Stage-bottle logic

OTHREE THERMAL PROTECTION

There are different schools of thought about the “best” way to manage gas volume when cave diving with stage bottles.

The so-called traditional method is to treat the gas carried in stages, exactly as the primary gas supply: breathe one-third on the way in; one-third on the way out; and leave one-third for contingencies. If nothing hits the fan on a dive following this method, divers surface with stages, and primary cylinders each about one-third full.

Yet another option is “half + 15.” With this method, contingency gas for the stage is carried in the primary cylinders. This method requires a little more thought and arithmetic; but is considered by some to be the most conservative and best method when multi-staging. If everything goes smoothly when employing this method, divers surface with stages close to empty, but with all the contingency gas in their primary cylinders, which — with a single stage — translates into the primaries (twins or sidemount) being around half-full or more.

And finally there’s the seat-of-your-pants method which like half + 15, allows around half the volume of the stage bottle to be breathed, but critically, unlike half + 15, does NOT preserve any additional contingency gas in one’s primary cylinders. Provided nothing goes awry, divers using this “technique” surface with empty stages and primary cylinders with about one-third remaining. You don’t have to have a phD. in risk assessment to realize this is the most “liberal” way to dive stages; if anything dramatic happens, it can mean that divers do not surface at all.

But let’s leave discussion on the pros and cons of each method as the topic for a later blog post. Let’s focus instead on an error we should avoid when diving with stages in a cave regardless of which gas management rule we follow. That error is dropping a stage immediately its turn pressure has been reached.

It seems to be a more logical, more conservative, and therefore better practice to carry the stage and it’s extra gas a little further into the penetration.

Let’s look at a couple of disaster scenarios, and see why the habit of carry stage bottles a little deeper tends to be the better option.

Two divers (the ubiquitous Diver A and Diver B) have planned a stage cave dive. For the sake of simplicity, each is using the same size primary cylinders and each has the same sized aluminum stage bottle. Each has identical consumption, and fill pressures in all cylinders are identical. (An unlikely situation, but convenient for our purposes!)

Also, to forego any confusion over bar/litres or PSI/cubic feet, let’s consider the starting pressure in the primary bottles as 3P; and in the single stages as 3S. Our divers, A and B opt to dive following the Rule of Thirds in both primary and stage bottles.

OK, scenario one: Our divers begin their dive and, conventionally, breathe from their identical stages to start their dive. After a pressure drop of 1S, they drop their stages… each has 2S of gas remaining .

They swim on breathing primary gas. They each consume 1P of primary gas and signal “turn the dive.” At precisely this moment, Murphy joins their dive, and Diver A has a massive problem with his primary gas supply. He signals his buddy, and they share gas. Now Diver A and Diver B are breathing from Diver B’s 2P volume of gas.

If things go well — no entanglement, no slowing down because of restrictions, no elevated breathing rates, no taking a wrong turn in the confusion, and no arguments over navigation — they make it back to their stages with zero pressure in Diver B’s primary cylinders.

They grab their stages, and spend the rest of their exit thinking about how close a call they just had. They each surface with 1S pressure of gas in their stages, but zero in their primaries.

OK, scenario two is similar: But in this case Diver A and B when they have consumed 1S of the gas in their stages, switch to their primary gas, and opt to carry their stages a five or six minutes, or more, further into the cave before dropping them.

At the same point in the dive — just after the turn — Diver A suffers the same disaster, and has nothing to breathe. So, both exit breathing from Diver B’s 2P volume of gas; however, in this case, they reach their stages a few minutes earlier than in scenario one. There is gas in Diver B’s primary cylinders when they pick up their stages and continue their exit, during which they give thanks that they carried their stages further into the cave.

They surface with less than 1S of gas in each stage having perfectly justifiably used some of the reserve contingency gas in those stages to exit calmly. Diver B has some gas in her primaries; and, as in scenario one, Diver A’s cylinders are still empty.

Now we might argue the likelihood of the type of complete gas loss Diver A suffered in both scenarios one and two as remote… highly rare, probably impossible. But what cannot be disputed is that in scenario two, by carrying their stages for just a few extra minutes during their swim in, they had contingency gas placed in a better place than in scenario one.

