Cave DPV Dive Planning

In this article I am going to make an attempt to tackle the subject of proper dive planning while using a DPV when cave diving. I am writing this article to try and dispel some myths that continue to permeate around the cave diving community, as well as try to make the reader consider things that may not have been covered in previous training. In this article I will give guidance on issues that should be considered in DPV dive planning that may have been overlooked in other formats. I need to be clear on one point: this article is not meant as a replacement for formal DPV Cave Pilot training, but instead it should be viewed as supplemental material to a formal class. To that end, I will not be covering emergency scenarios, such as sharing gas or how to tow a disabled diver. I also realize some individuals may find the tone of this article as blunt, and some may even take offense at the words written within. If you find yourself offended by the discussion below, or you find that the recommendations I suggest are overly onerous, perhaps you need to make a careful self-evaluation and re-think whether DPV cave diving is an activity that you are mature enough to engage in.

I want to start off this discussion by shooting a hole through one of the largest misconceptions about DPV cave diving: to be safe while riding a DPV in a cave, you always need to have twice the amount of gas required to swim out from your furthest point of penetration. The thought process behind this rule is simple – scooters are devices that may become disabled for any of a number of reasons; blades on a prop can break, electronic control systems can fail, o-ring seals can fail, etc. Based on this wrong mindset you need to be prepared to swim out of the cave when (not if) your scooter dies at the maximum point of penetration.

The way that dive planning is presented in this model is that a diver swimming at approximately 50 feet per minute with a surface air consumption rate of approximately 0.75ft3 per minute, will need to keep approximately 250ft3 of gas in reserve for a dive to 2200’ at an average depth of 90’.

Mathematically, this can be shown by knowing some basic formulas which are used to calculate (a) the amount of gas a diver uses in any given minute at depth and (b) the amount of time it will take to swim a given distance. With these two pieces of information, we can then calculate (c) the amount of gas the diver will need to keep in reserve. Please see the appendix below for an explanation of the mathematics.

While this sounds great on paper and is probably suitable for planning a scooter ride to the Hinkle in Devil’s Ear, it is my belief that this method of planning a DPV cave dive is overly simplistic and may lead people to think that their safety is ensured simply by bringing twice the amount of gas they require to swim out. The challenge is that this model breaks down rapidly once the DPV pilot ventures beyond the simple confines of relatively shallow caves and short penetrations.

Let me first explain how this approach fails on a deep dive.

A deep DPV cave dive that many people have done involves scootering upstream Eagle’s Nest to King’s Challenge and The Green Room, a distance of roughly 2200’ from the exit. The dive usually has a round-trip bottom time of less than 30 minutes with a total run-time of around two hours. However, any diver that attempts to swim out from The Green Room will find that with little flow, such a swim will likely take 60 to 70 minutes and during that exit the diver will consume roughly 400ft3 of gas. This means any diver using the “always carry twice the gas to swim” approach should carry 800ft3 of reserve gas for such an exit, a ludicrous amount that can only be met with a full set of double 104’s and 6 stage bottles. Additionally, with an average depth of 240’, such a swim is likely to increase the mandatory decompression obligation incurred by the diver by 4 or 5 hours! Woe is the diver that added 5 hours to their decompression obligation but failed to add several hours-worth of emergency decompression gas.

Because of the absurd amount of reserve gas needed and the increased decompression obligation such a swim would incur, clearly the strategy that to be safe you only need twice your swim out gas will not work on this deep dive.

Now let me shoot a hole through this same approach on a long-range scooter dive in a relatively shallow cave.

Several modern scooters allow a diver to go 8, 9, or 10,000’ into a cave (and out!) with no problems and any person that has the financial means to drop between $5k to $10k can own one. Isn’t technology great?

With an average depth of 85’ and literally miles of trunk passage, Manatee Springs beckons the person who just bought the new Zoom Zoom Extreme model DPV, which is rated by the manufacturer to go 20,000’ of travel distance. Carry enough stage bottles, point the scooter in the right direction, and whoosh you’re heading off two miles away from Catfish Hotel.

Now imagine this scenario, you are 10,000’ back and the electronics package in the Zoom Zoom Extreme scooter dies, rendering it non-functional. Thankfully, Manatee has a lot of flow and it may be possible to exceed a swim speed of 50 feet per minute and potentially even swim as fast as 60 or even 70 feet per minute. While swimming out may sound easy enough, even at the ridiculously fast pace of 70 feet per minute, it will take you close to 2.5 hours to swim out of the cave.

Let me repeat that for emphasis. Assuming you are able to sustain a maximal effort and swim at a pace of 70 feet per minute, it will take you over 2.5 hours to swim out from 10,000’ in Manatee springs.

I want every person that is reading this article to stop for a minute and conduct an honest self-assessment. How many of you can truly say that you have the physical fitness and stamina to sustain a maximal effort swim for 2.5 hours? I didn’t think so.

