Wrist Mounted Gauges v Console Computers

It is common in recreational diving (particularly with rental gear) to have not only an SPG, but a multipurpose console including a compass and computer, attached to the high pressure hose.

However, there are potential issues with this design and advantages to separating the console into an SPG and wrist mounted compass and computer or depth gauge.

Somewhat counterintuitively, mounting all the gauges together can discourage proper referencing. Rather than maintaining an active knowledge of each gauge, we simply glance over the console, almost instantly forgetting the readings—and being tucked away in the belt or trailing behind, often means the gauges are easily forgotten and rarely referenced at all during the dive.

Conversely, consoles can completely draw our focus, if we spend a significant amount of time referencing the one combined unit. This can be dangerous, leading to a loss of buoyancy or situational and team awareness.

Consoles are also cumbersome and often left dragging behind to damage the environment. Even when tucked away in the belt they can be an entanglement or environmental hazard. Either way, they reduce streamlining, causing drag, decreasing propulsion efficiency and increasing breathing rates.

By contrast, splitting the console into its components: SPG, compass and computer or depth gauge we avoid these issues.

Every few minutes we can reference our SPG, compass and computer individually. This small group of tasks is less likely to consume our focus allowing us to maintain control and reference the up line, our surroundings and our team between each reading, while simultaneously encouraging those readings to be more effective by breaking the task into smaller manageable units.

Breaking the console into components also greatly reduces drag and the likelihood of entanglement or environmental damage, by letting us replace the console with a small SPG and stow it out of the way, attached to a shorter hose.

By wrist mounting our compass, navigation becomes easier. We no longer have to hold a large console out in front while trying to maintain awareness and effective propulsion.

Perhaps the biggest advantage comes from wrist mounting our computer or depth gauge. We can easily maintain our decompression stops, use a scooter or keep good contact with our team and environment, all while periodically referencing our depth and time.

While a console has business advantages for rental equipment, there are great diving benefits gained by separating it into components.

The Goodman Handle

Commonly, any handle used on a canister light head is referred to as a Goodman handle. However the design and purpose of the Goodman handle is very specific and many fall short of these requirements.

In the 1970’s Bob Goodman, a Florida local, designed a hand mounted light that allowed divers to retain full use of their hands—very important in caves where it can be necessary for divers to pull their way through high flow sections. The other main advantage is the ability to use both a primary light and primary reel with the same hand—which was increasingly important as the use of scooters during exploration became common place, allowing divers to use a primary light, reel and scooter simultaneously.

Goodman handles must be rigid. While the primary light is usually on the left hand, it is sometimes necessary to temporarily switch hands, e.g. to dump gas, reference an SPG or retrieve something from the left pocket. The rigid handle allows the light to be moved into the right hand (holding it by the ballast) and then quickly and efficiently replaced on the left hand. Soft/elastic handles, while feeling secure when in place, make this more cumbersome and time consuming, requiring the strap to be wiggled back over the left hand.

Another important property of a Goodman handles is a flat low profile metal frame. This allows the frame of an exploration reel to sit flat against the Goodman handle in the palm of the hand and is very stable. The round handles found on many lights need to be ‘held’ by the fingers, reducing dexterity and full use of the hand and are very unstable when used with a reel.

Many explorers add a thumb loop to the light head which allows the right thumb to hold the light if required. Thumb loops are excellent for scooter diving when the fingers of the right hand are in use but the thumb is available.

So that’s it! A Goodman handle has a rigid and flat, low profile metal design for maximising utility in various situations and to maintain dexterity and use of the hands.

Be Back On The Surface With 50 Bar… Why?

Many divers accept the 50bar rule without understanding what it means and why it has become conventional wisdom in the industry. Amazingly, this wrote acceptance is not always limited to new divers.

Rather than just reciting “Be back on the boat with 50bar”, we’d prefer to illustrate the logic behind it, using some example dives.

To understand the 50bar rule and how to better apply it to our diving, we need to introduce a few basic concepts and some related numbers for use in our calculations:

Concepts

  1. Minimum Gas

    The absolute minimum volume of gas required for a diver and her buddy to ascend safely to the surface from the deepest point of the dive while sharing gas.

