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


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



Mine Quest 2.0

Bell Island Mine 2.0

Winter in Newfoundland can be bleak and is most definitely cold, but this week, a group of volunteers and Bell Island Heritage Society staff ignored the weather and did a huge amount of setup work getting things ready for Mine Quest 2.0.

As well as building a platform/staging area for the exploration team to work from, during mid-February’s expedition, they carried several hundred kilos of materials more than 225 metres down a ten-degree incline from the surface to the water’s edge. Before the building commenced, using pickaxes and shovels to clear away loose rocks from the roof and walls of the mine shaft, then installed temporary lighting.


After the clean-up… the mine shaft we will be working from

Eventually, it’s hoped the mine on Bell Island will feature permanent infrastructure that will add dive adventure tourism at the historic site to the world-class wreck diving found just off the island’s coast. For the time-being, the hard work will help simplify, and aid the success of an effort to add the the two kilometers of passage explored and lined during the 2007 project I was lucky enough to be part of.

Over the next several weeks, and certainly during Expedition Week (February 13 – 20), I’ll try to keep you up-to-date on progress and exactly what’s planned.


In the meantime, hats off to Mark ( Magoo) McGowan, John ( Johnny O) Olivero, Nick Dawe, Kyle Morgan, Rick Stanley, Ron Reid, Teresita ( Teddy) McCarthy, Des McCarthy, and Tom Spracklin.

Thank you for your efforts folks.


For a comprehensive line-up of who will be working on the project, visit my friend and co-leader’s blog… Thanks Jill.



Flying after diving… what are the guidelines?

Here’s a somewhat common scenario… perhaps one you have experienced yourself; or thought about at least.

Anyhow, here it is. You and your buddy are on a dive vacation someplace that requires airline travel… bummer, right!? Pack light. Hope the TSA doesn’t break anything on your way out. Hope customs at the destination doesn’t fuss over anything on the way in.

However, all those issues aside, every other piece of the planning puzzle is falling into place just fine except for one small issue. The flight home is scheduled wheels-up at O-Dark-Hundred in the morning, and there is an opportunity to dive something really, really cool the previous afternoon… late in the afternoon. The question is: Can you do that dive without getting bent like a pretzel on the flight home less than 12 hours later?

The whole issue of Pre-flight Surface Interval (PFSI) is a contentious one. The old-school guidelines were wait 24 hours after diving before jumping on a commercial flight. But that recommendation has been revisited in more recent studies and the PFSI shortened; with suggestions that various other factors such as breathing nitrox, the length of safety stops, gas breathed during safety stops, and the duration and depth of dive, can all influence by just how much the PFSI can be shortened.

A quick straw-poll of my dive buddies tells me that the definitive answer is a moving target. There is little agreement.

What we can take as read is that flying after diving has a strong potential to apply extra decompression stress on a diver and increases their risks of decompression sickness. There seems to be a direct relationship between the risk dropping and the amount of time spent out of the water increases allowing excess inert gas to be eliminated normally and harmlessly through the lungs. Some trials have estimated the PFSI necessary for a low DCS risk (read acceptable number of incidents of DCS) after relatively long single or repetitive no-decompression dive profiles sits between 11 and 16 hours.

The PFSI for dives requiring staged decompression stops, was around 22 hours. At first blush then, a 24-hour break after diving would seem in most sport-diving cases to be very conservative. But then again, what worked in a dry chamber on a couple of hundred test subjects, may not apply to the average dive tourist coming home from a week in paradise where the diving was punctuated with rum, grilled fish and late-night romps on the beach. Equally, it also may not apply to an informed technical diver who pads her/his decompression stops with extra time, and breathes pure oxygen for long periods during that PFSI!

Well worth the download and reading time is: The Influence of bottom time on preflight surface intervals before flying after diving, published by Undersea Hyperb Med. And authored by Vann RD, Pollock NW, Freiberger JJ, Natoli MJ, DeNoble PJ, Pieper CF. (2007). It is available from the ultimate diver’s research tool: http://archive.rubicon-foundation.org/xmlui/handle/123456789/7343.

The study’s conclusion suggests “that bottom time, repetitive diving, and a decompression stop may significantly influence the pre-flight surface intervals required for low DCS risk. Moreover, it highlighted the need for additional human trials to resolve the effects of exercise and immersion on DCS risk during flying after diving. Such information might assist in the calibration of dry, resting trials for the effects of immersion and exercise which would be useful as dry, resting trials are less expensive and faster to conduct because more subjects can be exposed per chamber dive. This might be of aid for improving the accuracy of existing flying after diving guidelines.”

Significant in that conclusion is the call for additional human trials to resolve the effects of exercise and immersion on DCS risk when flying after diving.

I volunteer.

However, I would be far from an average test subject since something seems to put me outside the bell-curve for DCS risk. For example, my experience with PFSI is far from what’s generally acceptable and my practices at times have been foolhardy. Furthermore, I fall outside the age category that most studies could ethically accept in any trial… but all that aside, I would love to be a guinea pig.


Cardiac Stress Testing and technical diving

Around this time every year, most of us hang up a new calendar, and polish up the New Year’s Resolutions. Like me, you probably have a few left over from last January 1. If you do, chances are good that one revolves around “getting fitter,” “getting in better shape,” or “working off all that Christmas pudding.” If that is the case, and you’re a diver, I’d like to suggest adding a slightly different twist for 2012.

During a few recent and very informal discussions with other tech instructors, one of the highest-ranking concerns has been the number of divers – particularly tech and rebreather divers – who have died of heart-related problems either while diving or soon after diving.

There are all kinds of issues that may have had an influence on incidents in the past, but the collective concern was how to help make 2012 a “better year” for the dive community.

One idea floated out was to ask students* to undergo a cardiac stress test as part of the list of prerequisites that need to be met before enrolling in advanced technical programs, such as CCR, trimix and advanced wreck and cave.

A cardiac stress test stimulates the heart – either by exercise or with intravenous pharmacological stimulation – and connecting the testee to an ECG. The American Heart Association recommends this kind of testing for patients with medium risk of coronary heart disease. This includes folks with personal risk factors such as smoking, a family history of coronary artery stenosis, people with hypertension, and folks dealing with diabetes and high cholesterol.

Who knows if it would make much of a difference, but what harm would it do? I’m old and get one for free every year through my insurance (BONUS!), and there is a level of comfort knowing that there are no serious issues with the old ticker.

I believe the cost of a cardiac stress test works out to about the same as the charter fees and fill costs for an open-circuit deep wreck dive. Worth the dough? I think so and certainly worth adding to that list of resolutions… Things to do in 2012!

* Students who have risk factors, or those 45 years and older.

Teaching an old(ish) dog, new tricks

A really good friend of mine who runs a charter boat out of Florida has a wonderful phrase to describe divers  who are really set in their ways and somewhat complacent when it comes to dive prep. You may have seen them on a dive boat near you. They always dive exactly the same gear package, right down to the back-up lights on their shoulder harness, double cylinders, a stage bottle, canister light and a full complement of reels, spools, and sundry accessories; including a scooter.  Now he is first to admit there’s nothing inherently wrong-headed about that, except they dress the same regardless of whether the day’s target is a 150 foot dive on a brand-new wreck or a 25 foot bimble in a local quarry.

He calls them One-Dimensional Divers.

“I think they are so blinkered and taken with the self-importance of being a technical diver,” he says. “They forget to stop, smell the roses, and kick back!” He says that the real sign of a one-dimensional diver is that they can turn the simplest of dives into a major undertaking. “And where is the fun it that?” he asks.

And after 18 years of lugging a full North Florida Cave Diver’s rig around the country, and using it on even the most straight-forward dives, I felt I’d fallen into the one-dimensional mode myself. I told my buddy things had to change; and he offered the perfect solution. “Buy a closed-circuit rebreather.”

Working for a training agency gives an old guy like me a slightly off-kilter prospective on dive gear, dive travel, and the whole business of diver education. For example I figured I knew quite a bit about CCRs (closed-circuit rebreathers) because I have an instructor rating on a SCR (Semi-Closed Rebreather), have proofed rebreather manuals, and have logged lots of hours on several different CCR units doing everything from try-dives to bona-fide courses.

How wrong I was.

The seed change was actually getting a unit of my very own to look after. Not a loner, not one that a manufacturer suggested I take a look at, but one that I had to take apart, clean, keep spiders from visiting, change its do-dads from time to time, reassemble, and learn to dive from ground zero with the express goal of getting comfortable enough on it to drag it halfway around the world to dive the wrecks of Truk Lagoon.

To be blunt, it was one of the best things that has happened to me and my diving in a long while; and it certainly has also been among the most instructive.

The reasons for this are varied and many faceted but let’s keep things brief and simple and start with the whole one-dimensional / complacency thing. No matter how hard one works at keeping focused and realistic about skills, planning, only taking into the water what’s needed on the dive, and doing things to the letter, human nature has a wonderful way of turning short-cuts into “best practice.”

On open-circuit dives, it is very easy for an experienced diver to become one-dimensional. So much so that at times, dive plans for commonly done personal dives – ones that fall into the “I have done this a thousand times before” category – became marginally adequate at best. As little as it turns out I know about CCRs, I did know enough to understand that the one-dimensional / complacent approach will quickly get you in a very deep pile of trouble.

Occasionally doing something totally outside the norm, helps adjust one’s attitude. Training on and then diving a piece of kit that resembles nothing you are used to diving, definitely turns a few knobs.

As you know, a rebreather recycles exhaled gas, scrubs out the carbon dioxide, squirts a little oxygen back into the mix to compensate for the stuff used by the diver’s metabolism, and is designed to keep the process going for hours at a time. It also mixes gas so the diver breathes “best mix” regardless of depth and it does all this in a compact package (read this to mean, less weight than a set of doubles!).

The other side of the coin turns up the nasty little vagaries attached to rebreather diving, and understanding and working around these is the central theme of a rebreather class.

In short, a CCR can deliver too much oxygen one minute and not enough the next; both harbingers of a bad day at the office for any diver. The little chemistry set that extracts carbon dioxide from the breathing gas can suddenly stop working for all sorts of reasons; most attributable to user error, and again bad news all round. The unit can leak a little making breathing an awful chore, or it can leak a lot, flood and cease working at all; both of which are good reasons to bailout and go home with one’s tail between one’s legs.

All this of course comes as a real eye-opener to the experienced open-circuit diver who has been diving the same kit configuration since Reagan was in the White House.

My other eye was opened by our CCR instructor, a good friend who for that reason alone cut me and my buddies zero slack during the whole week we worked with him to earn our certs on the Pelagian manual CCR we had opted to buy.  He pushed us relentlessly and continuously picked up on any fuzzy logic we fell into using. He watched us with the eyes of a caffeine-crazed hawk as we prepared our units for our underwater escapades; and once in the water we were on a very short leash and ANY moment of distraction or deviation from our plan resulted in yet another simulated failure and drilled contingency action. In short, he treated us like the rank novices we were and took no account of the combined 30 or so years of technical diving experience, and technical instructing we had between us.

Actually, that’s a lie. He did make a special mention of all those open circuit dives we had made. And that was what brought things into focus. “You guys,” he told us, “are swimming in dangerous waters.” He explained that we had to understand and believe that we were right back to where we were when we first started diving open-circuit scuba. We had to plan and dive beginner dives again and not be tempted to think that it was ok to dive to 60 or 70 metres because we’d done that on open-circuit a thousand times.

“It doesn’t matter much,” he said, “how many dives you have or where you’ve been on open-circuit. That was the stone-age and is all in your past. You are starting with a clean slate now, and it’s important you learn to paddle around in the shallow-end of the pool before you attempt to swim the English Channel!” (He’s a Brit.)

