Five hundred cave dives…

Next week I hope to log my 500th cave dive while visiting Jackson Blue, Hole in the Wall and Twin Cave, in Northwest Florida. Because I live a long way from any suitable caves, it has taken me more than 14 years to achieve this milestone, and a lot of hours spent behind the wheel or waiting for flights.

It also gives me a chance to reflect on some of those dives… most have been in Florida’s “tourist caves” but I’ve also been lucky enough to dive caves in Brazil, Mexico and the Caribbean. It’s been fun racking them up.

Also on the list are mine dives… while not technically cave dives, the NACD and NSS-CDS allows them to be counted… They too have been challenging and interesting… and sometimes sad. I’ve lost several friends cave diving. Perhaps that’s the reason for the cave organizations making a big thing out of logging 500 safe ones!

In any event, I still have a line arrow that belonged to Joe Steffen. Joe is one of my mates who died while diving. The line arrow is one of several he marked up prior to our exploration of the Bell Island Iron Mine a few years back and I retrieved it and four others during Joe’s body and gear recovery. One of his arrows is in the Bell Island Mine near a memorial plaque and container of his ashes. One is in the Eagles Nest, Florida. Two others are in caves in Dominican Republic and Grand Bahama.

When I place this last one next week, I’ll be with two other mates who knew Joe and who dove with him on many occasions. Erik Van Dorn, Jim Clark and I will have a little “ceremony” at depth… not sure exactly what the others will be thinking but I will be giving thanks to something or someone that through diving… particularly technical diving… I have met so many great people… including Joe Steffen.

Well, that’s about it.

Gas Planning 101: SAC/RMV and ways to make sure you have enough gas to complete your dive

(Part one of three-part lecture series, first delivered April 3, 2001


“Always plan ahead. It wasn’t raining when Noah built the ark.”
Richard James Cushing, 1895-1970, Roman Catholic Cardinal and Archbishop of Boston, MA

The reasons for bothering…
Noah would have had a couple of things going for him if he’d decided to become a technical diver. To begin with, he had two of everything, which is not a bad start down the road to contingency planning. Secondly, he is associated with water and lots of it. And finally, he was a guy who seems to have no worries making and following a plan while ignoring the jibes of the folks around him who couldn’t imagine forty days and nights of rain.
Planning is a wonderful habit to cultivate for anyone actively diving beyond traditional sport limits. Hold on… let me expand on that. Planning is a wonderful habit to cultivate for everyone diving beyond or within sport diving limits, but it is especially critical for anyone doing technical or advanced dives, because without a good solid dive plan, there cannot be a good, solid dive.
As we will discuss through the next several [chapters] there are abundant and assorted risks associated with advanced diving. A good solid dive plan helps to avoid or mitigate those risks and lies at the core of being a successful technical diver.
Among all the risks a diver has to account for, none is of greater consequence than gas management and no aspect of an advanced or technical dive plan is more essential than a concise, accurate gas management plan. This holds true for dives carried out on open-circuit scuba and on all flavors of rebreather – closed and semi-closed.
Nothing makes for a more stressful dive for an open circuit diver than running low on backgas or decompression gas, and nothing turns a rebreather diver’s hair grey faster than scrapping around the bottom of a diluent or oxygen cylinder for the last few litres of usable gas.