  2. Surface Consumption Rate

    The average volume of gas a diver uses per minute at the surface. SCRs are used to calculate expected gas consumption or gas requirements for a given dive.

  3. Safety Stop

    A short decompression stop for added safety during recreational non-decompression diving.

  4. Ascent Rate

    The speed at which we ascend from depth to our safety stop.

Numbers

Surface Consumption Rates:

  • 20L/min during the bottom phase of a dive
  • 30L/min for a stressed diver

Safety Stop: 3min @ 5m*

Ascent Rate: 9m/min from depth to our safety stop and then to the surface

Cylinder Capacity: 11L, AL80

Examples

First up, we will look at an average open water dive to 18m.

If you recall the concept of minimum gas, we need to plan our dive so that if something goes wrong at the deepest point we can safely ascend and perform our safety stop while gas sharing.

While having a great time on the reef, photographing nudibranchs and turtles, our buddy runs out of gas. This situation will tend to stress everyone involved, so we err on the side of conservatism and assume two stressed divers with an elevated SCR.

If we allow about 1min on the bottom sorting out the issue, donating our octopus and making sure everyone is ok, before ascending to our safety stop at 5m for 3min, then a safe ascent to the surface, we find our ascent profile and gas consumption for two stressed divers breathing at 30L/min will look something like this:

Depth Time Avg Depth (Pres) Divers SCR Gas
18m 1min 18m (2.8bar) 2 30 168L
18–5m 1min 30s 12m (2.2bar) 2 30 198L
5m 3min 5m (1.5bar) 2 30 270L
5–0m 30s 2.5m (1.25bar) 2 30 38L
TOTAL GAS REQUIRED 674L

In an 11L cylinder, 674L of gas = 674 / 11 ≈ 70bar

Using 10bar increments makes reading from your pressure gauge easier and we should always round up for conservatism, or we would be caught short!

This example illustrates that at 18m we need at least 70bar of gas in our single 11L tank to safely handle an out of gas ascent. 70bar to make it to the surface together.

If at any point during the dive we hit 70bar, the dive is over. Breathing below 70bar is putting ourself and our buddy at risk. Effectively, we are breathing our buddy’s gas. If something were to go wrong, we wouldn’t have enough to make a safe ascent together and might run out mid safety stop.

Next let us calculate the minimum gas for a deeper dive to 30m

Depth Time Avg Depth (Pres) Divers SCR Gas
30m 1min 30m (2.8bar) 2 30 240L
30–5m 2min 50s 18m (2.8bar) 2 30 471L
5m 3min 5m (1.5bar) 2 30 270L
5–0m 30s 2.5m (1.25bar) 2 30 38L
TOTAL GAS REQUIRED 1019L

In an 11L cylinder, 1019L of gas = 1019 / 11 ≈ 100bar

Deeper dives clearly require a much higher minimum gas and in this example we can see a possible genesis of the 50bar rule. To get two divers safely to the surface from 30m while gas sharing requires 100bar in an 11L cylinder. Half of that is 50bar. By aiming to be back on the boat with 50bar we are trying to account for emergencies.

Unfortunately, this conventional wisdom is not always enough. It fails to answer the most important question: When should we leave the bottom? Or more correctly, how much gas do we need for a safe ascent while sharing?

Of course, the answer depends on our dive profile, tank volume and surface consumption rates.

Minimum Gas Rules of Thumb

Tank Vol 0–18m 18–30m
11L 70bar 100bar
12L 60bar 90bar
15L 50bar 80bar

The Wash Up

Next time you are out on a dive, rather than simply following the 50bar rule, be aware of the logic behind it, use some rules of thumb or better yet, perform the calculations yourself.

And don’t forget:

Once you reach minimum gas, the dive is over.

* GUE divers use a different ascent profile (even in recreational diving) incorporating stops deeper in the profile, but for the purposes of this article we will use a standard recreational profile as taught by most agencies, with a safety stop at 5m. The concepts are identical no matter what type of ascent profile is being used.↩

Bob’s Tragedy

Diving, while not without risk, is relatively safe and with appropriate training and planning even many of the risks associated with tech and cave diving can be mitigated.