Now here is the cool part. As soon as he let us loose with cards that said we were certified to dive without adult supervision, we starting to rack up the hours on the type of dives we had not done for years.

We went back to shallow wrecks we had ignored for more than a decade and a half. We planned weekends of multiple two-hour dives in sheltered little spots we would have swum right by if we had been diving open circuit. We relearned the simple pleasure of gradually working around a very much narrower comfort zone and competence level. We practiced bail-outs, we obsessed, we had great fun, and in the final analysis, we changed back to being a little more multi-dimensional in our dive planning and dive execution. I think it’s fair to say that becoming a weekend CCR diver, improved my OC skills.

Oh, and Truk Lagoon. Well, a story for another day, but we worked hard to build our competence and it paid off. What incredible fun to dive a CCR in that environment, even if we did opt to give some of the deeper wrecks a miss… you see, as far as the CCRs are concerned, we’ve only been diving a year.

Some thoughts about cave training…

First off, I need to declare a bit of a conflict here: Since I am a tech instructor and more importantly work for a training agency (and we do have cave diving courses on the menu), my take on certain aspects of “diver education” are bound to be biased. But all that taken into account, the primary message goes something like: If you want to dive caves, get trained. Simples, right?

In my opinion, cave diving is the oldest and purest form of technical diving. A whole lifetime ago, when I lived in England, I was a dry caver and heard about a small group of nut-bar pioneers who were making pushes through sumps in the Mendip Hills on scuba. At about the same time in the USA, a similarly labeled group of local lads where exploring the network of caves that honeycomb Florida’s North-western quadrant from Tallahassee in the north, south to Hernando County. These folks wrote the rules for extreme diving and 30 years later many of the techniques and kit modifications that they learned by trial and error, have become the gold standard for tech divers around the world.

One of the early gifts from cave diving to the rest of the tech diving community is accident analysis and specifically a shortlist of things to help keep divers safe.

  1. Seek proper (appropriate) training
  2. Maintain a continuous guideline to the surface (safety)
  3. Work within proper gas management guidelines
  4. Observe depth limitations
  5. Use appropriate, well-maintained kit

Over the years, those five points, whose authorship is attributed to the late explorer Sheck Exley, have been refined and developed to take changing attitudes and different environments into account.

Regardless, these guidelines remain a pretty good first step in the process of risk management, and they form the basic structure for building a modern technical diving course.

In case anyone is interested and for the record, the current interpretation of Risk Management is the identification, classification, avoidance and mitigation of risk with regards: Attitude, Knowledge, Training, Gas Supply, Gas Mix, Exposure (the combination of Decompression and Depth), Equipment, and Operations. These are expanded a little from that original list but certainly owe a lot to it.

Anyway, in North America, the oldest technical agencies are the two originally formed to teach cave diving to local divers. The NSS-CDS (National Speleological Society Cave Diving Section) and the NACD (National Association for Cave Diving) have been offering structured overhead courses to punters for over a generation. They are both based in North Florida. They both have instructors operating in Mexico (another hot-spot for cave diving), and the Caribbean, and so by default essentially focus operations on North America. The global situation involves some other agencies such as IANTD, NAUI, TDI, CMAS et al. And today, cave training is available through lots of channels.

Bottom line, there is no excuse NOT to take training if you are interested in diving caves.

There seems to be a sort of consensus among the major agencies and the process of earning a full cave diving certification takes about eight days and is broken into three or four steps: Cavern, Intro, Apprentice, Full. There are “post grad” programs that teach more advanced techniques like scootering and diving with stage bottles, sidemount diving and so on but the vast majority of certifications fall into those first four categories.

Actual standards and outlines vary a bit from agency to agency but the outline from NSS-CDS runs like this:

Cavern Diver As originally conceived, the Cavern Diver course was a recreational diving course, taught to recreational divers using basic recreational diving equipment. It was assumed most participants had little interest in penetrating caves beyond sight of the entrance. Today the need for that sort of a program has diminished. With readily available cavern diving sites in north Florida, such as Ginnie Spring and Blue Grotto, and the system of guided cenote tours in Mexico, recreational divers don’t necessarily need to take a complete, two-day course in order to enjoy a safe cavern experience. What is more common now is to use the Cavern Diver program as the first step in the complete eight-day Cave Diver curriculum.

It is where we introduce students to basic cave diving skills, such as equipment configuration, guideline and reel use, and specialized buoyancy control, body position and propulsion techniques. It is also a way to screen students to make sure they possess the necessary abilities before allowing them in the fragile cave environment.

Basic / Intro Cave Diver This is where students begin making actual cave dives — under some fairly strict limitations. By limiting penetration gas to roughly 40 cubic feet, avoiding decompression and prohibiting any sort of jumps, gaps or complex navigation, we allow students to focus on things like basic dive planning, communication and emergency skills. Students who want to gain limited cave diving experience on their own, at the completion of this program, may do so — provided they understand that the cave community will be keeping them on a fairly short leash.

Apprentice Cave Diver By the time students complete the Apprentice level, we will have covered most or all of the academic knowledge and emergency skills required for full Cave Diver certification. Students may receive a limited introduction to decompression diving procedures, as they pertain to cave diving, and will make some simple explorations off the main line. It is at this point that students are ready to gain some more realistic cave diving experience on their own, if desired. Nevertheless, they are expected to keep all dives well within the limitations of their overall experience.

(Full) Cave Diver The final step in the process, the focus here is on gaining additional practice of all fundamental and emergency skills, under more challenging conditions. Students are expected to demonstrate their readiness to be full-fledged members of the cave diving community.

Although a total of 16 training dives is required to reach this point, it is not unusual for students to have made many more practice dives on their own before full Cave Diver certification.” One of the first questions most divers have about cave training is what will I get out of it?”

ANY technical training is designed to challenge participants and to show them exactly where the borders of their comfort zone are. This is very true of a cavern or cave course. Other side-effects would be greatly improved basic skills; for example, progress in a diver’s mastery of buoyancy and trim, situational awareness and emotional control are big indicators for an instructor that someone is “getting it.”

AND of course, a cavern/cave class will take you to places that “normal” folks just don’t get to.

The next pieces of the puzzle of course are to decide where to take training and with whom.

Where is easy: Train where you are going to do the majority of your diving. Cave diving in the Yucatan is a whole order of magnitude different to cave diving in Ontario or Wisconsin. France is different to Brazil. North Florida is not the same as Australia. They all have their moments.

If asked, the default location that gets my thumbs-up is always North Florida. There are a couple of reasons. First would be the variety of caves. There are little tiny ones that you have to crawl through pushing tanks ahead of you; and there are huge passages that could swallow a hockey arena (whoops, Canadian reference. Sorry).

The second reason to train in North Florida is the quality of instruction. There used to be about three cave instructors I’d recommend but that list has grown to about 30. Some are Brits who fly in just to teach a class; one is Italian; one German; most are Yanks and Canadian; and a couple are even real Floridians.

One thing that is a constant challenge is weeding out the wanna-be instructors from the real thing. Rather than publishing a list of names and forgetting someone, here are eight questions you can ask.

1. How long have you been cave diving and how many cave dives do you make for yourself outside of the training programs you teach?

2. Do you teach full-time or part-time?

3. What other programs do you teach besides cavern and cave?

4. What kit configuration do you use and teach your students to use and why?

5. Can you give me a typical course schedule including dive sites and dive profiles

6. What specific changes do you look for in students before you sign off on their certs?

7. How many students did you fail last month, and how many did you pass?

8. What should be my primary take away from your course?

Cave diving is what I do for fun and relaxation with a handful of special mates, when I want to get away from the dive industry. Ironic maybe but cave diving feels more comfortable and secure than any other type of diving… which is probably why I have managed to resist the temptation to teach it!

When someone asks which cave I like the best, there’s really no answer. I like them all. There are certainly some that I will go out of my way to dive.

When I got word that the Eagles Nest — a deep and massive cave system off in the woods near Florida’s Gulf Coast — was being shut down for an indefinite period about 12 or 13 years ago, I literally left a birthday party early (mine) drove to the airport in Toronto and flew down to Gainesville and a mate waiting for me with a set of twins pumped full of trimix and three decompression cylinders. Next evening, I flew home. The Nest reopened years ago and I occasionally go back, but of the deep caves in that area, strange to say, it is not my favorite. Diepolder II gets that vote.

The entrance to # II is a small pond in the middle of a Boy Scouts of America Sand Hill camp ground just off Highway 50. At the bottom of the pond and its pale blue water is a fissure in the limestone that is wide enough for a diver in back-mounted twins to drop down (head-first) starting at about 15 metres to around 55. At the bottom, the cave opens up into a gallery which on the downstream side is about 40 metres from floor to ceiling with depths of 100 metres or more. Really a very cool dive.

Jackson Blue is another real favorite.

Its entrance is directly below a diving board at the business end of Merritt’s Mill Pond in Jackson Blue Springs Park, which is a few kilometers from Marianna up near the Florida / Alabama border. Yep, really the entrance is directly under the concrete platform that houses the dive board.

This cave is not deep — the deepest part of the main passage is about 30 metres — but it is long — about 3 kilometers at last count — and has plenty of little nooks and crannies to explore. JB is probably best known as a scooter cave. Lots of visitors fly through the first five to six hundred metres with the throttle wide open.

That first section of the cave features a passage that is wide, smooth and straight; perfect for flying in formation and a great spot to practice handling a scooter. The next section — probably from the Hall of the Mountain King on to the Banana Room or Stratosphere — seems to have the major pulling power to bring divers to this cave; however, last November a buddy and I spent a total of about seven hours on CCR playing around in the first couple hundred metres of the cave and had an absolute blast. I guess the object lesson is not to overlook the familiar when rating caves. On that score, JB is a real winner.

Florida’s caves are not decorated with Speleothems — no pretty flow-stones or drapery, no soda-straws, stalactites or stalagmites. To see these, one needs to venture a little south east to the Caribbean or west to Mexico’s Yucatan Peninsula or a long way south to Brazil.

The easiest decorated caves to get to, at least from my home a little north of Toronto, are in the Bahamas, and if pressed, this might be the one spot I would choose to go to for excellent cave diving year round above all others.

If you are making a list, Abaco Blue Hole, Dan’s Cave and Owls Hole are places I would like to get back to, tomorrow if possible. Send money to…

OK, so those are a few of my favorites, how about yours?

Dive Report: Truk Lagoon, February 2010

Right up front let’s establish the parameters. One of the major reasons for Erik, Dave and I to get trained on and build experience on the Pelagian DCCCR was this trip. We wanted a simple, manual unit that could pack up in a small dive bag and be used almost anywhere in the world. The Truk trip was to be the acid test.

Pelagian in Truk LagoonAs with any long-distance dive trip offering hope of a successful conclusion, this one was planned well ahead. A tactic made more necessary since Odyssey – our 40 metre live-aboard – books dedicated group charters two to three years in advance. Frankly, time dragged for a while, but then the last six months somehow disappeared in a wild flash of various activities; some even connected to the trip.

What I mean to say is, despite of all the planning and worrying and preparations, this one kind of crept up and surprised us.

One bonus of having had a long lead time was that all the vagaries of diving CCR were worked through almost a year before our departure date. I’d met with Cliff Horton (the booking guy) at BTS the March before. I ordered the same scrubber material we dived at home, and found out what tanks would be available to us.

