Connect with us

Latest Features

The Case for Biochemical Decompression

How much do you fart during decompression? How about your teammates? It turns out that those may be critical questions if you’re decompressing from a hydrogen dive, or more specifically hydreliox, a mixture of oxygen, helium, and hydrogen suitable for ultra-deep dives (Wet Mules, are you listening?). Here the former chief physiologist for the US Navy’s experimental hydrogen diving program, Susan Kayar, gives us the low down on biochemical decompression and what it may someday mean for tech diving.

Published

on

by Susan R. Kayar, PhD
Header courtesy of A. Tocco Comex

Thirty years ago, the Naval Medical Research Institute (NMRI) in Bethesda, Maryland, hired me for what at the time I thought was the coolest job I could ever be asked to do.  I still think so.  I was hired to be the physiologist for their experimental hydrogen diving program.  Why dive with hydrogen?  A recent InDepth article by Reilly Fogarty, “Playing with Fire: Hydrogen as a Diving Gas”, does an excellent job of explaining this subject.  The short answer: because hydrogen is the smallest molecule. 

One  might think that in an era with excellent one-atmosphere hard suits, and multiple forms of submersibles and robotics, there is no need to send bare-naked divers to the sorts of depths involved in hydrogen diving, as will be described shortly.  If these alternatives to divers are so great, why do we still use commercial divers at all?  One needs to ask an operational person this question, rather than a scientist like me.  But I think the words “logistics”, “costs”, “safety,” and “the direct human touch” would figure in the answers.  

Just a snapshot of the enormous efforts needed to send works to the oceans floor. Photo courtesy of A. Tocco Comex.

Once a diver dives deep enough to exceed safe limits with regard to nitrogen narcosis, the usual gas switch for the diluent to oxygen is helium.  However, if a diver keeps on going into the range of 1000 to 2000 feet of seawater (roughly 300-600 msw), a helium-oxygen gas mixture becomes dense enough that the work of breathing becomes difficult.  Divers fight to move this dense gas into and out of their lungs, making the effort to breathe a serious source of fatigue and a distraction to their assigned jobs. (See “Maintaining Your Respiratory Reserve,” by John Clarke). Hydrogen is a diatomic molecule (i.e. H2) with two protons and no neutrons, and is therefore half the molecular weight of helium, a monatomic molecule with two protons and two neutrons.  Therefore  replacing helium with hydrogen, eases a diver’s respiratory distress i.e. work of breathing.  

There is also a phenomenon of ultra-deep diving known as High Pressure Neurologic Syndrome, or HPNS, (also known as High Pressure Nervous Syndrome) which is evidently a function of high pressure interfering with the transmission of signals in the nervous system.  Symptoms of HPNS can range from tremors to confusion to psychosis and are highly variable in depth at onset and from diver to diver.  For unknown reasons, hydrogen at high pressure is narcotic and can suppress HPNS.  Past a very high pressure that again varies with the diver, but generally on the order of 23 atmospheres partial pressure of hydrogen, its narcotic properties can become overwhelming and have their own psychotic effects.  

There are also serious issues involving the explosivity of hydrogen in combination with oxygen, but these issues are manageable with the care one always uses in handling oxygen and other combustible and hyperbaric gases.  Hydrogen and oxygen can be combined safely if the oxygen content is less than 4% of the gas mix, with dive operations usually opting for 2% oxygen as their safe upper limit.  A 2% oxygen mixture is breathable if the total pressure is 10 atmospheres (roughly 90m/295 f) or more.  This is normally accommodated by starting a pressurization with helium and then switching to hydrogen after 10 atm.  As a final consideration, the price of helium is rising, and may make hydrogen substitution increasingly attractive.  Consequently, for a variety of practical reasons, hydrogen has a potential place in ultra-deep diving beyond 10 atmospheres of pressure.

Investigating Biochemical Decompression

As the physiologist to the hydrogen diving program at NMRI, my assignments were two-fold: first, to determine if there are any dangerous biological effects that had been previously overlooked of breathing hyperbaric hydrogen,  and second, to look into something that NMRI was calling “biochemical decompression,” or “biodec,” a term they had coined themselves.  

Susan Kayar at her workplace. Photo courtesy of Susan Kayar.