Completely running out of something suitable to breath, will totally ruin everyone’s groove – CCR diver or traditional open-circuit diver, regardless of how close a buddy or a bailout cylinder may be.
Astonishingly, although drawing up a gas management plan is fundamental and ranks as a primary-level skill, the basic constructs are often misunderstood, and this leads to some exceedingly dodgy dive plans.
The root of the problem could be a carryover from sport-diver practices. These  essentially boil down to: start with a fully charged dive cylinder, monitor your SPG, and surface – or arrive at the safety stop – with something between seeds and stems and a sixth of your starting pressure – the ubiquitous 500 psi for those familiar with dive briefings on Caribbean dive ops. If followed, all other things begin equal and the SPG having been serviced, recently calibrated and working correctly, this technique will likely get a diver home. But if anything goes pear-shaped during the dive, it provides an inadequate gas reserve and an unsuitable margin for error.
The classic OOA (Out Of Air) Emergency for a sport diver is usually the inevitable result of operator error: one diver gets excited or tense and burns through his gas supply much more rapidly than expected. There’s no gas plan and no reserve so the sudden shortage of something to breathe comes as a total surprise. Either a late glance at an SPG or a sensation similar to having an overweight Labrador retriever sitting on his chest, triggers a wide-eyed grab for the nearest functioning regulator. This is usually in the mouth of an unsuspecting “buddy” who has little forewarning of what’s about to happen, and no idea how to deal with it. The usual “next step” is two divers closing in on panic as they take a rapid flight to the surface accompanied by the savage screams of ascent alarms.
In the majority of cases, both divers make to the surface with little worse than a scare and an open invitation sometime in the future with aseptic necrosis. Occasionally though the outcome is far worse with an immediate payoff. Some victims of a runaway ascent, even when their dive was shallow and short, surface with DCS or lung over-expansion injury.
In advanced or technical diving, the gas planning process has to be more thorough and circumspect since running low on gas and rushing to the surface is a surefire guarantee of a visit to an emergency room, hyperbaric facility or morgue.
Technical divers therefore estimate gas usage within much tighter tolerances. There are plenty of different methods that work. Probably the best is to draw on personal data pulled from previous dives to similar depths and in similar conditions. But that assumes divers take notes, refer to them on a regular basis and are familiar with the process of adjusting things to suit shifting circumstances. These are the divers who can tell you how much gas they will have left on their back  at just about any point during their dive. Chances are you are not at that level yet, so let’s work through an example.
First a confession: cooking up a gas plan does take some effort and doing it for the first time can be about as much fun as de-worming the family cat. But really it is simple work with a non-scientific calculator (no trig, no functions, no fancy stuff, just ratios). The secret of making it as pain-free as possible is to understand the steps, follow them and know when to round up, approximate or “eye-ball” numbers. Of course, it’s all worth the effort because the benefits are boundless. You will learn a vital skill, create a mental template that can be reused again and again, and your gas plans will be enviously sublime.
When doing something new for the first time, I find it helpful to set myself some goals, so let’s look at the goals you should have for your first crack at creating a workable dive plan. Aim for moderately accurate and conservative, not perfection. Plan for a tolerable margin of error and work at compensating for that error – shaving it finer and finer – as you gather more and more actual data from more and more dives. Your final destination is being so tuned into your gas consumption during a dive that will you know what your Submersible Pressure Gauge (SPG) is going to read before you look at it! If you’re really good, you’ll know what your buddy’s says too.
What follows then is a step by step breakdown in both sensible metric and insane imperial. This assumes open circuit diving. We’ll deal with CCR gas planning separately, but my advice is to follow along even if you dive rebreathers.
To draw up an example plan we’ll work out some figures for a couple of open circuit divers: Vlada and Joseph.
Just to make it interesting, Vlada dives metric while her mate Joseph is American and thinks in US imperial. Luckily, Joe also dives a CCR on occasion and understands metric.
The first step for Joe and Vlada is to know what volume of gas they each consume in a minute at rest on the surface. Outfitted with this figure, everything else is simple arithmetic. And in the best traditions of high school mathematics, this figure needs to be a constant for future calculations to work.
Now here’s where the semantics start.
Diving is an easy-go-lucky kind of sport and many terms used by divers are elastic in their application. This drives scientific types and the geeky kids up the wall. It fazes me too. When working out gas volume requirements for a dive, I like to have one constant for each diver’s consumption rate on the surface. Once armed with this, all the other considerations such as depth, time, workload, temperature, narcosis, mental stress, fitness levels, how we feel today and what we had for breakfast can be factored in. The key piece of information is having a constant for surface air consumption in a state of rest.
It’s always seemed to me that Surface Air Consumption (SAC) is the perfect candidate. SAC is a unit measure of gas consumption on the surface, and since we need to have a constant non-variable figure to hang all the other factors from, SAC seems to win on several scores not least of which is its name.
And so, when I am planning gas volume requirements, I use SAC as a constant to describe an individual diver’s air consumption rate on the surface – and most importantly – at rest.  This does away with the need to use an array of potentially confusing terms such as average SAC, resting SAC, swimming SAC and so on.
If SAC is a non-variable figure – that’s to say, a person’s SAC does not vary from dive to dive – we need another term to describe what happens on a dive. On a dive, gas consumption rate  is influenced by a bunch of variables all present in different strengths and forms. I nominate RMV (Respiratory Minute Volume). RMV is the volume of air which can be inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person’s lungs in one minute. RMV is a variable.
In common practice, many divers calculate how much gas they will need by working backwards from the volume of gas used on several logged dives. The standard method is to take the volume of gas consumed on each dive, divide it by bottom time and reduced that figure to a surface value by dividing by the depth expressed in atmospheres. The result is the amount of gas that they would have used each minute if their dive had been conducted on the surface. I have an issue with this from a detailed planning perspective, and feel the method yields inaccurate results because the consumption rate reflects how much gas is used while working… swimming, pushing dive gear through water, fighting current, and under various other variables like thermal stress, and narcosis.
In short, the figure arrived at using this method can’t accurately be used as since it’s invariably high. Typically at least half again over what true SAC would be. Not that this invalidates the method entirely. It’s just that with the weighting for all those variables already factored into what is supposed to be neutral number, it’s difficult to accurately forecast for widely different conditions.
Let’s return to our example. Vlada is new to technical diving and needs to work out her SAC rate, but she is not clear how to do it. Joe tells her to sit down at home watching TV and breathe from a small volume cylinder and keep track of time. Vlada sets up a 6 litre tank containing 125 bar of air and sets the timer on her stove for 30 minutes. She sits down, puts the regulator into her mouth and listens to the radio. After 30 minutes the timer buzzes and she notes that the SPG shows the remaining pressure is 70 bar. The calculation for her 30 minute consumption involves multiplying the pressure drop – 55 bar – by the cylinder capacity – 6 litres – and this gives 330 litres. She divides this by 30 to find out how much she breathes in one minute and arrives at 11 litres per minute. Vlada writes her SAC in her dive notes.
A couple of days later Joe and Vlada get together to create their gas plan for a dive the two intend to make the following Saturday afternoon.
Vlada and Joe plan to dive to 45 metres. At this depth, the ambient pressure will be about 5.5 atmospheres. Vlada arrives at this figure by moving the decimal point one place to the left to find the water pressure, and adding one to account for the surface air pressure (10 metres of water exerts about one atmosphere or which is close to one bar… one of those approximations it’s OK to make). So Vlada now knows that at 45 metres, the absolute pressure is about 5.5 atmospheres, and because of this she knows she will need 5.5 times the density of gas she would at the surface for each breath.
Armed with this information, she quickly works out how much air she would breathe in one minute at depth doing a similar activity to sitting in her kitchen listening to the radio: 11 X 5.5 litres or 60.5 litres.
Having gotten this far with the constant values, she and Joe start to plug in the variables for her estimated RMV. The variables measure estimates for increased breathing because of physical stressors such as workload, current, temperature, and the amount of gear she’ll be pushing through the water. She also needs to make some allowance for increased gas consumption because of mental stress caused by things like poor visibility, narcotic loading and diving in an unfamiliar spot. All these variables combined are known as the Dive Factor or DF.
The base standard DF for a dive in familiar waters with little workload and the minimum of stressors is 1.5. For example, if Vlada’s dive were to fall into this category she would multiply her 60.5 litres per minute by 1.5 to factor in the dive factor: 90.75 litres per minute. But the planned dive with Joe will be in unfamiliar cool water, carrying a stage bottle of decompression gas. Joe suggests a DF of 2 for her. This translates into a volume of 121 litres per minute for Vlada’s dive. This is Vlada’s Respiratory Minute Volume (RMV) for this dive and will form the central strut of her gas management plan.

(to be continued…)

Suggested procedure for controlling and surfacing with a Toxed Diver: Open Circuit Version…

(decompression diver and trimix class)

Central Nervous System (CNS) oxygen toxicity at depth usually results in a diver’s death. CNS toxicity itself is not fatal. But the stricken diver dies as a result of either a massive over-expansion injury caused by floating to the surface while in spasm; or by drowning as a result of the diver spitting out the regulator or mouthpiece while in spasm and then inhaling water when the episode abates. Any diver may present a CNS-like  episode without prior warning. Please bear in mind that almost any “informed” intervention on your part may increase the diver’s odds of surviving the episode.

If you and your buddies follow the established NOAA protocol for single dives and watch your 24-hour limits, it is highly unlikely you will ever see or suffer a CNS incident. However, as unlikely as it may be, you will be asked to demonstrate the following procedure during your TDI Techdivertraining program. This procedure is simply a suggestion of how to attempt to stabilize and surface with a diver who has presented the signs of a clonic / tonic episode. You may regard this as a basic solution and it is certainly open for further refinement.

