5 Things Tec Divers Do (that all divers should do)
FAR FROM BEING THE MYTHICAL DAREDEVILS OF DIVING LEGEND, technical divers are actually thoughtful, careful individuals who are attentive to detail and constantly looking for new ideas to improve the way they dive.
Over the past 25 years the technical community has proven to be a crucible of creativity from which several equipment and procedural innovations have emerged that have had an enormous impact on the sport.
These include nitrox and, more recently, sidemount diving.
There are a number of techniques that technical divers use that have not yet passed into the mainstream but that could be of enormous benefit to the wider community of divers.
Here are five things technical divers do that we should all be doing.
Technical divers constantly evaluate and re-evaluate the purpose of the equipment they carry with them under water, and the way they put it together.
Among other things, they make sure that everything has a function to perform on the specific dive they are planning, each item is secured and easily accessible and that they have more than one of any piece of equipment that is absolutely essential for the safe conclusion of the dive, so that, if one is lost, they have another to replace it.
They check that their equipment is balanced, and as streamlined as possible. They also make sure that, when they are in a swimming position, nothing is hanging down below them, where it might catch on a reef or wreck and break off.
If you have been diving for some time and your equipment is currently set up exactly as it was when you learned to dive, a review may be well overdue. I will discuss configuration in much more detail in the next article in this series.
2. THE WHAT-IFS
Most diving accidents are caused by an event that was predictable: an event that could have been avoided or handled comfortably had the diver anticipated it and planned and practised what to do if and when it happened.
This is the basic premise behind a process that technical divers refer to as “Assessing The What-Ifs”.
They look at all the things that could go wrong on a dive, and formulate a plan to combat each eventuality. They make sure they have all the knowledge, skills and back-up equipment they need to deal with it.
Then they practise the correct response until it becomes instinctive. In the corporate world, this would be called a risk-management action plan.
This was actually the concept behind the skills that you learned in your early diver training. Your instructors weren’t just harassing you for their own entertainment when they made you remove and replace your mask or scuba gear. They were teaching you what to do if your mask-strap ever broke, or if your cylinder ever slipped out of the BC cam-band.
3. AIR CONSUMPTION CALCULATION
The way to calculate how much air you breathe is something that everyone would find useful when they start diving, but it is rarely taught.
A technical diver knows his surface breathing rate as well as he knows his blood group, but few mainstream sport-divers are aware of this vital statistic. Non-divers might find this unusual!
Once you know your surface breathing rate, you can easily calculate before a dive how much air you are likely to breathe during a given time at a given depth, and can relate that to the volume of air in your cylinder.
This knowledge helps you plan the dive, alleviates stress and gives you confidence.
It’s a simple thing to do. Descend to a depth of 10m and record your cylinder pressure on a slate. Swim normally at 10m for 10 minutes, then stop and record your new cylinder pressure.
Let’s say you have used up 33 bar of air during your swim and you’re using a standard 11-litre (Luxfer S080) scuba cylinder, which has a water volume of 10.6 litres. A pressure of 1 bar in this cylinder equates to 10.6 litres.
That means you have used 33 x 10.6 = (approx) 350 litres in 10 minutes, which equals 35 litres per minute.
You were at a depth of 10m where there is an ambient pressure of 2 atmospheres absolute (ata), so if you had been swimming at the surface (at an ambient pressure of 1 ata) you would have used half as much air, that is 35 / 2 = 17.5 litres per minute.
This is your surface breathing rate, and you can use this to calculate how much air you will use on any dive.
For instance, if you dive at a depth of 20m (3 ata) you will use 3 x 17.5 = 52.5 litres per minute.
So, on a dive for 30 minutes at 20m you will use 30 x 52.5 = 1575 litres of air.
1575 litres in a standard 11-litre cylinder equates to a pressure of 149 bar, (1575 / 10.6)
So, if you start the dive with a pressure of 200 bar and use 149 bar in 30 minutes at 20m, you will have 51 bar left at that point, and it will be time to think about coming up.
Isn’t that useful knowledge to have in the back of your mind?
It’s a good idea to repeat the exercise a number of times and take an average.
Also, do the drill once or twice while swimming fast and breathing hard. You will see what a huge impact this has on your breathing rate and therefore on the amount of time your cylinder will last: again, good to know.
4. REELS & LINES
Technical divers will carry a reel and line on every dive. If using a reel is an integral part of the dive-plan, such as when entering a wreck, cavern or cave, they will carry at least two.
Deploying a reel requires a little tuition and a great deal of practice, as line in water can take on a life of its own and can seem wilfully to conspire against you.
However, perseverance carries the reward of being armed with a tool that you can use in a variety of situations.
For example, your reel can help you find your way back and forth from the shotline to a dive-site in poor visibility. It can allow you to raise a delayed submersible marker buoy from depth to act as an emergency ascent platform.
Or you can use it to tie yourself to a bouncing shotline and float free.
In recreational no-decompression-stop diving, the majority of any planning that occurs usually revolves around the “bottom” portion of the dive.
It is understandable therefore that divers tend to get into the habit of switching off once they begin their ascent, and focus their attention instead on the tea and biscuits waiting for them on shore. This is a tendency that instructors have to work hard to change when they initiate sport-divers into the technical world.
In technical diving, the marker of a successful dive is a safe ascent and decompression rather than the accomplishment of any specific mission. If you didn’t achieve all your aims on a dive, you can always try again later. A failed ascent could be life-threatening.
As with the “What Ifs”, this is a question of mindset. Recreational divers may not have the decompression burden that technical divers have, but planning a slow, controlled ascent is conducive to a successful dive, no matter what the parameters are.
After all, in scuba-diving going down and staying down are not the difficult bits – a brick can do that! Coming up again is the part that requires skill.
Technical divers always ascend slowly, even at the beginning of their ascent, and make a series of short stops before the decompression stops required by their computer or dive-table.
In the dive industry, we know from experience that the sort of tropical reef-dive profile that I describe below works very well, producing an extremely low incidence of decompression sickness.
At the beginning, you descend slowly to the deepest planned depth of the dive and start swimming along.
You ascend a few metres to an intermediate level when your computer shows 10 minutes or so no-deco time remaining, so you don’t have to worry about getting close to the limit.
Now you have plenty of no-decompression minutes to play with. Stay around this new level until the no-decompression time remaining drops to around 10 minutes again, then ascend to a shallower depth. Repeat as necessary.
As your air supply falls below 70 bar or so, move up shallower than 9m and spend the last part of the dive watching the action near the top of the wall.
Finally, when time is up, your air runs low or you are ready for a surface break, you ascend to 5m, do your safety stop, then make slowly for the surface.
Much of this dive is, in fact, a slow controlled ascent. Assuming that you have smooth conditions and plenty of air to breathe you can create a similar, albeit briefer, profile when you ascend from a dive with no shallow section, such as a mid-ocean shipwreck, by starting your ascent when you still have plenty of air left, and pausing for a few minutes at a couple of intermediate depths as you come up.
Read more from Simon Pridmore in Scuba Confidential – An Insider’s Guide to Becoming a Better Diver and Scuba Professional – Insights into Sport Diver Training & Operations, both available on Amazon in a variety of formats