If you are not regularly engaging in cardio workouts that last more than two-hours at a crack, the likelihood that you will be able to swim out from 10,000’ is NIL. In addition to the physical demands such a swim will place on your body, you will also go through over 400 cubic feet of gas during that swim (a set of 104s plus 5 stage bottles).

Some of you may be thinking “well, we could get a tow from our buddy!” The reality is that towing a buddy over a distance of 10,000’ is going to be challenging in the best of conditions. Add in the complexities of a cave with a large amount of vertical change and many restrictions along the way, and you may quickly realize getting a tow from 10,000’ is not a viable option either.

So how do we make DPV cave diving truly safe?

This may sound a little uncomfortable, but DPV cave dives will always carry an element of risk and they will never be 100% “safe.” However, we can minimize our risks and make DPV cave diving safer by recognizing that swimming out of a cave should never be part of your dive plan and thus we should plan our dives appropriately.

The first element of proper DPV dive planning is knowing the true capabilities of your scooter and not exceeding them. Just as no one in their right mind would consider entering a cave without a working pressure gauge or knowing how much gas is in their tanks, only a fool would begin a long or deep DPV cave dive without knowing how far their scooter can safely travel round-trip.

To know how far your scooter can safely travel, you need two pieces of information: how much energy your scooter uses under maximal work (LOAD) and how much energy your batteries can currently store (CAPACITY). Finding out this information involves conducting some tests on the motor and periodically burn-testing the batteries. I cannot understate this, periodically burn-testing your batteries is very important for safe DPV cave diving. As batteries age, they lose their capacity to store energy and their effectiveness diminishes. A battery that held 1000W of capacity when it left the factory may only be able to hold 860W two years later and you would need to limit your dive plans accordingly.

The prudent DPV pilot that regularly pushes their scooter close to its limits will burn-test their batteries at least once a year.

Armed with the knowledge of how many watts your battery pack can hold and the load your scooter generates, you can get an idea of its real range. A battery pack that holds 860 watts of energy will realistically last for 170 minutes in a DPV that consumes 300Wh under load.

If you know your scooter batteries will only last for 170 minutes, then hopefully you realize that you cannot ride that scooter into a cave for 150 minutes and expect a positive outcome when you turn to exit – you will come up short and kill your battery on your way out. You should never plan a dive that uses all of your battery capacity, planning a dive that kills your battery leaves you with zero safety margin and risks damaging the battery too!

Usually, I try to plan my dives so that I use no more than 70% of my battery life for the entire time I am on the trigger. This leaves me with a little bit of extra capacity in the event I need to tow extra equipment, or for brief periods, a buddy. Planning to use no more than 70% of the capacity also minimizes the risk of harming the battery.

There are several things that may impact how I distribute the time between penetration and exit. Factors I consider include diving in a siphon versus a spring, the amount of flow in the system, and how much additional equipment I will be carrying. Generally speaking, as a starting point you can split the time in half whenever you are diving into a spring. This means that if you have a battery pack that can run for 170 minutes and plan to use 70% of the capacity, you can use the scooter for 60 minutes while going in and 60 minutes while exiting.

That covers staying within the true capabilities of your scooter, but now let me discuss the second thing we can do to make DPV cave diving safer. While hitching a tow from a buddy may be sufficient for a short penetration in a shallow cave, it is not a realistic option for a long or deep cave dive. This means you need to bring spare scooters whenever you either go deep or go long, and only you can decide when spare scooters become a part of the dive plan.

Let me be clear on this point, every individual that is engaged in cave diving has to be a responsible adult that makes their own decisions on where the threshold is when “buddy tow” ceases to become an option and “spare scooter” becomes mandatory. However, I would suggest that any time that you are going deeper than 120’ or further than 3000’, that is when it becomes time to start packing a spare scooter. How many spare scooters a team brings will depend on the complexities of the dive and the capabilities of every member in the team. If you are not regularly practicing towing techniques, you should probably plan on bringing a spare scooter for each diver in the event you have two scooters that wind up becoming disabled.

I know this part stings, because it means that now that you bought your Zoom Zoom Extreme DPV, if you have any intention of using your DPV to the limits of its capabilities you also need to have a second scooter as a backup. The good news is that you do not need to buy two Zoom Zoom Extreme DPV’s, but the bad news is your tow scooter better be reliable because it has to be more than sufficient to get you out from the furthest point of your dive.

In conclusion, DPV cave diving is a lot of fun, but safe DPV cave diving is not as simple as carrying twice the amount of gas as needed to swim out. While swimming a DPV out or catching a tow from a buddy may be an acceptable answer for relatively short distances in shallow caves, that model breaks down rapidly once you start taking your scooter deep or taking it on long cave dives. If your dive plans include deep or long penetrations, you need to consider other options and give up the idea of swimming out.

Appendix: Figuring out the Maths

The purpose of this appendix is to try and help an individual understand the mathematics covered in the above article.