1/ Stabilize the convulsing diver. Control his position in the water column by making physical contact (either with his person or a piece of equipment.)
2/ Do your best to hold the regulator in his mouth (certainly the gas he is breathing MAY be causing the convulsions; however, breathing any gas is better than breathing water).
3/ Signal to other team members that you need assistance
4/ Do not attempt to ascend until the diver’s body relaxes, the convulsions cease and the diver resumes breathing.
5/ When convulsions cease, check the level of diver’s consciousness. If they are awake, signal them to switch regulators to a gas YOU KNOW is appropriate for your current depth. If they are breathing but are unresponsive (likely) you may not be able to switch regulators. That’s OK. MAKE SURE THAT WHICHEVER REGULATOR THEY ARE BREATHING IS ATTACHED TO AN ABUNDANT GAS SUPPLY  Monitor gas levels for the stricken diver often.
6/ Adopt recovery position** and begin ascent. Use the stricken diver’s buoyancy compensator to control ascent for you both. (Open the automatic vent on his dry suit and yours.) If you have another team member helping, sandwich the stricken diver between the two of you.
7/ If possible, blow a signal marker to tell your surface support that you have an in-water emergency.
8/ Complete your decompression schedule. You may choose to accelerate it if circumstances dictate, but DO NOT risk DCI to get the stricken diver to the surface… Remember, he has the same obligation as the rest of his team
9/ Be prepared for a second series of convulsions.
10/ Bring diver to surface and secure and remove gear (inflate wings, clip to equipment line, cut harness), get diver to surface personnel or on boat or on shore.
11/ Activate EMS. Note: The correct call to the Coast Guard in this situation would be a pan pan and NOT a mayday.
12/ Monitor. Document. Follow Instructions from EMS or Coast Guard. Reassure. Treat for Shock. Watch for signs of DCI. Set diver’s gear aside for inquiry… Either one among your team or group, or more formal.

* Oxygen Toxicity may present itself underwater in the form of a clonic-tonic convulsion. However, a convulsing diver may or may not be experiencing a CNS toxicity episode. You cannot diagnose precisely what’s going on, so always deal with the situation in a structured way and resist the temptation to second-guess the situation.

Do check to see if the MOD of the gas the stricken diver was breathing when they convulsed corresponds to the depth they were at. Do get them on a leaner mix or get them higher in the water column, as swiftly as is possible without compromising other safety protocols. Do Watch your own gas switches.

** Recovery position = Anything that works  Essentially, you will ride the stricken diver through the water column making sure you have control of their BC, their airway (keep it open) and the regulator (in their mouth). I find it difficult to completely control venting gas in a stricken diver’s drysuit (and my own in these circumstances) if I maintain a horizontal trim. I find I do better if I present them and myself in a semi-vertical attitude. I also prefer to be able to monitor the diver’s eyes, and so prefer to be facing them rather than being behind them. Try threading your right arm under theirs. Keep the drysuit shoulder vent up and OPEN. Bring your hang around their shoulder and hold their BC inflator in your right hand. Use your left hand to hold their regulator in place. Do your best and remember that style takes a back seat to function… Use any fixed aid — such as an anchor line or wall — to assist and arrest your ascent. This is one of the few exercises on your training course where you are  allowed  to hold onto ascent lines and walls, and where you will not be  penalized  for being vertical in the water.

N.B. several texts suggest not to try to replace a regulator that has fallen out of a diver’s mouth. The rationale is that if the diver tries to breathe, there is a chance that some water may be present and cause laryngospasm. Not replacing a regulator may be the correct “action” if the diver is being recovered from a few metres his rescuer is making a direct ascent to the surface. However, if ascent is going to take several minutes, and a regulator is not replaced, the diver most certainly will breathe water and drown. Make your own decision…

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:
Equipment:
Envelope (limits):
Site briefing:
Nav Plan:
Comm plan:
Gas Plan:
Depth & deco schedule:
Teamwork:
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.

Suggested procedures for liftbag deployment

(intro to tech, decompression diver and trimix class)

A liftbag may be used in several ways and is a useful underwater tool; however, perhaps its most common use is as a signal marker to show surface support — such as a liveboat captain — the dive team’s position in the water during free and drifting ascents. It is this use that the following procedure will outline. This procedure will be taught to you as part of your Techdivertraining TDI program.

Step-by-step procedures
(Assumes use of safety sausage type marker connected to open-faced spool containing more than 20 metres (70 feet) of #36 braided nylon knotted every 3 meters or ten feet)

A Surface Marker Buoy (SMB) or sausage-type liftbag is the most effective way to signal a team’s position in the water during an ascent away from a fixed ascent line in still water or during a drifting deco. The sealed or semi-sealed bags are preferred to an open-ended bag since this design can deflate when it’s on the surface in moderately rough seas. SMBs and liftbags should be brightly colored (but NOT white) and need to be marked to conform to any local regulations. In addition, it helps when diver’s name is written somewhere near the bag’s top with Sharpie-type marker.

Team deployment: single marker
Unless you are doing a skills session as part of your inwater assessment, it’s usual to deploy only one marker per dive team. This is often done when the team has reached relatively shallow water; usually sometime following any gas switch at 21 metres (70-feet).

Dive leader signals Deploy Marker and team members confirm. Each member should carry a marker and a spool but part of the dive briefing will have covered of whose marker and spool is to be deployed This team member will remove the spool and marker from her pocket or pouch, and display it for team to see. If the spool and marker are not pre-attached, she will do so and then hand the spool to her dive buddy. He will confirm that the line from the spool is firmly attached but ready to let out line unhindered and giving his buddy the OK” signal, will continue to hold on to the spool. She will confirm this signal. After a final check to see that the line is not fouling any equipment, she will begin to inflate the marker (see below for suggested methods). When it has sufficient gas to rise towards the surface she will hold the bag away from her body and in the center of the buddy circle, Her team members will give the OK” signal and she will then release the bag. The spool may be held lightly with the fingers or may be left to unroll itself freely in the water column. When the marker reaches the surface, the line is tightened and re-clipped to prevent the spool from dropping into the depths.

The spool may be left in the center of the buddy circle providing a good visual reference. The spool’s owner is usually responsible for rewinding line as the team continues its ascent, although this task can be shared. At no point is a spool or reel attached to an SMB to be clipped or tied to a diver.

