every year, giving longer burn times and smaller and smaller battery packs. Compared to what we used to use in the 90s: lead-acid battery packs that weighed around 3kg and were the size of a small diving cylinder, generally mounted on the twin set or on the right hip. Unlike todayʼs canisters, it was like having an extra stage cylinder on your harness. Large unwieldy light heads with, if you were lucky, a 50-watt halogen bulb to brighten the darkness. Between halogen bulbs and the LED bulbs of today, we had the HID bulb, which gave a greater light output but were very fragile and rather expensive to replace. They were not great for a light unit designed to be used by divers exiting a busy dive boat deck or cave diving. 


Ever since divers have started diving, decompression has played a large part in the sport and working environment for all divers. The act of allowing your body to adjust back to surface pressure after diving is still as crucial now as it was then. We canʼt beat physics and physiology. 

What has changed and continues to change is our understanding of decompression and the techniques of conducting decompression dives. Understanding that all dives put you, the diver, under pressure and require at least a minimum safety stop to choose the most effective decompression gas to return from deep open-circuit dives, or what fixed partial pressure and gas to run on your rebreather, is important. A lot of technical diving expeditions now conduct post-dive medical studies on divers to build the knowledge of decompression and papers are written fairly regularly with updated knowledge. A good diver will constantly update his knowledge on decompression and make use of the information available to stay as safe as possible. 

Boat Lifts 

I had just finished nearly an hour of decompression after a dive in 1998 in the English Channel. The wreck was at 80m and previously unexplored. On surfacing, I floated, talking to my dive partner, whilst waiting for the dive boat to come alongside and pick us up. The sea conditions were worsening, and the skipper indicated he wanted us on board as quickly as possible. Working my way along the line on the side of the dive boat and reaching the ladder to get back on board, I placed a regulator in my mouth and started to climb. A 12l steel independent twinset on my back canister, a dive light under each arm , and 10l steel decompression cylinders are a heavy load to climb a ladder with, especially after a deep dive. On this occasion, I really struggled to climb the ladder and only realized at the top of the ladder that I had put my trimix regulator back in and not the decompression gas regulator. Not only was I trying to climb a ladder with four cylinders in a heavy sea, but I was trying to do it with a reduced oxygen percentage. Spitting the regulator out and breathing air really helped. 

Today most dive boats that I use all have diver lifts. When the dive boat pulls alongside, the lift is dropped into the water, the diver swims in and places feet down and hands-on handrails, clear of the boat. A nod to the skipper and you are raised like a god to the dive deck. You have to love boat lifts. But, if a dive boat has no lift or the lift fails, then years of ladder use make this no problem, as long as the diver has good strength and fitness. 

Fitness and Attitude

Back when I started diving in 1987, I was using a single cylinder, a wetsuit, and an ABLJ buoyancy compensator. It took years to progress up to twinset diving and drysuits and finally caves, rebreathers, and instructing. However, those years were not wasted. They allowed us to gain the experience and also follow the changes within sport and technical diving. We found out what worked and what did not work, sometimes the hard way. We crash-tested the standards that are the norm today. 

Along the way, we realized diver fitness was crucial to stay safe in a sometimes unforgiving environment. Today diving is possible with much faster progression. Equipment is pretty much available to do most things, and the training is available to use that equipment. Whatʼs missing now is the attitude of slowing down and building on that training before launching on the next quest. A diver with a solid skills platform and experience at one level is ready to tackle the next with much more confidence and safety. 

I sat at my desk writing this during very strange times. Iʼm aware that I probably wonʼt dive for some time due to coronavirus stopping the world. What Iʼm doing is keeping my physical fitness up and keeping my mind sharp by reading, research and planning some dives for when we can get back in the water. These dives will not be teaching dives. They will be easy dives to refresh myself and rebuild muscle memory for the art of diving. Stay safe guys and remember, when we can, build up slowly again.

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8 replies
  1. Vas Proud
    Vas Proud says:

    Nice write up Michael.

    Having only read about much of the “old days” it is great to hear how things used to be and crucially how they have developed to make diving safer and more enjoyable.

    I don’t envy you the twinset exits though ????


  2. Richard Taylor
    Richard Taylor says:

    Brings back sooo many memories. We were diving deep air, using 02 for deco with scant information. Dived Trimix in 1994 before courses were available. They were good days, but the price was high. Lost a number of good friends. Training, knowledge & attitude are the keys now, and understanding that new equipment & new procedures have brought increase safety. We should never stop learning, or remembering the lessons of the past!

  3. Norman Hughes
    Norman Hughes says:

    The biggest difference then to now is that in 1997 it cost me $57.00 .for a T of helium and now if I could afford it a T is $440.. from the same supplier or $260.00 just to fill my doubles! It is now priced out of my league!

  4. Jon Friedman
    Jon Friedman says:

    I really enjoyed your article. I started diving in the late ’70’s. Equipment was almost non-existant. Octopus? Air Pressure gage? Pull the lever when you run out of air. Had a watch and depth gage. Lots of training. CMAS training, but instructors in those days were ex-Navy divers. I can attest to your Deep Air comments. Bach chorales never sounded so good as I thought I heard them below 50 meters. Most accidents were of experienced divers and every incident was analyzed by the diving community. I jumped at the chance to learn nitrox and mixed gases. An important, perhaps THE most important point that you made, IMHO, is diving fitness and mind set. This seems to be lacking in many younger, PADI, trained divers that I see at the dive centers. Many can hardly swim and would have difficulty dealing with a situation or even a mild change in weather. It is scary. I think that for sport diving the bar should be raised. Tech divers seem to have the right attitude.
    Hope we can all get out again soon.

  5. Ken Trethewey
    Ken Trethewey says:

    And do you remember how difficult it was to get dive computers that were practical to use for decompression diving on deep air? I did my open circuit trimix certification in 2000, and had been diving on deep air for 10 or 15 years before that. There were no online message boards to go to and find out what dive computers were viable for tech, so several times I would buy one, try it, find that it was of no use to me, and sell it or give it away immediately and buy another one. Most were unusable for elective decompression diving, as they would either give you hours and hours of deco time you couldn’t possibly complete, or just bail on you and go into gauge mode. Once I learned that they WOULD actually work for my needs, I think I bought three or four Aladdin Pros on the second hand market (since they weren’t made any longer) over the years as my backups, and the same number of Cochrans new as my primaries.

  6. Graham Powell
    Graham Powell says:

    Brought back lots of memories me, from starting Nitrox and Deep Air in 90’s. Spot on about many of struggling with the cost in the days and basically using whatever kit you had. Independent twins and most memorable was we all had different equipment configurations. I recently restarted tec diving 20 years later and thoroughly surprised at how drastically training and equipment standardisation has evolved and most notably improved. I lost many friends, so seeing now the evolution is remarkable.

  7. Chris Hazell
    Chris Hazell says:

    Ah takes me back. Equipment and training has certainly come along way since my fist dive in 1984. My equipment back then, as a 14 year old lad, was a horse collar ABLJ with no inflator hose (manual inflation only), with an emergency cylinder that had no conventional valve – the cylinder had to be twisted to open the in-built valve, a 45cu foot 1980psi cylinder with a plastic home made back plate and harness (plumbing pipe bands and car seat belts) and a single hose reg with only 1 LP and 1 HP port – a good job that first dive was only in a river to 2m. Then the training – seemed at the time like I was training for the Special Forces not a recreational hobby – long breath holds, open water free dive to 7m and of course the torturous weight belt swim. A far cry from the equipment and training we have today. Many thanks for a lovely stroll down memory lane.


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