    1. To calculate the amount of gas a diver uses in any given minute at depth, you need to multiple the individual Surface Air Consumption (SAC) rate by the depth, as measure in absolute pressure (ATA). The formula is RMV = SAC * ATA
      In practice, the average experienced technical diver has a swimming SAC rate of 75ft3. If your SAC rate is unknown, you can probably use 0.75ft3 per minute as a starting point.

      The formula for converting the depth of the dive into pressure (ATA) is calculated with the formula ATA = (DEPTH ÷ 33) + 1. If we plug 90’ into our formula, (90 ÷ 33) + 1, we get an ATA of 3.7.

      Therefore our average experienced technical diver has an RMV of 2.8 cubic feet of gas per minute while swimming at a depth of 90’ (0.75 SAC * 3.7 ATA). This means that for every minute the diver is at 90’, he is using 2.8 cubic feet of gas.

    2. To figure out the amount of time it will take to swim a given distance involves knowing a realistic swim speed, as measured in feet per minute. Many things can impact your swim speed, including the amount of drag from the gear that you are carrying, the amount of flow either going with you (exiting a spring) or against you (exiting a siphon), and your stamina and cardiovascular fitness.Generally speaking, most technical divers should be able to sustain a swim speed of up to 50 feet per minute when exiting a high flow spring, but that rate may be reduced to as little as 30 feet (or less!) per minute in a low flow spring, and even less in a siphon.

      The formula for calculating the time it will take to swim a given distance is TIME = DISTANCE ÷ SWIM SPEED.
      A diver exiting a high flow cave, such as Devil’s Ear, from 2200’ of penetration can reasonably expect that swim to last almost 45 minutes (2200 ÷ 50) = 44.

    3. The formula for calculating the amount of gas needed to swim out from any given distance is GAS = RMV * TIME. This means our average technical diver will use approximately 125ft3 of gas to swim 2200’ out from a high flow cave (GAS = 2.8 cubic feet per minute RMV * 44 minutes TIME).Using our “twice the amount of gas needed to swim out” standard, the diver needs to carry 250ft3 of emergency reserve gas to be safe on the cave dive.
    4. Calculating the load that your scooter generates may be a little tricky, as many manufacturers are not forthcoming with that data and there are many things that will impact the load a motor generates, such as drag and speed. However, one “hack” that many people have used is to begin with a fully charged scooter, ride it for 30 minutes on full, then recharge the battery while using a WattsUp meter to measure how many watts went back into the battery while recharging. You can then double that number to get the load in Watt-Hours (Wh).So, if your WattsUp meter records 150 watts when recharging a battery after you had ridden it for 30 minutes at full blast, then your scooter probably generates somewhere close to 300Wh of load on full.
    5. To perform a burn-test on your batteries, take a fully charged scooter and put a WattsUp meter in-line between the battery pack and a resistor pack. The WattsUp meter will display the watts consumed as the resistor pack drains the battery.Two pieces of warning! The first is you need to know what the low voltage cut-off threshold is for your battery pack and be prepared to remove the resistor pack before you hit that threshold, or you risk doing damage to the battery. The second is the resistor pack will get extremely hot while you are doing a burn test, you should conduct the burn test outside and away from flammable materials.

    6. Once you know how many watts your battery pack can hold, you can get an idea of real burn-time by using the formula HOURS = WATTS ÷ LOAD. You can multiple this result by 60 to calculate the number of minutes the scooter should be good for. So, a battery pack that holds 860 watts of energy will realistically last for 170 minutes in a DPV that has a motor that generates 300Wh of load, (860 ÷ 300) * 60 = 172.
    7. I never plan a dive to use more than 70% of the battery capacity. To calculate the dive plan upper limit, I use the formula TIME = REAL_BURN_TIME * 70%. So, if my battery is useful for 170 minutes, I would not plan a dive involving more than 120 minutes on the trigger. 172 * 70% = 120.

A Frank Discussion on In-Water Recompression

Decompression Illness (DCI), a medical diagnosis that encompasses both Decompression Sickness (DCS, aka “The Bends”) and Arterial Gas Embolism (AGE), is an unfortunate reality that cave divers may be forced to face. Inert gas stress, caused by deep dives and lengthy bottom times, coupled with the exertion of carrying heavy equipment to and from the water, puts cave divers at increased risk of a decompression related injury and it is important that we are well educated on how to identify and care for these maladies.