Although promoted as CCR-friendly, our group was mixed about 50-50 between OC and CCR and the only herding-cats-exercise was trying to coordinate everyone’s demands for tanks and gas mixes. This chore dragged on somewhat and in the final weeks I determined it better to ask for forgiveness rather than permission; that is, I ignored some of the less critical demands. However, kept front and center was the requirement for everyone, OC and CCR, to have something appropriate to breathe first thing on our first day. Other needs could be worked out after that. Also important was to make life easy as possible for the crew. It made sense that if the process of getting things ready for us could be streamlined, we would store up brownie points to trade for favors later.

Pelagian DCCCR in Truk LagoonYou should know that getting to Chuuk International Airport is a logistical exercise worthy of a TV reality show. Last minute changes also created challenges. My personal saga began early morning on Thursday in West Palm Beach, Florida instead of from my home airport in Toronto; Erik and Dave got an early morning call ON departure day telling them their flight from Rochester to Newark to hook up with their connection to Honolulu was canceled; they traveled on a different airline to Hawaii via Chicago.

However, things somehow worked out and instead of meeting in the President’s Club in Newark, we met up in the lobby of the Ohana Honolulu Airport Hotel to enjoy an eight-hour layover. Two things the traveler should know about the Ohana Airport Hotel:

  1. Do not eat the chicken caesar salad. It takes like cardboard dipped in printer’s ink sprinkled with budgie shit. And I am being diplomatic here.
  2. The staff are aware of the kitchen’s short-comings and at mealtimes are running scared and hard to find

In 1969, Jacques Cousteau and his team of happy pirate scientists and explorers dropped anchor in Truk Lagoon. It’s not clear if JC was the first to mount a dedicated expedition but close on the heels of the broadcast of his 1971 television documentary about the lagoon, its abundance of wrecks, and the history of Operation Hailstone, the place became a scuba diving paradise.

Cousteau had it easy though. I wonder how the viewing public would have taken to the notion of visiting Truk Lagoon if his original movie had been honest about the boredom of a half-day spent island hopping across the Pacific from Oahu / Honolulu to Weno / Chuuk with stops at Majuro, Kwajalein, Kosrae, and Pohnpei; each complete with a security inspection of the plane’s cabin. This phase of the journey reminded me of an episode of the Twilight Zone where the passengers are in purgatory but do not realize they have snuffed it. On a positive note, we had exit row seats, plenty of Cliff Bars and at least there were no crates of chickens in the cabin.

Pelagian DCCCR in Truk LagoonWe arrived in Chuuk mid-afternoon Saturday with all our bags but slightly disoriented. I would like to have blamed alcohol or drugs, but the culprit was the International Dateline. Well known, but poorly publicized in the travel guides; any journey that crosses more than a dozen time zones and incorporates rolling forward the date on your wristwatch magically flushes the human brain with the hormonal equivalent of Drano®

One other snippet of information travelers to this part of the world need to understand; this is the third world. Nothing you will see travelling through the countryside between the airport and your hotel remotely resembles a paved highway, roadside restaurant, CVS pharmacy, Winn Dixie, or Starbucks. Chuuk is uncomfortably poor. There is no veneer of gentility or quaintness hiding that poverty from the sensibilities of western tourists. There is no local tourist association or board of trade covering up the patina of rust and ruin with a lick of colorful house paint. Shanties line the potholed mud road. Collections of abandoned motor cars and pickup trucks punctuate stands of banana trees and flowering shrubs. Ugliness and graffiti dots walls and doorways. The island of Weno – the main island and Odyssey’s home port – has nothing in the way of tourist infrastructure outside of a couple of hotels. It seems that apart from wreck diving, the island offers nothing to pull tourists from passing planes and boats. The foreigners one does see are either wreck divers or missionaries; and there is little to distinguish one from the other except the messages on their T-shirts and the over-sized bling around the Christians’ necks.

Our “hotel shuttle” dropped us and our bags at Blue Lagoon Resort and our rooms were dry and cool, faced the ocean, and did not have restricted leg room. First order was a shower and a whole can of soda.

We were not scheduled to board Odyssey until 17:00 on Sunday so we had slightly longer than 24 hours to relax and acclimate and sightsee. The sightseeing was completed before supper and so we were able to spend a day lying around, checking TSA had not fiddled with our rebreathers too much, and sorting out wet from dry bag articles before boarding our home for the next week.

A quick word about rebreathers and airport security. Film-maker, explorer and CCR guru, Jill Heinerth, came up with the idea of labeling dive gear, especially rebreathers, with a note explaining the various suspicious bits and pieces in a manner that makes sense to the average TSA operative. I created a version of Jill’s template for our group. It featured TDI and NOAA logos, a breakdown of CCR components including the head and “gas” sensors (NEVER mention oxygen to anyone in the security industry), and the statement that the life-support system it describes offers no threat.

Throwing one of these notes into a dive bag is a great proactive move for anyone travelling with a ‘breather. Prior to our Truk trip, I had a conversation with the Canadian version of a TSA team leader while carrying the scrubber head of a Pelagian CCR through security at Toronto’s Pearson Airport. He read the official looking document, asked me if I worked for National Geographic and walked me through the screening area with a thank you, have a nice day.

Following a very laid-back day as guests at Blue Lagoon, and right on schedule, Odyssey’s tender picked up our baggage, and its skiff picked up the 11 of us and delivered us to the boat at anchor in the lagoon about 300 metres off shore.

The deal with our charter was its billing as a “Tech Week” the major difference between this and a non-tech week was that for us, nitrox fills and surface-supplied oxygen (fed to a bunch of second stages hanging off a solid deco bar under the transom at about 4 metres) would be free. Tech week also focused on a selection of dive sites in the 35 to 60 metre range.

What was the same and a constant on Odyssey charters was the cleanliness and size of the state rooms (flat-screen TVs and DVD players in each room is a nice touch) the level of service and hands-on help (high and appropriate), the quality food (most of us gained weight), and of course, the visual appeal and historic significance of the diving itself.

First impressions of the handful of our group who had not dived off Odyssey before was, Wow! This was closely followed by supper.

The majority of the wrecks in Truk are lined up in formation around the Dublon, Eten, Fefan and Uman Islands. The Fourth Fleet anchorage was just on the western side of Dublon and the repair anchorage to its east. There are many dive sites there. The wrecks on our agenda included: the Nippo, Hoki, Rio de Janeiro, Amagasan, Shotan, Fujisan, Shinkoku, San Francisco, Heian, Kensho, Nagano, and a couple more deepish ones that Dave, Erik and I did not dive and I did not take note of.

The pool opened immediately after a post breakfast dive briefing early on Monday. Another thing about tech week was that we punters were free to dive as we chose with the only restriction to be back for lunchtime. We took full advantage of this.

The water in Truk is warm (28 degrees by my bottom timers) and we had visibility that ranged from a few metres to about 30. We experienced little or no current and overall conditions were mild, except…

The trade winds blow in February and we were faced with “big seas” on several days. However, big seas in Truk Lagoon are manageable; especially when one dives off a big boat. The most daunting thing is the Odyssey’s tendency to put her head into the weather and shake her tail like a cat watching a bird feeder. This increases the task-loading of anyone hanging out at the deco bar to off-gas; and this was certainly a factor in our dive planning. In short, we planned to use the deco bar and the gas it offered only as part of a bailout plan – a contingency that did not arise for any of us. We carried jon-lines and finished our decompression either close to the mooring line or on the shallowest part of the wreck. When those obligations were finished, we swam to one of the stern ladders and grabbed on.

Pelagian DCCCR in Truk LagoonWe three Pelagian divers dove as a team. We had Franck and France (inspo divers) with us for some dives but not all, and sometimes we started out with OC divers but our plan on the shallower sites was to pull one long dive rather than do two shorter ones; and that meant OC divers did not have the gas to stay with us for two hours or more of bottom time.

Odyssey does not offer trimix, so we dived air diluent and oxygen in 4 litre (30 cubic foot) cylinders with an 80 cubic foot aluminum cylinder of ENA30 as a side-mounted bailout.

My comfort with CNS toxicity, specifically 24-hour or daily CNS limits would not cover the space between absolute zero and the freezing point of helium, therefore on deeper dives, we were severely restricted by the inability to run an oxygen set-point during bottom times lower than 1.3 to 1.35 bar. This caused some issues with our planning later in the week and we either passed on deeper dives or pulled OC-type bottom times.

For the record, 24-hour CNS limits are among a handful of issues that seem to have passed the tech community by. Bill Hamilton, who wrote the book on the topic, advises divers to be particularly mindful of and conservative with 24-hour limits. Therefore if the 24 hour limit of a 1.1 set-point was 270 minutes (which it was and still is) we were careful to plan our running exposure over the whole week of diving well within that limit.

OK, the units themselves performed like troopers. We took three units halfway around the world and had precisely zero problems. No cell issues, no battery problems, no software to kick up a fuss, nothing broken or misplaced, and no lost time fiddling with distractions. Score a huge positive mark.

Andy Fritz’s design allowing for the Pelagian to use any sized bottle without the need to buy a special frame or to make any adjustments – other than the cam straps – is a brilliant innovation for a travel CCR. The fact that we did not need to carry bottles with us, and that the boat could provide us with a bottles that held enough oxygen and dil to last for several dives, cut our prep time considerably. On a live-aboard offering several dives a day, this is a very nice bonus, so score another big positive point.

The unit’s compact profile and lightness – a real boon for airline travel – also translates into comfort in the water and stability while moving around on deck and on the dive platform. This trip was the first time for any of us to dive the unit in a wetsuit and of course, compact and light really shine when all you have on is booties, fins a mask and a 3 mm suit and hooded vest.

Erik and I use a HOG single-tank 34 pound lift wing. This configuration with a steel backplate and 2 kilos of lead balance weight provided enough lift with a single aluminum stage; but I would suggest more lift to carry additional bottles safely.

The dives themselves were spectacular. The wrecks are littered with the detritus of war; the holds filled with fighter aircraft, tanks, bulldozers, railroad cars, motorcycles, torpedoes, mines, bombs, boxes of munitions, radios, spare parts, and god only knows what else. Hulls, decks and superstructures are coated with sponges, corals, and invertebrates. Tropical fish, turtles, rays, sharks and jelly fish completed the picture. My logbook contains a fair number of expletives, all of a very positive nature.

I have dived in Truk before on open circuit, and it too was spectacular. It also presented less logistical challenges. No matter how you cut it, lugging a rebreather, even one as portable as the Pelagian, across 15 time zones had better have a payoff that makes up for the effort.

In my opinion, it did. Dave, Erik and I made dives that would have been impossible on OC. Always mindful of the limits of our bailout and experience, we pulled nothing epic, but a two and a half hour bimble at 35 metres would simply be impractical wearing doubles. We explored engine rooms for 40 – 50 minutes at a time. We went places where exhalation bubbles would have trashed the visibility in minutes, but exited without leaving a trace of silt. We were warm. Our dives were peaceful, and our decompression short. We left the water feeling great and had to invest little time setting up, refilling, disinfecting and rinsing our rebreathers.

I will return to Truk and so will the Pelagian. It will also be my companion on lots of other adventures because this trip underscored two things:

  1. diving CCR on a multi-day trip offers huge benefits
  2. the Pelagian is a very practical solution to travelling with a CCR

All photos are copyright Bill Downey

For information about Odyssey, visit http://www.trukodyssey.com/

The Six Basic Skills: Number Two, Situational Awareness

Situational AwarenessOf all six basic skills, Situational Awareness (SA) is my favorite skill to teach and coach. And, like Breathing, it is one that is virtually ignored in mainstream diver education programs, yet it is without argument a critical part of safe diving at any level; particularly in technical diving.

