Hi, my name is Bill and I’m here to help…

What exactly does Hogarthian mean?

“Man has such a predilection for systems and abstract deductions that he is ready to distort the truth intentionally, he is ready to deny the evidence of his senses only to justify his logic”

Fyodor Mikhaylovich Dostoyevsky, Russian Novelist: November 11, 1821 – February 9, 1881

Well a whole generation ago, if you were a cave diver hanging out in North Florida, you knew exactly what a Hogarthian rig was. You might not have agreed with it, but you knew who did, and the way they rigged their kit before going for a dive was easily recognized. Crap, you could even dive with the guy who lent his name to the system: William Hogarth Main.

In the interim, what used to be a pretty straightforward definition has become disturbingly fuzzy.

In the overall scheme of things, there’s no big deal in the kind of change that inches closer and closer to clarity, but I’m not a fan of change that moves in the other direction. Accordingly, indulge me today if I whine a little about a good idea gone wonky. Oh, and while we’re at it, let’s try to get a few historical ducks to line up in a row.

Let’s start with the ducks. Bill Hogarth Main is a real guy. Contrary to the views recently expressed in an onLine scuba forum by a newly minted tech diver and self-acclaimed “DIR Practioner” (whatever the heck THAT may be), Bill Main is not some fictional figure created to frighten the meek into conformity. He is just a guy who has been cave diving for a good while and, as far as I know, he still guides at a couple of select caves in North Florida, where he makes his home.

Hogarthian Gear Configuration is named after Bill because it is based on his minimalist approach to kitting up for a dive. Hogarthian has been referred to as the Zen of Cave Diving. Not a bad definition really since the Alpinist Way or Approach to any active, high-stress, high-risk sport is commonly linked to Zen. (I must add that as a Buddhist convert (maybe especially), this coupling is a mystery to me, but let’s leave it alone for the time-being and move on.)

When the concept was introduced to me, the principles seemed VERY straightforward and abundantly clear: Hogarthian kit was simple, serviced, standard, shared, suitable, and streamlined. I can still see my cave instructor standing in front of a white board with those words scrawled on it.

Before we continue, allow me to expand on those points just a smidge.

SIMPLE: nothing convoluted or contrived, and if something can be shaved off, filed down, or trimmed, do so. An example of simple: a piece of kit that can be fixed properly with stuff available from a hardware store. (This was explained to me when discussing dive lights with Bill Main and Lamar English back when I had hair.)

SERVICED: pretty easy to get this one straight. Nothing goes into the water as life-support that is not in working order.

STANDARD: you and the other members of your dive team have agreed on the appropriate kit for your dive and each of you therefore knows the operational niceties (and limits) of those tools.

SHARED: your buddy has your six-o’clock (your arse if you are only familiar with digital time-pieces). This principle can be applied to most of what is taken and what is needed in the water, but the FUNDEMENTAL thing shared is GAS. Tech divers follow gas rules that dictate that a portion of the gas in my tanks belongs to my buddy.

SUITABLE: if you do not need it, do not take it. More importantly, if a piece of kit was never intended or designed to cope with the environment you are going to take it into, resist the urge to push its functional envelope.

STREAMLINED: now this should come as no surprise to anyone who has read a book on technical diving. Short version: do not look like a Christmas tree, get rid of danglies, and aim for minimal resistance when swimming. I was once called on this score by Bill Main for wearing a drysuit to go cave diving… wow, that really is a shocker, isn’t it?

At some point, the definition Hogarthian got high-jacked and people started to apply it to kit choices and configurations that were many zip-codes away from what started out as a good idea. There is certainly nothing wrong with progress, and smart innovations in industrial design, electronic engineering, and materials manufacturing have made fools out of many of us who said: “I’ll never do that!” But I am not sure that moving away from the six basics that originally defined Hogarthian Configuration constitutes good thinking or best practice.

Those six guidelines actually hold true as much today as they did in the 1980s and early 90s when they were developed. As a CCR and OC sidemount cave diver I plead forgiveness for some of the choices I make, but I like to think that my diving philosophy is supported by those six “S” words.

Certainly when I look at divers who have adopted the more or less standard North Florida Cave Diver’s Kit consisting of back-mounted doubles, isolation manifold, wing/backplate, long-hose, bungeed backup, and a drysuit, the vestiges of Bill Main’s ideas are there… under the surface in some cases but the smell and taste remain.

What disturbs me though is that as functional as this layout has been, and how ubiquitous it has become in the technical diving community the world over, it is neither a perfect solution, nor does it conform to several of the basic tenets of Hogarth’s “Zen Outlook.”

Certainly to label it as “Right” or the best option available confronts the one principle of Hogarthian configuration that I neglected to add to the list above. I saved it until last because I feel it is the most important and deserves to be here at the end.

And frankly, without it, all the rest falls apart. What is it? Just this: Constant focus on improving the system, because nothing is perfect.

Thanks for your attention. History lesson over.

Accident Analysis (take two)

Enroll in any high-risk, high-stress endeavor, and the chances are that one of the first topics your instructor will throw into his or her opening conversations with you is how many ways you can kill or hurt yourself doing what it is you just signed up for. The first steps in just about every training program in the “adventure” category of things to do – from flying a plane to shooting a gun (at targets or bad guys) or climbing rocks or heli-skiing – will walk the activity’s newcomers through potential pratfalls. It’s a kind of universal mantra: learn from the mistakes of others.

Diving courses, well, certainly ones aimed at imparting skills for technical diving, work in a similar way. The politically-correct term used in the industry is Accident Analysis, and the framework for the AA modules I have been taught, worked with, or developed and written over the years follows closely the one first constructed and then refined for teaching cave diving. In its shortest form, an Accident Analysis module boils down to three stages: here’s some advice about what works, here are some examples of people ignoring that advice, now can we agree that they were stupid and that we will try not to follow their example.

For the record, here are three real-life scenarios that got people killed. I share these with tech students. See what you make of them.

Scenario one: August, 2009. Three experienced sport divers attempted a deep dive off the coast of California. The participants were a dive-store owner, his friend, and a 22 year-old shop employee and DM. Although the trio had done similar dives before, none was certified beyond sport-diving limits. The dive shop involved did run tech programs, but they were overseen by a third-party instructor. Worth noting is that this individual was NOT part of planning the dive in question and was apparently not involved at all. By the way, the dive was planned to be around 60 – 65 metres using air as back-gas. It turned out that the actual dive’s depth exceeded the plan at 70 metres plus. During ascent, the “team” lost contact with each other and the 22 year-old man was seen drifting away from his dive “buddies” and was sinking. After some time, his body was found on the surface.

Scenario two: November 2009. Two divers attempted to dive Eagles Nest on CCRs. On a previous occasion, the pair had been taken to the “cavern” area of the nest by an instructor teaching them a course on CCR which they did not pass. For the record, one must apply a very liberal definition of Cavern to describe any part of the entrance to Eagles Nest, an extensive and very deep (80 metres plus) cave in Hernando County, Florida. Also for the record, neither man was cave certified, nor was the instructor who had previously taken them to the cave for training dives, a cave instructor. During their ill-fated final dive together, the two CCR divers had opted to use a diluent in their rebreathers was hot for the depth they attained (reportedly one containing 18 percent oxygen). If this were the case, it would have made impossible at depth controlling their setpoint (partial pressure of oxygen) at recommended levels of 1.2 or 1.3. Also, a meaningful diluent flush, cell test would have been impossible. At some point, approximately 170 metres from the cave’s entrance area, one of the divers experienced difficulty and died. His body was recovered in one of the deepest sections of the cave some time later by a team experienced in deep-water body recovery.

Scenario three: In mid-November 2008, the bodies of two divers were recovered from Wayne’s World (aka School Sink), Pasco County, Hudson, Florida. Wayne’s World is considered an advanced cave dive yet only one of the buddies had ANY overhead training, and that was only an Intro-to-Cave card – well shy of what’s recommended to dive this site. The other diver carried only an Advanced Open Water certification. Both were wearing traditional North Florida Cave Kit with decompression gas. Recovery divers discovered both bodies within 80-90 metres of the cave entrance. Their bodies were separated by approximately 30 metres distance. One was found at a depth of approximately 14 metres with his oxygen decompression gas deployed (oxygen is considered highly toxic if breathed deeper than around 6 metres). The other was deeper in the cave, dead on the ceiling showing signs of distress. During inventory of the dead divers’ equipment, this diver was found to have his isolator closed with one cylinder empty and the other containing at least 3500 psi.

Here are the questions I use to begin the analysis process in the classroom.
Where did logic chain begin to break down?
What simple guidelines seem to have been ignored in these cases, and how might ignoring them have contributed to the seriousness of the situation these people found themselves in?
In all three cases outlined, whom do you feel should shoulder some responsibility for these deaths?

 

Of course, by its nature, this exercise is speculative since the process asks us to form conclusions based on a sandwich made from a couple of slabs of conjecture and a thin layer of fact. There is also a complex moral issue with us forming a judgment about someone’s behavior – which inevitably happens – without their input during our deliberations. After all, there may be rectitude in their behavior – although on that last point, experience does tend to suggest there are no fixes for stupidity.

 

However, all that aside, the exercise serves a purpose which is not to allot blame but rather to identify errors, understand how easy it is to mess up and from that deductive analysis, avoid repeating the same mistakes ourselves.

There’s one other shortcoming. Between you and me, I dislike using the word Accident to describe many of the examples we use to point out the kind of behavior that results in diver deaths.

What is an accident?
One definition of an accident is “any unplanned event that resulted in injury or ill health of people, or damage or loss to property, plant, materials or the environment or a loss of business opportunity”.
That’s OK as far as it goes. Certainly unplanned seems to be the pivotal point, but it begs some further investigation… and definition surely. Let’s take for an example scenario three above.
It’s well known that diving in a cave without training is a poor choice. Did the two guys who died know that diving without training, experience and kit in a cave was a poor choice? Sure they did. There’s a bloody great big sign to remind them at the cave entrance. They planned to dive ignoring that fact, and I’d wager the general consensus from fellow divers would agree as inappropriate using a definition that includes the term “an unplanned event” to describe their actions.
Given the circumstances of their dive, their behavior was risky: they took a risk and their calculations – whether conscious or not as to how likely their choice was to backfire and kill them – was incorrect. They screwed up, assuming naturally that their intention was not to kill themselves. Think about this: One guy had around half his back-gas available. All he had to do was switch regs or reach back and check his isolator. Yet signs at the site of his death indicated he drowned.
Is deciding to take a risk and miscalculating its inevitability an accident? Is ramming into the back of a parked car at high-speed with an alcohol level above the legal limit for a driver – whatever that limit may be – an accident? Surely it’s recklessness, carelessness or criminal. What do you think?
The Brits use the term “death by misadventure.” For the record, the definition of this phrase in Webster’s is “a death due to unintentional accident without any violation of law or criminal negligence. Thus, there is no crime.”
Death by misadventure does have a nice ring to it: no blame, just a couple of guys out on a lark that went wrong. Is that how you see scenario two, or is there more to it.? Is there some level of culpability, negligence?
A buddy of mine tells his students that cave diving is deceptively easy.

“Anyone can swim to the back of a cave,” he says. Another buddy tells his students that “Even an open-water diver can make a dive to 60 or 70 metres.” They also add that their statements are only true until something goes wrong. In a pear-shaped world, it’s finding the way out from the back of a cave or getting back to the surface intact from 20 storeys down that presents problems.

 

When things go wrong underwater, the fundamental skill becomes survival. In diver training, this is broken down into three major tasks:
• control the natural fight or flight (or freeze) response
• suppress panic
• work on getting your ass back home (This latter skill requires critical decision-making, physical and mental actions involving some level of multi tasking, which some people can do, and some cannot.)
The ability to react appropriately when things fall apart is an acquired skill even for those who have some natural abilities and the skills to survive. It takes knowledge backed up by experience and practice. How much of each is a hugely debatable point, but I believe the diving community as a whole agrees that it takes more experience and practice than one can gain during the average technical diving class… even when full knowledge of what to do and how to handle the situation has been taught.
Well, that’s a shocker, isn’t it? We certify divers to do dives but we believe they may need more experience and practice before they can survive something going pear-shaped!
If this were the case, our beaches would be littered with the dead and injured and clearly they are not. Most people leave a dive class – regardless of whether it is a sport diving or tech diving class – with a full understanding that what they just earned is an OK to go out into the real world and gain experience and practice, gradually. They have the knowledge to do so well within the limits of their training. And that is the key… within the limits of their training. Without training or with a disregard of what that training taught, all bets are off. They have no knowledge and are unlikely to live long enough to gain wisdom.
So what is the bottom line, take-home message from Accident Analysis?
I’ve always reckoned it to be the advice to take things slowly, to be cautious, and to stay within the boundaries of your comfort zone, which are the actions of a wise diver. What does Accident Analysis say to you?

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.

Helitrox Decompression… class notes


What you need to know about Helium
(a supplement for techdiverTraining Helitrox divers)

As a Helitrox Decompression Diver, there are a few things you should know about helium, this new gas you can now add to your scuba tanks, since your TDI decompression procedures textbook does not cover this topic at all. Luckily, the vital stuff – the things you need to know to help keep you happy – can be summed up in a couple of pages. Please read on!

We can start off by looking at some of helium’s properties.

Anyone who has organized a kid’s birthday party and bought party balloons already knows helium gas is lighter than air: it’s actually many times lighter than air. For those with an interest in these things, a mole of helium has a mass of 4 grams compared to 32 grams for the same quantity of oxygen and 28 grams for the same amount of nitrogen.

Just in case you forget your high-school science, a mole is measurement of quantity – a specific number of elemental particles or molecules – used in chemistry. For example, a mole of Ideal Gas has a volume of close to 22.4 litres at STP (Standard Temperature and Pressure – 0 degrees Celsius, and one atmosphere or 101.2 kPa). An ideal gas is defined as a hypothetical gas in which all collisions between atoms and/or molecules are perfectly elastic and in which there are no intermolecular attractive forces. This is unrealistic behavior for a gas but we use it in diving because diving is not an exact science. In the context of diving, we can say that 22 litres of helium weighs 4 grams compared to around 29 grams for 22 litres of air.

Is any of this really vital to you as a Helitrox Decompression Diver? Nah, not really. However, it does help to show us why a cylinder filled with trimix, has buoyancy characteristics that are different to the same cylinder filled with air or oxygen: it has a tendency to float, the oxygen cylinder does not.

One other issue that relates directly to the mass of helium is work of breathing (WOB). The deeper we dive, the denser our breathing gas becomes and pulling a lung-full of gas into our body requires more work and effort. Using air or nitrox, you may have already noticed that your regulator – which performs perfectly at 20 or 30 metres – starts to feel a little “tighter” as you venture past 40 metres (132 feet). The WOB, even on a well-adjusted, high-performance regulator, increases noticeably as we descend deeper than 60 metres (200 feet). This increased workload can play a major role in carbon dioxide build-up in a diver’s blood, which of course affects respiratory function.

In short, gas density affects a diver’s comfort, safety and performance. Adding helium to our bottom gas effectively thins out that gas making it easier to breathe at depth. With 20 percent helium in your back gas, you may notice your regs have never breathed easier!

Back to our high-school chemistry for a moment: Helium is a member of a handful of elements known as Noble Gases. The term “noble” probably comes from the fact that these gases have their outer electron shell completely filled, and this makes them (Helium, Neon, Argon, Krypton, Xenon, and Radon) “aloof” and in most circumstance, nonreactive or inert. Noble gases do not bond with other elements. Helium is pretty typical in that it does not burn, does not mix with other substances to form stable compounds, and – as with its noble gas bunkmates – is monoatomic; in other words, it does not even like to associate with itself and hence we write ‘He’ and not ‘He2‘ as we do with O2 and N2. The behavior of helium as a Noble Gas is only a concern to us as divers when we need to make exact calculations to mix gases accurately. Coles Notes version: for a given pressure and temperature, one gets less He in a scuba cylinder (fewer moles) than air or oxygen (i.e. 200 bar of helium is NOT the same as 200 bar of oxygen).

OK, so notwithstanding the all of the points outlined above, one basic question remains: Why do we use helium? I am not trivializing the importance of floaty bottles, lessened WOB at depth and how many moles we can cram into an aluminum “80”, but what else is there to know?

Probably number one is that helium is – for the purposes of diving at depths attained by recreational technical divers – biologically inert. Since it is not narcotic and non-toxic, it makes a great diluent for nitrogen and for oxygen. Adding helium to keep the partial pressures of both those gases to manageable levels is the real reason for this course. Your classroom notes should include the basic “Dalton’s Law” calculations for the suggested bottom-gas mix to be used on the pinnacle dive for this course… a 30 minute exposure at 45 metres (150 feet).

Just in case you do not have those notes handy, here is the short-form:

Ambient pressure at depth of 45 metres = 5.5 bar

Target Oxygen Partial Pressure at depth = 1.30 bar

Target Nitrogen Partial Pressure at depth = 3.16 bar (same as air at 30 metres)

Vacant partial pressure (Ambient – (O2 + N2) = 5.5 – (1.3 + 3.16) = 5.5 – 4.46 = 1.04

So, we have to fill 1.04 bar with something other than oxygen or nitrogen to keep the levels of those two gases within a tolerable range. Easy, we can use helium because it is a “diver-friendly” gas.

Now, at some point, we have to let someone at a dive shop know what flavor of trimix (or Helitrox) we want them to mix, and so we need to convert partial pressures in bar to a percentage of the ambient pressure. In other words, we need to calculate the ratios of each of the gases used.

Here are those calculations: 1.3/5.5 x 100 = 23.6% Oxygen; 1.04/5.5 x 100 = 18.9% Helium; 3.16/5.5 x 100 = 57.4% Nitrogen (rounded numbers which do not quite add up to 100%).

I am not sure what the folks are like where you buy your fills, but I could not bring myself to ask my supplier for a mix with fractions such as 23.6 or 18.9. It makes more sense to round the numbers up to whole numbers, let’s say a 23/20, and that is what I would dive. For the record, TDI suggests the mix for this class at this depth cannot exceed a 25/20. I cut back on the oxygen pressure just a little because I believe it better suits the water conditions where I do most of my diving.

OK, just two more small issues to deal with. The first is perhaps the biggest myth surrounding dives using trimix. The myth is that ANY mix with helium is going to give a diver a much longer decompression obligation that diving air. This is patent bullshit. I simply cannot categorize it any other way.

Helium is said to have faster transit times than nitrogen in a diver’s body; it is absorbed and eliminated more rapidly than nitrogen. This does result in ascent schedules with a slightly deeper off-gassing ceiling, calling for running stops beginning deeper in the water column, but overall ascent times are shorter NOT longer. Here is an example that’s relevant to the type of diving you will do as part of the graduation requirements to earn certification.

A dive to 45 metres for 30 minutes breathing a 23/20 trimix and a EAN50 starting at 21 metres on the way up. Total runtime = 63 minutes.

Exactly the same parameters for the dive but substituting air for the trimix on the bottom and keeping the EAN50 deco gas for the ascent. Total runtime = 74 minutes!

OK, so perhaps there’s a difference because the trimix has 23% oxygen and air only has 21%. Here the same dive with an EAN23 instead of trimix and all the other stuff the same. Total runtime = 71 minutes.

No matter how you cut it, the ascent time on trimix is shorter. (By the way, the first running stop on the trimix ascent IS deeper by about three metres.)

OK, so with that myth busted, let’s move on. The final item is thermal stress and the role of helium in hyperthermia. Helium does a poor job of insulation and pure helium would make a very bad inflation gas for a diver’s drysuit. I have dived in a cave in 20-21 degree water using pure helium in my suit. It was not a wonderful experience: I strongly suggest you do not try it for yourself.

TDI suggests using an alternative suit inflation system to one’s back-gas when ANY helium is being used. This is a great idea if you are diving in an area with a marked thermocline; however, many divers diving in water 20 degrees and above, find very little thermal effect when using a gas with only a moderate amount of helium in it. During this course, you should not have more than one-fifth of your back-gas given over to helium. You may find it unnecessary to carry a separate drysuit inflation system in moderate to warm water conditions.

Oh, one last thing, sound travels about four times faster in helium than in air. One result of breathing helium is that it makes one’s voice sound like Donald Duck or Minnie Mouse. This Disney effect is really funny. However, be aware that pure helium or helium mixes that do not contain at least 21 percent oxygen, are dangerous and breathing them may result in hypoxia and death or serious brain damage. Keep helium away from kids!

Thanks for your attention.

Steve Lewis

TDI instructor-trainer

Omitted Decompression and In-water Recompression (IWR)… some thoughts

Occasionally, in fact with an almost predictably cyclic regularity, two questions that surface on the internet dive forums ask about missed decompression and/or in-water recompression (IWR).

My standard answer on a public forum is to suggest that when the diver shows signs or complains of DCS symptoms, notifying EMS, keep the diver on the surface, warm and hydrated, monitor for changes in their condition (a correctly conducted five-minute neurological exam is a decent protocol for this), have them breathe pure oxygen (preferably from a demand face mask), take notes that will be useful for EMS/Hyperbaric staff, and prepare for fast evac.

The suggested strategy for a diver who has omitted a “deco stop” or safety stop but is SHOWING NO SIGNS or who is NOT COMPLAINING OF ANY SYMPTOMS, is the same as above but without the call to EMS and rather than preparing for evac., collecting their kit for them and keeping them out of the water for at least 24 hours.

However, neither is a very good answer to the actual questions posed, and occasionally, I throw my hat in the ring… something like this.

The first step for anyone brave enough to attempt an answer is to define the differences between the two topics; and in particular, the circumstances that might necessitate the call for a diver to conduct an omitted decompression protocol, as opposed to those that indicate IWR as an option.

Let’s start with the easiest: Omitted Decompression.


The protocols for Omitted Deco are discussed and outlined in several technical diving student manuals – including a couple of TDI manuals – and the procedure is taught as part of TDI’s decompression and trimix courses. It is based on the protocol published in the US Navy Diving Manual and may only be attempted when the diver shows NO SIGNS and has no SYMPTOMS of DCS; and the omitted stop was no deeper than six metres.

There are a couple of other prerequisites relating to water conditions, weather conditions, thermal protection, available gases in sufficient volume, having a tender diver available to monitor the subject diver during the whole procedure, and the diver being in a position to return to the water within five minutes of surfacing.

All that as taken and confirmed: First, return to 12 metres and conduct the stop required at that depth by the original ascent schedule PLUS one quarter of the omitted three-metre stop time. If no stop was originally required, remain there for one quarter of the omitted three-metre stop time. Ascend to nine metres at a speed no greater than three metres per minute (the ascent speed for the whole procedure) and remain there for one third of the three-metre stop time. Ascend to six metres and wait there for half of the three-metre stop time. And finally ascend to three metres for one-and-a-half times the scheduled three-metre time.

Here’s the way that looks for an omitted or partially omitted deco stop at three-metres.

Depth (metres/feet) Original Stop (mins)/Gas Omitted Stop Procedure
12 metres/40 feet None/ bottom gas 3-minute stop
9 metres/30 feet 3 / bottom gas 4-minute stop
6 metres/20 feet 5 / oxygen 6-minute stop on oxygen if CNS allows
3 metres/10 feet 12 /oxygen (omitted) 18-minute stop on oxygen if CNS allows

For the record, I have tendered for divers who have missed all or part of a decompression schedule and for whom the missed deco protocol worked.

Now let’s attempt to clarify the issue of IWR. This is suggested when a diver surfaces and complains of symptoms (type one) and IWR is the ONLY option available… i.e. there is no hope of stabilizing them and getting them to a hyperbaric facility.

Important to establish first off that this is a highly risky endeavor. The risks of IWR include several minor issues relating to thermal stress and volume of gases needed, but the strong emphasis in the entire risk assessment analysis center on the subject diver getting worse far worse once in the water and becoming, for example, paralyzed and/or losing consciousness. Oh, and then dying.

Various protocols and tables for IWR have been developed over the years. The recognized tables include the Australian, the Hawaiian, the US Navy, and the Pyle tables… I believe Pyle’s modification to the Hawaiian table are the most “up-to-date.” I am reasonably sure that NONE carries sanction from the major sport agencies. The technical agency I teach for, that I do consultant work for, and on whose training advisory panel I served for several years, does not sanction IWR either. Essentially, within the context of recreational diving (tech or sport), IWR is simply NOT an option.

Just in case we wonder why, here’s a checklist of the minimum kit and personnel requirements for attempting IWR in a remote location.

  • A heavily weighted shot line secured in a sheltered spot where surface waves will not influence comfort of subject diver and/or the tender (who will be in the water) and treatment supervisor (who will be on the surface).
  • Some way to hold the subject diver in place… a climbing harness works as does a sidemount harness with some modifications
  • Stages in the shot line to hold the subject diver at a set position in the water column… prussik loops and a locking carabiner work if tied and anchored correctly.
  • Full-face masks with coms to the surface and each other
  • Surface supplied gas (oxygen et al) supplied to the subject diver via umbilical
  • An experienced tender and supervisor who have at very least certification and some background in hyperbaric treatment
  • Adequate and possibly additional thermal protection for both subject diver and tender
  • A valid IWR treatment “table”


As someone who is occasionally involved in expedition diving (the only situation I can imagine where the whole team would discuss IWR as part of the SOPs during pre-trip planning sessions), IWR is considered highly risky even when ALL the above, and a few more details, are available. It is also understood that IWR (just as recompression in a chamber on the deck of a boat or in a medical facility) may not resolve the issue. In other words, the subject diver may die.

The preferred option if a portable chamber is NOT AVAILABLE – and something many expedition leaders seem to have less hesitation using – is saline IV (intravenous) therapy, oxygen and the use of pain medication all administered by a practicing medical practitioner of some sort… NP, Paramedic, MD et al. It is therefore considered best practice to have at least one of these as part of the team on ALL expeditions to remote locations.

(For the record, I have been lucky enough to lead several expeditions to various spots where there may have been a temptation to use IWR, and I have certainly tried to make sure that at least one team member is an experienced diving MD. To date, one of my team has had to supervise an autopsy on one of our fellow team members, but we have not had to deal with IWR. Therefore, my first-hand experience in this issue has been ZERO.

You can read more at Gene Hobbs excellent online resource:
http://archive.rubicon-foundation.org/xmlui/handle/123456789/5629

++++++++




CCR Cave… special circumstances or a walk in the park?

Following on from one of the main debate streams that surfaced during the NACD conference, a few buddies and I recently discussed the “deliverables” of a CCR Cave Diving course.

One of them — and it seems a valid topic to present to “new” CCR cave divers as well as experienced OC cave divers signed up for a cave orientation course — is gas volume management for bailout scenarios.

Typically, OC cave divers have a pretty simple set of rules to govern how much gas they need to carry with them. For CCR divers, those rules are not as simple because there is an extra variable. And that variable is the diver’s gas consumption rate once he has bailed out: it will vary a lot!

To better understand that why this is, we have to consider the reasons that would drive a CCR diver to abandon “the loop” to breathe open-circuit.

One example — perhaps the worse-case scenario — is carbon dioxide poisoning. There are a bunch of possible events that could lead up to this, but for the time-being, let’s just take it as read that the diver has experienced one almighty pear-shaped CO2 breakthrough event, and has ALMOST left it until too late before bailing out. He is hyperventilating and is close to panic.

So, what consumption rate is best to use as a benchmark?

For most to the OC stuff I teach — and in lieu of real data — a SAC rate of 14 litres per minute is a good starting point. (That’s about half a cubic foot for those struggling with imperial units.) To find the actual consumption (RMV), that number would be multiplied by the depth or average depth expressed in bar and the product of that calculation by a number to represent the Dive Factor (workload, thermal stress, etc.). For most OC dives, a DF of 1.5 to 2 is OK. However, for a CCR diver battling back from the edge of CO2 oblivion, a DF of 3 is the minimum recommended stating point.

To put this into a real-world example, consider a CCR diver bailing out around a 40 minute swim from the mouth of a cave with an average depth of 25 metres.

Our 14 litre per minute consumption rate now gives us 14 X 3.5 (depth in bar) x 3 (DF) X40 (minutes to surface) which equals 5880 litres.

That is a lot of gas, and effectively requires the diver to carry more than two fully-charged 12 litre cylinders (aluminum 80s) as bailout. Is this realistic? Is it realistic to imagine that the elevated consumption rate experienced immediately following CO2 break-through would persist for the full duration of the exit swim? Also, is it wise for the diver to have no redundancy in the event of one of those two bailout regulators malfunctioning?

What do you think?