Intro to Tech

Several people have asked me about my Intro to Tech Courses, what is involved with them, and what a person can expect to learn. I’ve put this article together to help people understand the purpose and value of taking this course.

First off, let me explain what “Technical Diving” means to me.

Historically, there have been four types of people that engage in diving:

  1. Military – These divers undergo specialized training focused on military operations.
  2. Commercial – These divers conduct special mission specific work, ranging from work in the oil and natural gas industries, boat yards, salvage, etc. Their activities are usually governed by OSHA regulations.
  3. Scientific – Scientific divers engage in conducting research and gathering data, or specimens, in a broad range of fields. Their activities and training are frequently governed by AAUS (American Academy of Underwater Sciences) standards.
  4. Recreational/Sport – Recreational divers are frequently hobbyists, but this also includes Divemasters and Instructors. Most recreational divers are trained under guidelines developed by the WRSTC (World Recreational Scuba Training Council), which limit a person to a maximum depth of 130’, a direct ascent to the surface at all times, and no decompression diving.

In the sense that Technical divers are not engaged in Military, Commercial or Scientific work, Tech divers ARE indeed recreational divers, but what makes us different is that Tech divers engage in diving activities that include dives deeper than 130’, or inside of overhead environments such as a shipwreck or cave, or partake in dives that require mandatory decompression stops before surfacing.

Basically: Tech divers are recreational divers that dive beyond the limits of sport divers and get more bottom time because of it!

Because Tech divers go beyond the limits of sport diving, we need specialized gear to help manage those risks. Managing that extra gear adds a level of complexity to our diving as well and so we need to develop special skills.

Tech divers also find that teamwork makes dives easier. Teamwork is an integral component of many successful tech dives. During an Intro to Tech workshop we will work on developing a team mindset.

Finally, technical diving involves planning – there is no such thing as a casual decompression dive, so we must be diligent in our preparation and planning.

On paper, an Intro to Tech course is about learning how to choose and configure dive gear, developing core skills like equipment handling, buoyancy/trim and situational awareness, developing a team mindset, and learning more about detailed dive planning based on your real gas consumption rate and risk management, and doing some drills to make it all stick!

I need to be clear on one point. This is NOT a Cave or Decompression course! Every dive we do will fit within the depth and time parameters of a recreational sport diving paradigm, that means no overhead environments, and no decompression.

At the most basic level, this course is about:

  1. Giving you a taste of what is involved in technical / cave diving.
  2. Familiarizing you with the gear necessary for future cave and decompression training.
  3. Developing key skills, including advanced buoyancy control, proper trim, and efficient propulsion techniques.
  4. Developing a team mindset.
  5. Teaching you more complex dive planning based on your individual gas consumption rate and “rock bottom” gas planning.
  6. Helping you become a more aware and better buddy by developing better situational awareness.
  7. Allowing you to make an honest self-assessment of your skills and preparedness for future technical diving.

Course Schedule

The course typically spans three days.

Day 1 – 8:30AM – 5PM

The first day will be exclusively in the classroom. In the morning we will cover the academics of the course. In the afternoon we will conduct an equipment workshop and practice a few techniques.

Day 2 – 8:00AM – 5PM

The second day will be conducted almost exclusively at Blue Grotto Dive Resort in Williston where will conduct 2 dives. Those dives will be 60-75 minutes long and we will have a video review of our performance in-between dives plus additional lecture.

During the dives we will practice the following:

Dive 1: Buoyancy, Trim, Flutter Kick, Modified Flutter Kick, Frog Kick, Modified Frog Kick, “Basic 3”, and a balanced rig test to see if we can swim our gear up.

In between our dives we will discuss SCR/RMV rates, how to calculate them, and the impact they have on dive planning.

Dive 2: START Drill, Valve drill, SCR Rate Calculation using appropriate propulsion techniques, “Basic 5”, balanced rig test – safety stop with near empty tanks.

Day 3 – 8:00AM – 5PM

The third day will also be conducted either at Blue Grotto Dive Resort in Williston or Troy Springs State Park near Branford. We will once again conduct two dives, between 60 and 75 minutes long and we will have video review of our performance in-between dives.

Dive 3: Dive planning with rock bottom gas, START Drill, Propulsion skills, Valve drills, “Basic 5”, Air Shares.

Between dives 3 and 4 we will discus diver rescues and how to deploy an SMB.

Dive 4: Diver Rescue and surface tow, SMB deployment, make up any skills.

You will want to have appropriate thermal protection for spending close to 3 hours in the water each dive day.


Overhead penetration (cave/wreck) and decompression diving are equipment intensive sports due to the inherent risks involved with being submerged in a water filled environment with a ceiling that prevents a direct access to the surface. Being able to solve problems in the water is a must, and redundancy is key to survival. Anyone wishing to engage in cave or decompression diving must have redundant equipment capable of providing for a safe exit for themselves and a team member.

This program is open to people that wish to begin their training in either backmount or sidemount. I can provide a list of recommended configurations based on the platform you wish to pursue.

Expectations to Graduate

Because this course is a pre-req to enrollment in a cave or decompression class, I want you to understand the expectations I place on all of my technical diving students. My goal is that all students that graduate any of my courses can safely execute dives within the limits of their training. Although there are “minimum standards” that will be required by the certification agencies, I have certain expectations of the skills and abilities that my students can demonstrate that are not necessarily listed in the “minimum standards.”

1. Proper mindset. Students must demonstrate a safe and mature attitude as well as good judgment and problem-solving ability and be able to work well in a team. Examples include creating safe and prudent dive plans within the limits of time/depth/exposure, properly analyzing and marking their gases, and having properly functioning and maintained equipment. While there is definitely a physical component to technical and cave diving, a proper mindset is the most important thing and divers that lack judgment, are unable to adequately solve simple problems on the fly, or are otherwise unsafe, will not pass my class.

2. Good buoyancy and trim. This means being able to perform all skills within a 3′ range (1.5′ up, 1.5′ down) from the target depth while also maintaining trim within 20° of horizontal. The reason for this is multi-fold; divers that are unable to maintain buoyancy may potentially hurt themselves by violating a decompression stop or dropping below the MOD of a gas. They may also potentially damage the cave environment by bumping into the ceiling or wallowing in the floor. Divers that have poor trim will be less streamlined, thus working harder, and they may also potentially cause a silt-out from prop-wash from their fins. It will be expected that to graduate from a class, you should be able to perform an S-drill neutrally buoyant and within trim.

3. Comfort and familiarity with their equipment. Under stressful situations, such as in an emergency, a diver must be able to manage their equipment, manage stress, and manage their physical condition. They should have muscle memory for where each piece of equipment is, what its’ purpose is, and how to use it. A diver that has to think about where a piece of equipment is, or how to use the equipment, is expending valuable “mental bandwidth” that could detract from their ability to manage a stressful situation.

4. Ability to manage valves. This means the ability to do a valve drill, efficiently and comfortably. The reason for this is that if there is a failure during a dive, such as a free-flowing regulator, ruptured hose, etc, you should be able to manage the problem.

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.

Lights are life support!

So you need a primary light?

A question I get asked frequently is “what primary light should I buy for cave diving?” Although light and battery technology is constantly changing, I am going to explain some general guidelines for things to look for in a primary light that will hold true no matter what lights are on the market in the coming years.


Primary Lights Are Life Support Equipment

The first thing I want to address is the basic tenet that lights used in cave diving are life support equipment. Caves have no natural light and cave diving is hard on your gear so you want a light that will provide you with ample lighting and can handle the rigors of cave diving.