For several years, the accepted standard of care for DCI was to treat an individual with oxygen while transporting them to a recompression chamber for treatment. However, the Diver’s Alert Network organized a committee to review medical literature regarding triage and various first aid strategies for DCI, and at the 2017 Undersea and Hyperbaric Medical Society Annual Meeting, a workshop was convened to discuss and review the data. The consensus of the committee members was released in March 2018 in the journal Diving and Hyperbaric Medicine, Vol. 48, Issue 1. In that article is the following statement:

Recompression and hyperbaric oxygen administered in a recompression chamber is acknowledged as the gold standard of care for DCI. However, in locations without ready access to a suitable hyperbaric chamber facility, and if symptoms are significant or progressing, in-water recompression using oxygen is an option. This is only appropriate where groups of divers (including the ‘patient’) have prior relevant training that imparts an understanding of related risks and facilitates a collective acceptance of responsibility for the decision to proceed.[1]

In plain English, the consensus of the committee was that as long certain criteria are met, the use of In-Water Recompression (IWR) as a first aid treatment of DCI may be appropriate. This article aims to review the process to decide whether or not IWR is appropriate, list the criteria that must be met before IWR should be considered, and outline two accepted IWR protocols. However, while it is the intention of this article to introduce an individual to IWR, it is not meant to replace training. Specifically, this article is not a substitute for the training of delivery and use of oxygen underwater (“aka advanced nitrox”), or training in In-Water Recompression.

Deciding if IWR is Appropriate

Categorization and diagnosis of DCI should only be made by a diving medicine physician, and divers should have contact details for communicating with EMS. In the United States, local EMS may be contacted by calling 911, and the Divers Alert Network may be contacted by calling +1-919-684-9111. Triage by telephone with a diving medicine physician at DAN should be used to help categorize a case of DCI as mild or severe.

Mild signs and symptoms of DCI include:

  • Fatigue
  • Joint and limb pain (note: girdle/trunk pain is suggestive of spinal involvement and does not fall under the classification of limb pain)
  • Skin rash
  • Subcutaneous (lymphatic) swelling (subcutaneous swelling was added to the definition of mild DCI for several reasons, please see the journal article for the full discussion, however it is noted that the value of recompression treatment for lymphatic DCI, while unknown, is not obvious)

Although mild cases of DCI do not necessarily warrant IWR, there may be some benefit and it should be relatively safe to proceed as long as the criteria needed to engage the IWR protocol are met.

Severe cases of DCI may have neurological symptoms similar to what you may see in a stroke victim, including:

  • Numbness and tingling, including in the hands and feet
  • Sensory loss, including loss of hearing, smell, and vision
  • Slurred speech, including drooping features in the face
  • Paralysis and unconsciousness

Additional symptoms of severe DCI may also include:

  • Dizziness and nausea, potentially from an inner ear bend
  • Respiratory distress and trouble breathing, potentially from bubbles overwhelming the heart and lungs
  • Girdle (torso/trunk) pain, potentially indicating a spinal bend

In cases of severe DCI, IWR may be warranted if there is no ready access to a recompression chamber, and all of the criteria to proceed with IWR are in place. However, there are some contraindications that will preclude the use of IWR. To be blunt, IWR should never be considered if any of the following are occurring in the victim:

  • Hearing loss / vertigo / vomiting – this indicates a possible inner ear bend, which could result in nausea and vomiting, which could result in a choking or drowning hazard. Return to water would be unsafe.
  • Change in consciousness / shock / physical incapacitation – return to water would be unsafe.
  • Respiratory distress – return to water would be unsafe.
  • Preceding Oxygen Toxicity event – elevated risk of recurrence of Oxygen Toxicity / convulsions / drowning, return to water would be unsafe.
  • Diver is unwilling to return for IWR.

Criteria that must be met to proceed with IWR

Assuming that a group has decided it is appropriate to use IWR as first aid for a specific case of DCI, certain criteria must be met before proceeding with the procedure.

A team consisting of, at a minimum, three individuals, should be assembled. The team includes the victim, an in-water tender that will accompany and monitor the victim throughout the IWR protocol, and a surface supervisor. Ideally, there should be a fourth team member that can assist the in-water tender and relay information to/from surface personnel.

Because of the elevated risk of CNS oxygen toxicity from PO2 exposures up to 1.9 BAR, all members of the team should be properly trained and practiced in decompression procedures using 100% oxygen. Specifically, they should understand the risks of, and how to identify the symptoms associated with, CNS oxygen toxicity, and how to properly deal with a convulsion.

The team must have the appropriate equipment for IWR using oxygen. Because cold divers do not decompress efficiently, the diver should have adequate thermal protection that could keep them warm up to four additional hours in the water. The team must also have sufficient oxygen for both the in-water and surface portion of the treatment; at a bare minimum, a team performing IWR on open-circuit scuba should be prepared with 120 cubic feet of oxygen.

The team must have a method to maintain a stable depth for each of the stops, including the slow ascents during stops. A down-line would be very helpful for the ascents between stops.

Finally, the team must have a method of communication (wet-notes/slate).

It is also strongly recommended that the injured diver use a full-face mask, or mouthpiece retaining device, throughout the procedure. However, under no circumstances should divers that have never used a full-face mask use their IWR session as a time to learn new skills — stick with equipment that you use regularly and are familiar with already.

Because the use of breathing gases other than oxygen for IWR is not recommended, IWR should only be accomplished with the patient breathing 100% oxygen. During an IWR procedure, a maximum depth of 30fsw (9msw), should be observed.

Under no circumstances should an individual ever breathe oxygen below 30fsw (9msw) while underwater.