Put briefly, SA is the chess-player’s skill but applied in an environment where checkmate can result in real physical harm, and not just a wooden game piece being knocked over sideways.

SA has been a core concept in high-stress operating environments, such as the military and aviation, for many years. SA skills support the ability of individuals operating in this type of environment to handle complex and rapidly changing situations in which informed decisions need to be made under tight time constraints.

The simplest definition I’ve found is that SA is being aware of what is happening around you and understanding how information, events, and your own actions will impact your goals and objectives, both now and in the near future. Sounds exactly suited to the underwater realm to me.

definition of Situational Awareness

The most authoritative voice in the study and application of SA is Mica Endsley, and I would suggest you find a copy of her white-paper: Toward a Theory of Situation Awareness in Dynamic Systems if you are interested in digging deeper into SA theory and practice. But it’s not required reading. As Endsley says, prehistoric humans probably had an innate understanding of SA in order to survive so the basics are hardwired into us all. We just have to work at pulling the skill out from behind all the civilized creature-comfort complacency that prevents us from bringing it into the game at playtime.

Endsley defines SA as, “the perception of elements in the environment within a volume of time and space, the comprehension of their meaning and the projection of their status in the near future.” And she breaks SA capability into three levels:

1/ Perception – of cues and stimulus from the environment
2/ Comprehension – involving the integration of information to facilitate relevance determination and sense-making
3/ Projection – the ability to forecast future situation events and dynamics

In addition, Endsley highlights the importance of temporal factors to SA, for example in understanding:

    a/ how much time is available until some event occurs or some action must be taken
    b/ the rate at which information is changing currently to help project future state

Divers need to be on top of all three levels, and are required to make decisions in an environment where time is always in short supply.

Situational Awareness DiagramDeveloping SA, and being “good at it” is important, and a learned skill just like playing chess. As divers, we can we improve our SA through a few very simple techniques.

1/ Divide the dive into manageable segments to limit task loading
2/ Set way points and do not become distracted
3/ Track actual progress against dive plan
4/ Make allowances for Murphy
5/ Make adjustments within the constructs of the dive plan and only within the dive plan
6/ Identify problems early. This is key. If something appears to be going off the rails, it probably is. Do not ignore it!
7/ React immediately or before! Seriously, act to correct a minor infraction before it grows into a problem.

As a diver’s SA becomes more attuned, he notices more about his surroundings and situation.

Typically, a novice diver has a limited awareness of self, some awareness of equipment, but can easily loose track of his buddy and be taken off guard by changes in his surroundings. Just by being in the water, he is task-loaded and his SA drops off to zero. If you are going to function as a good technical diver, your SA has to be at a seven or eight at least! Be aware of yourself; how you feel and how comfortable you are. Be aware of your kit. Does it feel right and is it functioning correctly? How about your buddies? What’s happening with them; does everything look as it should? And finally, your surroundings; are they what you planned for? Is there anything out of place or not as you expected?

Situational Awareness really boils down to being alert and cautious. For example, a technical diver only looks at his SPG to confirm how much gas is left in his cylinders; elapsed time, and his work level will already have informed him what reading to expect. Situational Awareness also informs a good diver if a team member is uncomfortable or stressed by reading his body language and small hints like breathing rate (assuming open circuit of course). It will also allow him to notice that a team member has a piece of kit out of place before that team member does.

LACK OF SA is the most common reason for a student at this level to fail his course!


Technical Diver's Credo

Something worth remembering. Please write this down. Any diver can thumb any dive for any reason… no questions asked.

During our time together, if you feel uncomfortable, stressed or feel that things are not going as planned during a dive and want out, do not hesitate to CALL THE DIVE.

There are a number of mistakes a diver can make at this level. One of the most SERIOUS is to put-off calling a dive.

Some random thoughts on teaching buoyancy… one of the six skills

I have to be a bit pedantic here… in the real world outside of diving where there exists some semblance of respect for the constructs of everyday science, there is a place where there is no neutral, positive or negative buoyancy. It is a happy place and I like it there.

Neutral, Negative, Positive. These are outcomes and not states of buoyancy. I know it is a hard habit for divers to break – like referring to the Gas Laws as physics when they belong in the realm of chemistry – but I would suggest at this level you should understand the distinction.

Things float, things sink, things maintain their position in the water column: Which of these outcomes corresponds to our state as a diver, depends on the balance between gravity and buoyancy.

It will help us understand this skill more completely, I believe, if we first understand that balance is the variable while gravity and buoyancy are the constants.

So just to recap, there is no such thing as negative buoyancy; that is like saying a color is whitish black or a cup of coffee is Hot Cold.

Positive buoyancy is redundant term at best. But it could also mean that a buoyant force is optimistic; which is just plain wrong.

Neutral buoyancy assumes some all-powerful entity has suspended the Laws of Physics.

Any questions?

Custom Mix vs. Standard Mix: Best Mix is a question of balance

Based on an article written in 1998 with additional material adapted from various talks and presentations made from the mid-1990s to the present

“We’d hold a chord for three hours; if we could.”
Attributed to John Cale, Welsh musician and co-founder of Velvet Underground, born in 1942

Here is a simple question for all the experienced open-circuit technical divers in the audience: what gas would you use for a dive to 45 metres (about 150 feet)? How about  one to 85 metres followed later in the day by another to 35 metres (that‘s about 280 feet and 115 feet respectively)? Would you carry decompression gases for every dive? If so, one gas, two gases, lots of gases? Would your answers change if the water around you was warm or cold; and how about different currents and turbidity? And finally, what flavors of decompression gases do you think are best; pure oxygen, high-test nitrox, how about an oxygen-rich trimix of some sort; or maybe heliox?

Picking suitable gases for complex dives (whether shallow, deep or in between) is a balancing act. The objective is to find the best overall solution to manage Oxygen Toxicity, Inert-Gas Narcosis, Decompression Obligation, Expediency, and a handful of other concerns.

The difference between choosing an optimal gas and one that isn’t depends to some extent on the parameters of the dive; and what I mean by that is there is more flexibility and tolerance for sloppiness on a 35 metre dive than one to 85 metres. The price for using a less than perfect gas for a 35-metre dive might be a bad dive. But for a dive to 85 metres that price runs through a spectrum of possible outcomes that start with post-dive fatigue, pass through severe narcosis and unsuccessful decompression all the way to central nervous system toxicity, serious injury and death.

That is why divers should be able to provide answers to ANY question concerning the flavor of gases best suited for their dives without ambivalence; and with something approaching logic and common sense to back up their choices.

There are thousands of different blends of gas available to recreational divers, but the component gases to make all these blends are few and they are simple: oxygen, nitrogen and helium. There are many other gases used in military, scientific and commercial applications, but they are not readily available to recreational divers because of their scarcity and associated high cost — neon for example —  or, like hydrogen, are very difficult to handle because of bad habits like exploding at the most inopportune time.

Argon has a minor walk-in part inflating dry suits in cold-water recreational diving. The jury is still out on its benefits compared with garden variety air, but regardless of that debate, recreational divers do not use argon as a breathing gas.

So there are only three gases, and with these blended together in differing proportions we can make a staggering array of nitrox, trimix, heliox, and heliair. Alas, this in itself seems to be a problem for some folks and one’s choice of gas or gases can draw heated and heavy debate in some circles; something like the Great Schism but without the sensory relief of gold inlay and burning incense or an immutable core argument such as Papal infallibility.

And as with the 11th century Holy Catholic Church and the black and white outlook begat by any closed-minded dogma — there are two strongly opposed schools of thought concerning the selection of the right gas for the job. One side supports so-called standardized mixes and unremittingly refuse to dive anything other than a small collection of prescribed blends; while others refuse to see ANY benefit to standardization swearing instead on custom mixes.

Custom mixes are blended specifically for each dive with the proportions of oxygen, helium and nitrogen tailored for the specifics of the dive. This requires new calculations for mixing and new decompression schedules for every dive; a sort of bespoke solution. Standardized mixes is more like buying clothing off the rack. The choices with standardized mixes are limited to a handful of blends that work over a range of depths, typically a range of 12 to 15 metres or more. Examples of standard mixes are the two nitrox mixes promoted by NOAA (containing 32 and 36 percent oxygen) and the small selection of gases used in the exploration of Wakulla by the WKPP and later adopted by the non-profit group spun off from that project; Global Underwater Explorers (GUE).

Happily for those who find little time for circular debate, there is a third, more pragmatic approach that borrows from both schools. It uses standardize mixes and custom blends depending on circumstances; kind of like wearing a bespoke jacket with jeans. I put myself firmly in this camp.

Specifically, the advantages of standard mixes come to the fore on open-circuit dives from 10 to about 60 metres (30 – 200 feet) but custom mixes, custom back mixes, provide a better solution on deeper dives. We’ll discuss the merits and failings of each method in more detail as we progress, but for any of that discussion to make sense we have first to understand a little more about the gases themselves; and their distinctive characteristics, and behaviors.

Oxygen is highly reactive; a chemical term that means this gas is the universal buddy and will bond with almost anything. Oxygen itself is not flammable but requires careful handling because most things will burn fiercely — oxidize — at the drop of a hat in an oxygen-rich environment including the filling station’s plumbing.

Scuba gear used for mixing and delivering hyperoxic gases cleaned of hydrocarbons, fitted with oxygen compatible components (including special lubricants), and be carefully stored and used so as to prevent contamination with dirt and grease of any kind, even the leftovers of a bacon and fried egg sandwich.

{SIDEBAR} Oxygen molecules are so “friendly” that they cram up nice and tightly when being compressed; so at a given pressure and temperature, there will be a greater quantity of oxygen than either nitrogen or helium. This is useful information for those divers who blend their own gases, and who are interested in accuracy. Without fudge factors or calculations modified via Van der Waals’ or Beattie-Bridgeman equations that take into account the different compressibility of component gases,  mixes will have higher than planned levels of oxygen in them. In the field, fudge factors are a workable solution. Using simple math to calculate the fill-pressures of each component gas and then cutting back a little on the amount of oxygen, does work. But with the proliferation of gas-blending programs that run on smart phones, “doing it longhand” seems pretty retro and in the general scheme of things, unnecessary outside of a classroom situation. {/SIDEBAR}

For those of you who like details, oxygen has a density of approximately 1.43 grams per litre at normal room temperature and pressure (20 degrees, one atmosphere).

Of course oxygen is what we breathe and is the active ingredient in air and necessary for our body to function. Divers must be extremely careful to take into account both low (hypoxic) and high (hyperoxic) partial pressures of oxygen. Our bodies need a partial pressure of at least 0.16 bar to sustain activity (about 0.18 if we hope to swim or make sense of the world). Less oxygen partial pressure than that and the brain begins to shut down and, unless things change rapidly, there is a chance we will pass on to our reward in heaven.

High oxygen partial pressures — that‘s to say anything more than the approximately 0.20 bar we are all subject to at sea-level in normal air — have the potential to cause a diver grief.  And that grief arrives in three varieties: Pulmonary, Ocular and Central Nervous System Toxicity.

Oxygen limits deserve their own special discussion (Editor’s Note: See previous chapter), but forgive me taking the time now to restate some cautions and to set a couple of parameters that seem to be generally accepted as the norm among the open-circuit technical diving community.

Most recreational technical dives are of a depth, duration and frequency that compels oxygen planning to focus completely on Central Nervous System (CNS) toxicity. It is prudent to make a point of managing closely both single-dive and multiple-dive or 24-hour CNS limits using NOAA/Lambertsen tables. Probably worth noting here that diving experts in this field, such as Bill Hamilton PhD, remind divers consistently that the interpretation of CNS toxicity limits and the “extrapolations” used in the tech community to manage a dive team’s approach to those limits (the CNS Clock specifically), have no foundation in hard data or science!