This means you should plan on making an investment in a quality dive light from a reputable manufacturer. For a person that is interested in cave and technical diving in North America, I would look at lights made by Dive Rite, Halcyon, Light Monkey and Underwater Light Dude. All four manufacturers have solid products with great customer support and they develop their products with cave diving in mind.

Let me be very frank with you. Primary lights break and eventually it is likely that yours will break too. In 13 years of active cave diving, over a 22-year period, I have yet to own a light that has never failed on me.

Halcyon? Yup, had one fail. Dive Rite? Yup. Light Monkey? Yup them too. And although I’ve never owned an Underwater Light Dude, I know a couple of guys that had failures with theirs too.

In most cases, the failures are wear and tear items – batteries eventually die, light cords and switch boots need periodic replacing, etc. But occasionally the failure may be more dramatic (I blew up an LED emitter once). By having a light that was made by one of the companies listed above, I know that when it breaks, getting it fixed will be quick and easy.

I also know that any light made by one of those four manufacturers will have excellent build quality, fit and finish. It will be well made and should be able to handle a fair amount of wear and tear (i.e. abuse) from cave diving.

Sure, you may save some money up front by buying a cheap foreign made light, but the amount of frustration and aggravation you will encounter due to lost diving opportunities and time spent fiddling with the gadget will more than eat up any savings. And wouldn’t it stink to find out that the company that manufactured your light disappeared overnight and now you can’t get it fixed?

If you go the “cheap route” and buy a no-name foreign light, you will likely wind up buying a top end primary light eventually anyway, so why buy twice?

Price wise, buying a good primary light means you’re probably looking at spending at a minimum $700 and more likely around $1200. I know that is difficult for most of us, but as I said up front, primary lights are life support, how much is your life worth? If you look around, you can probably find a good deal on a used light by one of these manufacturers too – I have a friend that bought an older technology HID light for $350 because he was patient.

Whew, now that that is out of the way, let’s talk about some specifics of what to look for in a light.



I’m a firm believer that you want a light that has a “Goodman” style handle. This means that light head rests on top of your hand, rather than being held in the palm of your hand. The advantage to you is that you will be able to use your fingers to grab and hold things while you are still using the light.

Goodman handles come in either hard or soft types. I personally prefer a hard Goodman handle that is adjustable to the thickness of my hand. The advantage to the hard handle is you can very easily swap back and forth from left to right hand and it rests easily on your hand.

Others prefer the soft handle because, well, it’s soft and they find that more comfortable.

You will need to decide for yourself which you prefer, hard or soft Goodman handle.

Canister or Handheld

When I started cave diving our primary lights had very large lead acid battery packs that were very very very heavy. We had no choice but to have the batteries in a canister and a light head that was connected by a cord.

With the advancements in batteries and LED emitters that we’ve had in the past decade, this is no longer the case and there are some excellent handhelds on the market.

The new Dive Rite H50 can be converted from a traditional canister light to a handheld


Some of the pros to having a handheld light are that you do not have a light cord that is a potential failure point and they’re small enough that you can keep an extra one in a pocket in the event of a light failure.

The trade-off is that the entire light is encapsulated in one package and there is more weight on your hand.

Personally, I am still using a canister style light, but I can see myself picking up a handheld in the not too distant future (are you listening Santa?).

Canister lights have a couple of advantages and disadvantages over handhelds too.

First, and probably most important, is that they can handle much larger battery capacities which means you can get more dive time out of them. However, with most handhelds providing a three to four hour burn-time, this may not be a big consideration for the majority of divers.

The second advantage is that most battery packs can be fitted with an E/O connector. The E/O cord allows you to unplug the head from the canister underwater. A pro to this is that you can swap the head in the event of a failure, but the cons to this are that you may accidentally unplug the light head if the cord gets caught on something (been there, done that) and the E/O connectors can corrode if you regularly take them into salt water. One serious advantage to the E/O connector is that you can also use the battery pack for something else, like a heated undergarment or with a different light head. Once again, this may not be a big advantage for most people, but it is worth noting and these are some of the reasons why I’m not ready to get rid of my canister lights just yet.

A third benefit is that in the event you drop your light head, a corded light will still be attached to you by the cord. Of course, as I said above, if you’re using an E/O connector it is possible for the head to pop off from the battery and to lose the head (yup, I did that one too).

The major con to a canister light is that the light cord is a potential failure point. As I mentioned in the beginning of this article, cave diving is hard on gear. My experience has been that I’m replacing light cords every 18 months, and I have even once nicked one causing a canister flood.


Batteries and Burn Times

Over the years, primary lights have been made with different battery technologies.

A HID light with a Lead Acid Battery Pack (circa 2000) and a LED light with a NiMH battery Pack (circa 2015). Both lights have an approximately 5 hour duration but slightly different size and weight.


NiCAD batteries, both wet and dry cells, were used for many years, but they had various problems including battery memory. These batteries were replaced by Sealed Lead Acid “Gel Cells,” which were the standard throughout the 90s. The SLA batteries were very heavy, but the batteries did not suffer from memory issues and they were very inexpensive to replace, which was good because you had to replace them annually.

Currently, most primary dive lights are made using either NiMH or Li-ion cells. These cells are substantially more expensive than previous technologies, and are a major part of the cost in today’s lights. Both battery technologies have some unique characteristics that you should be aware of.

NiMH – NiMH batteries do not have the energy density of Li-ion batteries. This means you need a larger physical size to store the same amount of energy. NiMH batteries, if charged and then left unattended, will slowly discharge over time. This means you should top up any NiMH battery pack the night before a diving day just to make sure it is fully charged. NiMH batteries can be cycled between 500 and 2000 times, depending on the cell, and a good NiMH battery pack that is well maintained will last for years.

One major downside to a NiMH battery is that it will generate a constant, or near constant, voltage as the battery is used. This means it is very difficult to detect how much of the battery capacity has been used and your light may function “as normal” until it cuts out without warning because it has been drained. Some light manufacturers have developed circuits that can detect the slightest drop in voltage, and will alert you when the battery is getting close to being discharged.

Li-ion – Li-ion cells have much higher energy density. This means a smaller pack may have a longer burn-time. A fully charged Li-ion pack can be left unattended for extended periods without losing a charge. Li-ion packs have a much shorter usable life-span, they typically start losing their ability to hold a full charge after ~300-400 cycles. Li-ion cells also have a more linear drop in voltage as the battery is used, which means that it is easier to detect when a battery has been used and how much of the capacity is remaining.

One con to Li-ion cells is that the FAA has regulations regarding lithium batteries and you need to make sure you understand the regulations and the impact regarding any particular Li-ion battery pack you may have. While your light manufacturer should be able to provide you with a written statement regarding air transportation and the battery pack for your light, there is an upper limit to what you can take on a plane. Note this means you should not pack a Li-ion battery pack in your checked baggage, but instead you must carry them on with you.

Both NiMH and Li-ion batteries do not fare well in hot environments. Leaving them in the trunk of your car on a hot summer day will damage them and shorten their usable life. Li-ion batteries should not be left fully charged for extended periods of time either, that is bad for the cells.

What about SLA (Lead Acid) batteries? I cannot think of a manufacturer that is currently producing a light with lead acid batteries, however, you may run across a used light that has them. The major downside to SLA batteries is their weight for the amount of battery capacity, but if you are willing to live with that in order to get a primary light for a slightly reduced price, they may be a good option for you. SLA batteries are very inexpensive, I recently replaced a set for $30. They also only last about 100-200 cycles, so you will need to replace them on a regular basis.