Finally, the entire team must be willing to accept the chance that IWR may not result in complete resolution of DCI, and may in fact cause additional complications due to the exposures to high PO2’s.

Two IWR Protocols

The Wikipedia article on “In-Water Recompression”[2] lists five in-water recompression protocols. Three of the protocols outlined on the Wikipedia page include initial deep spikes to compress bubbles, followed by a gradual ascent to 30fsw (9msw). However, at a TEKDive USA 2018 presentation on IWR, David Doolette discussed that recent data indicates that the efficacy of the deep spike was questionable, and so I will only cover the Australian and US Navy In-Water Recompression protocols here.

Australian Protocol

The Australian Method was developed by the Australian Royal Navy and was first published in the Journal of South Pacific Underwater Medicine Society in 1979.[3] Under this protocol, oxygen is supplied at a maximum depth of 30fsw (9msw). In mild cases, ascent to the surface can begin after 30 minutes. In severe cases, ascent can begin after 60 minutes if significant improvement has occurred, but if there has been no improvement in significant cases, the time at 30fsw can be extended by 30 minutes to a maximum time of 90 minutes.

During ascent to the surface, the diver remains on oxygen and maintains an ascent rate of 12 minutes per meter (roughly 4 minutes per foot). Once surfacing, the diver alternates between breathing oxygen and air at 1-hour intervals for the next twelve hours.

Total in-water treatment time via the Australian method ranges from a minimum of 150 minutes to a maximum in-water time of 210 minutes.

US Navy Protocol

The US Navy developed two IWR treatment tables that are published in the US Navy Diving Manual.[4] The table used depends on the symptoms diagnosed by the medical officer, either Type I (mild) or Type II DCS (severe).

In both tables, the treatment begins at a depth of 30fsw (9msw) with pure oxygen. For mild cases of DCI, an ascent to 20fsw (6msw) begins after 60 minutes, but in severe cases, ascent begins after 90 minutes. After leaving the 30fsw (9msw) stop, the diver ascends to 20fsw (6msw) where the diver will stay on oxygen for 60 minutes before ascending to 10fsw (3msw). Once arriving at 10fsw (3msw), the diver will stay on oxygen for another 60 minutes before making their final ascent to the surface.

The ascent rate between each stop, 30fsw->20fsw, 20fsw->10fsw, and 10fsw->surface is a consistent 2fsw (0.6msw) per minute. Each ascent between stops should take 5 minutes to complete.

When the diver surfaces, they must remain on surface oxygen for 3 hours.

In-water time for the US Navy method ranges from 190 to 220 minutes.

Modifications to the protocols

Both the Australian and US Navy methods were derived to provide treatment for young, physically fit, active, military divers and if you believe you fit the mold, you may find these protocols suitable for use without modification. However, for the benefit of the rest of us, I believe slight modifications to the protocols are worth discussion.

Neither protocol allows for back-gas breaks from oxygen throughout the in-water portion entire procedure. Personally, if I were to use IWR to treat an injury to myself, I would take periodic gas back breaks that align with the same procedure I use during standard oxygen decompression, extending the treatment time accordingly to account for the breaks. For example, if the protocol that I use for back gas breaks calls for a 5-minute break after every 15 minutes on oxygen, a 60-minute stop would be extended by 20 minutes. That schedule would look something like this:

Description Gas Being Breathed Time Remaining
Start Start on Oxygen 60
15 minutes “On” Oxygen 45
5 minutes “Break” Air 45
15 minutes “On” Oxygen 30
5 minutes “Break” Air 30
15 minutes “On” Oxygen 15
5 minutes “Break” Air 15
15 minutes “On” Oxygen 0

Other Protocols

Within the past three years, an article surfaced at several places on the internet, including online diving magazines and a training agency blog. That article recommends descending to a maximum depth of 60fsw (18msw) to begin breathing oxygen while following a US Navy Treatment Schedule 5. I only mention this article because it was fairly wide-spread on the internet, but it is my opinion the article is irresponsible and anyone breathing pure oxygen below 30fsw (9msw) is foolish. Members of the Duke Diving Medicine Team posted the following statement on-line at ScubaBoard, and I believe it is worth quoting here:

The procedure and recompression profile advocated in the article place a diver at grave risk of serious injury or death and should not be attempted. Treatment Table 5 is designed for use in a hyperbaric chamber, not for in-water recompression. For a number of reasons, divers under water are at much higher risk of CNS oxygen toxicity than patients in a hyperbaric chamber, and a TT5 exposes divers to an inspired partial pressure of O2 of 2.82 ATA, far higher than the generally accepted safe immersed exposure limits of 1.3-1.6 ATA. The consequences of a seizure under water while breathing from an open-circuit regulator are obvious, and the article only mentions a full-face mask as a consideration, not a must.[5]

I agree with Duke Diving Medicine and believe nothing more needs be said on this dangerous practice.