Team deployment: multiple markers
Putting more than one bag and line up usually means the exercise is part of a skills session. In this case, deployment is done individually (see procedure below). However, each diver waits her turn to deploy her bag. DON’T try to throw several bags to the surface at once. You’ll simply end up with a bird’s nest of tangled lines.

Individual deployment
Take spool and marker from pocket ensuring that line is firmly attached to marker. Hold spool in right hand and marker in left and show to buddy. They should confirm they have visually checked that you are clear to inflate. Begin to inflate marker until it is pulling lightly for the surface. Hold line and marker in front of you making sure no equipment is fouling the line. Watch for your buddy to give the OK signal and allow the marker to ascend.

Further notes:
A common mistake is over inflating a marker so that it is impossible to control at depth. Remember Boyle’s law. The second most common mistake is under inflating an SMB! To be effective as a marker, an SMB must float upright with at least its top half out of the water. This requires it to be filled with gas and for the diver below to put some downward force on the line. This will help keep the marker visible to surface support personnel.

There are several ways to fill an SMB. Semi-closed models can be filled by transferring gas from the wing into the bag using the LP (low-pressure) inflator/deflator. Additional gas can be added to the bag using the wing inflator but be careful to add gas in short spurts especially in cold water. Closed bags are inflated with an LP inflation hose. This can be a dedicated hose attached to a stage bottle or the drysuit hose can be disconnected from the suit, used to inflate the bag and then be reconnected.

Exhaling into a bag may work but it puts the bag and the line attached to it very close to the diver’s face and gear. Entanglement is a real possibility. Purging a spare regulator into a bag may work in warm water but can be a guaranteed way to start a freeflow.

Divers should practice bag deployment in shallow water when they have no decompression or safety stop obligation.

It’s vital that divers break surface no more than three meters from the marker especially where surface traffic or heavy seas may be a factor.

Diver alert markers can also be used to signal surface support that there is a problem with the dive team. Some advocate the use of different colored bags for this… I am not entirely comfortable with that option. I prefer instead the practice of sending a second marker up the same line. A message slate or note can be attached to the first or second bag explaining the problem. Naturally, whichever practice you opt to use, it is necessary to discuss this with your surface support prior to EVERY dive.

One last tip:
Knotting the line on a spool (say every three metres or ten feet) can help you measure things like the length of a hatch cover or how far you are from the surface Very handy and reassuring in low-vis situations, and required when you practice bag deployment with mask off or blacked out.

Suggested Procedure for Gas Switching during Decompression Diving

(decompression diver and trimix classes)

During any staged decompression dive it is standard practice to switch from backgas to a more oxygen rich gas at least once during ascent. Because of the potential risks associated with breathing high partial pressures of oxygen, divers are strongly advised to adopt a set procedure for gas switching which includes standardized safety protocols. The following is a suggested procedure.

Step-by-step procedures

All scuba cylinders should be dedicated to standard decompression gases and be marked clearly according to Standards. In addition, decompression cylinders should be marked with actual Maximum Operating Depth (MOD) of contents with removable tape on two sides of cylinder valve. This MOD must be based on recent analysis and calculations for acceptable dose of partial pressure at that marked MOD and should show NOTHING but MOD in meters or feet clearly marked in large numbers. (See cylinder labeling procedures for full details.)

All decompression cylinders should be worn on diver’s left side with valve orifice facing diver and valve on/off knobs pointing to left. Divers enter water with regulator(s) on decompression cylinders charged and valve(s) closed.

During ascent, each diver will begin gas switch procedure prior to reaching switch depth (gas MOD). Deployment should follow the following steps.

Each team members “unstows” hose and second stage of selected decompression mix and pulls hose across her body with regulator second stage in right hand. Starting with dive leader, each members asks a buddy to “Look at my gas. Please confirm it is correct for next stop.” Buddy must follow hose to first stage, read actual MOD and confirm that the regulator will deliver the correct gas for the coming gas switch. This query / confirmation cycle will be done one diver at a time.

Divers will then follow schedule and proceed to MOD for gas switch. Once there, they will switch regulators and with left hand on cylinder valve will breathe hose dry while checking SPG on selected decompression gas. As reading drops, indicating once again that regulator is indeed connected to the correct cylinder, they will turn on the decompression valve allowing decompression gas to flow normally. Once they are sure regulator is breathing normally, they stow the backgas regulator they were formerly using. At the same time, each team member should indicate the status of their gas switch to dive leader. Once each team member has signaled “Switch went OK,” decompression at that depth will start.

This procedure is repeated for each gas switch made during the dive.

Some further thoughts and notes:

Do not breathe a gas which has not been analyzed by you or in your presence. There should be no exceptions to this rule.

It is imperative that all team members have similar decompression gases which can be switched within a depth of one meter or less.

Gas switching is perhaps the most stressful exercise performed during a normal ascent from a technical dive. It should never be executed in a cavalier or complacent way because the potential consequences of sloppy procedures are simply too severe. Second stage should be inspected for foreign matter before being breathed… muck, critters et al.

Whenever possible, use gases that all team members are familiar with such as EAN50, 50/25/25, pure Oxygen for decompression. However, when you are in the field and these “standard mixes” are NOT available, it is even more important (if that’s possible) that you follow the procedure outlined here!

Actual Decompression Planning… (part two)

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Taken from a presentation first made March 13, 2001, updated April 2008
OK. Let’s go back to what is meant by accelerated vs optimized decompression and look at how two quite different approaches to the same dive, illustrate some core differences.

First we need a dive to use as an example and we’ll take something very simple: an ocean dive to 35 metres (about 120 feet) for 25 minutes. I’ve chosen this dive because there’s nothing about it that’s mind-blowing. The depth is within the range of an experienced advanced diver – certainly a diver interested in learning about technical diving – and the volume of gas needed to complete the dive – a topic we’ll discuss at length when we talk about gas management – can be carried by an open-circuit diver without surface support More germane for our current purposes, the total ascent time – including any required stops – will be moderate (about the same as the bottom time). In short, this is an entry-level technical dive and a good place to begin our discussions.

Now, what remains is to choose gases that will work for this dive and a set of tables or an algorithm to give us our ascent schedule. The dive could easily be conducted using air, but from the perspective of decompression management, a 30 percent nitrox would be a better choice. There are other options too but let’s keep this uncomplicated. EAN30 will deliver an oxygen partial pressure of 1.35 bar at depth. This is perfectly acceptable. Now for decompression gas, our diver – who we will call Jennifer, a fairly new decompression diver – has 100 percent oxygen.