What about Lithium-Polymer (LiPO) cells? A LiPO battery pack is essentially the same as a Li-ion cell, but with the battery electrolyte in a flexible bag rather than a rigid container. There have been a large number of fires caused by bag rupture or distortion, just think about the recent spate of Samsung phone recalls. I consider LiPO cells unacceptable for diving applications because I personally believe the rigors of cave diving will put the cells at risk of damage, meaning they could potentially spontaneously catch fire – yikes!

No matter what battery technology you wind up with, you want to get a light with at least three hours of burn time. Although you may only be doing 1 hour dives right now, it’s very likely to do two or three 1 hour dives in a day, and you want a light that will last for a full days worth of diving. My general rule of thumb is I want a light that will last for 50% longer than my planned dive day, so if you are planning for 2x one hour dives, you want at least three hours of burn time.

One thing is for certain, you will eventually need to replace the batteries and periodic testing of the health of the batteries will allow you to know when you need to replace that pack. I try to burn test my lights at least once every six months and at the bare minimum I test them annually. There are multiple ways to test a pack, including using specifically designed battery test gear, but I prefer to use a low-tech method that gives me accurate and reliable numbers and did not cost me much to assemble.

My simple test consists of filling a 5 gallon bucket with water, turning on my fully charged light and placing it in the bucket. I then start a stop watch and keep periodic tabs on the light until it dies. For the first 90 minutes I ignore the light, but after that I begin checking it every 20 to 30 minutes to make sure it is still working. Once I get within 30 minutes of the expected burn time, I begin checking it every 5 minutes.

After the burn test is complete, I re-charge the pack and make a note of the burn-time in a log-book that I keep for this purpose. This allows me to compare the health of the battery to the previous burn test, and I can proactively replace the batteries when the burn test gives me 80% of previous tests.

The author burn testing a lead acid battery pack. The bucket of water prevents the light head from getting damaged by overheating.



Lumens versus Lux and Lord Kelvin

Pay close attention to advertising that describes a light by Lumens and advertising that talks about Lux because those advertisements are describing completely different beasts with different numbers (700 lumens, 10,000 lux). Making sense of what those numbers mean would require a PhD in optical physics, or at least it feels that way sometimes, but I’ll try to explain this in an easy to understand way.

In simple terms, “lumens” is a measure of the total amount of light output, and “lux” is a measure of how much of that light output hits a fixed target at a set distance away. Comparing lumens numbers is pretty straightforward, but when comparing lux it is important to also make sure you are comparing the distance from the light source. One vendor may advertise their lights with a lux rating based on a 3m (10’) distance and another may advertise it with a 1m (3’) distance and those numbers would be drastically different.

Although higher output numbers seem like they should correspond to a “brighter” light, this is not necessarily the case for a couple of reasons:

  • Light output is determined by the total amount of light coming out of the front of the light.
  • Peak beam intensity represents brightness as perceived by the human eye, and it is related to how the beam is focused by the entire system, including the reflector, lens, or optic.

So, which is more important? At the end of the day, what you will likely care about is how much light gets emitted and I tend to believe that when you start going beyond ~700 lumens, the more interesting thing to look at is the Kelvin (“temperature”) of the light. The higher the Kelvin, the whiter the light and once you go above 6000K, the color in the cave will really begin to “pop.” What I mean by this is that the blue in the water will stand out and colors in clay banks will be rich and natural, basically everything will look better at 6000K.



There are two competing light technologies currently on the market, HID and LED.

The venerable 21w HID was the preferred light of many for several years


HID uses a gas arc system that requires a ballast to function. The advantages of the HID system are that they are very bright, they operate at a high Kelvin temperature, and the beam can be focused from a broad wide angle to a precision “laser” dot. The down-sides to them are that the ballast or bulb can fail, they have a higher power consumption, and it is expensive to replace a bulb if they break.

LED uses an electronic emitter that is solid-state and robust, it should last for well over 5000 hours before failure. Until recently, the main down-side to the LED lights were that it was nearly impossible to focus them and they lacked the “punch” in murkier water that HID offers. The advantages of LED are that they will last a long time and they typically have a lower power consumption.

Although my primary “go-to” light is currently a 21w HID, I believe that modern LED lights are now at a point where there is no longer a reason to purchase a HID light unless you have a very specific reason for one.

What about Halogen/Xenon? Well, filament based bulbs were very popular years ago, and the bulbs are incredibly cheap to replace, but those have gone the way of the yoke manifold and dodo bird and should be retired.



In cave diving, we use our lights as our primary means of communication. We know our teammates are with us when we see their light beam and we use our lights for highlighting an interesting feature, signaling OK or signaling distress. Because we use our lights for as a primary source of communication, I’m a firm believer that any light used for cave diving should be able to have a tight focused beam. We call that tight beam the spot. My recommendation is that a primary light for cave diving should have a beam angle of no greater than 8° and a tighter beam, such as 6°, is preferred.



I started working on this article two months ago, and as I am wrapping it up, two of the manufacturers have just announced new lighting systems which offer brighter lights with multiple battery options for 2017. As I said early on in this article, technology is continually marching forward, but there are a few guiding principles to think about when selecting your next primary light:

  • Lights are life-support. Avoid cheap crap just because it’s inexpensive.
  • Goodman Handle.
  • Battery Technology should be Li-Ion or NiMH with a minimum 3 hour burn time. Burn time is affected by the light head.
  • Batteries should be tested every 6 months.
  • Should have at least than 700 lumens, with a Kelvin temperature greater than 6000.
  • Should have a focused “spot” of no more than 8°; 6° is even better.

Dive safe!




Always check your gas!

I recently heard a story that happened to a good friend and it compelled me to write this article. My friend was doing a dive on his CCR and everything went flawlessly on the dive. I wish I could say that the story ended there, because I would have not spent the time putting together this article, but it doesn’t. When he got back to deco and was sitting at 20’, he could not get his PO2 above 0.9. Even doing multiple oxygen flushes did nothing to help the problem.

For non-rebreather divers, performing an O2 flush involves venting all of the gas in the breathing loop, and holding down the oxygen addition button to re-fill the loop with pure O2. When you’re sitting at 20’, performing an O2 flush should spike the PO2 output up to 1.6, but here he was stuck with a reading of 0.9. This could have been caused by a number of things, the most likely being either bad oxygen cells, or something like gas contamination.

During rebreather training we’re taught “when in doubt, bail out” and I’m glad to say that my friend bailed out to open circuit, finished his decompression and his story has a happy ending. During the post-dive analysis of his gear he identified the cause of the problem; in his haste to set up, he never analyzed the oxygen supply for his rebreather, and what was supposed to be pure O2 was in reality only 50% nitrox.

While forgetting to analyze his gas was a non-event for this friend, I knew two other people that were not so lucky due to cylinder marking and gas analysis, and two that were just wrong.

It was the summer of 1995, and the Technical Diving Revolution was in full swing when Bobby McGuire drowned. Although I only met him once or twice, by all accounts he was a heck of a diver and a heck of a nice guy too.

He was doing a 150’ deep cave dive, and his dive plan called for using a stage bottle filled with 25% nitrox on the bottom, and a stage bottle of 50% nitrox for decompression from 70’ to 20’. Stage bottles are an additional aluminum 80 cylinder with a working first stage, second stage, and pressure gauge, that is carried by the diver to provide additional breathing gas. Typically, the bottles are carried underneath a divers body. Frequently, divers will put different breathing gas, such as oxygen or 50% nitrox, in a stage bottle to speed up decompression.