In Conclusion

In summary, while IWR may not be suitable for all cases of DCI, it may be an incredibly useful arrow to have in any cave divers quiver. Obviously, the best choice is to get a diver to a proper hyperbaric facility for treatment, but there may be times that this is impractical, if not impossible. The deeply personal decision on whether or not to engage in IWR as a first aid treatment for DCI should only be made after proper categorization of the DCI event has been made by a medical physician, all of the equipment necessary to complete the procedure, including adequate amounts of personnel and oxygen, are assembled, and everyone on the team accepts the risks that are associated with breathing hyperbaric oxygen under water. It should also be noted that there is not a doctor on the planet that will ever recommend IWR as a treatment option for a specific case of DCI, your team will have to make that decision on your own.

It was my goal to help educate you on the review process that must be made before deciding to use IWR, list the criteria that are necessary to begin IWR first aid treatment, and outline two accepted IWR protocols that have been published in several scientific journals. Divers that wish to continue to educate themselves on the subject of IWR may find the Rubicon Foundation Web-site a useful resource and should visit for more information.

[1] “Consensus Guideline: Pre-hospital management of decompression illness: expert review of key principles and controversies.” Mitchell, SJ, et. al. Diving and Hyperbaric Medicine. Vol. 48, Issue 1. pp45-55.

[2] In-Water Recompression, Wikipedia Article referenced on April 30, 2018.

[3] “Underwater Oxygen Treatment of decompression sickness.” Edmonds, Carl. Journal of South Pacific Underwater Medicine Society, referenced from Rubicon Research Repository on April 30, 2018.

[4] US Navy Diving Manual, Revision 7, Section 17-5.4.2, “In-Water Recompression.” Referenced on April 30, 2018.

[5] ScubaBoard Post on IWR, referenced on April 30, 2018.

Thoughts on cave training

For years, there has been a myth that the best divers in the world are cave divers. In support of that myth, perhaps you have heard that the hallmark of a cave diver is to have incredible buoyancy control, the ability to move through a narrow passage without disturbing the least bit of silt, and the ability to remain calm while facing the most stressful situations.

Back when I started cave diving there were pretty much two groups of people that took up the sport. The first group was made up of people that started out as divers that wanted to dive and explore the caves and springs in the area. The second group was made up of cavers that wanted to learn how to dive so they could continue exploring past sumps and partially flooded caves.

Every cave instructor that I knew who was teaching during this period was a highly skilled and dedicated cave diver, with years of teaching and cave diving experience behind them. One of the credos of cave instruction was that cave instructors did not try and encourage people to take up the sport, but would steer individuals toward training when those individuals expressed a strong desire to pursue the activity. When discussing the training, instructors focused on the safety aspects of the program rather than selling the sport for other reasons.

With the growth of internet forums, including rec.scuba and eventually sites such as ScubaBoard, the stories about cave divers being the best in the world started to grow. As the stories of how great cave divers were, demand for cave instruction increased, and we saw an increase in cave instructors to meet the demand. Some instructors began actively promoting cave training to recruit more students.

Unfortunately, this does not always serve the best interests of the students enrolled in these courses, and to my chagrin, I am sure that some people have been encouraged to continue cave training even though they have no business doing so. Because the dangers in cave diving including a risk of death due to failure to perform, some people simply have no business taking up the activity. Cave instructors have a moral obligation to discourage some people from pursuing the sport.

Hopefully, every cave diver you ever meet does have incredible buoyancy control, great anti-silt technique, ice water in their veins, and are some of the best divers you will have the pleasure to dive with. But that does not mean you need to become a cave diver to be a great diver yourself. If you live thousands of miles away from flooded caves, and are not drawn to see the cave environment, then you really do not need to take up cave diving. You can develop great buoyancy control, anti-silt technique, and a calm cool demeanor without ever going into an overhead environment if you just put the effort into it.

Cave Exploration in Merida (1999)

(ed. I wrote this article in 1999 after returning from Merida. I never published it).

Merida.. Where do I start? Oh yeah, the beginning..

Some guys from Texas A&M contacted a friend of mine, Jesse Armantrout, to have us explore an underwater cave system they had received permits to dive.

The A&M guys had done the last of the exploration in there, but couldn’t get more then 1000′ into the cave. They contacted my group because the depths of the system were greater then they had experience diving (190′ on the floor in the deepest parts), and I’m part of an exploration project that is considered to be the most experienced in the world at deep cave exploration (a sidebar, check out last months National Geographic for more information, if you read the stuff on the Woodville Karst Plains Project exploration at Wakulla Springs, well, that’s us).

They told us that if we could add an additional 100′ of explored passage to the system we’d pretty much be considered the local heros. Heh, boy were they in for a shock.

The people from our group that decided to go on the expedition included Jesse Armantrout, Brent Scarabin, George Irvine, Dawn Kernagis, Bill Mee, Derek Hagler, John Rose, Chuck Noe, and myself. In our pre-trip planning we concluded that every diver would need to ship a set of doubles, a couple of stage bottles, and a couple of deco bottles down there. We all decided to carry our scooters on the plane, but shipped the batteries with our tanks to save the weight. Granted, this was before crazy airline baggage fees, but it was a way to lighten the load.