We can debate how best to manage contingency gas volumes in stages (there may be benefits to each method), but in most cases it seems a better, more logical option to think before you drop; and wait.

Dive Safe!

A thought experiment concerning “team bailout” when diving CCR in a cave…

LongO'THREE

First off: Can anyone explain the rationale behind “Team Bailout?”

Hang on… that needs to be rephrased.

Let’s start with this: Is it just me or is the concept of “Team Bailout” for CCR Cave Diving just bat-shit crazy?

Yea, that’s way closer to what I was thinking…

Ok, for those of you who may not be familiar with the team bailout concept, it suggests that a buddy team diving CCRs in a cave environment – you know, wet rocks, hard limestone overhead, perhaps an hour or more from the surface – that they carry sufficient bailout gas “…to get one team member back to fresh air from the point of furthest penetration.”

In certain circumstances, this approach may sufficiently protect team members from harm, but those circumstances should not include the category of diving the vast majority of us engage in.  I believe, a better, more satisfactory practice is for EACH diver to carry MORE gas than is required to get themselves back to fresh air from the point of furthest penetration.

The arguments I’ve heard against using this more conservative tactic is: 1) carrying multiple bailout cylinders is a pain; 2) the likelihood of more than one CCR failure among a team is too slight to consider; 3) calculations for the volume of gas required in a high-stress situation adhere to a well-defined formula corrected for all variables, and therefore it is possible to calculate with a degree of accuracy sufficient to be safe.

Experience is a better guide to best practice behavior than deductive logic, and I have limited experience in this area. So, perhaps my paranoia is unjustified; but here’s a scenario we might all give some thought to before our next cave dive.

Here goes:
Three CCR divers were in the back of a low-flow cave. Each carried an aluminum 40 filled to capacity, which lumped together was enough gas to get any one of them out of the cave and back to dry land. Even at double their normal consumption rate, this was the case. Their dive was well within the parameters of team bailout therefore.

At the worst possible time, Diver A’s CCR went belly up. He could not revive it in any way, and has to bailout. The team began its swim out. A little sooner than expected, but still more than one-third of the way out, Diver A’s bailout cylinder was empty, and he asked Diver B for her cylinder. She suddenly realized that by giving it up, she will have no contingency gas herself. The surface was still a good swim away. Very reluctantly, she handed over her bottle. Momentarily distracted by her thoughts, she floated to the cave’s ceiling and took a minute to recover, which held the team’s progress to the surface still further. Stress levels in all three team members was now peaking. None of them was comfortable.

They were in fact, more small failure, one additional glitch away from a total melt-down. A surprisingly short while later, Diver A – who had been thinking for the past several minutes, what would happen if he got a bottle with a dodgy regulator or had a free-flow, and whose respiration rate had understandably elevated – once again was down to seeds and stems. This time in his second bailout. He turned to Diver C. Diver C had been thinking about this hand-off for a while. He was VERY uncomfortable donating his gas… however, he did so. Several minutes later, the team arrived in the cavern area. Diver A had barely sufficient gas to conduct a safety stop, but did so. Just as the team left the overhead, his regulator began to breath very, very hard.

On shore, while shucking their gear, the group was uncharacteristically silent, each with their own thoughts. What do you think the outcome of this incident was:

  1. This group did not cave dive together ever again
  2. This group rethought their bailout strategy
  3. This group  continued to dive team bailout

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Don’t even think about asking for an overfill in your aluminum cylinder…

LongO'THREE

I don’t trust the integrity of aluminum scuba cylinders… at least, not enough to:

  • overfill any aluminum cylinder (in fact I often under-fill aluminum stages and decompression bottles keeping below the manufacturer’s suggestions for working pressure);
  • keep them in service more than a year or two after their first hydrostatic test cycle (which is every five years where I live);
  • wander very far from a very conservative approach to the frequency of formal visual inspections, choosing instead to follow the manufacturer’s suggestions for cylinders in Heavy Service;
  • miss Eddy Current testing as part of the VIP procedure (EVEN WITH BRAND NEW CYLINDERS!);
  • be trusting of loners and rentals, especially those with the look of being in service since, and taking direct hits during, the Gulf War.

