FOR THE MANY DIVES WE DO that are uneventful, there is always the odd one on which something happens to remind us of our vulnerability under water.
This often involves the failure of a piece of equipment, and many of us are guilty of not thinking too deeply about what to do if something goes wrong, or how to prevent an incident occurring.
I’m going to run through a few of the problems you are most likely to encounter, and discuss the precautions you can take and the drills you can practise to make sure that they remain annoying niggles and don’t turn into major emergencies.
Technical divers refer to this process as planning for the “what ifs”.

1. O-RING BLOW-OUT
The regulator first stage to cylinder-valve O-ring, which is found on the first stage of your regulator if you are using DIN, or on the valve itself if you are using an international yoke fitting, is a tiny but crucial link in the process of moving the air from the cylinder to your lungs.
If this O-ring is missing or damaged a seal cannot be formed, the air will escape when the valve is opened and you will not be able to breathe properly from your regulator, if at all. On land or on the boat, you know immediately when your O-ring is missing, because there will be a loud high-pressure hiss when you open the cylinder valve.
At which point you may go a little pink with embarrassment and make a mental note to check the O-ring before connecting your regulator next time.
Even if the O-ring is present it can be frayed or slightly torn, in which case it may pop suddenly, and of course this will often happen at the most inconvenient time. As all instructors know, when you have a group of new students walking out through shallow water on a beach dive, there is an excellent chance that one of their cylinder-valve O-rings will fail.
This is why smart instructors always keep a couple of spare O-rings on their watch-strap or in their BC.
You may choose to do the same so that you have an O-ring easily to hand and don’t have to ask for help at a time when the others around you are getting their own gear together, and have their own problems to solve.
Under water, it is very unusual for the cylinder-valve O-ring to fail, although I have seen it happen. If this O-ring does fail during a dive, the only way to stop the problem is to shut down the valve, which is possible if you are carrying another cylinder containing a breathable gas for your current depth.
If you have only one cylinder, obviously you’re not going to shut it down. Your only option is to surface as quickly as safety permits, remembering that it is infinitely better to miss your safety stop than to run out of air under water.
You will still be able to breathe through the regulator as you ascend, but only for the short time it will take for all the air to rush out of your cylinder. This is a great reason to a) avoid going into deco when you have only one cylinder, and b) to practise air-sharing ascents with your buddies from time to time.

2. REGULATOR FREEFLOW
Your regulator is designed with a downstream valve so that, if it fails, air will pour out of your scuba cylinder uncontrollably until it is empty.
When you first learnt to dive, your instructor described this as a good thing, and you probably went along with that because at the time you were more worried about suddenly having no air to breathe than having too much.
Of course, this is not a good thing.
In your beginners’ course, you kneel on the bottom of the pool and breathe from a free-flowing regulator to give you the experience of breathing across a fast-flowing air stream.
This is good training in one respect, in that, having had this experience in a controlled environment, you are less likely to panic when it happens for real.
On the other hand, the training is flawed in that it might mislead you into thinking that you should remain stationary in the event of a regulator freeflow.
In fact, unless you have an independent air source to which to switch, a freeflowing regulator simply means that you are running out of air, and running out of air fast.
So, rather than stay put, the thing to do is to make a controlled move in the direction of the surface.
It seems to be obvious advice that the best way to prevent your regulator freeflowing is to keep it well maintained, follow the manufacturer’s service schedule and take it to a reputable and manufacturer-approved service centre that uses new, dedicated equipment and repair kits. However, no matter how good the service centre’s reputation, it is not a good idea simply to throw your newly serviced regulator in your dive-bag and take it off on a deep dive or a big trip to a remote place.
Give it a test-dive first if you can, in a pool or somewhere local that is shallow and protected, just to make sure that the technician did a good job.

3. RUNAWAY CYLINDER
This is something that happens much more frequently than it really should.
You’re swimming along when suddenly you feel unbalanced, and the regulator in your mouth starts to pull your head backwards. Your buddy points at you in horror, then disappears from view.
The next thing is that you can feel someone start shoving you from behind. It’s at this point that you realise that your cylinder must have slipped out of your cam-strap, and your buddy is trying to push it back in.
You can fix this yourself. If you are close to the seabed, make sure it isn’t covered with fragile marine life.
Settle down on your knees, reach behind you with your right hand to support the cylinder, undo the BC clip and Velcro at your waist and shrug off your BC as if you were removing a jacket, left arm first, keeping your teeth tightly clamped on the regulator mouthpiece.
Bring the whole set-up round to the front of your body, keeping it very close to you, (especially if your weights are in the BC), and refit the cam-strap calmly before donning the BC again and resuming your dive.
Even if the seabed is not close, you will be surprised how, with a little practice, you can remove your BC and cylinder and swim along with it in front of you while you fix whatever has gone wrong. This is something you can practise at any time in a pool or shallow confined water. It will improve your buoyancy control as well as boosting your underwater confidence.
Of course, it is much better if the cylinder never falls out at all! One way to reduce the likelihood of this happening is to soak the cam-strap with water before you lock it down onto the cylinder.
The best way, and the method most guaranteed to have a 100% success rate, is simply to buy a BC with twin cam-straps.

4. MOUTHPIECE MALFUNCTION
The mouthpiece on your second stage can pose a couple of problems. The rubber can split and you can find yourself inhaling a fine mist of sea water with each breath, or the cable-tie securing the mouthpiece can snap and cause the second stage to separate, leaving you with a mouthpiece between your teeth, a mouthful of water and nothing to breathe.
Make a point of checking both the mouthpiece and the cable-tie that holds the mouthpiece on as part of your pre-dive equipment check. Carry spares of each in your save-a-dive kit.
Even a small split can be more than just inconvenient. A diver once approached me and said that he loved the sport but was going to quit because after every dive he would get chest pains and flu symptoms for about 24 hours.
I had heard of divers who liked using a certain brand of regulator famous for being “wet” who had experienced similar problems, so we checked the mouthpiece on his regulator. Sure enough, there was a tiny split in it, and once we changed it and he started checking it before each dive, he never encountered the problem again.
During each dive, he had been inhaling sea water into his lungs with every breath and giving himself a form of bronchopneumonia!
If you ever find that you’re sipping water as you breathe, or if the cable-tie breaks and you lose your mouthpiece, no problem. You don’t have to continue to suffer, just switch to your octopus and continue the dive. This is one of the many reasons why your octopus second stage should be just as good a regulator as your primary! (More problems next month)

Read more from Simon Pridmore in:
Scuba Confidential – An Insider’s Guide to Becoming a Better Diver
Scuba Professional – Insights into Sport Diver Training & Operations
Scuba Fundamental – Start Diving the Right Way

All are available on Amazon in a variety of formats.