However, poor training and planning often leave divers exposed to increased and largely unnecessary levels of risk, and as diving accidents can be serious and potentially life threatening, thorough accident analysis is important for understanding both what happened and how to avoid similar incidents in the future.

Following is an analysis of an incident originally appearing in DAN’s Alert Diver Asia Pacific magazine. In our opinion a variety of issues tipped ‘Bob’ into the incident pit, ultimately leading to his tragic death1.

Incident Summary

For those of you without access to Alert Diver, the incident is summarised, in good faith and without material misrepresentation, here:

  1. Jamie and Bob had been tech divers for about a year.
  2. Bob does all the planning as he enjoys it and has more experience.
  3. Plan: 25min @ 50m; Back gas: twin tanks, Air; Deco gas: 36% & O₂
  4. After descent they separated to dive independently.
  5. After 20min Jamie was surprised to see Bob appear and signal that he wanted to turn the dive.
  6. Jamie turned to signal some other divers and when he turned back Bob was gone.
  7. Jamie ascended to 42m, the first of their planned deco stops, to find Bob already there, wild eyed and breathing from his 36% deco gas.
  8. Jaime understanding that Bob was breathing 36% well bellow its MOD, attempted to share his back gas with Bob, who refused.
  9. During this time they sank several metres.
  10. Bob panicked and swam for the surface. Jamie attempted to catch him, but stopped at 36m hoping to avoid bending.
  11. Bob broke the surface frothing at the mouth. He was blue and not breathing when the boat crew retrieved him.
  12. The boat crew had no first aid training and could provide no treatment.

Analysis

Given the relatively vague account provided, it’s difficult to perform any detailed or definitive analysis, but we can talk about some possibilities, make inferences about Bob’s tragedy and gain some insight into risk management and problem solving.

  1. “Bob does all the planning as he enjoys it and has more experience.”

    Dive planning: All team members should be involved in and understand dive planning. Familiarity with the dive plan and contingencies is mandatory for any dive, especially in the technical range.

  2. “Plan: 25min @ 50m; Back gas: twin tanks, Air; Deco gas: 36% & O₂”

    Inappropriate gas choice: Air at 50m has an END of 50m well beyond the 30m END where narcosis becomes a significant concern. Diving narc’d is similar to driving drunk—reaction times and mental capacity are degraded and problem solving ability is greatly impaired. Deep air is still common throughout the industry exposing divers to unnecessary risk particularly when something does go wrong. At this depth it’s likely that Bob was, on top of everything else, narc’d.

  3. “After descent they separated to dive independently.”

    Leaving the team: Diving independently exposes divers to far greater risks. Bob’s greatest asset was Jamie—a redundant gas source, a second brain for problem solving, reassurance during problems—and they decided to separate during the dive. Whatever else happened, matters were only made worse by him being alone as problems started to emerge. Jamie’s surprise at finding Bob near him at the 20min mark highlights this point even further, they were so separated that they had very little if any awareness of each other during the dive. It’s important to note that Bob made this mistake twice. Once during the planned dive, and once when he took off for the decompression stop at 42m. A better awareness of team diving and appropriate planning would have ensured that Jamie had ample gas for Bob to share while they completed their decompression.

  4. Out of gas?

    Bob appears to have been out of gas, or at least thought he was, after 20min. This could be the result of many factors including poor fitness, poor equipment maintenance, poor gas planning, no flow check or insufficient gas monitoring.

    Poor fitness: Unfit divers, especially smokers, are far more susceptible to over work on a dive, especially when carrying lots of equipment as on a tech dive. Elevated breathing rates and poor gas exchange in the lungs could contribute to higher than expected gas consumption rates.

    Poor equipment maintenance: Poorly maintained tanks, valves, regulators and SPGs etc could all lead to gas loss or increased consumption during a dive, either through leaks or elevated breathing rates.

    Poor gas planning: Unexpected out of gas incidents can also be the result of calculation errors on the surface during the planning phase or a failure to verify tank contents before diving.