My reasons for being a “mother hen” are based on a professional ‘cover everybody’s arse’ strategy to risk management. And a certain knowledge that high-pressure vessels have an enormous potential to harm. I’ve witnessed the aftermath of two separate aluminum tank failures and have a very strong mental image of the chaos each caused. I read somewhere that the amount of energy stored in a “recreational scuba cylinder,” which one can take to mean an aluminum 80, is about the same as two WWII British military hand grenades. A sobering thought.

Of course, one should be equally cautious with steel cylinders, which have a similarly dangerous potential. However, aluminum cylinders more easily carry the scars of mild to moderate abuse in typical everyday service. Couple this with their inherently different reaction to repeated filling and emptying – aluminum’s fatigue limit – and the dramatic reduction of an aluminum cylinder’s endurance limit from several hundred thousand fills to perhaps hundreds when it is over-filled – and its potential for failure is increased.

Of course, an easy out would be to avoid using aluminum cylinders altogether, but the buoyancy characteristics of aluminum makes 80s and 40s excellent stages, bailout, and decompression bottles. Besides, avoiding their use would be a dramatic over-reaction.

Working within manufacturer’s limits and the handling guidelines they supply us, aluminum is safe for many, many more fills than any of us is likely to ask it to endure.

But we do need to be mindful of those limits and guidelines.

Luxfer, the manufacturer of a popular brand of aluminum scuba cylinders of all sizes including the ubiquitous aluminum 80 writes the following about safety and its products… all great advice!

“If the cylinder is used in heavy service then it should be inspected every four months.

“Heavy service” means any one or more of the following:

  • Cylinders being filled or “topped off” five or more times per week;
  • Rental cylinders in use during the ‘season’ and ‘off-season’ times;
  • Cylinders used wherever damage is more likely than in normal use or where the
  • care and/or maintenance is slightly below recommended care.

If the cylinder is known to have had any unusual treatment or condition, it should be immediately visually inspected, prior to its next use.

“Unusual treatment or condition” means if the cylinder:

  • Dropped, fell, was struck, was in an accident, or when the care and maintenance of the cylinder is obviously poor;
  • Was stored improperly, and shows signs of damage;
  • Has obvious corrosion since the last visual inspection;
  • Has a gouge, dent, scrape, cut, dig or, in any way, has been damaged since the last
  • visual inspection;
  • Was stored with water, material or matter inside the cylinder;
  • Shows signs of exposure to fire or high heat, including any one or more of the
  • following:
    • Charring or blistering of the paint or other protective coating;
    • Melting or charring of the metal;
    • Distortion of the cylinder and/or any cylinder accessory;
    • Melting of fuse plugs, valve handwheel, valve protector, and/or any other
  • valve component or cylinder accessory;
  • Has been partially or fully repainted or treated to hide damage and/or
  • fire damage;
  • Is known or suspected to be leaking; or,
  • Is known or suspected of having a crack.”

 

Dive Safe… be careful out there.

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Fixing a lack of skill with complex gear… Nah, try a swimming pool!

Nick Hollis in SMS75 Hollis SM harness

Nick Hollis of Hollis Gear showing some skills in swimming pool like conditions…

Few of us learned to dive without the help of a buoyancy device of some sort. Not to say that wearing a jacket-style BCD, sidemount harness, or backplate and wing automatically gave any of us pin-point control over our position in the water column: it certainly did not!

The vast majority of the divers — sport, technical, rebreather, open-circuit, whatever — earned that particular skill with patience, perhaps a little help from a buddy or mentor of some description, and a bunch of practice.

Swimming pools or ‘swimming pool-like conditions’ (warmish, reasonably calm, clear-ish, current-free shallow water), are awesome for gaining something approaching buoyancy control right from the first open-water class: and then fine-tuning that skill by return visits as often as practical. I will still take time, whenever I can, to simply “hang about” in the water. A visit to the pool is a great place to test new gear, adjust weighting, check that old favorites still work the way you want them to.