One final decision is what algorithm are we going to have Jennifer and her buddy use on this dive. We’re spoiled for choices, but I want to suggest using something that should be familiar to most experienced sport divers – hard tables. We could say: “Just follow what your PDC tells you to do, but that’s not much of a learning experience. We could also have them generate custom tables with one of many available decompression software packages. But these applications do ALL the work and at this point in Jennifer’s development as a decompression diver, I think she should work through the process longhand and make informed decisions about things that might affect her well-being.

No dive tables put the PGB at zero but the DCIEM serial tables are considered a lot better at putting it close by the “experts.” I like them for this sort of dive planning even though they’ve been designed around a premise that low-grade post-dive bubbling is acceptable for some profiles, and they’re a popular choice for people in that transition between experienced sport diver and neophyte technical diver.

These tables, for the record, were developed by a diving research team working for the Canadian military starting in about 1962. The name of the model comes from the research facility in North Toronto, Ontario, where it was originally developed (the Defense and Civil Institute of Environmental Medicine, now renamed Defense Research Development Canada by the way). Part of the development process involved setting up what has become the most comprehensive decompression database in the world, containing recorded details of all research dives at DCIEM and DRDC since 1964.

The Sport Diving Tables are considered one of the most conservative available, and particularly applicable to cold water dives since testing was carried out with working dives in cold water. The methodologies employed at DCIEM and DRDC included extensive Doppler testing of subjects pre- and post-dive, and a circumspect interpretation of the data from those tests. The other unique thing about the DCIEM table – and something that sets it apart from neo-Haldanian cousins – is its construct as a serial model. In the DCIEM model there are four compartments each with about a 21 minute half-time with only the first compartment exposed to ambient pressure. As gas tension builds in the first compartment it bleeds into the next and so on. The Haldanian and neo-Haldanian models have all compartments exposed to ambient pressure. What difference does this make? Intuitively it seems to be a model that better reflects what may actually be happening in a diver’s body, and it results in dive profiles that are better suited to recreational diving – both sport and technical – than say the US Navy tables.

So, given all this, we will draw Jennifer’s ascent information from the version of DCIEM Sport Diving Table published in 1995.

Now a quick explanation about the choices of bottom mix and deco gas. We should already accept that using nitrox on the bottom and switching to a richer nitrox during ascent is a perfectly acceptable practice because it seems to lessen decompression stress. The EAN30 certainly gives a little edge compared to diving air. Its equivalent air depth at 35 metres is about 30 metres ( ([FN2 X (Depth + 10)] /0.79) – 10). Not much but every little helps. As stated before, the partial pressure of oxygen at depth with this mix is about 1.35 bar which Jennifer sensibly rounds up to 1.4. That gives a single dive limit of 150 minutes and a daily limit of 180 minutes. There’s an acceptable buffer for CNS loading for this type of dive.

The oxygen is an efficient finishing gas. There is no nitrogen in the mix and therefore by switching to oxygen at its maximum operating depth (MOD) for a resting decompression, which is about 6 metres or 20 feet at 1.6 bar PO2, will create the maximum theoretical increase in vacant partial pressure for the nitrogen dissolved in the Jennifer’s body. The result should be efficient gas elimination and some experts suggest that stop times derived from air tables can be cut by about one third when breathing oxygen. Of course, there is a downside because the CNS loading at 1.6 bar is high… about 2.3 percent per minute We will look at some options to manage this in a while.

Let’s look at what ascent time the DCIEM tables give for Jennifer’s dive. It is an ascent of 15 metres a minute plus or minus three metres and a straight 10 minute stop at six metres and another 10 minutes at three metres. These figures are based on air as a breathing medium.

An aggressive approach to her decompression obligation would have Jennifer ascend at 15 metres per minute, to arrive at her six metre stop ready to start breathing from her decompression gas. Since it is oxygen, she has decided to maintain the five-minute stop but when she ascends to three metres she cuts that stop from the suggested ten minutes to five. Her logic is that the tables called for two stops totalling15 minutes. She is using oxygen and therefore feels she can eliminate one third of that time. The choice to keep the six metre time unaltered and to cut the three metre stop in half was based on nothing more than her understanding that a five-minute safety stop at six metres is required regardless of what gas she might be breathing. Strikes me this is a good rule to follow… especially in this case.

Her decompression schedule then is two minutes to ascend from 35 metres to six metres, five minutes there and then an additional five at three metres and from there to the surface for a total of a little more than 12 minutes ascent time. Accelerated decompression. Short as possible and as aggressive as hell.

An optimal approach considers the variables on the day of the dive. Perhaps the diver is not as well hydrated as she should be, the water is cool and is moving, and there is another dive planned for later in the day, the moon is full, whatever it is, it’s accounted for. To push the odds in her favor with regard to off-gassing, Jennifer plans her ascent a little differently.

Firstly, she ignores the advantage given her by her nitrox bottom mix. She will use no EAD and therefore her decompression stops would be 10 and 10. Secondly, she slows her ascent to the slowest allowed by the DCIEM table… that’s 12 metres per minute. Lastly, the oxygen time. Although she could abbreviate both 10 minute stops to about seven each, she cuts only the six metre stop and it by only two minutes. The last stop at three metres she leaves intact.

Her ascent time then is two and a bit minutes travel time from 35 metres to six metres, eight minutes waiting there breathing oxygen and then an additional 10 minutes at three metres. She also makes the last stage of her ascent to the surface very slowly… perhaps taking a full minute between finishing her three metre stop and breaking the surface for a total of 21 to 22 minutes. Optimal decompression. She has take full advantage of every tool available to her to help eliminate as much inspired inert gas as is practical. Her aim is to surface with minimal bubbling rather than as quickly as possible.

And so, we now have some base from which to work at planning our own forays into staged decompression diving. You must ask yourself if you are interested in accelerating decompression or optimizing it.

Actual Decompression Planning: navigating around accelerated vs optimized deco

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Taken from a presentation first made March 13, 2001, updated April 2008

“Smile, breathe and go slowly”   Thich Nhat Hanh, Vietnamese Buddhist Monk, Teacher
All dives and certainly every staged decompression dive carries a very real risk that the people making it will suffer some sort of decompression stress… either sub-clinical or full-blown. The likelihood of getting bent depends on the variables; Who, When and How more than constants such as the type of brand of decompression model used. And of course, depending on variables produces variable results.