Because he planned to use one bottle at one point of the dive, and the other at another point in the dive, he labeled the stage bottles “1” and “2”.

Bad Analysis Marking

During the dive, Bobby picked the wrong bottle to breathe from and he breathed 50% nitrox at 150’. Being under 5.5 ATA of pressure, this gave him a PO2 of almost 2.8 – double the recommended maximum recreational limit of 1.4! At some point during the ascent, Bobby suffered a grand mal seizure from CNS oxygen toxicity, and because he spit out his regulator during the seizure, he drowned.

What should Bobby have done differently?

Although I do not know for sure what Bobby was thinking when he labeled his tanks, my best guess is that he marked them the way he did because he would use cylinder “1” on the first portion of the dive and “2” on the second portion.

As hard to believe as this incident sounds, back in the early 90s, tank labelling and marking were not universally standardized and the reasoning that led to his tanks being labeled this way is understandable given the accepted norms at the time. It took several incidents, including Bobby’s, to make technical divers come to a consensus on how to label Nitrox tanks. If he had taken a different approach to marking his stage bottles, there’s a strong likelihood that he would be alive today.

The best method for labeling stage bottles that I can think of is the one adopted by the WKPP and other people. It’s simple and allows for both self-checking and buddy verification. There are two components of this stage bottle marking technique.

The first component is to place in a location that the diver can read, on the cylinder neck, a piece of tape with the cylinder gas analysis in big numbers. You should also put the date of the analysis, your initials, and the MOD on the tape. I typically carry the gas analysis out to the 1/10th of a percent, but given that our oxygen sensors are only good to within ± 1%, that may be overkill.

Analysis Marking

The second step is to place a label with the MOD on either side of the cylinder, horizontally in such a fashion that everyone on the team can read it. There should be nothing except the MOD on these labels, the only exception is pure oxygen, which should simply read “oxygen” so that it is not misread at an inappropriate depth, such as 120’.

Most divers using this strategy will find themselves dedicating a few cylinders to certain depths, and attaching permanent MOD stickers. The most common depths include 190’ (either 18/45 or 21/35), 120’ (usually 30/30 or 32%), 70’ (50%) and Oxygen, and permanent labels can be found for those depths at many dive shops. If you decide not to dedicate a cylinder for a specific depth, you should at the very least use a piece of duct tape and label the MOD for the gas that is in the cylinder in this fashion.

MOD Markings

Remember, the key with the MOD marking is that everyone on your dive team should be able to visually see what gas you are breathing quickly, so both sides of the bottle need to be labeled. Some people have recently adopted the practice of placing a third MOD label on the bottom of the cylinder in such a manner that a diver following behind can also see the MOD.


I was introduced to Jonathan Gol in 1997, and he and I did about a dozen dives between 1998 and 2000. In November 2001, after recovering from a prolonged viral infection, he decided to go on a dive in Jackson Blue Spring. When he got to his 20’ decompression stop, he switched to an aluminum 40 that he normally kept filled with oxygen for decompression, and he was dead within a minute.

Although we do not know for sure what events transpired before he died, we have a theory and it is a pretty good theory. He made two fatal mistakes that cost him his life and what happened is a lesson that we should all learn from.

His first fatal mistake happened a couple of months before his death. Jonathan was a home blender and usually had several helium bottles at his house that he rented from a local gas supplier. When he became sick with the viral infection, he decided he did not want to pay the monthly rental on the helium cylinders and he used his Haskel to fill an aluminum 40 with the helium from those bottles before returning them.

His second fatal mistake happened the day he died. Once he was medically cleared to dive, he packed up his truck and drove the ten hours from Houston to Marianna. In his haste, he did not analyze the tank that should have had pure oxygen in it. The cylinder label said “100%,” but in reality, it was 100% helium and not oxygen. Being anoxic, it was incapable of supporting life. He died as a result.

What should Jonathan have done differently?

The first thing that he should have done differently was not to fill a tank dedicated to one gas with something else. Once a cylinder is dedicated to a gas, i.e. it is labeled permanently for that gas, you should NEVER fill it with anything else. If it’s an oxygen bottle, it should only get oxygen. Period. Ditto for 50% (70’), 32% (120’), etc.

And then the most important thing he should have done differently was that he should have VERIFIED the contents of the gas before he put a regulator on the tank.

A lot of people dislike analyzing their cylinders at the dive site because of the effort it takes to do it correctly, but do you see what I wrote in the paragraph above? I used the word VERIFIED, not “analyzed.”

You should analyze your tanks whenever you fill them at the shop, and label them as I described in the section about Bobby. However, you only need to VERIFY them whenever you are about to put a regulator on them.

The difference is simple: to properly analyze a tank you need to use a flow meter and calibrate your sensor with a known gas (typically air). These things take a little bit of time, and most of us “normal humans” dislike the extra time it takes to do a proper gas analysis in the field and so we won’t do it.

However, VERIFYING the contents is very quick and can be as easy as holding the sensor face into the flow. The oxygen reading will likely be off by as much as 3%, but the purpose of this step is to confirm that the gas is what you are expecting and not wildly off the mark. It only takes a few seconds to do, and if the gas is wildly off then you can do a more time consuming analysis to find out exactly what is in those cylinders.

Dirty Analysis

If Jonathan had done this simple check, he would have quickly seen that his “oxygen” bottle did not have oxygen in it. This step would have only cost him 10 seconds, rather than the cost he paid by skipping it.

Sadly, Jonathan’s story was not unique, and as recently as 2013 there was an oxygen toxicity evet that took a divers life under a similar set of circumstances (dedicated bottle, no verification).

You don’t always know what you think you know…
In 2013 I found myself teaching a decompression procedures course to a couple of guys that worked at a scientific program which had a fill station. The program had several sets of doubles for use in pool training, and they each checked out a set of doubles from their dive locker. In their minds, because their fill station was incapable of pumping anything but air, and those doubles were reserved for pool use only, they should only have had air. Nothing else.

As they were assembling the gear for the first dive of the course, I asked them to analyze their tanks. They both laughed and said “why are you making us do this, these have air!”

Travis went first. He put my analyzer on his set of doubles, and it quickly read 28%. He told me, “I think something’s wrong with your analyzer, it’s reading 28%!”

I verified the analyzer on a set of my tanks, and handed it back to him. “Check it again,” I said, and once again, it read 28%.

We then handed the analyzer over to Ian, and his doubles read 29%.

“There’s no way!” he said, but he analyzed them again and got the same reading a second time.

A week later the mystery was solved. It turns out that someone else from the same program had checked out multiple sets of doubles, and filled at a local dive shop with nitrox so they could go cave diving. Figuring that the tanks would never be used except in the pool, the culprit failed to label them.

What if someone else made the same assumption as Travis and Ian and checked out a set of doubles to do a deep wreck dive, such as the Hydroatlantic (175’ to the sand)? That could have gone bad really quick.

The lesson here is that just because you think you know what is in your tanks and what you are filling them with, that does not mean you are correct and you still need to analyze and verify your tanks.

Even when getting fills from a “dedicated nitrox fill station,” you should take the time to analyze your tanks. I cannot believe how many times I’ve seen people say “I don’t need to analyze my tanks, I got them filled at <insert dive shop name here> and they always fill 32%!” and that kind of laziness needs to stop.