With no ideas as to what depths we could expect, we each went ahead and mixed several stage bottles and doubles for 230′. Getting the gear to Texas was orchestrated by Jesse Armantrout. He loaded up a trailer full of our gear and took it to the boys at Texas A&M. They were then responsible for getting our gear to Merida. I’m not sure what the customs agents thought of a van full of college kids and scuba tanks.

Nine members of our team arrived in Merida on Friday the 12th (March). We were picked up at the airport by the A&M guys, and delivered to our hotels. We spent the rest of the day preparing our dive gear, making sure all of our tanks made it in good shape, and getting ready to start the exploration of the system the next day.

The cave system was at the Cenote X’Lach which is in the middle of the Maya Ruins at the Archeological Site of Dzibilchaltun. This was a pretty big deal, Dzibilchaltun is about 25 minutes from Merida, and is more extensive then other well-known Maya ruins (such as Tulum, Uxmal, etc). There have been over 8500 structures identified at Dzibilchaltun, and at the height of the Maya culture (circa 1200-1400 AD) it is believed there were over 50,000 inhabitants. Pretty damn impressive for a bunch of people in the jungle 700 years ago. It was also really cool as hell to go diving and surface to find yourself surrounded by a ton of ruins (I’m big into that stuff).

Merida is the capital of the state of Yucatan. The governor of the state of Yucatan was extremely happy to have us there. For the past 10 years or so, the state of Quintana Roo (which is adjacent to Yucatan) has become a serious tourist destination (ever here of Cancun or Cozumel?). In particular, Q. Roo has gotten very popular for their cenotes diving and snorkling tours. Cenotes are essentially sinkholes that open up into the aquifer underneath, but the cenotes in the Yucatan Penninsula are quite decorated with beautiful stalagtites and stalagmites from the last ice age. Because the cenotes in the Akumal (Q. Roo) area are fairly shallow, they’ve become prime tourist attractions.

The governor of Yucatan wants to develop the cenotes in the surrounding area to Merida as a tourist destination as well. Unfortunatly, most of the cenotes that we saw in Merida are much deeper then is considered safe for recreational scuba divers (recreational divers are recommended to stay shallower then 130′, several sinkholes in Merida are in the 200-400′ depth range). At any rate, they were excited as hell to have us there. The governors office had a representative from the Department of Ecology and Tourism act as our guide. This guy carted our tanks around in his truck, loaded them and unloaded them, and busted his butt for us. The hospitality of everyone in Merida is truly amazing, it makes you think differently of how people in US cities act (when was the last time you went to a place where strangers invited you into their house and fed you just to talk to you?).

We got started on the exploration on Saturday. We had two objectives, explore the cave system, conduct some science for the profs at A&M. We decided we’d focus on exploration on Saturday, and continue with that until it got too ridiculous then we’d focus on the science. Remember what I said about that 100′ that they’d think we were gods?

Our first dive team went in, they proceeded to extend the exploration of the cave out to 2300′ from the exit, exploring an additional 1300′ of passage in the process. A slight miscommunication from that team inhibited the second exploration team (mine), we were under the false impression they had finished the exploration of the cave system, so we spent the majority of our dive looking for side passages. This cave is absolutely amazing, the walls are 120-150′ wide, floor to ceiling is 30-40′ wide, the floor sits at 180-190′, the ceiling at 150′. Some parts it gets smaller and we have an interesting phenomenon where the salt water and fresh water mix, which produces an effect like looking through vasoline on your lenses in those smaller passages, pretty wild.

When we reached the end of the previous teams exploration line we were shocked to find out the cave still went, so we tied in an exploration reel (you have to use lines in underwater caves to find your way out in case you get lost), and extended the exploration out to around 2800′.

The third dive team (we work in teams of 3, 9 divers=3 teams) went in and continued exploration. They explored the cave out to 4300′ where it pretty much was finished. So, in one day we finished the known exploration and extended the cave by over 3000′, quite a bit more than anyone expected.

After dumping 3k of line and walling out the cave on the first day, in a rather nonchalant voice, one of our team told our hosts, “Well that was a fun day, do you have anything else for us?”

On Sunday we went back, just in case we missed anything. We did some science (I set some traps for blind crayfish in 190′ of water 2000′ from the exit), and during our decompression, one of my dive team members discovered another section of the cenote. This was a never before discovered area that was too narrow for a diver wearing tanks to negotiate the entrance. Later that day a friend of mine went in pushing a tank in front of him, and found pottery and bones which made everyone excited. We had a professor of ecology from the university in Merida there, and he was pretty stoked by that find.