Once we accept that getting bent is a real probability – albeit with a variable risk – we can begin to manage decompression diving in a realistic way and work at cutting the unpredictability to an acceptable level. None of us wants to take a ride in a recompression chamber – touch wood, I’ve managed to avoid it so far – but it’s not something we can ignore or be frightened by.

So what do we need to know as divers… decompression divers… to keep us healthy? Decompression from a dive – every dive – consists of two phases that can be broadly defined as ascent beyond the off-gassing ceiling and surface off-gassing… or, less formally, in-water decompression followed by a surface interval. Whether formal or not, we cannot say a dive has been successful until both phases are completed and there are no complaints of joint pain, paralysis, skin rash or any other signs or symptoms caused by decompression stress. Doppler testing has shown bubbles persisting in divers for as long as several days, so the waiting period is probably longer than many of us admit to. This of course should have each of you thinking to yourselves: “I still want to conduct successful staged-decompression dives… but it looks like I need help to make that happen!”

When we discussed the Alchemy of Decompression [previous chapter], we saw that being successful is a broad combination of several factors including education, scepticism, conservatism, adequate health and fitness, adopting and following diving practices that conform to an accepted norm, and, perhaps most importantly, some luck.

Unfortunately, luck will always be an influence in the outcome of your diving. Your job is going to be concentrating some considerable effort on the other factors so that the percentage of luck in your personal equations is kept to an absolute minimum.

At some point, and it may as well be right now, you should make some sort of determination on how hard you are prepared to work at this job. You have a straightforward choice to exert some control over what happens to your body… or not. You will never get the luck quotient to zero but I feel it’s well worth trying. I hope you do too.

While you work through that… and I expect an answer before we go diving together… consider that many divers make their first staged decompression dives under the auspices of an experienced decompression instructor. The chances are that their instructor will suggest various strategies to draw up ascent schedules that keep “everyone safe.” These may include wearing a personal dive computer (PDC), using existing “hard” tables – such as those from Buhlmann, DCIEM, BSAC, US Navy – or cutting “custom” tables using decompression software.

Some instructors may employ combination strategies that typically consist of custom tables backed up by individual dive computers or a PDC backed up by custom tables. The hope is that the student leaves the class with an understanding that there are several workable strategies to manage decompression stress. They also leave with a handful for dives to supply empirical evidence of what worked for them. This empirical stuff – data from actual dives – that’s the gold standard for them and their future dives but few realize it; but more on this later.

During a decompression course, students are guided towards making desicions that conform to some acceptable norm arrived at by their certifying agency, their instructor or an amalgam of both. Regardless, course dives are inherently conservative – or should be. This strategy is partly due to the standards published by the agency for the courses themselves. Typically exposures are limited to a specific maximum total ascent time or a ratio of decompression time to bottom time or limited by the flavor and volume of gas participants are “allowed” to carry. The reasoning behind this is pretty simple: instructors make a living teaching not riding in a chamber or waiting for their customers to finish a table six recompression. If your instructor has to teach another similar course starting the day after he or she finishes up with your course, my guess is course dives will not feature aggressive profiles.

Oh, a quick definition. An aggressive profile is one where decompression – either in-water or on the surface or both – are accelerated. In other words, at least one factor pushing for a conservative approach has been swept aside or ignored. An optimal profile on the other hand is one where every practical opportunity to make the diver’s probability of getting decompression sickness close to 0 is taken. We will contrast these two approaches to deco planning a little later.

When a diver graduates a decompression diving course and begins to plan his or her own dives, they will typically follow pretty much the same general format that was presented during their course. By dive eight or nine post class, it’s normal for some slight changes to have taken place. The Human Factor usually pushes the needle closer to one as time passes. In rebreather diving we talk about the “Death Zone,” a time when the diver’s wariness of new technology begins to wear off and their experience as open-circuit divers begins to over-rule caution. Complacency causes small leaks to appear in the dyke. Water starts to trickle in. The hope is that they notice something is going on and smarten up before a full-on breach washes them away. Well the same effect is true of decompression diving. Over time, some level of complacency almost always sets in. If we could see probability of getting bent (PGB) as a straight line with 0 (no chance) at one end and 1 (100 percent certain) at the other, we might see what happens a little clearer.

Zero probability of getting bent means not diving. So, the probabilistic pointer is obviously somewhere to the right of that. On their last course dive executed with an instructor – assuming they did not end up on oxygen, clear fluids and being driven to a chamber – the pointer was closer to 0 than to 1. For the sake of illustration, let’s say that for every 100 times that profile is dove, between three and four people get bent. That’s a 0.035 PGB, and that’s high but no higher than for many tables accepted in the diving community.

OK, so now they plan their first post course dive the following weekend and most divers will try to do everything exactly as shown… very little is different (apart from not having an experienced decompression diver watching them like a mother hen). However, over time, small changes take place. Perhaps during a stop that was supposed to be at 9 metres for three minutes, they made a mistake and only stayed for two minutes and 30 seconds. “No biggy,” they think. Perhaps they were holding onto an ascent line and it was moving around. “That’s OK, I got away with it,” they say. Perhaps their decompression gas was delivering a partial pressure of 1.3 bar when the tables they used assumed 1.4 bar. “I did not notice much difference,” they explain. Maybe because they were not on a course, they drank a second glass of wine at supper the night before… Whatever it is and how trivial it may seem, something was changed and usually that change means their probability pointer is shifted closer to 1. But they get away with it – for a while – and this begins to insulate them from the lessons presented to them by their instructor. It can happen to any one of us. So what can we do to fight it?

I’m a strong advocate for taking notes after every decompression dive and allowing this to become a habit. The notes can be short but should be contemporaneous, and contain at least the ascent profile followed – including ANY and ALL deviations – gases used, overall feeling post-dive compared to pre-dive, and notes about any other factors that may have influenced the outcome – was the diver well-hydrated, were they rested, did they work during the dive, were they warm or cold during the dive, did the decompression go smoothly, were gas switches slick and so on. By listening to what his body tells him after a dive, a diver builds his own probabilistic dive table which can be refereed to again and again.

Look at it this way. The first time we follow a custom decompression table or a PDC profile, we are trusting it to keep us safe and whole but there is no guarantee it’ll work. The PGB is somewhere between 0 and 1 but we really cannot be sure where exactly. It’s a crap shoot. Our profile might carry a PDC of 0.01 or 0.10… who knows. If we dove the same profile last week or last month and felt fine after it, and today start the dive in better shape – let’s say better rested and better hydrated – there are still no sure bets but at least we know the odds are in our favor and the good money is on the PGB being close enough to 0 for the dive to be doable.