    No flow check: An often overlooked pre dive step, the flow check is a simple procedure for verifying that all valves are open before diving. On twin tanks this ensures that both posts are open and breathable and that the isolation valve is open. If Bob’s manifold was closed he may have gone ‘out of gas’ with an entire tank still full. In the worst case, a diver could enter the water with no valves open, leaving them with not only no breathing gas but no inflation. This could be a potentially fatal error, particularly for divers with limited experience in valve manipulation.

    Insufficient gas monitoring: Divers should have a good knowledge of their SCR and regularly monitor gas consumption during a dive. Regular checks would have alerted Bob to any problem long before it became urgent, allowing him (and his team!) to either deal with the issue or make a controlled ascent while gas sharing.

  5. “… wild eyed and breathing from his 36% deco gas.”

    Panic response: CO₂ is a nasty gas, often overlooked in diving. It is extremely narcotic (many, many times more so than nitrogen), causes drowsiness, unconsciousness and ultimately death, is implicated in an increased risk of CNS oxygen toxicity, it drives our breathing cycle, causing increased breathing rate and gas use, and it also drives our panic response, its build up creating a feedback loop that leads to extreme panic and irrationality. All of these factors make it arguably the most dangerous gas we have to deal with as divers and most of the factors mentioned so far are likely to have increased Bob’s exposure to CO₂ leaving him ‘wild eyed’ and panicked.

    Incorrect gas switching procedures: Not only did Bob leave his team and race off to the decompression stop, he switched to a decompression gas without verification from his team. At 42m he was well bellow the MOD of his 36% decompression gas, exposing himself to a PPO₂ of almost 1.9 bar, well over what is considered safe, and a real risk of CNS oxygen toxicity. Given he was carrying two decompressions gases, was probably narc’d and was already in a panicked state, Bob also risked mistakenly switching to his 100% gas. If that had happened Jamie would most likely have discovered him already dead.

  6. “During this time they sank several metres.”

    Poor buoyancy: Poor buoyancy control simply makes everything more difficult underwater. Divers expend more energy and expose themselves to greater risk in problem situations. Bob was so panicked at this point that he refused to share gas and while they tried to resolve this, Bob and Jamie descended several metres, exposing Bob to an even higher PPO₂ and increasing their decompression obligation.

  7. “Jamie ascended to 42m, the first of their planned deco stops.”

    Poor understanding of deep stops: 42m is an incredibly deep first stop for a 50m dive. Decompression planning is a balance between getting shallow enough to start offgassing, slowing the ascent enough to control bubble growth and limiting time at depth to control ongassing. VPM conservatism 2 indicates that offgassing does not start until 36m, which is where their first deep stop should have been. Staying too deep during decompression is not conservative, it increases your decompression obligation.

  8. “Bob panicked and swam for the surface.”

    Blowing all stops: Bob’s final and ultimately fatal mistake was to blow his decompression and shoot to the surface. After so long at depth, it is unlikely Bob would have recovered, even had the boat crew been appropriately trained.

  9. “The boat crew had no first aid training”

    Poor planning: This is inexcusable and negligent on the part of the operator and the divers. They simply should not have entered the water without appropriately trained and equipped surface support.

Closing Thoughts

These sort of incidents are tragic and made worse when the actual problems are not identified. In our opinion Bob’s tragedy was the result of poor training, procedures and planning, lack of understanding and poor situational and team awareness.

No single issue or event caused his death (other than in the direct sense that blowing that sort of decompression obligation is likely to cause significant injury or be fatal). Rather, Bob’s death was the result of a series of mistakes and poorly managed problems. At every juncture there were opportunities to resolve the situation before it spiralled out of control.

This is what we call the incident pit. Accidents are rarely the result of a single issue. They snow ball. Missed procedures, mistakes and unresolved problems build and build, increasing diver stress and eventually leading to panic and unresolvable problems that are ultimately unsurvivable.

1. There are no doubt more details than those appearing in the article and this post represents our opinions and observations based on the incident as reported. It is really about risk management rather than the specifics of Bob’s tragedy. ↩

The Submersible Pressure Gauge

The Submersible Pressure Gauge is vital piece of equipment for every diver—functioning as a cylinder contents gauge, much like the fuel gauge of a car.

Most people learn to dive using a console containing an SPG, a compass and either a computer or depth gauge. Superficially, this seems like a good idea, keeping all those handy instruments in one place. However, there are some serious drawbacks to such an approach.