The unknown dangerous biological effects portion of the research was addressed first.  The short answer to that was “none”.  We found no evidence that inhaled hydrogen could participate in any unwanted biochemical reactions in the body, discounting whatever reactions eventually make hydrogen narcotic.  We still do not know exactly why hydrogen becomes narcotic, but it is unlikely from the physical properties of hydrogen that its narcotic effects are permanently harmful post-dive.

Then we got to the really exciting part of the hydrogen research program at NMRI: biochemical decompression.  A few years before I was hired in 1990, a biochemist at NMRI, Dr. Lutz Kiesow, heard it was possible for divers to use hydrogen as a breathing gas.  He knew there were many microbes that possessed a hydrogenase enzyme allowing them to consume hydrogen gas as a metabolic source equivalent to the consumption of oxygen as a metabolic source for most land organisms.  End products for hydrogen metabolism can vary with the microbe, but is often methane (CH4).  Hence, as a class, such microbes are called “methanogens”.  

Dr. Kiesow proposed that NMRI establish a research project to isolate the hydrogenase from a methanogen, and insert it somewhere in the body of a diver to effectively create  a chemical scrubber unit for hydrogen.  If a diver could continuously scrub out some of the hydrogen going into solution in his body during the dive, the diver would have a reduced body burden of inert (to the diver) gas, and could subsequently decompress more rapidly with lower risk of decompression sickness (DCS).  

What a cool concept!  I loved it from the moment I heard it.  But the real challenge was to resolve Dr. Kiesow’s “somewhere in the body” requirement into a safe, readily reachable, functionally useful body location.  The director who hired me understandably warned me that divers would be opposed to receiving routine injections, or any sort of biological implant making them Bionic Men, permanently different from their former selves or from other divers. So what was left?  

Susan Kayar today, sharing her knowledge with the world. Photo courtesy of Susan Kayar

On my first musings with the scientific head of NMRI when I was hired, I wondered if we could perhaps encapsulate the hydrogenase enzyme, or better yet just whole methanogens, and swallow the capsules down for delivery to the large intestine as the working location for this scrubber unit. The scientific head instantly responded he had been thinking the same thing, but had not wanted to bias my thinking by saying it first.  The approach met all our criteria. Taking capsules by mouth is as easy and as non-invasive a way to get things into the body as there can be.  The large intestine has many microbial species living there safely and performing many jobs that we are slowly realizing are important to our health.  

Trust Your Gut?

Methanogens typically are anaerobic organisms that would die quickly if exposed to oxygen, and the large intestine is the only part of the body that provides an anaerobic environment.  Some species of methanogens are even a normal part of our intestinal flora, where they consume traces of hydrogen manufactured by other intestinal microbes.  We were therefore confident that adding more methanogens should do no digestive harm. The amplified population of methanogens in the intestine would be likely to stay high only for as long as the divers breathed hydrogen, and return to baseline shortly after the exposure to hydrogen ended. The methane end product of this hydrogen scrubbing has a safe means of escaping from the intestine.  

The methane-releasing issues were the only parts of this research that got a little weird at times. I was very carefully coached by Navy people to use lengthy euphemisms such as “the methane is released to the environment following the path of least resistance,” or “methane has an obvious means of egress from the intestine.”  I was warned never to use what I have come to refer to as “the four-letter f-word” for methane release.  But the euphemisms never helped.  All audiences instantly understood the euphemisms as such.  

The first dive to 701m. Photo courtesy of A. Tocco Comex.

Indeed, I came to consider it a sign that my audience was truly listening to me and following the science when they suddenly started squirming in their seats and trying with greater or lesser success to cover their laughter when I started explaining the fate of methane. Jokes followed. One Navy brass listener asked me if the implementation of hydrogen biochemical decompression meant a negation of the stealth intended for Navy SEALs when they used closed-system (i.e., non-bubbling) breathing rigs.  The only sensible thing for me to do was laugh along with the room.  

An interesting phenomenon happened as soon as people got over their initial laughter at this childishly scatological word that I did not say but that they obviously thought of themselves. They started thinking about the physiology and the gas transfer physics I was describing, and they liked it.  No more laughter after that moment of enlightenment arrived. So go ahead and laugh now. “Better out than in” applies to laughter also.  I got a million of ’em. I am known in some circles as the “Queen of Farts” with good reason. 