So take notes.

OK. Let’s go back to what is meant by accelerated vs optimized decompression.

(to be continued…)

Pelagian Rebreather Course… a simple deconstruction

 

This is the tale of the first North American Pelagian air-diluent diver course. I’m unsure whether the three participants (Dave Taylor, a doctor from Rochester, New York, Erik Van Dorn, CFO of a large construction firm and also from New York, and me, neither from New York nor smart enough to have a real job) are early adopters or misguided rebreather Luddites. But in the final analysis, none of that really matters. The course was eventful… and enjoyable.First of all, the course scheduling demons had played havoc with the execution of our course. Pelagian instructors are thin on the ground: I know of only about six world-wide. Ours was a mate of mine from Northern Ireland. Our third attempt at it had us diving during the first week of November in the Thousand Islands region, which is on the Canada / US border where Lake Ontario, the last of the Great Lakes, empties into the St. Lawrence River. Ask me generally about doing courses in this location at this time of year and there’d probably be a couple of expletives in my reply.

Don’t get me wrong, Fall is great in central North America, but November anywhere in the Great Lakes Basin can be bitterly cold, windy (the gales of November, right) and generally miserable. Planning course work in the area in November is always a crap shoot and the thought of a minimum of two hours a day in the water and the potential of surfacing with blowing snow in the air was not a great confidence builder. However, we lucked out and had sunshine, high teens and low twenties for air temps and water on most dives around 11 or 12. (The River unlike the Lakes rarely has waves taller than knee high so we also had no blow-outs or rough conditions to deal with. The only exception was Saturday morning’s dive which was our last… and it was conducted under grey skies and light rain… easy!)

A quick word about the overtext for this class. I am not sure how much you know about rebreathers in general. Simply put they are nitrox gas mixing machines which re-circulate breathing gas while removing carbon dioxide (bad gas) and replacing it with fresh oxygen (good gas)! In many units the addition of oxygen is computer controlled, but the Pelagian is a completely diver controlled closed-circuit rebreather (DCCCR). There are no electronics governing the partial pressure of oxygen in the diver’s breathing loop. The diver controls this him or herself, manually with an “add button” which simply purges pure oxygen into the gas on the inhalation side of the loop, and by means of an adjustable needle valve assembly, which serves to automate the process somewhat at depth. Oxygen partial pressure is monitored by a couple of fuel cells situated in the head of the scrubber unit. Their reading is displayed on a simple gauge which can be worn on the diver’s wrist or be clipped to the diver’s harness. The unit is very compact, can accommodate almost any sized cylinder for diluent (air in our case) and oxygen, and is commonly worn with a traditional cave-diver’s backplate, wing and harness. Everything about the setup including work of breathing at depth was great. For additional security, we carried an open circuit bailout system which is a stage bottle complete with SPG, first and second-stage regs and in my case, a low-pressure inflation hose for wing inflation.

And a quick word about me. I work for a dive education agency and teach for a living. For me to be on the receiving end of a diver-level course is a rare treat and a multi-level learning experience since I am professionally engaged to assess the instructor’s teaching style as well as needing to learn as a student. As an aside, I was Dave and Erik’s Advanced Trimix Instructor on Open Circuit. Needless to say, this made the classroom dynamics interesting.

I picked our instructor, Stephen Phillips, up from Toronto’s Pearson Airport late Tuesday lunchtime. He was a little early and we missed rush-hour traffic across the top of the city arriving at our hotel in Rockport about an hour ahead of schedule. Dave and Erik were already there and over supper that evening, we chatted about the course and what would be expected of us.

At the core of a rebreather program is the need for students to demonstrate a cautious approach to diving the unit. Any underwater adventure carries risk but CCRs bring a whole new category of challenges to the picnic table. These new and enhanced risks include toxicity from too much oxygen, toxicity from too much carbon dioxide and unconsciousness from too little oxygen. I knew that both Dave and Erik are cautious and contentious technical divers… but also realized that this is not necessarily the optimal starting point for learning the basics on a rebreather! Like me, they had many habits to unlearn.

Our first full day together was brilliantly sunny and warm. It was spent doing some basic classroom stuff, assembling units (all three of us had oxygen and dil in 6 litre aluminum luxfers), making the necessary adjustments and setting off for a local waterside park about 15 minutes away in Brockville. Our first task was trying to get our weighting squared away.

As a team. we found weighting a special challenge. The unit needs less ballast than most CCRs but all the information we’d gathered – from various sources including the guy who designed the units – did not translate cleanly to drysuit diving. Bottom line seems to be that for nobs like us, a steel backplate and about four to five kilos of lead works well with trilam suits and Fourth Element Arctic undies.

Once we had that sorted, we ventured into the vast depths (about four metres) to work through basic operations on the unit and some simple tasks such as buoyancy, trim and staying alive. I had an advantage over my classmates because of some experience with semi-closed rebreathers and other CCRs. Plus I had spent an extra day and a half with our instructor earlier in the summer. But none of us was immune to newbie missteps. Dave for example seemed determined to go “swim-about” which understandably made our instructor have kittens. After a few words though, we settled into something resembling a working tempo and proceeded to go through a long check list of drills on the units.

I immediately felt at home on the unit. Certainly the streamlined design of the counter-lungs and the positioning of the various loop connections helped keep our configurations clean, and the biggest initial challenge after weighting was how to load up a 6 L bailout bottle at the beginning of the dive without help. (We had this down pat by the end of day three but day one was agonizing!)

After day one, I was impressed with the concept of DCCCR. For an experienced OC diver, it seems somehow more natural to control the oxygen level manually and once minimum loop volume is kind of mastered, driving the gas, establishing something like a balance between buoyancy and gravity, and staying conscious engaged only about 90 percent of my awareness!

Day Two and another sunny morning spent changing bits and pieces of kit… Drings underneath the counter-lungs are about as useful as ashtrays on a motorcycle, so they were the first things to undergo metamorphosis. I also added a second, second stage to my bailout cylinder… one worn around my neck and held in place by a necklace – very much like the secondary reg carried for years on my OC rig – the second bungied to the tank ready for those complete failure drills I suspected would happen at some point… Regardless of the potential additional drills our instructor might have in store for us… particularly me… I was sure that I am not ready to buddy-breathe from a bailout cylinder while wearing a CCR.

Anyway once all the frittering was done, we headed back to the water. The spot we worked in was perfect for us to stay focused on running the units and practicing drills… very few distractions, no current, decent visibility (notwithstanding a few fin drags… actually, getting horizontal in the unit was a cinch and I take full responsibility and make no excuses for the John Deere award Erik presented me with at the end of the day).