Multipurpose consoles are large and cumbersome, often dragging along the bottom or catching on coral or wrecks. In an overhead environment stirring up silt could be disasterous, reduced visibility leading to disorientation or worse. Ask yourself how often you have seen a console dragging along, impacting the environment and out of reach when needed.

The computer or depth gauge and compass are better positioned on the wrist where they are easily referenced without subsuming your entire focus and unable to impact anything—leaving only the SPG on a shorter, cleanly stowed high pressure hose.

SPGs are best made of brass and glass. Plastics are easily broken and scratches on a plastic facing can make the gauge difficult to read. On deep dives plastic can even flex inward causing the needle to stick and the gauge to read incorrectly. A brass and glass SPG withstands higher pressures at depth and gauges manufactured this way tend to be of a higher quality and more accurate.

High pressure hoses are usually around 36”/92cm, an excessive length that bows out from the body, causing additional drag and potentially snagging. Ideally, a high pressure hose should be 24”/61cm and clipped off to the left hip using a stainless steel bolt snap. Stowed this way the SPG and hose are streamlined and protected. Like anything, practice is needed to become proficient at quickly unclipping and reclipping the SPG when referencing it.

The bolt snap should be fastened to the SPG with cave line, allowing it to be cut away in the unlikely event the bolt snap jams. Using cave line instead of o-rings or zip ties is far less prone to unexpected breaks.

The connection between the SPG and high pressure hose contains a tiny swivel pin sealed by two tiny o-rings. These o-rings wear over time and the degradation is accelerated by salt, grit and sand. Consequently, you should keep your SPG clipped off and out of harms way when not reading it. With the SPG safely stowed, we also no longer need a rubber boot protecting it. These boots seem like a good idea initially, but actually trap salt, grit and sand, simultaneously degrading the swivel pin o-rings, while hiding any damage and potential leaks.

Configuring your SPG this way simplifies your equipment, makes deploying and referencing the gauge clean and easy and keeps the SPG safely tucked away, minimising drag and damage to both it and the environment—all contributing to a more pleasant, comfortable and safe diving experience.

Hose Logic, Part III: Routing

As we saw in parts I and II, as GUE divers we use a long hose for our primary regulator and that regulator, the one we’re breathing, is the one donated in an out of gas situation. Part II highlighted some of the reasons for this:

  1. It eliminates the possibility of donating a gas inappropriate for the current depth.

  2. We ensure the diver in need of gas gets a functioning regulator. If your backup is fouled or otherwise not functioning properly, you are much better placed to deal with the situation than the already stressed, out of gas diver.

  3. Formalising the procedure ensures consistency, whether breathing back gas, stages or decompression bottles, and with practice donation becomes a conditioned response—allowing pre-emptive action at the slightest hint of a problem.

  4. Panicked divers will often attempt to grab the regulator in your mouth anyway. Accommodating this possibility avoids confusion and compounding the problem.

  5. Using the long hose gives both divers room to move and manoeuvre, helping calm and control the situation.

  6. It becomes easy to restow the long hose after deployment. Trying to restow a long hose that is bungied to a tank or otherwise not easily reachable or deployable, can be quite time consuming and challenging.

Consequently, the long hose is run from the right post:

  1. The right post won’t roll off when impacting an overhead. At worst a significant impact will jam the post in the on position. If the long hose were running from the left post the opposite would be true. An impact would roll the post off, possibly jamming it in that position. Needless to say this stops the gas supply to the out of gas diver and could be fatal—the out of gas diver having no way to reopen the donating diver’s right post and the donating diver potentially being unaware of the problem—particularly while negotiating a restriction in single file (the original reason for the long hose).

    Conversely, a left post roll off will be noticed immediately by the donating diver as their backup regulator would become difficult to breath or stop supplying gas altogether. If the post becomes jammed and the donating diver is unable to reopen it, they have access to a tertiary backup and can start breathing from their wing inflator by depressing both the inflate and dump buttons simultaneously. An option not available to an out of gas diver, no matter their routing.