On Monday we were taken to another cenote to look at. You had to repel down 100′ to get to the water, and the cenote was a good solid 2 hours from Merida. The locals setup a pulley system to belay all of our gear in the water (which was a metric crapload, let me tell you, scooters weigh 100lbs each, tanks rigged a good 100lbs as well). Over the course of that day the local Merida news station came and interviewed everyone, which was kind of cool. Also, the local “mayor” (more like village chief) for the little village near the cenote had his wife cook all of us lunch and brought it out to us so we had a nice warm meal after diving.

Tuesday I took off from diving since we weren’t really accomplishing much. Myself and three other people of our team went to Chichin Itza, probably some of the most famous of the Maya Ruins. It was a 90 minute drive to get there from Merida, and the whole trip was $20 (including transportation, meals, a beer, and admission). Pretty cool, especially climbing the great pyramid and looking out over the jungle. I had been to Chichin Itza four years before with my wife (we had done a trip to Cancun), but it was still cool going there. Also, there was a lot of excitement because the equinox was that Sunday (if I knew that I would have stayed over for a few more days), and during the equinox at sunset you can see the image of “Culcucon” (the rattlesnake god in Maya mythology) race up and down the pyramid (those Maya were meticulous).

When we got back to Merida we were informed that the governor wanted to have dinner with us sometime while we were there, but unfortunately that never happened because we could never get the schedules straight. The other group spent the day cruising around looking at other cenotes.

Wednesday we went back to Dzibalchultun. This time I had to go pull the traps I had set a few days before. We decided to take one of the A&M kids on the dive since they’d been really hospitable to us, and man the kid told me the 30 minutes spent on that dive were one long orgasm. Heh.

Thursday I flew home. End of trip. Needless to say, I had a pretty good time overall. The people in Merida were REALLY REALLY REALLY friendly, and they all bent over backwards for us. Plus it was really inexpensive (I spent $240 in Mexico, that included a weeks stay in a hotel, all of my meals, a fifth of Cuervo Especial as a gift, a trip to Chichin Itza, and quite a few Dos Equis Lagers). Merida is about an hour from the coast at Progresso (there’s a big beach there), and within 2 hours of several ruins (Uxmal, Chichin Itza, Coba, as well as Dzibilchaltun, Tulum is probably about 3-4 hours away but very beautiful).

Falmouth – Cathedral Radio Locations

Some of you know that I have been spending most of my free time over the past few months working on the Falmouth-Cathedral Springs project, which is a joint project between Karst Underwater Research (KUR) and the Woodville Karst Plains Project (WKPP). I will be writing up a lengthy article in the near future, but Cathedral Canyon is an extensive system which was made famous by Sheck Exley for setting a world record distance penetration in the system. An entire chapter in Caverns Measureless to Man is dedicated to this system.

However, the system is also very important as a lesson in how agriculture and development can impact our water resources. The system connects to the Suwannee River at Ellaville Spring, and trends east several miles past the town of Falmouth. The system cuts underneath a chicken processing plant and several farms from the source on it’s way towards the river.

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Current exploration of Cathedral has put the cave system out approximately 19,000′ from the nearest entrance, but to say that exploration in this system is a challenge would be an understatement. In addition to the large distances from the nearest exit, the visibility tends to run 15′ and the depths vary throughout the system from 70′ to 185′. This depth variations can cause sinus problems and waste precious inflation and diluent gas.

Underwater cave survey is conducted by a simple method – you install a line with knots every 10′ during exploration, and on exit count the knots while taking the azimuth and depth readings every time the system changes direction. Although this method works relatively well, when you start talking distances on the order of 2-3 miles, minor errors can be magnified. A 2.5° error in the azimuth, plus a 3-4″ error in the distance for each knot, can put the cave survey off by up to a 1/4 mile at these distances.

This past weekend, on December 12th, we decided to validate and shore up the survey data by placing radio location beacons in the cave system at 6000′ and 10,200′ penetration. On the surface we then located where the beacons were placed by using radio receivers, which essentially allow us to triangulate in on the signal emitted by the beacons. This did two things for us: it allowed us to validate the survey, and it also gave us proof that the system runs under the spray fields.

Additionally, I believe this may be the furthest distance that anyone has successfully deployed and used an underwater radio location beacon.

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Here is the impressive thing we discovered: at a distance of 10,200′, Sheck Exley’s survey was off by only 80′. That’s less than a 0.8% error rate — incredibly impressive given that he used 1980’s era technology when he did his exploration.

This weekend would not have been possible without the help of a great team of people. Derek Ferguson needs to be given a lot of credit for coming up with the initial idea for the project, and proposing to do a radio locate at those distances. Jon Bernot and Charlie Roberson have been driving forces for the project, as well as performing some amazing new exploration. Ted McCoy has been an incredible member of the team — working out logistics in long range exploration, getting the habitat ready, or ready to hop in the water for a 7 hour excursion. Howard Smith has been a silent but steady assistant, always ready to lend a hand and never complaining of the work asked of him. And of course, Andy Pitkin has done an amazing job of converting the raw survey data into a usable format, and organizing and conducting the radio location beacons.