In fact, if you are an instructor looking for ways to increase student comfort, add to general diver safety, and build on the basic skills your students learn on your courses, you’d do well to offer a few extra hours of pool time regularly. I have a buddy whose open-water students leave her classes with demo-quality buoyancy control and near-perfect ‘cave trim.’ Her secret is additional pool time, which her students gladly pay a little extra for because she’s taken the trouble to explain the benefits of buoyancy control to them. They get it: they know it takes a bit of work: and they are not looking for a fast fix.

So, imagine my disappointment to see an ad for a piece of kit that is such a convoluted bunch of “Heath Robinson” engineering that at first I thought it a joke. The product, and it is real apparently, is pitched as: “An industry standard premium diving jacket, dive computer with connecting links to allow the computer and jacket to manage diving processes according to the selected settings just like an aircraft autopilot.”

What have we come to when the simplest of devices, and a little practice to master its use, has to be replaced by something with Catastrophic Failure (or something else with the initials C-F) written all over it.

Please, if you want to get your buoyancy squared away because it wasn’t taught to you as a beginner, take a cavern or intro-to-tech class from a good instructor. Contraptions that offer instant mastery through technology are like magic pills that promise to shed pounds of belly fat without diets or exercise. The word to describe this type of promise is bullshit.

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Want to ignore the rules? Then do this…

There really are no scuba police, and here in most of North America at least, government bodies give the diving community the closest thing to a free-rein. We can, in essence, do exactly as we please. We can dive without training, ignore warning signs, flaunt best practice, exceed both whatever certification we have and the experience earned on previous outings. We are free agents. Great stuff.

But the downside is awful. A couple of days ago, I read of another stupid death — highly preventable and caused by several breakdowns in the system… that tragic alignment of holes in the safety net that which is in place to help diving “accidents” NOT happen.

What’s frustrating about many of the deaths we read about online, in diving magazines, and in diving forums, is that the people involved had been warned. At some point, either in their training or general involvement with the diving community at large, they had been told what they had planned, was foolhardy or against best practice.

But they went ahead anyway.

Just as sad is that their behavior does have the potential to change the status quo. Their silliness may create a situation where some agency or quasi-government entity starts to pay attention to our activities… and arbitrarily start to shut things down.

I am reminded of something my mate, Wayland Rhys Morgen suggested for anyone who is about to — either figuratively or actually — hand their beer to someone and say: “Here, watch this…”

The next time you intend to deviate from best practice, take a piece of note paper and divide it into two columns. Write in block letters at the top of the left-hand column: “What people usually do.” On the right, also in block letters, write: “What I am going to do instead.” Then in the appropriate column write clear, concise language an explanation of each behavior associated with your planned dive. So, these ‘behaviors’ would cover things like analyzing and labeling gas cylinders, limiting depth and duration according to your training, recent experience, and the vagaries of the environment… stuff like that. Read it back to yourself — both columns — then sign and date it. Then give it for safekeeping to someone you trust: lover, spouse, son, daughter, best buddy, favorite cowgirl. It really does not matter much to whom, just hand it over. Tell them to give it to the people or agency that leads the inquiry should something bad happen to you on your adventure.

Building the odds in favor of a good outcome…

LongO'THREE

A simple tip from the closest thing you’ll find to an expert

I have one of the best jobs imaginable… I get to dive for a living. It has drawbacks just like any job… I spend a lot of time away from home and the people I love; sometimes I am compelled to jump into the water when all I really want to do is sit on my arse and veg out; and there are few constants in a very fluid and organic field of research about diving, which means lots of reading, lots of lectures, lots of changes in what we teach and what we reject.

However, there are also a bunch of positives… including the list of things on the drawback list: I travel, I dive a lot, I get to feed my brain new stuff all the time.

One of the best things though is the people I meet. The so-called technical diving community is packed with cool folks. These are the men and women with open minds, boundless curiosity, and a willingness to share what they’ve discovered. They are stellar human beings and it’s a gas to hang out with them, and learn from them.

One guy who always has something interesting to say is Dr. Neal Pollock. Neal is ex-pat Canadian scientist. He’s a research physiologist working in the States, and has a background in zoology, exercise physiology and environmental physiology. He is also a diver and part of his research relates to decompression stress.

