|ANYONE WHO HAS HAD TO EXPLAIN something to a child will know about those little (and not so little) white lies we tell them. The sort of explanation we give in response to questions such as: Where do babies come from and Why have I got one of these and my sister hasnt|
Telling these simple lies is something we do to avoid a more detailed explanation, an explanation we think is too complicated for them to understand, to emphasise what they need to know without distraction, and to protect ourselves from getting drawn into a more involved discussion. Its a convenient and easy way out.
Such a strategy for explaining things doesnt stop with children, however. It carries on into adult life, sometimes to excess. Think of the irritatingly patronising way politicians explain things in boiled-down over-simplicity to us voters.
Is it really surprising that there are parallels in diving training
1: Dont hold your breath
One of the first things any instructor tells a training diver is this: Just keep breathing. Whatever happens, dont hold your breath.
To go with this, beginners are taught to blow small bubbles whenever they dont have a regulator in their mouth. This enables the instructor to establish at a glance that they are not holding their breath.
The funny thing is that most experienced divers soon begin to hold their breath, and for a wide variety of reasons.
In one form this is called skip-breathing, where we hold each breath briefly to lower our air consumption. The manuals say we are not supposed to do this, but everyone does it to some extent, learning by bitter experience that overdoing it can cause headaches.
We also use our lung capacity to make minor adjustments to buoyancy, breathing out and holding it to start descending, breathing deeply and holding it to help stop a descent, and breathing in and holding it briefly to ascend a little bit.
Photographers will often hold their breath for a minute or more to prevent their bubbles from scaring a fish. They may also ask their models to hold their breath, to keep bubbles out of a picture.
Of course, its best to do all this by delaying an inhalation, rather than holding back an exhalation.
Looked at in more detail, the only time that holding breath can actually be dangerous is during an ascent. So, rather than the blanket beginners rule to keep breathing normally and never hold your breath, more accurate guidance would be to be very careful about how long you hold your breath when ascending.
But that would involve instructors getting into a discussion about all the possibilities, and giving guidance about what sort of breathing would be safe under which situations. Thats why trainee divers receive the simplified version.
2: Always carry a knife
A divers knife is part of the standard equipment that were all supposed to carry. We see them used regularly in movies to fight off sharks and giant octopuses, to kill enemies by stabbing them or slashing their regulator hoses, and to prise the lids of chests of gold.
In practice, the main reason we are supposed to carry a knife is to cut our way free of accidental entanglement in ropes, nets and fishing lines. But if these are the hazards we have to fight off, there are better tools than a knife to cut our way free.
Many diving knives make allowance for this, by including a hooked net-cutting section on the blade. But this is just a bodge on a tool not really suited to the job. The tool that is best suited is a pair of shears. These will make short work of monofilament and thin line, and can still chop through ropes of moderate thickness.
Shears can also be used one-handed, because there is no need to hold or tension the net or line while cutting. There has been more than one incident report of entangled divers accidentally cutting their hand or even stabbing themselves with their diving knife. With shears, your other hand doesnt need to be anywhere near the blades.
The final advantage of shears is this: while you can easily pay £50 for a proper diving knife, you can pick up a pretty solid pair of kitchen shears for under £10, and buy a dinner knife to butter your sandwiches from the small change. If you really need to prise the lid off a treasure chest, get a small jemmy or pry-bar from a builders merchant.
To be fair, if stainless-steel shears had existed when this training mantra was first invented, they would have changed it to always carry a pair of shears.
3: Always surface with 50 bar
This is a gem of dogma we come across in nearly every dive briefing. To be back on the boat with 50 bar left in our cylinders is the ideal. It all comes from way back when military divers used to have a twin-set with isolator valve, single regulator and no pressure gauge.
The divers would keep the isolator closed, breathe one cylinder down until the regulator got sticky, balance the gas between cylinders by briefly opening the isolator, then repeat the process.
They would then have 25% of their original gas left, and ascend.
While dive gear has progressed and pressure gauges are pretty much standard equipment, the balancing practice is still used by military, police and commercial divers working in zero visibility.
If the original cylinder pressure were the US standard 207 bar, this double balancing routine would result in divers beginning their ascent on 52 bar. This got rounded in numbers and time to become the sport-diving dogma of finishing a dive with 50 bar remaining.
Just how much gas a cylinder pressure of 50 bar really provides and what we can do with it all depends on the cylinder capacity.