During a presentation at the DAN Technical Diving Conference in January of 2008, titled CNS Oxygen Tolerance: The Oxygen Clock, Dr. Hamilton’s take home message was be conservative and modify behavior to lessen risk however you can — don’t push limits, keep carbon-dioxide levels low, use intermittent exposure to pure oxygen. Hamilton also pointed out several instances where over-the-counter meds. seem to have played a role in CNS episodes recently.

The most prudent general advice then is to plan dives so that CNS loading is well below published limits for single dives and 24-hour exposure. Most technical divers are comfortable with a 1.6 bar oxygen pressure briefly during decompression (Hamilton suggests a few minutes at this level then move up the water column to drop it to 1.5 or less). Once again, the best practice seems to be to run bottom gases much leaner than operational limits common to sport diving exposures and to adjust conservatism according to depth and duration. For example, for non-working dives to 40 metres (about 130 feet) or less, with bottom times shorter than 40 minutes, 1.4 bar oxygen is generally accepted as the norm. For deeper or longer dives requiring long decompressions, it is common practice to cut the oxygen loading gathered from bottom time by dialing back the oxygen pressure to 1.3 or 1.2 bar. Deeper than 70 metres and 1.2 bar of oxygen is a generally accepted default. Following Hamilton’s advice, most technical divers find working with these variable limits helps to balance decompression obligation and toxicity concerns comfortably. As an aside, on closed circuit, 1.2 bar of oxygen with a variable partial pressure during ascent, is usual for most CCR divers on most dives.

If any of this is going over your head, you need to brush up on your basic nitrox theory! Anyhow, let’s continue to get some background on the other two gases bearing all the above in mind.

Nitrogen is a colorless, odorless, tasteless and mostly inert gas — lithium and magnesium will burn in a nitrogen atmosphere but for our purposes, nitrogen is close to chemically inert. It makes up roughly 78 percent of Earth’s atmosphere by volume, and for the trivia buffs, nitrogen is slightly less dense than oxygen (about 87 percent as dense) and at room temperature and pressure has a mass of 1.25 grams per litre. It is not quite as easy to compress as oxygen. At low pressures — less than 20 bar or so — the difference is minor but becomes more and more apparent at pressures commonly used to charge scuba diving cylinders.

Nitrogen is significant to scuba divers for a couple of reasons. As a diver descends and the partial pressure of nitrogen increases, more and more nitrogen dissolves in the bloodstream and from there diffuses into various tissues inside the diver’s body. Rapid decompression (specifically in the case of a diver ascending too quickly) can cause nitrogen bubbles to form in the bloodstream, nerves, joints, and other sensitive or vital areas, which in turn can lead to potentially fatal, and certainly debilitating, decompression sickness.

The other reason nitrogen is important is narcosis. On the surface, nitrogen is metabolically inert — we function just fine with it at these levels and just fine without it, but when it’s inhaled at partial pressures in excess of about 3.0 to 3.3 bar — encountered at depths below 30 metres —  nitrogen begins to act as an anesthetic agent. This nitrogen narcosis is a temporary semi-anesthetized state of mental impairment.

Judgment can  be compromised and reaction times slowed. For some divers, mild narcosis manifests itself as a benign sense of euphoria, and for others the effect is like the arrival of the four horsemen of the apocalypse. Narcosis has been likened to an alcoholic buzz, nitrous oxide (laughing gas), sedatives and having one’s head stuffed with cotton balls. At extreme depths, narcosis can cause hallucinations and  unconsciousness.

The intensity and perception of narcosis varies from diver-to-diver and day-to-day. Two similarly experienced and conditioned divers, using similar equipment and bottom gas, may come back from a dive with very different stories about what they saw and how they felt. To a third-party observer, they may respond equally appropriately to outside stimuli and conduct themselves with similar results, but during debriefing one may explain he felt narced while the other will say he felt fine. The next day, same conditions and same depth, the roles may be reversed. This begs a series of questions.

The biophysics of nitrogen narcosis are pretty much solid state. The actual changes made to the nervous system would seem to be a constant; and although not completely understood, are considered to be linear; that is to say, the deeper one goes, the more intense the effects.

There are some interesting studies suggesting that multi-day exposure to high pressures of nitrogen, lessens these changes (see sidebar), but even if we buy into this concept, it does not account fully for the dramatic variations in the risk and severity of narcosis that divers experience. The only logical explanation is that factors aside from nitrogen partial pressure play an important role in narcotic loading. These factors certainly include stressors such as cold, poor visibility, carbon dioxide retention, mental stress, task-loading, tiredness and poor cardio-vascular fitness.

Many divers, myself included, report that mental alertness is compromised diving in cold water and diving following a rough night’s sleep; in a cramped bunk on a boat in high seas for  example.

Another factor worsening the effects of narcosis may be mental pre-conditioning — divers who have been told that narcosis will be debilitating report severe narcosis at shallow depths than does the general community. The influence of this perception shift and other factors such as poor breathing habits (skip breathing) can make a huge difference to a diver’s enjoyment and ability to execute a dive safely.

We can therefore take as read that narcosis is a factor in diving and it’s as real as gravity. Its effects have to be accounted for during every dive. Each diver should develop a personal test for narcosis. Because of the nature of the beast, I like to run a little diagnostic from time to time regardless of depth and even when using trimix.

The classic “fingers test” is taught in many open water classes. It works like this. Periodically one diver will show her buddy a number of fingers. Her buddy‘s response is to show one less if five or more fingers are shown first and one more if that number is less than five. For example, if my buddy holds up nine fingers, I’ll display eight and follow that with an OK sign. I might then display three fingers and expect four back followed by an OK sign. If either of us makes a mess of the arithmetic, we suspect narcosis; and take the necessary precautions.

The best advice is for ANY diver getting into advanced open circuit diving to select a personal limit for nitrogen partial pressure and stick to it as rigorously as they do to an oxygen partial pressure. Time and experience may affect your choices — you may increase or decrease your nitrogen depth as you fill more logbooks — but do the in-field experiments and start doing the research now. For example, my personal benchmark in most of the waters in which I dive is 3.1 or 3.2 bar of nitrogen. I’ll put up with more if circumstances dictate, but this level —  about the same as diving air to 30 metres — is well within my comfort zone.

Helium heads up a select group of six elements aptly called Noble Gases. All are monatomic (hence helium’s chemical symbol is He and NOT He2), chemically inert (helium will not burn and bonds with nothing, even itself, under normal conditions), colorless (as a gas), tasteless, and odorless. For the record, the five other Noble Gases are neon, argon, krypton, xenon, and radon — more pub trivia for you.

Helium is second lightest and second most abundant element in the universe, and has a density of 0.1785 grams per litre, or about one eighth the density of oxygen, one seventh that of nitrogen. Its small mass and the small size of helium particles makes it an easy gas to move around — through dive regulators for example.

Because of this, filling one’s lungs with helium mixes at depth takes less work compared to air and nitrox. Low work of breathing (WOB) is a characteristic a trimix diving sometimes cited as a reason to use helium in bottom mixes for relatively shallow dives since WOB is a contributing factor to carbon dioxide production and build-up. And of course high levels of carbon dioxide cause severe complications to divers; from blinding headaches and increased susceptibility to narcosis, through lowered resistance to oxygen toxicity, loss of mental focus all the way up to unconsciousness and death!

While the physics suggests the drop in WOB with a helium mix would be measurable, modern high-performance regulators function pretty efficiency. Any additional carbon dioxide contributions from a regulator suitable for deep diving and used under normal dive conditions would pale compared to the levels of CO2 coming from poor breathing technique. In other words, if a diver uses good quality, well serviced regulators, but finds himself suffering from carbon dioxide headaches during or after diving moderately deep profiles (less than say 50 to 55 metres) or when swimming at a moderate pace, throwing helium into his mix is most likely only a Band-Aid solution. He should check out his breathing technique first!

Given all that, helium is used in recreational diving primarily as a diluent for oxygen and nitrogen. It is mixed in varying proportions with air, oxygen and nitrogen, or nitrox (usually the latter) to ensure that partial pressures of both oxygen and nitrogen at depth remain within tolerable levels. In other words, helium helps to manage oxygen and nitrogen toxicity.

Helium can make an appearance in both bottom mixes and decompression / travel mixes. Since helium is not narcotic and does not have any toxicity associated with its use in recreational diving, there’s no limit to how much of it one can use in a mix; at least from the toxicity and narcotic perspectives.

But in keeping with the axiom that there is no such thing as a free lunch, helium does exact a penalty.

Number one is that divers need to be aware of is the decompression curve for helium. Helium on-gases and off-gasses much faster than nitrogen — about two and a half times as fast. This has several advantages, but also throws up two general cautions. The first: divers breathing helium cannot make speedy ascents. A ballistic missile / breaching humpback whale impersonation on helium will get the majority of divers as bent as a pretzel. Helium divers have to control their ascent speed, and although that speed depends on a couple of factors, as a general rule a diver breathing helium will have to execute an ascent at variable rates; never faster than about nine metres (30 feet) per minute and at times around three metres or ten feet per minute.

Secondly, bottom mixes containing helium require stops deeper in the water column than dives of the same duration and depth using nitrox or air. Because of this, a decompression schedule (or computer) designed for a nitrox or air diving, is not a lot of good for a trimix dive. There are some exceptions as always, but a trimix dive (even a relatively shallow one) needs to be planned and executed with care.

Another caution with helium is that while it’s about one quarter as soluble as nitrogen in lipid tissues, its diffusion rate is much more rapid. In brief, this means that switching from a breathing mixture delivering a high helium content to one which delivers none, can cause “spontaneous” bubbling in certain soft tissues. This phenomenon is called Isobaric Counter Diffusion and can be a concern on deeper dives. For example, for the 85-metre dive mentioned in the introduction, I’d think long and hard about using a hyperoxic trimix rather than nitrox to begin my decompression.

And finally, helium does a rotten job of keeping heat where a diver wants it . Many open circuit divers complain that high helium content in their back mix “wicks away” heat from their body as they breath and makes them feel the cold more easily. Because of helium’s thermal characteristics, few divers intentionally use high helium content mixes — say above 25 percent helium — to fill their drysuits. And so for deep diving, a separate inflation system is the norm; another cylinder, more clutter, more potential failures.

Now that’s enough about gases, let’s talk a little about actually diving with them.

A good dive plan, ANY dive plan, begins with deciding what flavor of gas or gases to use; and then getting it blended or blending it yourself, analyzing it / them and making any necessary adjustments. A quick note on blending gas. With the right equipment and a little training and experience, gas blending is a remarkably straightforward process; about as easy as making toast and boiled eggs. Especially true when one opts to use a “standard“ mix. And this is one huge advantage of picking a mix and using it again and again; one get pretty good at mixing it, and given the methodology used is sound and constant, any margin of error becomes smaller and smaller.

What other advantages are there to using the same gas again and again rather than doing the custom thing every time?

Probably the most compelling for me is that I get to know what works for me. Logging a bunch of successful dives on the same mix, builds a dataset based on actual in-water experience. This experience is golden. Nothing compares to it and it tells me that the balancing act between decompression, oxygen toxicity, narcosis and thermal comfort went off as planned. The way I see it, every dive has a little of the crap shoot built into it, so working with the same mix again and again, eliminates one major set of variables.

But of course, what do we mean by the term standard mix? Standard by definition means something accepted as normal or widely used, and one could come up with a set of standard mixes of one’s own. But there’s really no need, because the grunt work has been done for us, and there are several variations in general use (see sidebar). However, it is a good idea before blindly following someone else‘s suggestions, to understand what logic is backing those suggestions up.

