DEEP BREATH


Is ignorance or naivety the cause of so many kamikaze buoyant ascents? This is a job for diving and training officers.


The Polaris Principle


It seems that maverick lifting bags and delinquent delayed SMBs have brought a whole new meaning to the already colourful comedy of "uncontrolled buoyant ascent", a term that has earned high rank among my favourite diving euph-emisms.
The Polaris Principle, as I prefer to think of it, has been with us since the dawn of scuba. Divers' never-ending abilities to taunt the demons of decompression have long since ceased to surprise me, but DOC '96 uncovered some new angles to the art of overtaking your own bubbles.
My diving experiences contrast starkly with some of these sport diving projects that turn technical. This applies especially to deployment of "positive buoyant energy in underwater engineering" - otherwise known as "lifting bags".

The standard of basic training is not at issue here. That standard has always been based on the diving safety of you, your buddy and companions.
But even this rigorous club training runs out of line when swimming underwater ends and technical exercises with heavy stuff begin. At this point we depend for safety guidance on the experience of diving and training officers.

Lifting bags are the most useful tools in a high proportion of underwater engineering exercises. unrivalled in their portability-to-power ratios, they are the nearest we will ever get to a diving "sky-hook". With infinite opportunity for innovative engineering under water, it understandably tests the scope of organisations like the SSAC to devise regulations to cover all contingencies. But lifting bags are predictable tools and should, I believe, be included even if only in general guidelines within present diver training.

They are predictable because their power is a matter of simple physics. Physics might present something of a barrier to diving's rednecks but lifting bags are an extreme extension of those simple rules of buoyancy that anyone who has mastered the principles of diving can conquer.
It is this easy: when air is pumped out under water, it creates a bubble. The water that was there before has to find somewhere else to go. It can go only into the surrounding sea, so the whole sea is pushed out by that small amount. The sea doesn't like this, so naturally it pushes back. The referee in this contest is a law of physics, and it is a very fair referee. It rules that it is OK for the sea to push back, but only with the same weight as the area of water that was pushed out.

Nature does not go in for stalemates, so the bubble is left with only one way out of the dilemma, and that is to use that squeezing energy to propel itself back to the world of air above. That energy used by the bubble, as designated by the laws of physics, is the same as the weight of water it pushed out of the way.

Now imagine a large captive area, about the size of an average lifting bag, and fill it with water on dry land. It would take a grown man with two hands and braced legs to lift that weight of water. Put that captive area under water and fill it with a big bubble of air. It is easy to imagine that upward escape force having the same "weight" as the bag full of water did on land.
If that is easy, so is imagining removing the force of gravity that helped us brace the lifting bag on land, and imagining yourself weightless under water with that amount of energy threatening your survival.
The latest diving incidents report suggests to me that either stupidity or naivety about the dynamics of advanced buoyancy tools was responsible for so many runaway lifting bags and delayed SMBs dragging their attached victims surfaceward at dive-bending velocity.

How often have I seen a diver, already stimulated by a dive, almost overcome with excitement when he makes a "find"? In the old days he would be struggling at the surface so overburdened with portholes that all his air had come down his direct feed to the airbag around his neck, rather than the airbags in his chest.

Thus manacled with brass, many a good man has released his precious hold on the surface rather than release his precious cargo.
Nowadays, the scenario is curiously reversed. That treasured goodie no longer sinks our diver but threatens to surface him in an abrupt manner. Not only abrupt, but goddam dangerous!
The question I must put to diving and training officers is this: