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The Thought Process Behind GUE’s CCR Configuration

GUE is known for taking its own holistic approach to gear configuration. Here GUE board member and Instructor Trainer Richard Lundgren explains the reasoning behind its unique closed-circuit rebreather configuration. It’s all about the gas!

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By Richard Lundgren
Header photo by Ortwin Khan

Numerous incidents over the years have resulted in tragic and fatal outcomes due to inefficient and insufficient bailout procedures and systems. At the present time, there are no community standards that detail:

  • How much bailout gas volume should be reserved
  • How to store and access the bailout gas 
  • How to chose bailout gas properties

Accordingly, Global Underwater Explorers (GUE) created a standardized bailout system consistent with GUE’s holistic gear configuration, Standard Operating Procedures(SOP), and diver training system. The system was designed holistically; consequently, the value and usefulness of the system are jeopardized if any of its components are removed.  

Bailout Gas Reserve Volumes

The volume of gas needed to sustain a diver while bailing from a rebreather is difficult to assess, as many different factors impacts the result— including respiratory rate, depth and time, CO2 levels, and stress levels. These are but a few of the variables. All reserve gas calculations may be appropriate under ideal conditions and circumstances, but they should be regarded as estimates, or predictions at best.

The gas volume needed for two divers to safely ascend to the first gas switch is referred to as Minimum Gas (MG) for scuba divers. The gas volume needed for one rebreather diver to ascend on open-circuit during duress is referred to as Bailout Minimum Gas (BMG). The BMG is calculated using the following variables:

Consumption (C): GUE recommends using a surface consumption rate (SCR) of 20 liters per minute, or 0.75 f3 if imperial is used.

Average Pressure (AvP or average ATA): The average pressure between the target depth (max depth) to the first available gas source or the surface (min depth)

Time (T):  The ascent rate should be according to the decompression profile (variable ascent rate). However, in order to simplify and increase conservatism, the ascent rate used in the BMG formula is set to 3 meters/10 ft per minute. Any decompression time required before the gas switch (first available gas source) must be added to the total time. One minute should be added for the adverse event (the bailout) and one minute additionally for performing the gas switch.

BMG = C x AvP x T

Note that Bailout Minimum Gas reserves are estimations and may not be sufficient! Even though catastrophic failures are unlikely, other factors like hypercapnia (CO2 poisoning) and stress warrants a cautious approach. 

Decompression bailout gas volumes are calculated based on the diver’s actual need (based on their decompression table/algorithm), and no additional reserve is added. 

It should be noted that GUE does not endorse the use of “team bailout,” i.e. when one diver carries bottom gas bailout and another diver carries decompression gas based on only one diver’s need. A separation or an equipment failure would quickly render a system like this useless.

Common Tech Community Rebreather Configuration

  • Backmount rebreather (note side mount rebreathers are gaining in popularity)
  • Typically, three-liter oxygen and a three-liter diluent cylinder on board (each hold 712 l/25 f3) 
  • Bailout gas in one or more stage bottles which could be connected to an integrated Bailout Valve (BOV).
Divers on the AP Diving Inspiration rebreather in typical backmount configuration. Photo by Martin Parker.
Cave diver in the DiveSoft Liberty sidemount rebreather. Photo courtesy of Marissa Eckert.

Containment and Access

Rather than carry bailout minimum gas (BMG) in a stage bottle, which is typical in the rebreather diving community, GUE has designed its bailout system as a redundant open-circuit system consisting of two 7-liter, 232 bar cylinders (57 f3 each) that are integrated into the rebreather frame, and called the “D7” system, i.e. D for doubles, 7 for seven liter. Note that GUE has standardized the JJ-CCR closed-circuit rebreather for training and operations.

Photo by Kirill Egorov.

These cylinders, each with individual valves, are linked together using a flexible manifold. This system holds up to 3250 liters of gas (114 f3), of which only about 10% is used by the rebreather as diluent. Hence, close to 3000 liters (106 f3) is reserved for a bailout situation. This gives a tremendous capacity and flexibility in a relatively small form factor for dives requiring additional gas reserves (when direct ascent is not possible or desirable). 

The following advantages were considered when designing the bailout system:

  • The D7 system is consistent with existing open-circuit systems utilized by GUE divers. A bailout system that is familiar to the user will not increase stress levels, which is important. A GUE diver will rely on previous experience and procedures when most needed.
  • The system contains the gas volumes needed according to the GUE BMG calculations as well as the diluent needed for a wide range of dive missions.
  • The system is fully redundant and has the capacity to isolate failing components, like a set of open-circuit doubles and still allowing full access to the gas.
  • The overall weight of the system is less, compared to a standard system with an AL11 liter (aluminum 80 f3) bailout cylinder. In addition, it contains 800-900 liters/20-32 f3 more gas available for a bailout situation compared to the AL11 liter system. Weight has been traded for gas.
  • The system does not occupy the position of a stage bottle which allows for additional stages or decompression bottles to be added.
  • If the ISO valves on each side were closed, the flex manifold can be removed and the cylinders transported individually while still full.

Bailout gas can be accessed quickly by a bailout valve (BOV), which is typically configured as a separate open-circuit regulator worn on a necklace, consistent with GUE’s open-circuit configuration. However, some GUE divers use an integrated BOV. After evaluation of the situation, while breathing open-circuit from the BOV, the user can transition to a high-performance regulator worn on a long hose if the situation calls for it.

The long hose is carried under the loop when diving the rebreather. The chances of having to donate to another GUE rebreather diver is low, as both carry redundant bailout. Still, GUE maintains that the capacity to donate gas must be present. The process is more likely to involve a handover of the long hose rather than a donation. 

Photo by Jesper Kjøller.

Still, if needed, such a donation is made possible by either removing the loop temporarily or by simply donating the long hose from under the loop. 

Bailout decompression gasses are carried in decompression stage bottles. If more than three bottles are needed, the bottles that are to be used at the shallowest depths are carried on a stage leash (i.e. a short lease that clips to your side D-ring to carry multiple stage bottles). Maintaining bottle-rotation techniques and capacity through regular practice is important and challenging, as this skill is rarely used with the rebreather.

Bailout Gas Properties

The choice of bailout gas is extremely important, as survival may well depend on it. It is not only the volume that is important, the individual gas properties will decide if the bailout gas will be optimal or not. As the D7 system contains both the diluent and bailout gas, both gasses share the same characteristic. The following gas characteristics must be considered when choosing gas:

Density

The equivalent (air) gas density depth should not exceed 30 meters/100 ft or 5.1 grams/liter. This is consistent with the latest research by Gavin Anthony and Simon Mitchell that recommends that divers maintain maximum gas density ideally below 5.2 g/l, equivalent to air at 31 m/102 ft, and a hard maximum of 6.2 g/l, the equivalent to air at 39 m/128 ft. You can find a simple gas density calculator here.

Ventilation is impaired when diving, due to several factors which increase the work of breathing (WOB); when diving rebreathers, the impairment is even more so. High gas density, for example, when diving gas containing no or low fractions of helium, significantly decreases a diver’s ventilation capacity and increases the risk of dynamic airway compression. CO2 washout from blood depends on ventilation capacity and can be hindered if a high-density gas is used. The impact of density is very important, and the risk of using dense gases is not to be neglected. Note that this effect is not limited to deep diving. Using a dense gas as shallow as 30 meters/100 ft reduces a diver’s ventilation capacity by a staggering 50%.

Narcosis

The (air) equivalent narcotic depth should also not exceed 30 m/100 ft, or PN2=3.16. Rebreathers and emergency situations are complex enough without further being aided by narcosis.

Oxygen Toxicity

The PO2 should be limited to allow for long exposures. GUE operating standards call for a maximum PO2 for bottom gases of 1.2 atm, a PO2 of 1.4 for deep decompression gases, and a PO2 of 1.6 for shallow decompression gases. GUE recommends using the next deeper GUE standard bottom gas for diluent/bailout when diving a rebreather in combination with GUE standard decompression gases.

Bailout gasses are not chosen in order to give the shortest possible decompression obligation. They are chosen in order to give the best odds of surviving a potentially life-threatening situation. 

Two GUE CCR divers in California. Photo by Karim Hamza.

In Summary

GUE’s D7 bailout system is flexible and contains the rebreather’s diluent as well as bailout gas reserves needed for a range of different missions. The familiarity the system, along with the knowledge that they are carrying ample gas reserves, gives GUE divers peace of mind. Choosing gases with properties that will aid a diver in duress while dealing with an emergency completes the system.

GUE did not prioritize the ease of climbing boat ladders or reducing decompression by a few minutes. These are more appropriately addressed with sessions at the gym, combined with finding aquatic comfort. Nothing prevents a complete removal of the entire system at the surface if an easy exit is needed.


Founder of Scandinavia’s Baltic Sea Divers and Ocean Discovery diving groups, and a member of GUE’s Board of Directors and GUE’s Technical Administrator, Richard Lundgren has participated in numerous underwater expeditions worldwide and is one of Europe’s most experienced trimix divers. With more than 4000 dives to his credit, Richard Lundgren was a member of the GUE expeditions to dive the Britannic (sister ship of the ill-fated Titanic) in 1997 and 1999, and has been involved in numerous projects to explore mines and caves in Sweden, Norway, and Finland. In 1997, in arctic conditions, he performed the longest cave dive ever carried out in Scandinavia. Richard’s other exploration work has included the 1999 filming of the famous submarine, M1, for the BBC; the side scan sonar surveys of the Spanish gold galleons outside Florida’s Key West in 2000; and the search for the Admiral’s Fleet, an ongoing project that has already led to the discovery of more than 40 virgin wrecks perfectly preserved in the cold waters of the Swedish Baltic Sea.

Diving Safety

The Flexibility of Standard Operating Procedures

Instructor trainer Guy Shockey discusses the purpose, value, and yes, flexibility of standard operating procedures, or SOPs, in diving. Sound like an oxymoron? Shockey explains how SOPs can help offload some of our internal processing and situational awareness, so we can focus on the important part of the dive—having FUN!

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By Guy Shockey

Header Image by Derk Remmers

At first glance, the title reads like a bit of an oxymoron. How can a standard operating procedure (SOP)—which implies a ‘one size fits all’ solution to problem solving—also be flexible? How can flexible also be firm?

One of the things that initially attracted me to Global Underwater Explorers (GUE) was the presence of SOPs. For anyone with a military background, SOPs were our bread and butter. You can create a good SOP while you have the time to think and plan. You can put them into practice, refine them over time, and keep them in place until new or better information comes along to change them. 

For example, airline pilots have a binder full of SOPs for various contingencies. When something comes up, they turn to the correct page and find a list of actions to follow. Pilots understand that these SOPs represent the collective knowledge of many aviators and engineers that have come before them. Many of them have also been revised multiple times, codified, and then even revised after that. Some SOPs require commitment to memory because there may not be a lot of time, and pulling out a three-ring binder or flipping through your iPad to the correct page isn’t the appropriate action. In that case, then those same pilots practice these situations regularly in simulator training. 

One of the primary values of an SOP is that it frees up a lot of situational awareness information processing. You are able to match up “mental models” to the current situation and, rather than processing your information in small bite-sized pieces, you are able to process “chunks” of information that match patterns of something that you know or are familiar with. 

Let me create an analogy that may help make this clearer. If I were to give you a bowl of tomato sauce, some slices of pepperoni, some mushrooms, some cheese, and a piece of baked dough, you could eat them all one at a time and try to figure out what it was you were eating. Or, I can put all those ingredients on that same piece of dough, bake it, and you would instantly know that you were eating pizza. You don’t have to process all the ingredients one at a time. You already have an existing mental model that says “pizza.” We do this when we solve problems. We pattern-match and identify existing mental models all the time, and it’s actually the only way we can actually think as fast as we do. Many problems are actually solved with multiple mental models being applied together. 

Photo by Derk Remmers.

Having an SOP gives you the ability to solve problems more efficiently and effectively because you have a ready-made mental model or solution to a recognized problem. Think of every first aid course you have ever taken and the “ABCs” of first aid. SOPs are incredibly valuable in nearly every environment that includes potential risks. 

If an SOP is shared, it also allows diverse groups to work together. It is no surprise that SOPs from various militaries of the world are often similar, even if they are written in different languages. From personal experience, NATO countries can coordinate and execute complex military operations because they share common SOPs that, if not identical, are very similar and don’t require much adjusting to mesh together. Common expectations and goals can be shared toward a common purpose. 

When in time-sensitive environments, many of these SOPs and the corresponding mental models they help develop can be lifesaving. This doesn’t just apply to the military, but also to law enforcement, paramedics, firefighters, pilots, and any other profession that is often faced with time pressures in making critical decisions. 



Do you share a common operational picture?

There is an interesting term often used in military circles called the “common operational picture” (COP). This is exactly what it sounds like, and is sometimes referred to as “a single source of truth.” Everyone involved in a decision-making cycle needs to be privy to the information that affects their decision. Sharing that information allows us to make informed decisions that often include SOPs. You could argue that we are creating a mental model that lets us apply another mental model!  

Alright, so how exactly does all this apply to diving and GUE diving in particular? I’m pretty sure that many of you have already connected many of the dots. 

In the GUE world, our divers create a COP at the beginning of the dive. We help reiterate this COP with our GUE EDGE pre-dive checklist, which is a great example of an SOP! We review the goals, team roles, our equipment, and the operational parameters of the dive, all in a standardized format that efficiently accommodates teammates from multiple different languages and cultures. I have performed GUE EDGEs in about 10 different languages and I only speak two!  The fact that we were doing this in a standardized fashion meant I could follow along and knew what they were talking about. 

As the dive plan complexity increases, so too does the COP become more complex. Some of our more ambitious exploration projects require even more time spent in planning than actual execution. But because there is a COP, coupled with SOPs (I know that’s a lot of acronyms), these projects usually go off without a hitch. 

Photo by Derk Remmers.

During the dive, there are multiple times that we have team-expected actions that are based on SOPs, and this contributes to and reinforces our COP. It is almost as if we are filling in a PDF form as we go along and confirming the various pieces of information that we need to complete the entire “form” or plan. 

In the case of emergencies, we have ready-to-implement SOPs for just about any equipment malfunction from valve failures to losing your mask. We practice these SOPs so that, in real time, we can employ them in a timely fashion and resolve the problem. These SOPs are just like the ones I mentioned at the beginning of this article and were developed over time and refined with successive reviews and after-action analyses. Finally, they have been codified, and you can now find them in our GUE SOP manual! You will also notice that this manual is of a particular “version,” which tells you that the SOP is constantly being fine-tuned in a dynamic process.

How Can An SOP Be Flexible?

In reality, it isn’t the actual SOP that is flexible, but it is the degree of flexibility it provides to the dive plan itself that is of value. Let me give you an example from the technical diving world. 

Imagine the team is diving on a wreck and experiences a delay on the bottom for whatever reason. It could be that it was done on purpose (discovery of pirate gold!) or maybe it was imposed upon the team as a result of any number of problems, like dealing with an equipment problem or an entanglement, for example. The dive is longer, the decompression obligation is now going to be longer, and there are some decisions to be made. 

Having an SOP here can help provide a solution to the problem with no mess and no fuss. The divers dig into the bag of tricks they learned in GUE technical training, and because of their common operational picture and team-expected actions, they apply the SOP they practice regularly and modify their decompression schedule to suit the new bottom time. What could have been an exciting moment for many divers turns into just another discussion point for their debrief after the dive!

Photo by Alexandra Graziano.

So, while SOPs are usually not flexible in and of themselves, they allow for a great deal of flexibility while diving by freeing up mental processing power and providing ready-made and practiced solutions to potential problems. 

GUE SOPs presuppose the presence of personal diving skills at a high level, and assume that factors such as good buoyancy and trim are second nature. In fact, many of the SOPs state the first step in resolving a problem as “stabilize” or “stop” in all three dimensions. GUE divers see that, as the diving gets more complex, the SOPs also get more complex. For a new GUE Fundamentals diver, demonstrating some of the SOPs required to pass muster as a Tech 2 or CCR 2 diver look more akin to channeling “the force” than anything else. However, like most things, perfect practice produces perfect performance, and so it’s just a matter of putting in the repetitions. 

For me, diving has never been the end but the means to the end. Anything I can do to make those means take up less mental and physical horsepower means that I can devote more of the same to the end goal. And at the end of the day, I am really all about that pirate gold!

Additional Resources:

Note that GUE members or divers taking a GUE course receive access to GUE’s 30-page manual, Standard Operating Procedures.


Guy Shockey is a GUE instructor and trainer who is actively involved in mentoring the next generation of GUE divers. He started diving in 1982 in a cold mountain lake in Alberta, Canada. Since then, he has logged somewhere close to 8,000 dives in most of the oceans of the world. He is a passionate technical diver with a particular interest in deeper ocean wreck diving. He is a former military officer and professional hunter with both bachelor’s and master’s degrees in political science. He is also an entrepreneur with several successful startup companies to his credit.

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