Let us look at the scenario for the dive to 45 metres mentioned in our original question. A standard mix for this dive could be a 21/35 trimix. This is, nominally at least, a blend of 21 percent oxygen, 35 percent helium, and the remaining 44 percent made up of nitrogen.  To calculate what partial pressures of oxygen and nitrogen this breathing gas will deliver at the dive’s target depth we could engage a mess of algebra; or we can make things a bit more simple and use ratios.

The calculate using the ratio method, first we need to know the total ambient pressure at 45 metres, which is 5.5 atmospheres or bar. Multiply 5.5 by 0.21, and we know that the partial pressure of oxygen (the gas that makes up 21 percent of our trimix) will be about 1.16 ata or bar. If we multiply 5.5 by 0.44 (the fraction of nitrogen in the mix) we know that the partial pressure of nitrogen at depth will be around 2.4 ata or bar.

Both partial pressure values for oxygen and nitrogen are well within normal limits. So this is an acceptable mix.
The standards that 21/25 is drawn from uses a nitrox 32 as the base mix. Let’s see what happens when we use a standard based on a nitrox 30 mixed with helium.

A dive to 45 metres is on the edge of the working depth for a 23/25 trimix. Doing the same ratio calculations we learn that this mix will deliver an oxygen partial pressure of 1.3 bar and a nitrogen load of 2.9 bar (both rounded up). Once again, both within normal limits.

As an aside, for a dive to 45 metres for 30 minutes and using the same decompression gas, both 21/35 and 23/25 net similar decompression obligations; bracketed a couple of minutes either side of an ascent time equaling bottom time (i.e. either side of 30 minutes making the total run time about 60 minutes).


STANDARD MIXES (using EAN32 and Helium)

Bottom mixes (depth ranges)
10-100 3-30m 33% Nitrox
110-150 33-45m 21/35 Trimix
160-200 48-60m 18/45 Trimix
210-250 63-75m 15/55 Trimix
260-400 78-121m 10/70 Trimix

Decompression mixes (MOD)
20 6m 100% Oxygen
70 21m 50% Oxygen
120 36m 35/25
190 57m 21/35

STANDARD MIXES (using EAN30 and Helium)

Bottom mixes (depth ranges)

3-32m 30 % Nitro
33-45m 23/25 Trimix
46-60m 19/36 Trimix
61-70m 16/45 Trimix


Decompression mixes (MOD)
6 m 100% Oxygen
21 m 50% Oxygen
40 m 30/25


Now let’s consider the 85 metre dive mentioned in the intro.  The Nitrox 32 standard suggests a 10/70 trimix. We will do the same ratio calculations as before. The ambient pressure at 85 metres is 9.5 bar, therefore the partial pressure of oxygen would be 0.95 bar and the nitrogen would stand at 1.9 bar (an equivalent air depth of about 14 metres). Also, this mix is hypoxic and will not support life on the surface and so travel mix would need to be used. This does not seem like the most efficient option since the range of depths served by this mix spans approximately four atmospheres or 40 plus metres! Now in all fairness, reason for this probably rests in the operational restrictions of the environment for which these standards were developed: supported push dives in a deep, unexplored cave. The divers laying new line, had very little idea what depths they would encounter. They knew the cave was vast and deep and seemed to have opted for flexibility over optimal.

The Nitrox 30 standard does not have a suggestion for this depth, so a custom mix seems appropriate.

Once again there is some textbook algebra we could use to calculate a mix, but let’s use ratios again and work from our personal gas partial pressure limits.

Yours may vary but at this depth, an oxygen partial pressure of 1.2 bar is my top limit. In addition, and in most conditions that an 85-metre dive makes sense, the narcotic load that would be acceptable is 3.0 bar of nitrogen. This totals 4.2 bar. Since the ambient pressure is 9.5, there is a vacant partial pressure of 5.3 bar that must be filled with helium.

To turn those ratios into fractions or percentages, we simply do some division and we end up with  12.5 percent oxygen, about 56 percent helium and 22.5 percent nitrogen (by dividing the gas partial pressures we‘ve worked out as acceptable by the total ambient pressure).

For the record, the decimals are artifacts of the arithmetical process and reflect some rounding up or down. Also for the record, if I were to mix gas for this dive, I would most likely start with slightly more helium in my cylinders and then add Nitrox 30 because that is the default gas in my banks. Experience tells me the final analysis would turn up about a 12.8 oxygen reading and 57 or 58 percent helium; close enough in the real world#.

Well there is only one dive left from our list; and that is one to 35 metres. The option to use a straight-forward nitrox 30 certainly exists, but let’s go back to those personal limits I mentioned earlier. At this depth on a normal non-working dive, an oxygen pressure of 1.3 should be fine, and a nitrogen pressure of 3.1 would be acceptable. That’s a total pressure of 4.4 bar; but the working depth is 4.5 bar. So there is a decision to make. One way or another, this depth presents a challenge. I really cannot say whether diving  a nitrox or a trimix is more “correct.” Without knowing the environmental conditions, the parameters of the dive and a whole raft of other factors, it would be tough to guess. But here’s a suggestion. Since this dive is scheduled to take place after the 85 metre dive, and I would certainly have mixed a good quantity of 30/25 decompression/travel gas for that dive, it seems the best option for me would be to use that gas, 30/25, for the bimble to 35 metres! Thank you for your attention!

Presentation to 41st NACD* Conference. November 21st 2009

Forgive me for straying somewhat from the agenda, but it seems the diving community needs your help; needs help from us all.

As many of you know, there appears to be a general misunderstanding among the general diving public about standards, protocols, guidelines, rules. Call it what you will, but something is just not squared away with the tech diving community; and people are getting themselves killed because of it.

Every one of us knows that diving is dangerous. And we know that anyone telling us otherwise is either delusional, completely ignorant in the art of risk assessment; or they are lying.

Technical diving, what we are most interested in, is extremely dangerous; perhaps an order of magnitude more risky than common or garden sport diving. But we render the risks manageable by simply following some really basic rules. These boil down to staying within the limits of our training, our skills and our experience; making a dive plan that takes into account the lessons learned from accident analysis; PLUS we adapt our plan to account for the actual environmental conditions we find at the site on game day; and, of course, we stick to our plan.

Risk management is even better assured by resisting any temptation to push our comfort zone or that of our companions. And we are well armed against the wiles of Murphy if we are prepared to react creatively when the dynamic nature of diving presents us with “real-time” challenges without warning.

In any high-risk activity where we want to weigh the odds of a favorable outcome, the normal path is to follow what’s called Best Practices or Best Practice Behavior. It’s really just a label we stick on a process that leads us along the, statistically speaking, safest pathway through a series of conditions that present threat; either physical, societal, financial or psychological.

However, there are few guarantees and every year divers die.

In rare cases, divers die even though they have followed best practices. They do everything according to the book, but die regardless. The issues in very many of these incidents are truly accidental; often an underlying unknown health problem; and heart problems seem to top that list.

But in the great majority of cases, people die as a direct result of NOT following best practices.

In some cases, their mistakes or the mistakes of their buddy or instructor were errors of omission. What I mean by this is that they forgot to do something important or maybe were unaware that conditions, equipment, personal needs or a combination of all three were going to demand something they could not provide. These events are sad.

At the other end of the scale of culpability, and a factor in the majority of diver deaths, are mistakes that are errors of commission; which in this context I take to be deliberately refusing to follow what they knew at the onset of their dive was best practice. They knowingly did something negligent and these events are tragic in the truest sense of the word because they are avoidable; totally, 100 percent avoidable.

Now, all this is pretty obvious to you and me, but in the past couple of years, our community (the technical diving community at large) has suffered several shock looses and almost every one appears to have been a direct result of divers trying to pull off dives using the wrong gas, wrong kit, having inadequate skills, or inappropriate training. In at least one case — a young man diving air to 75 metres (about 230 feet), well beyond the most extreme limits for that gas in consideration of narcosis and oxygen toxicity — a strong influence would appear to have been pressure from an employer slash instructor; in other words, someone they looked up to.

When invited to come down here and talk to you folks today, I jumped at the chance because I like cave country, I like cave diving, and apart from a bias against Alabama in favor of the Gators, I feel comfortable among cave divers.

My intention was to give a light-hearted presentation pointing out some of the influences that North Florida cave divers have had on the wreck diving community and underline the way we wreck divers have evolved the basic cave diving kit and skill sets to fit a very different environment. We are still going to look at that but from a viewpoint influenced by several recent deaths. None of us knows much about any of these incidents, but there is a common theme in at least almost every case; Lack of Training. Specifically here in North Florida, divers who had no cave training, dying in caves; what a sordid cliché that is, and how sad it’s still happening.

Of course it begs the questions: what can be learned from the misfortune of others, and how can you and I help prevent, by example or influence, others from repeating the same mistakes?

Let’s start with a few declarative statements.

Number one: Wreck diving is very different to cave diving. They are cousins, siblings even, but certainly not identical twins.

Number two: If we accept number one, it follows that the skills required for diving wrecks and diving in caves are NOT interchangeable. The skills have the same names but their deployment is different because the environment is different.

As a result of these two issues, it is NOT possible to train cave divers in wrecks nor can one train wreck divers in caves. To attempt one or the other is wrong and it is dangerous. Since technical diving is risky to begin with, sending the wrong message to the people we train in either of these activities just throws a wrench into the whole risk assessment / risk management exercise.

OK, let me add one more statement to those two. Without simulating or demonstrating the specific risks associated with a special environment – such as a cave – those risks do not exist for the student. In other words, taking a student into any overhead environment OUTSIDE of a course specific to that environment, be it cave or wreck, sends the wrong message. As mentioned, the risks do not exist unless they are explained and outlined with the big black magic marker of demonstration, guidance, performance, feedback and repetition.

OK, let’s start with some history, because if we go back to the start, we may get a better idea where the confusion comes from; and why some people think wrecks, caves and deep open water are similar.

A generation ago, when technical diving was coming out of the closet and before it became a convention, there really was only one place to go to get serious training. And that was Florida. Cave diving was and still is as far as I am concerned the original and purest form of technical diving. If you wanted to become a better wreck diver, and you wanted to learn techniques to make it so, you made your way to High Springs and signed up for a cavern/cave class, because organizations such as the NACD were the only ones offering an alternative to mainstream sport diver education.

Without doubt, because of this simple slice of history, almost everything that is the norm among technical divers around the world today, from Sydney Harbor to Seattle owes a serious debt to Florida Cavers. The classic back mounted rig; backplate, wing, doubles, long hose et al, had its genesis here in North Florida. Today, for some mystifying reason, this rig gets called DIR, Hogarthian, DW2, and god knows what else… but you and I both know that it is just standard North Florida Cave Diving Kit, and if it were not for the malleability of the road signs used by the Department of Highways, and Greg Flannigan‘s ingenuity, we’d all be diving poodle jackets.

The same is true of side-mount diving. Wreck divers are turning more and more to side-mount configuration for open-circuit wreck diving. In doing so, they are copying or borrowing from the kit configuration cave divers have been using for at least a couple of decades.

The connection is there. Cave divers and cave training agencies wrote the screenplay for wreck diving techniques and training. And so, if they are siblings, then cave diving is the older sister.

But over time things have evolved. Driven by a void or need within the wreck-diving community, technical instructors and training agencies have developed specialized technical wreck or advanced wreck programs. The starting point may have been the NACD cavern course but the program now has morphed into something more appropriate for the wreck environment and with attention being paid to skills that are not required in cave and cavern diving.