A few simple rules
My friend is a very experienced diver, and he knew better than to dive a tank that hadn’t been properly analyzed. However, we are all only human and sometimes we get a little complacent and skip our simple checks. But when playing around with gasses and diving, we need to keep on our toes. In summary, here are a few simple rules to follow:

1. Always analyze and label your cylinders when you get them filled. Label them with both the gas content on the neck in a place easily visible by the diver, and MOD on the sides in such a way that everyone on the dive team can see it.
2. Never fill a dedicated cylinder with something other than the correct gas. If you do, it’s no longer a dedicated cylinder.
3. Always VERIFY the contents of your cylinders before putting a regulator on it. This step takes only a few seconds, and can save you your life.

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).

Mending a broken heart (or how I found out I had a PFO)

Over the past five years I got used to getting bent.

A lot.

I really mean a lot.

I never really thought much about how frequently I got bent, I just sort of took it for granted that I would get some form of DCS every now and then.

Skin bends? Yup, that one was pretty common. Itching, rashes, those were pretty frequent occurrences. I probably got a case of skin bends on one out of ten cave dives, and I just considered it one of those things that I had to contend with if I wanted to keep doing longer dives.

Joint pain? Those were rare, but I had a couple of them too.

My first “type 1” hit was in my elbow back in 1994. A friend of mine and I tried to do a swimming stage dive to the well at Little River. We were in wetsuits, and diving air. We were young and dumb. Diving air meant a lot of decompression, and I was cold while waiting for my computer to clear.

After that dive, my elbow felt like someone had tried to hammer a railroad spike into it.

It hurt.

A lot.

My wife fell off of a horse that day. We spent the evening cuddled in bed, icing our injuries and chewing down Advil.

Oddly enough, I did hundreds of dives without getting bent, and I never got bent on a “recreational” profile.

Between 1994 and 2001 I did hundreds of deep and long cave dives, and only got bent about once a year. Although one of the hits was bad enough that I spent a weekend in Tallahassee Community Hospital at the chamber, I really didn’t think much about it because it was well within the realm of what my friends were also experiencing on some of our dives. We were experimenting on ourselves with different decompression profiles, and my experience were not that unusual. But something happened during my break from cave diving, and when I came back I started getting bent regularly.

As I said, the common one was skin bends. I was averaging about one hit a month, and just grew to accept it as normal.

However, in spring 2014, that changed for the worse.

I took a type 2 (CNS) decompression hit after a four-hour dive in Indian Springs. The profile was nothing really absurd, but about two hours after the dive, I was drooling in my dinner.

No Bueno.

I wasn’t sure what was going on with me, but suspected I had a PFO.

For those of you unfamiliar with the term, a Patent Foramen Ovale, or PFO, is a hole between the right and left atria of the heart. This shunt in the heart allows blood to by-pass the lungs, and continue circulating throughout the body. Every person has a PFO while they are in their mothers’ womb, but they usually close shortly after birth.


It is estimated that 25%-30% of the general population have a PFO that failed to close. In some people, the PFO is closed the majority of the time, but can open when under certain physiological strain (walking a set of heavy gear out of the water, Valsalva maneuver, bearing down like you’re trying to go poop).

What a PFO means to a diver is that as the diver is off-gassing (decompressing) from a dive, blood that is rich with inert gas micro-bubbles may potentially by-pass the lungs and pass into arterial circulation. As the diver ascends, there is a potential for the bubbles to expand into bigger bubbles, and cause decompression illness.

And for non-divers, a PFO can mean an increase in risk for stroke.

But the idea that I had a PFO did not make much sense to me. As I said, I had done a lot of deep diving and been a very active diver.

Aside from a dissection of the heart, there are only three tests available to determine if an individual has a PFO, and I tested negative on the “gold standard” test back in 1998.

The tests are:

  • Transthoracic echocardiogram (TTE). It is the most common type of echocardiogram, and is entirely non-invasive. A technician injects a saline contrast with bubbles in it while monitoring to see if they pass through a PFO with an ultrasonic transducer. The probe is placed against the rib-cage on the outside of the body. This test is not considered very reliable because of the potential for it to miss a small hole due to the probe being external to the body.
  • Transesophageal echocardiogram (TEE). This test involves a probe being inserted into your esophagus, and usually the patient has to be under mild sedation. A saline solution with bubbles is injected into the blood stream while actively being monitored by the probe. This test had been considered the “gold standard” for a PFO test for many years.
  • Transcranial Doppler (TCD). Recently, this test has become more widely accepted as a way of identifying a PFO. A probe is placed on the outside of the skull while a saline solution with bubbles is injected in the body. It is completely non-invasive.

In 1998, after an incident that caused me to spend a weekend in a hospital doing chamber rides, I underwent a TEE. I tested negative on that test, and just assumed I was in the clear. But, after the hit in 2014, and the frequency of skin bends on decompression dives, I began to have doubts.

After a consultation, my GP referred me to a cardiologist. The cardiologist reviewed my case history, and having previously treated other divers with a PFO, decided to send me for a bubble study.

A week later I was in the clinic having a TTE – first the technician took an ultrasound of my heart without the saline contrast, then an ultrasound with the saline bubble solution to watch the flow through the heart to the lungs. Finally, it was time to test for a PFO; the technician ordered me to bear down and perform a deep Valsalva to try and get a PFO to open, and injected the bubble solution.

Eureka! She could see the bubbles shunting across my heart!

The cardiologist scheduled a follow-up for additional testing. He wanted for me to undergo a TEE to see if they can determine the size of the PFO.

Because the TEE requires mild sedation, the cardiologist wanted to have it performed in a hospital. Two weeks later I found myself in North Florida Regional Hospital’s cardiac wing to have the TEE.

The nursing staff at North Florida have a strange sense of humor. The conversations I had with several of them went something like this:

“My name is Joe, I’ll be your nurse today. What procedure are you having done?”


“Oh, I’m so sorry. You don’t want to see a video of what they’re going to do you.”


The surgeon that would ultimately repair my heart came in to talk to me, and he explained the steps in the TEE. He also told me they would administer a mild sedative to inhibit the gag reflex when they insert the probe down my throat.


A few minutes later, an attendant came in and administered a shot of propofol (the same stuff that killed Michael Jackson).

Nappy time.

The next thing that I remember is being woken up in the recovery room.

The doc came in and told me that I tested negative on the TEE. His speculation was that my PFO was small enough that I needed to do a deep Valsalva in order to trigger it to open, and that the propofol interfered with my ability to do that.

Ya’ think? I’ve since heard from one other person who also had a PFO closure, and she tested negative multiple times on the TEE. Hmm, gold standard?

He also decided to go ahead and schedule surgery to implant an Amplatzer Septal Occluder.

The septal occluder is essentially a wire mesh plug that gets inserted into the hole in the heart by a catheter. Your heart muscle then grows around the mesh and the PFO closes.


As I was being discharged from the TEE, we scheduled the surgery to close my PFO for Friday, September 19th, 2014.

The week prior to the surgery I was pretty calm and collected, but the morning of the surgery I started to panic.

What if something went wrong?

What if I had a stroke, or worse, while on the operating table?

What if the surgery didn’t work and I still got bent like a pretzel?

In a nutshell, I was scared shitless. But in the month between verifying the PFO existed and that morning, I had spoken with several people who had undergone the procedure. Every single one of them spoke positively about the success of the procedure, and those conversations gave me the strength to continue.