  2. While not as important as 1., this routing allows the long hose to run naturally from the first stage down the side of the tanks, across the front of the diver’s body, behind the neck and into the right side of the second stage, where most standard second stages feed from. Running the long hose from the left post would necessitate an abrupt change in direction, tight bend in the hose or a left feeding second stage to accomplish the same thing.

The LP inflator hose is also fed from the right post:

  1. Running the LP inflator from the same post as the primary regulator gives immediate feedback if the gas flow to the inflator in interrupted—the diver’s primary regulator would also stop delivering gas. Placing the LP inflator on the opposite post to the primary regulator introduces the possibility of a gas delivery failure to the wing going unnoticed until needed—a potentially dangerous situation, considering emergency scenarios that may require immediate inflation.

  2. In the event of a stuck inflator, disconnecting the LP inflator hose to prevent uncontrolled ascent is undeniably effective. However, it is not always possible, e.g. when a loss of intermediate pressure control in the first stage (high pressure seat failure) causes ice to form around the quick disconnect. If the LP inflator can’t be disconnected effectively, excess gas can be dumped from the wing with the left arm, using the rear dump valve (on the left of most wings), preventing a runaway ascent, while simultaneously shutting down the right post with the right arm. Running the inflator from the left post would make this impossible.

  3. Feeding the LP inflator from the right post runs the hose behind the diver’s head. Gas flow through hoses, particularly when using helium, is audible at depth, and serves as another indicator of possible problems, e.g. leaks.

  4. As mentioned, the LP inflator is a tertiary backup regulator. By feeding it from the right post we ensure that it is always available, never rolling off, and can be used by the donating diver if their backup fails or left post rolls off. Both divers can then still breath from the right post.

The backup regulator, hanging on a bungie necklace just below the chin, runs from the left post:

  1. Splitting the responsibility between two first stages, ensures a redundant gas supply. The backup can be hung with the mouthpiece pointing up, allowing the diver to grab it without using their hands.

The SPG is fed from the left post:

  1. The probability of a first stage failure is highest for the primary regulator—the stage with the greatest demand. Having the SPG on the left post ensures it remains relevant for the greatest length of time.

  2. If the isolator happens to be closed, e.g. failing to run through the appropriate pre dive and pre filling checks, the indicated pressure won’t fall over time, giving the diver timely feedback that there is something amiss.

  3. DPVs/scooters are typically operated with the right hand, leaving the left to manipulate the LP inflator, drysuit inflator, nose for equalisation, light head for signalling, reel, etc. Running the SPG from the left post gives the diver the same freedom to check it, without letting off the trigger.

GUE divers use a similar hose routing for single tank diving as well. However, for obvious reasons we run everything from a single first stage—with a standard right post style valve, i.e. no roll offs. While clearly losing some redundancy in a single tank setup, maintaining the same overall hose routing ensures consistent responses and equipment configuration for all of our diving.

Hose Logic, Part II: Why We Use a Long Hose

The principle of the long hose is what finally convinced me to undergo GUE Fundamentals training—after seeing other GUE divers in the water and thinking: “Man, I want to look that good in the water”. Working as an instructor and guide in the Caribbean, I occasionally assisted out of gas divers. Swimming while connected to another diver by a standard octopus hose is uncomfortable to say the least, but more importantly: ineffective.

GUE teaches an alternative system, using a long hose—allowing divers to maintain a comfortable distance while sharing and making their way back to their exit.

The long hose system involves having your primary regulator on a 5’/7’ hose and a backup regulator on a short hose running over your right shoulder and hanging just under your chin, attached to a necklace made of bungee chord. The long hose runs from the right post first stage, along the tank, around under your right arm or light canister, across your chest, up behind your neck and around into your mouth—for obvious reasons the hose is not wrapped around your neck! This method of stowing the long hose makes it trivally easy to restow if it was deployed temporarily. You wont need help stuffing the hose back into a bungee on your tank or have to otherwise deal with 7’ of troublesome regulator hose.

Originally developed for cave diving, it became clear that the long hose’s benefits apply equally to gas sharing while swimming through a cave restriction, a passageway in a wreck or side by side on an open reef—there is no real difference. Handling any out of gas situation is more comfortable, more effective and less stressful, allowing divers to maintain buoyancy and trim, while giving them room to move and manoeuvre even in the tightest of spaces.