He also has a very “English” sense of understated humor in his writing and presentation style which appeals to me. I particularly appreciate lines such as: “The approximation of decompression status predicted by current deterministic algorithms should not be confused with ‘truth.'” Honest, insightful, and funny.

Anyhow, his latest blog is a hugely interesting read. It’s entitled “Flexible Control of Decompression Stress” and you’ll find it here: https://www.shearwater.com/news/flexible-control-of-decompression-stress/

Take the time to visit and read. You’ll learn something.

Surviving the Rottweilers

LongO'THREESeven tips to help protect you when things go wonky underwater

You may have read somewhere that underwater emergencies are rare. I’m not so sure that rare is the best way to describe them.

While underwater incidents causing bodily harm or death may be infrequent, close encounters with potential disaster are frightenly common. Spend a week or so at a dive resort or on a live-aboard, and you’re guaranteed to hear stories that support this view. “I ran out of air,” “we got separated from the guide and had no idea where the boat was,” “We ended up way deeper than expected,” “My computer went into deco and I had no idea what to do,” “My regulator started to spew bubbles and I panicked… I did not know what to do,” “We skipped our safety stop,” “I felt odd and confused, but managed to hit the inflate button and shot to the surface,” “I signalled the divemaster but he misunderstood me and continued with the dive.”

‘Victims’ of these little brushes with catastrophe fall into three categories. Some give up diving altogether. They get the crap scared out of them and opt for golf, fishing, stamp-collecting. No foul.
Some learn from the experience and avoid the traps that painted them in a corner in the first place, and they become more informed and safer divers.

And some learn nothing. They carry with them the potential to make similar mistakes again and again… sometimes with ruinous consequences.

Here are seven strategies that may help divers enjoy their diving, and avoid becoming a statistic.

      1) Learn to say no! Too many new divers are fooled into believing that it’s OK to do trust-me dives with a dive guide or divemaster. They may have a good sense that diving once or twice a year does not prepare them for a 40 metre-plus dive (that’s 130 feet or more), in current, with rented gear, but a divemaster, instructor, sales-person talks them into doing it. This is dangerous bullshit. No agency condones this type of practice, but it is common in many dive resorts, and needs to be stamped out.

 

      2) Learn your limits and stick to them. There is nothing wrong with pushing yourself to learn and grow your diving experience and comfort zone, but be realistic about your starting point. Being an occasional diver means you start from zero at the beginning of every dive trip. Scuba skills are perishable. Even experienced cave instructors take the time to “brush up their skills” if they have been out of the water for a while.

 

      Even if you are lucky enough to dive every week, understand that your experience, training and gear limits the types of dives that you can safely undertake. Listen to your inner wimp.

 

      3) Learn self-reliance. Too many “rescues” end up in disaster or near disaster for all participants. Get training, learn what kit to wear to help deal with gas emergencies, PRACTICE. Most of all, STOP, THINK, ACT, REASSESS.

 

      4) Maintain your kit, and use a checklist when you assemble it and when you inspect it prior to EVERY dive. Equipment problems are the easiest underwater emergencies to avoid. Don’t fall into the trap of believing that something is good enough… if it “ain’t perfect” don’t dive with it.

 

      5) Plan your dive… Dive your plan. Understand the risks, make sure everyone is capable of doing the dive, and ensure everyone have the skill and kit to deal with contingencies should they arise.

 

      6) Be aware! The best way to deal with a diving emergency is to stop it before it gets out of hand. The vast majority of diving emergencies begin as small inconveniences that cascade rather like dominos falling over. Keep an eye on your buddy(ies), be aware of changes in the conditions, monitor yourself. The best blanket advice is to take things slowly.

 

        7) Have an escape strategy. When something goes pear-shaped, the top priority is to make sure everyone has something to breathe… next is to get yourself and your mates as far away from the spinning fans as possible. Cave divers talk about always having a continuous guideline to the surface. Sport divers can take a lesson from that: Always know the location of a safe, protected exit… in other words, someplace where you can surface and be found or find your way to your entry point.

Steve Lewis is an explorer and experienced cave diver, who has been teaching technical diving programs for more than 20 years. He writes and lectures on topics related to diver safety in North America, Europe and Asia.