The nurse came to prep me for surgery, and then about half-past 8 in the morning I was wheeled into the OR. This time there would be no anesthesia to knock me out, just a local so I would not feel the procedure.

Did I mention that the surgery involved a catheter inserted in my groin region? The room was cold, and I was conscious, and my junk was on full display for the world to see. The attendants prepped me and got me ready, and then my surgeon came into the room.

What happened next was a weird, surreal, experience. It must have been nerves, but I was talking like crazy and I carried on a conversation with the surgeon while he was probing and plumbing around, inserting tubes into my body, making his way to my heart.

We talked about family vacations, travels, and the like.

He talked about his kids, and I talked about my wife and our trips to the islands and my god kids. I also offered to teach his kids scuba (he hasn’t taken me up on it).

About ten minutes after he started, he announced he found and plugged the hole. He also told me it was one of the smaller ones he has ever had to close.


I was wheeled out of the OR and brought to a recovery room. Because of the dual incisions, and the amount of blood thinners I had been given, they wanted me to lay flat on my back for several hours to let the wound close. A few hours post-op they asked me to sit up, but unfortunately I started to bleed. Luckily for me they got it under control, and I stopped bleeding.

That afternoon, probably around 2 or 3, the doc came in to talk to me and see how I was doing. He told me I was not allowed to dive for six weeks with no really deep diving for three months. He also said I was not allowed to run for a week, I was not allowed to lift anything heavy for four days, and warned me that I would probably have some bruising near my groin.

He wasn’t kidding about the bruising – two days after the surgery it looked like someone had taken a baseball bat to my psoas region. Oh and it was sore.

Regardless, recovery went well and I did quite a bit of walking after the first few days.

On Halloween Day I was cleared to dive again, and I started off with a bang by teaching a NAUI Cave 2 course. Every dive in a NAUI Cave 2 course is a stage dive, and we booked five days to do two stage dives a day – that’s a lot of bottom time.

I don’t think that was what the doc had in mind, but you might as well jump in with both feet.

I felt great after every one of those dives, but the true test would be on a deeper dive. However, I continued to do shallower, but progressively longer dives. I also co-taught a full cave class in early December, which was another five days of back to back to back dives.

Christmas break marked the three-month period, and I had the chance to really test the new, improved, bionic heart. I had an opportunity to go do a few dives at Eagles Nest and Diepolder III, and those dives would all be deeper than 250’ deep.

Time to spend some money on helium!

The first dive was at D3 and I remember getting back to deco and wondering if that dive was going to leave me bent. At one point I actually started to get tense – would I be sitting there scratching my swelling belly two hours after the dive, or would I feel normal and fine?

Well, the good news is that I was perfectly fine after the dive. Actually, I felt incredible. No problems what-so-ever. Eureka!

Fast forward to today. In the eighteen months since having the surgery, I’ve logged a little over 350 dives. I’ve also slowly bumped up my gradient factors, decreasing the conservatism in my diving.

An easy estimate is that over 200 dives since the surgery involved some form of staged decompression, and with all of the diving we did in Cathedral this past fall, at least 50 of them were deeper than 150’, including a couple of dives with 7 hour run-times (two with 3 hour-bottom times @150’). There have also been at least 20 dives deeper than 220’, with two just shy of 300’.

I’ve only had one minor incident out of those dives, and that was on a hot day where I humped a bunch of gear a long haul immediately after a four-hour dive.  That’s a far cry from where I used to be, and all in all I’d say the procedure was a huge success.


If you find yourself getting weird skin bends, or other issues, you might consider getting checked for a PFO. And be sure to have multiple different tests done – the TEE can definitely have a FALSE NEGATIVE, so don’t rely only on one test. If you find out you do have a PFO, while I will tell you I had a positive experience, only you can decide if the risks associated with the surgery are worth it or not. I know people that have chosen to not take those risks, and they are living full productive lives.



Successful OW Checkout Dives for New Instructors

I originally wrote this article to help out a couple of new instructors at the UF scuba program. I am releasing it to the public for any other new instructor.

Successful OW Checkout Dives

By Ken Sallot

There’s a saying, “failure to plan is planning to fail.”  Given that scuba diving is a recreational activity that can be dangerous, or fatal, it’s important to be properly prepared to lead and conduct the open water student evaluations.  This article is not all encompassing, but will cover many of the key points necessary to have a successful session.  It is my hope that you can use it to help be prepared, and give you an opportunity to think about the types of scenarios you may encounter.

NAUI Requirements for Certification

NAUI requires every student to be evaluated through a minimum of four open water dives.  Prior to the standards update in December 2012, NAUI required a minimum of five open water dives, or four open water dives and a skin dive.  UF continues to use the five open water dives for their certification matrix.

Per NAUI standards, you may not conduct more than three dives on any given day.  If a third dive is to be conducted on a given day, you may not exceed 40’ for that dive, and you may not engage in any out-of-air ascent training exercises on that third dive.  This means you may not conduct alternate-air-ascents or controlled emergency swimming ascents on the third dive in a day.

To be counted as an open water dive, NAUI requires that you have one entry and one exit, and your underwater activity conducted while breathing scuba last for at least 20 minutes at a depth of at least fifteen feet.  If the conditions are unfavorable, you may have multiple entries and exits to achieve the minimum time.  To quote the NAUI S&P, “For example, an excursion involving an entry, 12 minutes of underwater activity on scuba, and an exit, followed by a later entry, eight minutes of underwater activity on scuba, and an exit would comprise one scuba dive.  A series of excursions in a course involving 80 minutes of underwater activity on scuba would comprise four scuba dives.”

The minimum SIT time between two dives is 10 minutes.

The student to instructor ratio is 8:1 in ideal conditions.  If you have a certified DM you may go up to 10:2, and if you have two DM’s you may go up to 12:3.  You may not expand the number beyond students no matter how many DM’s are with you.  If the conditions are less than ideal, such as poor visibility in a lake, high current, or rough seas, the ratios should be reduced.  The students are to be under DIRECT supervision of an instructor at all times, this means the instructor is in the water with the group and can halt any activity that could cause harm to the student.

Equipment considerations: You MUST have a snorkel.  The minimum equipment to be worn by students includes: mask, fins, snorkel, tank, regulator w/pressure gauge and octopus, bcd with low pressure inflator.  Instructors must have the same equipment PLUS a timing device, depth gauge, knife, emergency signaling device (whistle / mirror / smb).  A compass is required with visibility less than 10’.  And a quote from the S&P: “Instructors and dive leaders must also be similarly equipped as their students are during training, i.e., when students are using open circuit scuba, the instructor must also use open circuit scuba.” This means that if you are teaching students that will be using a single cylinder in a backmount configuration, then you must be wearing the same configuration (no doubles, no sidemount).

The skills a student must demonstrate in order to be certified include several “subjective” skills, such as being able to be a safe diver, responding correctly to signals, and properly using the buddy system.  It is worth spending a few minutes to review all of the required skills in your NAUI S&P.