On a 12-litre cylinder, 50 bar is 600 litres, or 15 minutes diving at a depth of 10m and a surface RMV (Respiratory Minute Volume) of 20 litres/ minute. The underwater time would drop to 12.5 minutes for a 10-litre cylinder, or stretch to almost 19 minutes for a 15-litre tank. If the quantity of gas left on surfacing was really critical, the magic pressure should be more for a 10-litre cylinder and could be less for a 15-litre cylinder, but thats not what we are told.
On a shallow dive, or the shallow part of a multi-level dive, we could safely use a fair part of this remaining gas and still have enough left to handle problems and the final few metres of ascent. Pottering about at 5 or 6m while using up some of this gas will actually make our dive safer from a decompression point of view.
When we get on to more complicated diving, such as decompression, cave or technical diving, 50 bar does not enter into the equations.
Divers learn to plan their gas requirements so that they have enough gas to return safely to the surface following any single equipment failure or the need to share with one other diver.
No-decompression cave-diving begins planning with a rule of thirds: 1/3 in, 1/3 out, and 1/3 reserve, or about 70 bar depending on starting pressure. But this is only a starting point. Detailed planning to allow for decompression may lead to a greater reserve pressure; or to less, where multiple stage cylinders are brought into the calculation.
So 50 bar is not a hard and fast rule. Its just an arbitrary number with plenty of margin to keep beginners very comfortably safe.
4: Always wear a snorkel
Think about how often you use a snorkel. Perhaps on a surface swim at the start or end of a dive - but most divers prefer to swim on their backs.
Perhaps in the surf when entering or leaving the water - but using a regulator is a better solution in the surf. Perhaps at the end of a dive while waiting for a boat - but it is usually easier simply to inflate the BC and float there.
Is it really surprising that the vast majority of experienced divers do not have a snorkel permanently attached to their mask straps Those who actually take a snorkel diving with them are more likely to keep it in a pocket for the rare occasions when it may come in useful.
If we look carefully at the wording of various training standards, they tend to say something like carry a snorkel and nothing about actually wearing it. Always wearing a snorkel is a common misconception, propagated by instructors who dont read the words.
5: A long hose is for panicking divers!
Start adding a bit of technical kit to your dive bag, and one of the first things to get incorporated is a 2m-long regulator hose.
A long hose is the required accessory for donating gas to another diver when exiting the confines of a wreck or a tight cave. But what use is such a long hose in open water
Our other lies to trainees are relatively benign matters of convenience, but one often-given argument for a long hose is downright dangerous.
I dont want a panicking out-of-air diver anywhere near me. So I give him the long hose and push him well clear is a boast I have heard from more than one technical expert, who has probably received more of his training from dodgy websites than from a real instructor. To my knowledge, none of the technical training agencies support such a justification for long hoses.
What is a panicking diver most likely to do Bolt for the surface by swimming, inflating his BC or dropping his weightbelt.
If he is out of reach at the end of a long hose, he may not be able to attack you, but equally there is nothing you can do to stop him from bolting. If he bolts for the surface at the end of your long hose, the chances are that he is going to tow you up with him.
And this isnt a hypothetical analysis - it has actually happened.
If you really have to give air to a panicking diver, you need to keep him close, where
you stand some chance of keeping him under control.
So what is the use of a long hose As noted at the start of this section, a long hose is to give divers sharing gas room to manoeuvre, whether it is inside a wreck or cave, or just for a bit of elbow room in open water. You dont want to let a panicking diver anywhere near the full extension of your long hose.
6: The leader must maintain control
Group control is an essential part of a divemaster course, then its pounded home again in instructor training. Instructors or divemasters must stay in control of their group of divers.
Now we have moved beyond lies to trainees. What we have is a lie to trainee divemasters and instructors.
Superficially, being in control sounds right. After all, the instructors or divemasters are employed to guide or instruct. They are responsible for the group.
If something went badly wrong, they would be held to account, so why shouldnt they be in control at all times
New professionals often take such grave responsibility to heart, and try to micro-manage every aspect of a dive or training session. Their charges return from the dive disappointed. But it isnt the lack of diving experience they complain about. They wanted the freedom of the fishes, and they suffered the rigorous herding of a naïve control freak.
What older and wiser instructors and divemasters have learned is that being completely in control of everything is an impossible objective. There is no human way they could be in complete control even of a single diver, no matter how much detail they put into micro-managing the dive, let alone a larger group.
What their responsibility really amounts to is that they shouldnt let things get dangerously out of their control. In this way, they can focus their attention where it is needed, and cut the divers a bit of slack the rest of the time. Its more fun for everyone and less stress for the instructors and divemasters.
Can you think of any other lies we tell trainees