ON ONE OF THE FIRST extended-range courses on which I instructed, getting on for 20 years ago, I was teaching gas shutdowns.
At the time, one object lesson I liked to make, driven from my own difficulties with the gas-shutdown drill, was that if you find it difficult in training, think how much more difficult it would be if you ever needed to do it for real.
If you have difficulty doing a gas shutdown drill, you either need to practise until you can do it flawlessly, or get rid of the manifold and use independent cylinders.
At the time I had a close-fitting 7mm neoprene drysuit. It was indestructible, but it wasn’t very flexible. Neither am I.
To do a shutdown, my technique was to loosen my waist-strap, go slightly head-down to let the cylinders slide up, grab a handful of hoses with one hand to pull the taps closer, then reach back and use my other hand to catch and turn the relevant tap.
Before the lesson, I explained various methods to my students, and advised them that we would be experimenting to find out which worked best for each of them.
In water, I dutifully demonstrated the full shutdown drill. Not to show that it was easy, but just to show that it was possible. Bear in mind that this was back in the days when anything technical was monstrously evil and, according to PADI or BSAC, would kill you instantly. The idea of an isolation manifold or gas shutdown was alien to most divers.
The first student was a tall gangly bloke, a bit like John Bantin in dimensions, but younger and prettier.
He simply reached over his head with his right arm and turned the tap. No messing with his harness, no hesitation – he just did it. He could even turn his left tap with his right hand, or his right tap with his left hand.
I suspect that any current reader with an isolation manifold and twin-set will, even with this little evidence, be able to spell out many of the failings of my technique.

OVER THE YEARS, I got myself sorted out on gas shutdowns, then started using a rebreather. I have not taught a technical course for several years, so these days the only time I use a twin-set with manifold is occasionally when I am overseas.
Because it’s something I rarely practise, the first thing I do with any borrowed set is to make sure that I can do a shutdown, even though I have never needed to use the skill in anger.
At last year’s TekCamp, I followed as instructor Mark Powell taught this basic skill. Regulars at the dive shows will recognise him from his well-attended talks on decompression theory and on solo diving.
Any of the other instructors would have taught gas shutdown in much the same way, “except for GUE, which does it in a different order”, says Mark. We’ll come back to the sequence later.
A drysuit that is cut right for shoulder movement is almost taken for granted.
A few years ago the unwelcome advice that “maybe you should look for a suit that allows a bit more shoulder movement” was commonly heard from instructors on technical courses, but I didn’t hear it at all at TekCamp.
Suit manufacturers have caught on that divers need some shoulder flexibility, and size the suits accordingly.
Shop staff ask divers to check shoulder movement when they try on suits.
The same goes for undersuits. They are almost universally either cut for shoulder movement or include flexible panels at the shoulders. Drysuit and undersuit fit should no longer be a hindrance to doing gas shutdowns.

THE POSITIONING OF THE manifold makes a big difference. Too high or low, and it is much harder to reach.
Ideally, the isolator should be level with the back of the diver’s head; pretty much such that you could knock your head on it if you leant backwards.
The harness needs to be tight enough to stop the twin-set sliding up or down, but not so tight as to restrict movement.
Before kitting up, Mark made an important point about positioning: “Keep your head up! Looking down restricts how far you can reach back.”
He demonstrated this by standing with his back against a post, first tucking his chin onto his chest and barely reaching the post behind him, then keeping his head up and showing how much more reach he had.
As his students kitted up, Mark offered some advice that I hadn’t heard before: “Pull your suit up before putting your kit on, so you don’t leave all the room for movement on your legs.”
On the kitting-up bench, Mark illustrated another aspect of reaching behind for the taps: “Stretch your arm out forwards, then fold it back and over. You get more reach than coming in from the side, even if your elbow does rotate out a little in the process.”
As a final reminder, before getting in, the students were reminded that simply staying in a controlled and stable horizontal position in the water is key to any skill, including the shutdown drill.

AT A COMFORTABLE training depth of 10m, Mark gave a similar demonstration of keeping his head up and stretching his arm forwards as the first part of reaching back for a tap.
One of the students was only just able to reach the isolator, and Mark reminded him to keep his head up, but his body horizontal. By the end of the session, my best picture of this position was actually of one of the students.
What advice would the students offer “I’ve been able to do it, but it has always been an exhausting exercise for me, especially doing it in the least amount of time,” said Richard Roethe. “The big thing today has been making it less of a struggle. Keeping my head up and then stretching my arm forward has made a big difference.”
“Keep a stable position in the water,” said John Belchamber. “Resist any temptation to drop your head; keep your chin up and keep looking forwards.”
So, finally, back to the sequence and how the training agencies differ.
The convention from most technical agencies including TDI (for which Mark teaches), IANTD, PADI and PSA, is to shut down the isolator first.
The GUE convention is to shut down the tap for whichever regulator you suspect is giving the problem, and then to isolate.

TekCamp: www.tekcamp.co.uk; Vobster: www.vobster.com