Other skills that a student must demonstrate:

  • Orally inflate / deflate self and buddies BC
  • At the surface, remove and replace each of the following: mask, fins, weight belt, scuba unit.
  • With face submerged, breathe through snorkel while resting and swimming.
  • Self and buddy cramp releases
  • Safety stop
  • Mask clearing, including removal and replacement
  • Regulator recovery from behind the shoulder (“reach” method)
  • Hovering
  • Unclasp and adjust the weight belt underwater
  • Underwater navigation with a compass
  • Measure, record, and calculate individual air consumption as surface air consumption rate using a submersible pressure gauge, depth gauge, and timing device.
  • Perform a dive at a depth between 40 and 60’.
  • Use the NAUI tables to calculate repetitive dive information (LG, SIT credit, RNT)
  • Transport for a distance of at least 50 yards a budy who is simulating exhaustion.
  • From a minimum of 15’ share air and ascend in a controlled manner with another diver both as the donor and recipient.
  • Perform a relaxed, controlled, emergency swimming ascent (CESA) from a depth of at least 15’.
  • Bring a diver simulating unconsciousness to the surface from a depth of approximately 10’. Remove weight belt, mask, and snorkel.  Simulate in-water rescue breathing.

Whew, that’s a lot!  But you can get it all knocked out over two days, and still have time to take the students for a tour if you are organized and prepared.

Beginning of the day

You will need to prepare and bring some equipment for a successful weekend.  Bring with you the following:

  • The roster of students that are diving that day.
  • Their student record folders (and verify they are properly filled out)
  • An O2 kit
  • A first aid kit
  • A “save a dive” kit (spare gear, parts, and tools). I bring a spare BC, several pouches of soft weight, and a spare regulator on top of a normal save a dive kit.
  • Writing utensils
  • A dive slate properly prepared for the activities

Make sure the students know when and where you are meeting them.  Manatee springs has a limit on the number of divers that can dive in a given day, and we have been running into other groups as early as 7:30AM.  A backup plan to Manatee would be either Troy Springs (deep), or Fanning Springs, which is approximately 10 miles north of Manatee.  Please note, Fanning is barely 18’, so while you will meet the minimum depth standards…

You should endeavor to be at the site at least 10 minutes prior to the time you announced to the class.  As a scuba instructor you are a diving professional, act like one.

Some students will be there before you.  Some students will be there much later than you told them to be there.  This is just the way it is, think of it like herding cats.  You may have some success by telling students if they are not there by XX time they will not be able to dive, but that will not always work.

As you are waiting for the few late arrivals, you can use the time to go over the waiver reaffirmations with your students.  They are part of the NAUI student folder, and basically it is an opportunity for the student to re-attest that they are aware of the risks and wish to continue with the scuba training.

Site Briefing

Once you have collected all of the students and checked into the dive site, it is a good opportunity to give a broad site briefing.  Take the students on a walking tour of the dive site, giving a description of the site.  Briefly describe the depth of the site, and notable features such as entries and exits. During the tour, also discuss emergency procedures, spare gear, O2 locations, and an overview of the days events.

Some students will likely want to go to the restrooms upon arrival.  Maintaining control of the group is important, if you decide to let one or two wander off then others will wander off as well and eventually you will have lost control of the group.  If you decide to let the one or two people use the facilities, then go ahead and let EVERYONE use the facilities but give them a deadline on when to return – “there are the restrooms, everyone you MUST be back here in ten minutes so we can do our site briefing.”

At Manatee Springs I like to perform my site briefing in the following manner:

Gather the group in the parking lot, do a head count to make sure everyone is there, then tell them where we are and how many dives we will conduct.  I mention there are two sites, and then bring them to Catfish first.  On the walk over to Catfish I mention how many groups there will be, and talk about the order of the dives.  Once we arrive at Catfish I give a description of the sink, pointing out the duckweed surface and how it’s clear underneath (I save the “how to exit” part until the actual dive because the students will forget it anyway), but I do mention that the bottom is silty and I talk about the cave system.  I usually tell my students if I ever catch them in the cavern I will kick them out of the water and fail them, but I explain to them that this is for their own safety.  I also point out the shower right next to the deck.

I then take the students as a group to Manatee and continue the briefing there.  While walking over to Manatee I may discuss things like ticks, or mosquitoes, or Bubba’s depending on what I see around me.  Once at the head spring I make a point to discuss how strong the flow is, and how divers can be propelled from 25’ to 12’ very quickly and that it’s important to exhale; I usually tell them to “shout WHEEEEEE! At the top of your lungs!” as they are being pushed by the current.

After Manatee, I walk them over to the snack shack / concession area to show them where the restrooms are and point out they need to wash their feet before going in to use the facilities.  I usually comment that the rangers get upset when people track mud in there, and I don’t want to hear about UF students being the problem.  I also show them where to wash their booties/shoes.

And this is where I conclude my site briefing.  I will point out that they are now at the restrooms, and that we will regroup in the parking lot in 10 minutes to start gearing up and getting ready.

Pre-dive Briefing

Once the students have been split up, and we are ready to begin diving operations it is time to do a pre-dive briefing.  You should ALWAYS conduct a pre-dive briefing for every single dive, and you need to be very detailed during the briefing.  Make sure all of your students are there and paying attention during the briefing.

EVERY pre-dive briefing should include the following:

  • Entry and exit locations, as well as ascent and descent.
  • Establish the limits of the dive (every dive has three limits: depth, time, pressure).
  • Describe the bottom conditions – give them precautions for the environment (silt?)
  • On the first dive of the day review ALL signals you care about. Up, Down, OK, Uneasy, Ears, Pressure, Counting (I usually just have them show me their gauge), Out of Air, Buddy, Look, Follow, Hover, Stop, Slow Down, Speed Up, Low on Air, Turn-Around, Turn-Around based on limit (I use a T).  For every dive you should review any signals specific for the skills on the dive (different UF instructors have different signals for mask removal / replacement for example).
  • Before every dive, describe the skills/activities you will have them perform, and be very excruciating in the detail: “I will arrange you in a semi-circle around me, then will come up to you one by one and ask if you are OK. If you are, then I will hold on to your shoulder strap just to help control your buoyancy, and then I will ask you to partially flood your mask.  Remember, the spring water will be colder than the pool, so don’t let that startle you.  After you have cleared your mask, I will ask you to remove your mask and then clear it.  Once you are OK, I will then move on to the next person and repeat the process.  The rest of you, when I am working on the skills, you are to just sit there and watch us.”
  • Talk about any emergency contingencies; for instance, if you do not have a DM that can monitor the group in the event a student bolts on you, then you may choose to say something like “if I have to ascend to the surface for any reason, you all must come up too because you are uncertified divers and you can not be diving alone.”

Check their gear, and make sure they all have enough air for the dive.  You should never let a student begin a dive with less than 1500 psi, realistically probably not less than 2000 psi.

Conducting the dive

FILO!  First In, Last Out.  This statement is about YOU the instructor.  You should be the first person in the water, and you should be the last person out of the water.  If you are already in the water, you can assist students that are having problems as they enter, but if you are not in the water then you cannot render assistance.  I cannot count how many times I have had to grab a student and physically swim them back to a trail line in a swift current in the ocean, or had to stop a student from going diving solo.  Being in the water first makes these tasks easier.

The risk to FILO is that it’s possible that a student may have a problem on land (broken fin/mask strap, forgot weight belt, etc).  This is one reason why you should do a gear check of your students before getting into the water.  If you have an assistant, you can have them be the last one in the water so that they can help with these problems.

During any training dive, the most likely place for student / instructor separation is during the descent and ascent.  Invariably, especially in either rough seas, strong current, or cold water, there will be one student that has problems equalizing their ears.  I like to use a descent line to minimize this problem, I tell my students that we will descend down the line as a group; if one person has problems, we bring the entire group up.

If you are diving in the ocean with a strong current, it is a good idea to tell the students to hold onto the descent line, otherwise they will not be able to fight the current.  If any of them are not holding onto the line, grab their hand and put it on the line.   Do not be afraid to ask the mate on the boat to run a granny line to the bow for a controlled descent.