We do not have time to drill down into the nuts and bolts of each course and do a line item comparison, but we do have time to think about some major differences. So let’s look at them to justify our statement that the two types of diving are not the SAME.

Here is a partial listing of the skills tested during a TDI or NACD cavern and Intro to Cave courses.
• Gas Management
• Propulsion Techniques
• Deploy Guideline
• Lost Line
• Lost Buddy
• Air Share with Buddy in contact with line
• Air Share with Buddy blacked-out mask through restriction
• Light and Hand Signals
• Light Failure
• Problem Solving
Here is a partial listing of the skills for a TDI Advanced Wreck program.
• Gas Management
• Propulsion Techniques
• Deploy Guideline
• Lost Line
• Lost Buddy
• Air Share with Buddy in contact with line
• Air Share with Buddy blacked-out mask through restriction
• Light and Hand Signals
• Light Failure
• Problem Solving

They look the same don’t they; well, of course they are the same… But if we advocate and advise that caves and wrecks are different, how is that so? The answer is that it is in the application of the skills to the specific environment and not the skills themselves.

Gas Management: The Rule of Thirds is sacrosanct to cave divers and wreck divers but there are few wrecks offering several hundred metres of penetration; and so the rule’s application in wreck diving is far more like the Hub Plan used by CCR cave divers than the classic and simpler one third in, one third out used by OC cavers.

Propulsion Techniques: Wreck divers may have to employ a modified pull and glide to navigate narrow corridors inside a wreck where ANY fin movement is guaranteed to reduce visibility to zero in seconds. One other difference is that when a wreck diver kicks a wall by mistake is moves… it might even fall down. Anyhow, finning is NOT the default propulsion technique in “real” wrecks.

Guideline: Cave divers are warned about line traps. Cave divers can follow and usually do follow permanent lines for miles. Wrecks are one big line trap and a permanent line is the stuff of dreams. One might also consider that a continuous line to the surface covers a wreck diver’s need to be able to deploy a DSMB and decompress in blue water. In fact, that constitutes a required skill: hang off knotted line… keeping track of the knots to judge depth, with a blacked out mask, and counting breaths to track time.

Lost Line: Not a big issue when you carry the “permanent” line on a reel in your hand, but a required skill nevertheless for a wreck diver. However, more often than not, during their search for the lost line, students manage to get a manifold, spg, fin or something wrapped up in hanging cable… or their instructor’s simulation of hanging cable. Last time I audited a cave class, tying up the student was not part of the course work. It is in a wreck class. Another time for rodeo work is when students exit through a restriction with blacked out masks sharing air.

Communications, light failures and so on, are no different, but problem solving is. In a cave, the shortest route to fresh air is almost invariably back the way you came. In a wreck, the surface is closer but not necessarily easier to get to. And once there, getting out of the water may be a challenge.

Now if we stopped right now, some of you might leave here thinking, wow, wreck diving sure sounds tougher than cave diving. And in lots of ways, it is. But if things were that simple, how come we are not looking at a bunch of dead cave divers dying in wrecks instead of a bunch of wreck divers who are dying in caves. To be honest, I am able to turn up a constant and irreversible answer to that. But l have a theory…

Any of you who ski will have seen on the various ski runs leading from the top of the mountain back to the beer and nachos waiting at the bottom of the hill, a classification system indicating how difficult each trail is. A green run is the most straightforward; blue involves more slope and turns; a black diamond is technical and demands experience; a double black diamond is for experts and carries a real and present danger of injury or worse.

A skier can break his leg on a Bunny Hill (the simplest of green runs), but at least this classification system let’s punters like myself know which slopes to avoid on the morning of the first day of skiing after an eight month hiatus.

We avoid the black runs until we have our legs back under us.

There is no really well-established and universal “indication of risk” system in wreck diving or cave diving.

The powers that be do not post a series of Green, Blue or Black buoys above a wreck site for example. Perhaps one of the reasons for NOT posting colored indicators is that an errant fin kick, misplaced line wrap or simple quirk of fate can instantly turn a green dive into a black diamond. All experienced divers can all tell stories about a dive that started as a Green or a Blue but that went completely pear-shaped and immediately became a double black diamond.

But the point here is that many wreck dives and all open water dives offer the potential of a green or blue level dive. And in many cases, the journey to the wreck site is undertaken in a charter boat which gives some opportunity to restrict access to the dedicated black diamond sites.

So let me pose a proposition, and this flavors the magnitude of the request for help that I made earlier: I don’t think ANY CAVE DIVE can be classified as a Green dive. ALL cave dives, even a simple bimble in a place like Peacock, start out as a Black Diamond.

In addition, many cave dives on the other hand are “drive ups,” leaving them more open to abuse.

Touching the hull plates of the Empress or Ireland, counts as a dive, but swimming around the basin at Orange Grove is not a cave dive. If an open water diver wants to “give it a try?” he is totally committed and once beyond the grim reaper sign is participating in a Black Diamond level dive.

In addition, sites like Wayne’s World, the DiePolder system, and Eagles Nest are beyond double black… triple black perhaps. Yet we have divers with zero training, zero experience, who have no business being in there, diving in these spots… and not making it out

Now; who is at fault and how do we change things?

The easy out is to blame the agencies for not “controlling” the situation. But this is a rather naive take on the whole affair. It’s “Tooth Fairy Philosophy;” we can talk about it all we want… it’s still a myth, and believing in it will not make it any more likely to happen.

The agencies have an important role in things; they write standards, they enforce them – under the ‘strong recommendations’ of their insurance underwriters – and they set up a QA infrastructure for the network of men and women who teach under their banner. But agencies can’t work in a vacuum, they need feedback, information.

That leaves us. You and me; and to be completely clear on this, I have no foolproof plan. No guidelines for intervention. No killer argument or presentation of logic that is going to win people over when you bump into them getting ready to take their “Try It” dive in a site where they stand a good chance of topping themselves.

All I can suggest is that we work to educate and lead by example, and become more involved.

And as with any massive change or revolution, it begins with you. Each of us should ask ourselves the question are we diving the plan? Are we diving within the parameters of our experience and training?

As I recently wrote in partial jest, but the sentiment is real… All of you are now deputies, so get out there and kick ass… but before you do so, make sure YOU are without sin before you cast the first stone.

Thank You.

* National Association for Cave Diving


Modified from a handout given to sport and technical instructor candidates

“There are just two things in life: but I forget what they are…”
John Hiatt, American poet, musician, b: August 20, 1952

It’s nobody’s intention to throw cold water in your face, but please resist the temptation to call yourself a professional educator on the strength of graduating from a scuba instructor class: technical, sport or otherwise.

In the space of a couple of weeks — the duration of the average sport instructor program — or a couple of days — the average length of programs upgrading existing teaching credentials — there is little opportunity to make it otherwise. Your instructor’s certification card is only a ticket to ride… an invitation to start the process of learning how people learn; and by dint of hard work, teaching yourself how to teach.

With luck, experience, quite considerable additional effort, and some bloodshed — which I hope is entirely metaphoric — the best you can hope for is that you’ll become an empathetic, well-informed, process-driven and safety conscious lay educator. And in the greater scheme of things, and the absence of a PhD in education, that’s not an insignificant achievement.

Our industry’s goals for you are surprisingly modest… follow the supplied guidelines, deliver the prescribed curriculum with enthusiasm and accuracy, and the chances are very good that you will fulfill them. However, I am sure you have higher ambitions and want to do better than average, so let’s see what we can do t0 help you in that regard.

Coloring inside the lines… sometimes
An instructor’s purpose is to guide students through a set curriculum towards effective learning. Always, always effective learning. That’s a winding path. Or perhaps it would be more accurate to say that there are several paths leading to effective learning. Some are well beaten, pretty obvious and relatively safe. Others are more circuitous, overgrown with all sorts of interesting vegetation harboring countless temptations and distractions; but they also end up in the right spot.

And of course some paths look promising but go off on a complete tangent wasting everybody’s time and effort only to peter out someplace miles from the destination. The trick of course is to pick the pathway that best suits your students’ interests and your teaching style; and often that is not the most direct or well-worn route.

A decent map helps. A map helps everyone in the class avoid the tangents and points out which pathways lead in the right direction. With a map in hand, a motivated instructor can guide his charges around the obvious and accompany them along the more engaging route, and still arrive at effective learning changed but intact.

The map we hand you as a newly-minted instructor is rather like a page torn from Ptolemy’s Atlas with huge areas labeled Terra Incognita, and you are expect to fill in the blanks. The biggest help I can offer on that score, is to suggest you look over the shoulder of a professional educator — someone who understands the way learning works — and copy bits of their map. It’s not cheating if you mention your source.

The conditions of human learning: Gagne’s Nine Events of Instruction
I cannot think of a better first shoulder to look over than that of American educational physiologist, Robert Gagné.

Gagné had a profound influence on a broad spectrum of American education including military, institutional and industrial training. His theory on instructional design and what’s now called Task Analysis was detailed in The Conditions of Learning, originally published in 1965 by Holt, Rinehart and Winston. If you can find a copy, I recommend reading it cover to cover.
The theory detailed in The Conditions of Learning remains influential, and grew from Gagné‘s work as a training designer during WWII. His challenge then was to develop teaching materials that could be used by subject experts with little or no formal training as teachers. They needed to impart very specialized technical skills to thousands of raw Army Air Corps recruits in a ridiculously short time… about two years worth of on-the-job experience had to be crammed into about a month.

Based on his experience and research cracking that problem — and further developed until his death in 2002 — Gagné became convinced that in most training situations, effective and efficient learning takes place when the final task is first broken down into a set of component parts.

The analogies between the farm hands Gagne helped turn into aircraft mechanics in a month, and the challenges facing scuba instructors and instructor-trainers are simply too similar to be ignored.

Gagné identified the conditions necessary for effective learning based on the way mental events are triggered in adults by various stimuli — visual, audible, tactile etc. Gagné created a nine-step process that he called, the events of instruction. These events correlate to and address the conditions of learning.

The nine events of instruction are: Gain attention; Inform learners of objectives; Stimulate recall of prior learning; Present the content; Provide learning guidance; Elicit performance; Provide feedback; Assess performance; Enhance retention and transfer to the job.
With very little mental juggling and word substitution, that list should sound awfully familiar to anybody who’s sat through an Scuba Diving International™ Instructor Development Course. But let’s recap a little here and take the time to “enhance retention…”

Gain attention
Gagné tells us that in order for any learning to take place, an instructor’s first task is to capture the student’s attention. We can do this effectively in a number of ways and the more varied and creative those attention-getting actions are, the more attention they’ll attract.
One example could be the opening segment of a multimedia program that has wild animation accompanied by sound effects or music. This would wake up the senses with auditory and visual stimuli. But after a while, even that approach would become ho-hum and a change of tempo would be key.

Something to interleave with that type of approach is to ask a thought-provoking question or hit the audience with an out of the ordinary, lesser-known fact. Even better if its relationship with the topic about to be discussed is not immediately obvious but requires thrashing around in one of those leafy thickets of interesting vegetation beside the pathway to completely understand. Curiosity motivates students to learn. So does self-preservation and stressing the importance of a topic by marrying its importance to staying ‘safe’ is another good punctuation to a bunch of whiz-bang AV effects.

To anyone familiar with the physiology of sales, this is the benefit statement / value proposition. Effective learning can certainly begin by walking learners though a strong value proposition. And my experience as an instructor-trainer informs me that individuals with a sales background have a leg up on their instructor course classmates understanding how to gain a learner’s attention.