We worked until late afternoon on diluent flushes, cell validations, simulated problems with oxygen levels, various failures and toddled around scaring bass and small sunfish. Another couple of hours on the units and I was beginning to feel where the loop volume should be to facilitate gas circulation and control of buoyancy. I was still making the occasional mistake thinking that my lung volume will have an effect on buoyancy, but started to feel less engaged with the unit and more so with actual diving… which must be progress. One huge advantage over OC very apparent at this point is the lowered thermal stress. After a couple of hours spend in chilly water which on OC would have me a little chilled, I was finishing dives feeling toasty.

The next hour or so was a blur of activity… Fills, rinses, reassembly and supper in the local pub. All good stuff and the dawning of Day Three saw us all bright-eyed and bushy-tailed heading into Brockville for a visit to the bank (bloody Canadians were giving me no premium for US dollars… ironic since I was the only one who arrived with nothing but US cash and am also the only Canadian in the bunch)! While there, we had breakfast in Taitt’s Bakery… breakfast burritos… and then headed to our dive spot.

The plan for Day Three was to venture into slightly deeper water and this required a lengthy swim. I lead and hooked up with the line from shore out to a small wooden wreck sitting near the main channel… the St. Lawrence Seaway… passing freighters sound different on a CCR!

The current was slight and the swim an easy 20 – 25- minute kick. The deeper water skills included more structured use of the oxygen flow meter, which is brilliantly simple and worked like a charm. We all got it dialed in and performing as it’s supposed to. The drills on this day were more complex… multiple things to attend to and the focus was on dealing with problems while maintaining the loop. The one thing that’s a drag is running the unit semi-closed (taking a few breaths then venting gas from the loop into the water and then activating the Automatic Diluent Valve which added fresh air to the loop. This exercise is one way around a depleted oxygen supply and is a pain in the rear but at the point we were doing this we were heading back to shallower water and the “skills” platform, so I put up with it.

Now, deploying a DSMB on a rebreather presents a whole different set of issues, but my buddies and I managed to get our markers to the surface with a minimum of muppetry. I saw Stephen cross himself only twice during the exercise, and took that as a sign there’s been a marked improvement over earlier attempts. One of which had me snorting with laughter.

We finished in good time and headed back to Dive Tech… likely one of the best shops in this region of North America and certainly a boon to us at all stages of our course (Thanks to Dan, Beth and the dive staff). Exam night but first we quickly prepped the units for a deeper “final” dive on Saturday (maybe two dives), and headed back to the hotel in failing daylight… This was our best day yet.

No real issues with the exam… but during our run-through with Stephen later that night, we all have suggestions for future Pelagian courses and some comments on a few questions… I put this down to Andy’s core experience being in a wetsuit and warmish water and not in Great Lakes conditions. For example, RMVs here are higher and consequently critical gas volumes for bailout are higher… essentially, as a group we decide that a fully charged 6 L bailout is the minimum-sized security blanket any of us will dive with. Our scenario in fact required us to plan a dive with our bailout bottles containing no less than 670 litres of gas on hand for each CCR diver. In any event, bull**** baffled brains and we all passed!

Overnight, someone in the weather office flicked a switch and we woke to cooler temperatures, overcast skies and rain. Our plan was to get in a one-hour dive before breakfast and then review the situation. The dive spot was within a two-minute drive of the hotel and we were doing bubble checks before anyone else in the area was up and about.

The dive went exceptionally well. The site was different to our previous dives and we were able to hit target depth quickly and swam along the base of a rock wall covered in freshwater sponges and dotted with bass and the occasional catfish. The skills required of us were to actually dive and follow the plan we had created the previous evening.

By this point in our development as CCR divers, we had all begun to get the feel of the unit. My lasting impression was that the work or breathing on the unit was very low and maintaining loop volume was part science and a lot of art both tempered by a slow, methodical approach. Adjustments to buoyancy via wing and suit have to be much more controlled than with OC. However, once buoyancy is set, it remains rock solid. I thought we all looked pretty good swimming along… back-finning, doing turns, avoiding each other and old dock work like pros.. Well at least like beginner CCR divers.

The only wrinkle was Dave’s stomach and we turned about five minutes early than planned to head back to the exit point… or a point that looked similar but which actually was a surface swim away from the actual exit point. Our ascent was slow, controlled and “safe.” (I am told the sharp stabbing pains are normal and they went away after a few days!)

Once on the surface, Stephen shook a few hands and we called it a day in time to go back to the hotel, change and head into the local café for a tea and a toasted western. I think we arrived back at Dive Tech before 10 am.

Some thoughts on the course and Pelagian… I learned a lot, and will incorporate some of those things learned into courses I teach in future. A special thank you to Stephen, Dave and Erik for their contributions to a great experience. It was challenging and it was a week spent doing some very worthwhile training. At the end of a few days, we are getting comfortable with basic operations within the limitations of our comfort zone and so on… so lots to go on that score.

My personal take on the whole DCCCR philosophy is very positive. I like being completely in control of my oxygen partial pressure. One observation is that the learning curve towards being ready for staged deco will be steeper than on a computer-controlled unit simply because maintaining a setpoint is harder. (A little sidebar here. Since control and stabilization of the oxygen partial pressure is key to working out actual decompression stress, it will be a while before I feel comfortable planning dives beyond the NDL on this unit.)

The unit itself is very compact. It took all of about 30 minutes to begin getting comfy with the position of various controls and less time to attain some control of buoyancy and trim… this can be put down to the position of the lungs (along the side of the diver’s body), the way the tanks are slung (just like a set of doubles) and the flexibility inherent in building your unit from a “kit” which means you dictate things like hose lengths and position of attachment points on the harness. Thanks to Andy for that.

Hope this ramble helps someone. Certainly if you’re thinking about DCCCR feel free to contact Dave, Erik or me… we may be able to give you some advice.

One final point… a few people have contacted me and asked why I’ve “moved away” from an electronically controlled CCR. Actually, I have not moved away from anything. My belief is that diving one unit is not a put down of any other unit. They each have different strengths and weaknesses and each is the right tool for a specific application. My original interest in Andy’s unit was triggered by its simplicity and its potential for packing down into a small carry-on package for air travel. At the end of the course, its further attractions are how wearing the unit was really not much different to wearing my basic cave/technical kit configuration… except for the obvious reduction in overall mass…