Once everyone is on the bottom it is time for the skill evaluation.  In Manatee, I usually arrange them in a semi-circle around me outside of the flow.  I will go to each student one by one, ask if they are OK, if they are then I will grab hold of their BC with my left hand and have them run through the skill sequence.  My right hand is usually holding onto my octo, or otherwise prepared to grab a regulator and shove it in their mouth in the event that something goes wrong.

If we are doing multiple skills, I will have each student do all of the skills before moving to the next.  If they struggle a little bit that is OK, they are probably not used to wearing wet suits and being in the cold spring water will feel different to them.  But obviously, don’t let them sit there struggling with a regulator recovery for 2 minutes before giving them a regulator to breathe.  Make sure to congratulate them for successful skills!  And don’t be afraid to ask them to repeat a skill you are unhappy with.

Remember, you are evaluating the students, not teaching them; there should be no reason for you to demonstrate any skills on the day of check-out dives.  If they could not display mastery of a skill in the confined water, then they should not be allowed to participate on a check-out dive.

I usually check all of the students air supply every couple of minutes.  Perhaps between every other student that you evaluate, i.e. evaluate student 1 & 2, check all air, evaluate 3 & 4, check all air, evaluate 5 & 6, check all air.  If someone is going through their air quickly, perhaps move to them sooner and then have the DM escort them to the surface when their air is low.

If you have an assistant with you, make sure to have them watch the entire group.  They can be behind the group ready to spring into action in the event they are needed.

If you do not have a DM your attention will be focused on the student that you are evaluating.  Try to keep an eye on the rest of the group peripherally, but realistically, if a student has their regulator out of their mouth or their mask off their face, you are 100% focused on them.  After completion of each skill look around to the rest of the group to see what they are doing, and make sure they are not getting into too much trouble.

If there is a problem and a student bolts, you MUST slow them down as much as possible and ensure they are exhaling to avoid harming themselves.  Seriously, punch them in the stomach to force them to exhale if you need to.  If you have a DM, he can collect the rest of the group and bring them to the surface.  If you don’t, well let’s hope you told all of your students that they need to ascend if you need to ascend in an emergency…

After the evaluation is over, check all of the students air supply, and if there is plenty left and you are still under the 20 minute mark, do a brief tour.  Eventually, regroup to the down line and begin your ascent as a group.  Make sure they are properly controlling their ascent rate, and not doing elevator rides on their way up.

Post-dive evaluation

I like to do a post-dive review on the surface while everything is fresh in my head.  For specific behavior that could be dangerous (elevator rides, for instance), I will go ahead and single the person out but make sure everyone understands why the behavior is risky.  For general issues, I will just speak about them to everyone.  Also highlight GOOD behavior and publicly praise.

Specific Skills

  • Mask Clear – I usually begin with a mask flood then a removal and replacement. You MUST be holding onto the student in case they bolt.
  • Regulator Recovery – I start with the sweep method then do the tank tilt/reach method. You MUST hold onto the student.  I usually hold onto my octo with my right hand in the event the student struggles with finding their reg and I need to shove a regulator in their mouth, and hold on to them with my left hand.
  • Weight belt removal – You should hold onto the student in the event they lose their weight belt.
  • Gear removal and replacement @ the surface – I usually do this as a surface interval between two dives. I start with having them take their fins off, then put them on, then their weight belt off, then put it on, then their BC off, then sit on top of it, then put their BC back on (they may need to deflate it a little), then finally the coup de gras is taking their mask off, and putting it back on.
  • Out of air share – Each person must be the donor and recipient. I usually have them get into the air share position, then ascend as a group.  Once they ascend, the donor orally inflates the BC of the out of air diver (thus combining two skills!).  We then stow the octopus, switch who will be out of air, descend, and do it again.  I usually use this skill as the last thing on the dive, so we will have already done the other skills then a tour, then I point to one person from each buddy pair and say “you are out of air”, etc.
  • CESA – The key here is controlled. They can ascend as fast as 40’ per minute during this skill, but they need to be in control. The student must ascend a distance of 15’ while exhaling a continuous breath of air, but they can only do the skill on one breath. You MUST give a very good briefing of this skill, and make sure they understand the skill.  You MUST perform this skill using a fixed down line so that you can arrest the ascent in the event of an emergency.  You should have one hand holding on to the down line, and one hand holding on to the student during this skill.  The student keeps the regulator in their mouth with their left hand on their BC inflator/deflator to control their ascent during this skill.  I usually hold onto them with my right hand, and give them a 3 second count down (3-2-1, UP!) with my left hand while resting the line in the crook of my left elbow.  When the student begins their ascent I position my left hand around the line ready to grab hold it to halt their ascent.  I always tell my students to get a good breath of air when I give them the UP signal then hum loudly on the ascent, but I rarely hear them if I am wearing a hood, so I have to also watch for bubbles as they exhale.  If they are not exhaling, I stop them.  If they take a breath, I stop them and make them go back to 15’ to repeat the skill.  I usually do this skill at the beginning or end of a dive, and leave the other students on the surface while I conduct the CESA individually with each student. You should never leave uncertified divers unattended on the bottom!
  • The are descriptions of the other skills in the NAUI S&P, also feel free to ask any of us, we will be more than happy to share.


Sample Schedule

I write out the dive’s and the skills I will have them do on my slate.  I also write out their names on the other side, this helps me with their names in the event I am diving another instructors students.   My slate looks something like this (text in RED is not written on the slate):

Day 1: Dives 1-3 (Local Springs)

Dive 1

Snorkel to down line

Mask clears

Regulator Recoveries

Weight Belt Removal & Replacement


Out of Air Share (both)


During the SIT we will go over logs and tables.  This allows us the chance to do their SAC rates as well as their letter groups.  Swap tanks.

Dive 2

CESA <- get it out of the way at the beginning, but your ears will be ringing after 8 of these…

Hovering / tour

Rescue (both) <- During the rescue I have them do a do-si-do tow for 50 yards

Surface Gear Removal

Cramp Releases

During the SIT we will stay in the water and do surface gear removal and replacement and cramp releases.

Dive 3

Hovering / Buddy System

Just do a tour dive.  They have had a busy day, let them relax.  The water level has been so high in Manatee that we’ve done some nice dives throughout the cypress knees in July.

After the dive, log all dives and activities over lunch as a group!

Day 2: Dives 4-5 (Keys)

Group control on Dive 4 & 5 is really critical.  We can have rough seas, poor visibility, and high current, so you need to make sure to follow FILO and give a very detailed pre-dive briefing before beginning each of these dives.  As part of that briefing, you should stress to your students that they need to stay with you as a group, that they should use the down line, and that they should monitor their air and let you know if they are running low.

Dive 4

Deep dive (40-60’).


Safety Stop


Dive 5

Compass Navigation Dive <– send them out on a heading (or natural navigation) for 10-15 kick cycles.


I usually then take them on a tour, then write the following in my wet-notes if I am comfortable with them, “congratulations, you have just passed.  You may go off with your buddy but be back here within X minutes or no less than Y psi.”  I adjust X and Y to the situation, such as their current air, how long we have been down.  I usually try to let them go for about 10 minutes, but not too much more than that.

Post dive, we will go grab lunch and fill out logbooks, handout c-cards.  Usually Mike K. is snarling about the logbooks.


Then it’s party time in the keys with the cookout…  Maybe if you’re lucky, someone will bake slutty brownies.


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.