Why The Primary?

During an out of gas situation your number one priority is to get gas to the stressed and possibly panicking, out of gas diver. Do you really want to give them a regulator that has been tucked into your BC? A regulator that may have come loose and been dragging in the sand? A regulator that may take some time to locate and donate? A regulator that may be running from a post that has rolled off? You have gas, you are calm and in control. The best course of action is to donate the regulator you know is clean and functional.

Attempting to donate your secondary regulator, introduces uncertainty and risk related to all the questions above, increasing the chance that an out of gas diver, already stressed and desperate for air, is going to reach for your primary regulator anyway. It is better to be prepared for this and deal with the immediate priority by donating your primary in the first place.

A quick dip of the head allows you to quickly and smoothly punch out your primary regulator, freeing the majority of the long hose and getting gas where it is needed. Now it becomes apparent why we call the secondary regulator a ‘backup’. It is your backup, and is easily found and popped into your mouth once you’ve donated the long hose. Being on a short hose and hanging around your neck, the backup regulator is unlikely to be contaminated with sand or silt and any leaks or free flows would have been immediately identified and remedied during the dive.

Once you are both settled, the remainder of the long hose can be deployed, any other cleanup performed and you can comfortably call the dive.

The long hose gives the out of gas diver control of the hose and lowers the risk of it being pulled from their mouth. It also gives both divers room to communicate effectively, maintain situational awareness, use effective propulsion techniques and to position themselves as dictated by the environment—try swimming single file through a restriction sharing a standard length regulator hose. Swimming on your back dragging an out of gas diver to the boat is a thing of the past!

Some divers express concern that donating their own regulator could leave them without a functioning gas supply. But if you really think this through, it is not an issue. Maintaining your equipment, using correct hose routing (see part III) and performing appropriate checks before and during the dive ensures your backup regulator is on and functional.

Learning and practising safety- or s-drills ensures we are proficient and can deal with an out of gas situation efficiently and effectively—before stress becomes panic. A skill worth learning takes refinement and your diving routine should include regular s-drill practise, whether you are an experienced or novice diver, ensuring you are a valuable team member, not just a buddy.

Watch out for Hose Logic, Part III: Routing.

Hose Logic, Part I: Lengths

One of the characteristics that define a GUE diver is our equipment configuration. It is often what draws divers to the agency. The goal of the configuration is to be comfortable, streamlined and efficient in the water, avoiding entanglement risks and unnecessary drag. An important part of achieving this goal is the hose logic, something many divers pay little attention to or conversely, overcomplicate.

This series of posts will explain GUE hose logic, starting with standard hose lengths, in part II we’ll discuss why we use a long hose and in part III we’ll explore hose routing for a single and twin tank set up.

Many divers taking Fundamentals are amazed at the difference correct hose lengths make in the water. A short backup regulator hose makes a huge difference when routed over the right shoulder, instead of hanging down or flapping around over your arm; and a long primary hose makes donating and sharing gas effortless. All the hoses are sized for streamlining—long enough for their purpose and no longer. The long hose, at first glance, can appear unwieldy, but as we’ll see in a future instalment, with proper routing a long hose is still clean and out of the way until required.

Standard GUE hose lengths:

  • Primary Regulator: 7’/210cm
  • Backup Regulator: 22”/56cm
  • High Pressure SPG: 24”/61cm
  • Low Pressure Inflation: 22”/56cm
  • Drysuit inflator if using an argon bottle: 22”/56cm

A 5’ long hose may be used for single tank diving, when you have no light canister or pocket to stow the excess hose (though it can be stowed in the belt), however for any twin tank diving or diving where there are restrictions forcing the team into single file, a 7’ long hose is essential.

Some divers prefer a slightly longer 24” backup hose when using Apeks regulators, due to the port configuration, however for Scubapro Mk25, Halcyon or other similar regulators 22” is perfect.

When traveling we tend to take two 22” regulator hoses and two 9/16” male to low pressure inflator adaptors. That way the hoses can be used for the backup regulator, wing inflation or drysuit inflation.

Divers of any height can use these hose lengths, helping team standardisation and logistics, and improving comfort, streamlining and efficiency in the water.