Although gaining attention is labeled the first task, it is also the most constantly called upon. Effective Learning will not take place if the learner’s attention is not coupled to the “lesson” from start to finish.

Inform learners of objectives
Tell them what you are going to tell them and explain what outcomes to expect! Does, “at the end of this presentation you’ll be able to…” sound at all familiar? It should because it’s an essential step integral to the success of an SDI™, TDI™ instructor training course. Early in each lesson students should be presented a list of learning objectives. This fires-up expectancy in their minds and helps motivate learners to buy into the lesson and complete it.

Perhaps more importantly, the list of lesson objectives forms the base scaffolding that assessment of performance and certification are built upon. Therefore it is essential that this instructional event be clearly presented and completely understood by everyone in the class. The phrasing of objectives, the way an instructor presents his or her expectations to the class, colors everything else that happens during the course. Instructor trainers evaluating the progress of instructor candidates, will heavily weight these actions in that evaluation.

Stimulate recall of prior learning
Associating new information with existing knowledge. This event can be triggered by the instructor, by the student or by some other source. The classic opening, “Have you ever experienced your ears popping or hurting when driving through the mountains or when flying?” is an example of this event in action. Establishing some comparison to past shared experience and lessons learned will facilitate the learning process for a new concept. It is easier for students to encode and store information in their long-term memory, when there are ties built between it and pervious personal experience and knowledge. The way this was hammered home to me was, “New concepts will not stick without old associations to hold them in place.” I thank long-time friend Bret Gilliam for that particular nugget.

Perhaps the most simple and straightforward way to stimulate recall is to ask students questions about previous experiences. Having them dig around in their memory and then build the associations with previous concepts themselves is the sort of rich-content experience that will have them thinking their instructor is a genius; when in fact their instructor sat back and watched… no more.

Present the content
Tell them what you told them you were going to tell them. This is where the meat, potatoes and crème brûlée of the new content is served to the student. The size of the portions and how they are arranged on the plate depends on the way the course work was designed. However, effective learning is best guaranteed when content is rationed out and organized meaningfully, and typically is explained and then demonstrated by the instructor or an assistant (divemaster for example).

To maximize appeal and broaden the impact and effectiveness of this event, a variety of presentation styles and media should be used. Text, graphics, audio narration, video, self-directed exploration, even chalk and talk all qualify. Also, with a well-designed course and rationally executed learning materials, the content message will be audience appropriate and presented in a logical progression. For example; a detailed discussion on Fick’s Laws of Diffusion and their influence on dual-gas phase decompression algorithms, with a group of newly-certified open water divers is likely to be a one-sided conversation. On the other hand; cut the topic down to its core essentials — several factors can drive bubble growth in a diver’s bloodstream — make it appropriate for beginning divers — ascent rates are important on all dives including those within the NDL — and effective learning may take place.

Provide “learning guidance”
An instructor’s role is to help students grasp the core essentials. Demonstrate, show examples, dispel myths, indicate erroneous examples, explain with diagrams, help with mnemonics and analogies. Ask questions. Different students respond to different stimuli in unique ways… and the same student may be motivated to learn by changing stimuli from one day to the next. An instructor’s challenge is to recognize these subtleties in the classroom, swimming pool, ocean or lake. The key traits for an instructor during this step are empathy and patience. The guidance offered during this event, will help learners encode information ready for storage in long-term memory.

Elicit performance (practice)
This is the event of instruction during which the student confirms for themselves that they have a correct understanding of what’s being taught. In the case of an in water skill such as clearing a mask of backward fining, they get to perform practice drills that test the new skill or demonstrate changed or new behavior. Repetition further increases the likelihood of retention and mastery of the subject/skill.

Provide feedback
Not to be confused with the following step, exercises within tutorials, presentations and dive-skills demonstrations demand the instructor discuss correct and incorrect solutions with students by providing specific and immediate feedback. If the performance is a physical skill demonstrated in-water, video is unbelievably helpful for doing this effectively. Additional guidance and answers provided by the instructor at this stage are called formative feedback.
Formative feedback is quiet special because it can and usually does come from several directions. During debriefing of skills dives, it’s not uncommon for other students to crack the nut for one of the class who is having trouble mastering a skill.

When I first began teaching technical diving programs, I had a hugely difficult time with a particular student who was unable to perform a compound but really quite simple skill the rest of his class mastered after just a few attempts. The skill was core to the course and it had to be mastered before we moved on. I demonstrated it to the student on dry land, in the water, and even had his two classmates run through it for him while I watched him watch them.
Back on the surface, it was one of his buddies that explained which part of the process he was missing. I did not see it.

A similar thing has happened to me in an academic setting. Trying to explain a “basic” maths process to a student who simply did not get it only to have their buddy use an analogy that placed the problem in terms they grasped immediately.

I think my point here is to encourage feedback from everyone involved in the class. Often, I sit back and listen while each member of a class does a step-by-step, blow-by-blow analysis. Direct the process; but don’t suffocate it.

Assess performance
Once instruction is finished and demonstrations are completed, students should be required to take a post-test, exam or final assessment. This assessment must be completed without the additional coaching, feedback, or hints from the instructor. Mastery of material or a pass certification is typically granted when the student attains a certain percentage of correct answers, or demonstrates a skill within the range of acceptable proficiency.

With a written test or exam, this assessment is relatively simple to accomplish but with underwater skills, subjectivity CAN become a muddling factor. Strive to be objective. With skills where no guidance has been provided, set the bar for a pass or fail based on 80 percent of your own performance. Never be afraid to fail a student who is unable to master a skill or retain and understand a concept. The fact is, not everyone can dive. Not everyone can cave dive, wreck dive, deep dive, do staged decompression dives! As instructors, we have a responsibility to get that message across.

Enhance retention and transfer to the job

Essentially, use it or lose it. In diving, there is a sort of built-in mechanism that aids students to apply skills learned from a training program “back on the job.” The environment and the divers themselves self-select, and instructors should make this clear to graduates. Often the imperative for enhanced retention and transfer of skills is survival. A bungled skill — let’s say valve shut down — or misremembered concept — nitrogen uptake for example — sooner of later will cause a serious problem, perhaps injury or death. The environment will test skills without pity and in the technical diving realm, where skills are more complex and numerous than in sport diving, skills need to be tested with detachment regularly. A diver who has learned effectively will realize their shortcomings and ask for help from other divers, will reread texts or research the answers… but most of all, practice.

Events of a Lesson
Applying Gagne’s nine-step model for instruction to a training program is the single best way I know to ensure effective learning. Above all else in education there is no substitute for sound instructional design. There is no substitute, even with the Niagara of information pouring out of our computer screen, for an instructor who can help students maximize the effectiveness of information processing.

Gagné believed that all lessons should include the key steps of motivating the student to learn; giving clear objectives; directing focus on pertinent information (this based on the instructor’s “read” of the materials and the student’s personal learning style); stimulating recall by tying new concepts to previously learned material; providing guidance with hints and illustrations that appeal to the student’s curiosity; enhancing retention by adding familiar examples; promoting the transfer of learning; allow the student to show off what they have learned and providing feedback.

Strive to be the best instructor you can. Use the guidance available from visionaries such as Gagne. Etc.

Dive Debrief: How to participate in and get the most from a post-dive discussion

A primer for Scuba Diving International and Technical Diving International instructor candidates

Just as every dive should begin with a discussion about what’s planned, every dive should finish with all the team sitting together talking over how the dive went. A Dive Debrief is an important part of a systematic approach to building personal experience and strengthening bonds within a buddy team. For a dive leader whose job is to help students to get the most out of their training and experience dives, debriefings are an important, AND required part of the curriculum. But how do you run one?

In the simplest possible terms, a debriefing allows every participant to discuss openly what they expected from the dive, whether those expectations were met or exceeded, what they learned, and what they will do differently on their next dive.

It’s also a time for each diver to talk openly about how they felt during each segment of the dive, and if anything stressed them or made them uncomfortable. Lastly, it’s a forum to discuss both positives and negatives about the team dynamics.

As the instructor, your job is to make sure all these topics are brought up and talked about openly, and constructively. Most of the time, this is not a challenge. There are just a few cardinal rules to help keep debriefings on track.

This is a fun pastime. It carries real risks, and those always need to be addressed fully, but your students dive for fun. They are not being trained to swim into the middle of a war zone for a black ops mission, so keep it light. Never, never lose your temper with a student. Remember, they asked you to help with their education because they knew they lacked something. And in the final analysis, sometimes you have to put in a little extra effort to make a difference.

Almost without exception, do not air your opinions until everyone else has finished. Move the conversation along but give everyone an equal opportunity to express themselves. And when they are done, share your assessment of the dive and their performance with them in a professional manner working logically from the start of the dive – gearing up – until everyone was back on the surface, out of their gear and sitting around for the debriefing. It will help make your recall of the dive better and help with your debriefing  if you break the dive up into bite-sized slices and mark each with a specific waypoint: doing bubble check, reaching target depth, etc, etc.

Start the debrief by asking each student to share their broad overview of the dive. What did they expect to happen and what did happen? This is extremely telling when the goal of a dive is to execute a list of drills that students are attempting for the first time. Regardless of how poorly they did or how negatively they feel about their performance, try to get them to end their overview with something positive. One student who had everything that could possibly go wrong on a skills dive go horribly wrong, looked gutted when we surfaced. He had gone through more than 70 minutes of misery with less than perfect coordination. I asked him to kickoff the debrief and at the end of his introduction, he said: “The good thing is that we made it back and nobody is lying prone breathing oxygen, so the team did OK didn’t we.” This broke the group up and defused what could have been a really tense situation. Humor is a good thing!

Once overviews are finished, pick one student to talk through the dive from pre-dive checks to surfacing. Prompt them to recall details of each phase of the dive and at each step, ask the rest of the group to comment. (This works best with no more than four students.) Ask if anyone has anything to add. Find out how they felt at each waypoint. Ask what they found challenging, and what was easy. If someone made a mistake and points it out themselves, immediately ask them what the fix is. Have other team members confirm the remedy is the right one… or at least one of the right ones. Encourage positive, constructive criticism. Suggest a better solution if one exists, suggest alternatives when they exist.

Finally, ask each person in turn what they learned from the dive. Have them focus in particular on any positive reinforcement for any core skills specific to the course: air sharing, valve drills, buoyancy control, etc. And have each team member suggest ways to make the team dynamic more solid. One thing that I notice often with technical teams (three divers) is that when one diver has a ‘simulated’ emergency, one buddy will help while the other “stands around with his hands in his pockets.” Encourage teams to work as a team.

When this is over, work through your debriefing. If someone made a mistake that was missed, now is the time to mention it. Be direct. Be unemotional. Be professional. When you mention a negative, follow it with a suggestion about how best to fix the situation. Take the time to explain why things need to be fixed and how to improve a skill or do it better next time.

Running a good debriefing does take a little extra effort, but following a simple plan (segmenting the dive in your own mind, letting students work through the debrief process first, keeping the mood light and focused, using positive reinforcement, and suggesting alternatives when they exist) will result in better results and happier students.


A good friend suggested adding a example checklist to this document. He said he likes, “to use a written checklist for briefings, and then use the same checklist for the debrief.”

The checklist may be simple or complex, depending on the dive, but the essential elements are –
Overall dive objectives:
Envelope (limits):
Site briefing:
Nav Plan:
Comm plan:
Gas Plan:
Depth & deco schedule:
Emergency plan:

He explained that by using the same checklist for the debrief that was used for the dive brief, there’s a double benefit. You make sure every element that was briefed gets debriefed, and deficiencies in the brief can be used to modify future briefs/debriefs.

Thanks Ricky.