Stay tuned for Hose Logic, Part II: Why We Use a Long Hose.

Gas Procedures: It’s Simple Logic

When diving with gases other than air, the biggest risk is breathing the wrong gas—leading to incorrect decompression planning or at worst CNS toxicity at depth, which is likely to result in death.

Recognising these dangers, the WKPP developed a simple set of procedures to ensure this never happens. GUE, founded by divers from around the world including the WKPP, adopted these same procedures and both organisations still use them today.

The risk of breathing the wrong gas at depth is real and has killed many divers, including some who were very well known and experienced. A recent tragedy being Carl Spencer’s death on the 2009 Britannic Expedition.

Standard Gases

The first step we (WKPP & GUE) took to mitigate these risks was to standardise our gasses. This means that for any given depth range we know exactly what gas to take and that all bottles in the team will conform to that standard. As you can imagine this greatly simplfies gas planning, logistics and blending.

After thousands of decompression dives, our standard gases were based around a working PPO2 of 1.4 recreationally, 1.2 for technical diving and 1.6 for decompression (decreasing to 1.4 beyond 36m), with a maximum END of approximately 30m.

Gas Analysis

The second procedure we use is to analyse every bottle. No analysis, no dive. Preferably you should analyse on the day of the dive, to avoid accidental tank content changes and the analysis tape should contain the gas mixture to one decimal place, the date of analysis, your initials and the tank pressure.

Bottle Marking

However, standard gases and analysis only get you part way there. Another important procedure we have to prevent divers breathing the wrong gas, is to mark each and every bottle, other than back gas—every decompression bottle and every bottom stage.

There is no excuse for not permanently and properly marking bottles, no matter what gas is used. It could mean your life. Painted numbers can be erased with a swipe of PVC cleaner, and new ones painted on. Alternatively, MOD stickers (white with 75mm high black numbers) are readily available and are easily read underwater. Nothing else should be on the tank to indicate contents—just the MOD and the dated analysis. Any other markers merely confuse the message and introduce ambiguity where non need exist. What does a green nitrox or custom mix sticker actually tell you? Nothing of value. You must of course follow local laws regarding bottle markings, where they exist, baring in mind that the goal is clearly marked tanks with no ambiguity as to their contents and MOD. Clean, uncluttered tanks, marked correctly say a lot about the diver and their attention to these important details.

MOD markings (75mm numbers on a white background) should appear horizontally on either side of the bottle, oriented so the diver and team can read them underwater. It’s that simple.

As a 6 can look like a 9, 6m oxygen bottles are marked OXYGEN 6 to avoid any confusion. The diver’s name can also be on the bottles, clearly separated from the MOD marking. This is useful during dives where bottles are left at a decompression station or clipped to a cave line.

Gas Switching

When correctly marked, it makes no difference where bottles are located on the diver, though to maintain a clear and freely donatable long hose, GUE divers always carry their bottles on the left. No attempt need be made to identify a gas by which side it’s on or its regulator colour—these practices can be error prone—we need only identify the bottle by its marking. The diver and team can clearly see the MOD and verify that everyone is switching to or breathing the correct gas.

Bottles are always turned off and the regulator stowed on the bottle when not in use. Stowing regulators aids team identification of breathing gas when all bottles are carried, however in cave, we never carry a bottle past its MOD. The risks introduced by trying to push a gas past its maximum operating depth, particularly in a cave or overhead environment, are simply not worth it.

If you can not see the bottle or can not identify the gas, do not breathe it—stick with a known breathing gas until you can make a positive identification. Missing a little decompression gas is far less risk than toxing.

When finished with a gas, stow the regulator back along the bottle and turn it off. It’s common to see divers surfacing with two or more decompression gas regulators around the back of their neck. This creates unneccessary clutter and in an emergency complicates gas donation, impeding the donation of both the breathing gas and potentially the long hose.


Clearly, proper procedures around gas choice, analysis, marking and switching are paramount for safe diving. There is no need for elaborate, overly complex and error prone systems, only simple, streamlined systems like that summarised here. You either follow the procedure and know what you’re breathing or you don’t.

It’s simple logic.