Measuring Flatulence err Farts

I retired from Navy civilian service years ago, so I can say whatever I wish.  I measured farts. Measuring farts is funny. And measuring farts in rats and pigs is exactly how my NMRI team and I succeeded in demonstrating the feasibility of hydrogen biochemical decompression to reduce the incidence of DCS following hydrogen dives by roughly half. As far as we know, methane release rate is the only variable that can be biologically manipulated with a measurable effect on DCS incidence following any kind of dive. There is nothing humorous about reducing DCS incidence.  

Photo courtesy of Aqua Magazine, Susan Kayar.

The methanogenic species we chose has a rather grand first name but oddly mundane last name: Methanobrevibacter smithii.  It is native to the intestinal flora of many mammals, including humans and pigs, and thus does not cause digestive issues when added to the intestines.  The metabolic equation for M. smithii is the following: 

4H2 + CO2 = CH4 + 2H2O

To speed things along in the lab, we surgically injected M. smithii cultures into the upper end of the large intestines of our lab animal models of divers, which were initially rats and later pigs.  The animal-divers were then placed in a hyperbaric chamber which we pressurized with hydrogen and oxygen.  Some hydrogen and oxygen breathed by an animal-diver dissolves in the blood for transport throughout the body.  When the blood circulates through the vasculature of the intestinal wall, some hydrogen diffuses down its partial pressure gradient into the intestinal cavity, where the M. smithii are housed.  

Figure 1. Sample hydrogen dive with a rat using biochemical decompression.  A rat with a culture of M. smithii in its intestines was placed in a hyperbaric chamber.  As the pressure of hydrogen (green squares) increased in the chamber, increasing quantities of methane (red dots)  were released from the rat.  When the chamber was decompressed, methane release initially spiked as hydrogen became super-saturated in the rat, and then fell as hydrogen was removed from the chamber. Diagram courtesy of Susan Kayar.

Oxygen is taken up by the cells of the intestinal wall and aerobically metabolized to carbon dioxide (CO2), some of which also diffuses into the intestinal cavity. M. smithii metabolizes the hydrogen and carbon dioxide to methane and water. The animal-diver safely absorbs the water. It is a real scientific benefit that the methane exits the body as easily as it does. Since no mammalian cell manufactures methane, we could track the metabolism of our methanogens inside our animal-divers simply by measuring the rate of release of methane from them to the surrounding environment by gas chromatography. As the hydrogen pressure in the chamber increased, we measured increasing quantities of methane in the chamber gases 

Figure 2. Risk of DCS was significantly reduced in rats with methanogens following dives in hydrogen. Rats with M. smithii in intestines had significantly fewer cases of DCS (5/20) compared to untreated control rats (28/50) and rats undergoing the same surgical procedure as the treated rats but without M. smithii injections (13/20). Diagram courtesy of Susan Kayar.

When we then decompressed our animal-divers, on average, the animals with supplemental methanogens had approximately half the incidence of DCS as those without supplements. As the volume of methane they released during the dive increased, their incidence of DCS decreased.

Figure 3.  Injected activity of methanogens correlates with methane release rate and lower incidence of DCS in pigs following hydrogen dives (Kayar et al., 2001).  

Knowing from the metabolic equation above that four hydrogen molecules are consumed for each methane molecule manufactured, we could easily estimate the rate of hydrogen-scrubbing inside our animals.  Based on the solubility of hydrogen in body tissues (which we guesstimated as being similar to water), and the time at pressure of the dive, we could estimate how much hydrogen would dissolve in an animal of a given body mass by the end of the bottom time, and what fraction of that body burden of hydrogen had been eliminated by our process.  We computed that when M. smithii eliminated approximately 5% of the hydrogen dissolved in our animal-divers’ bodies, DCS incidence was reduced by 50% (Fahlman et al, 2001).   

Human Biodec

Having succeeded in demonstrating hydrogen biochemical decompression in a small animal model, the rat, and a larger animal model, the pig, we are at least scientifically prepared to extend this work to human divers.  A diver would make a saturation dive (commonly abbreviated to “sat”, meaning a dive sufficiently long i.e. 24 hours or more, to saturate the diver’s tissues with the breathing mixture) using a hydrogen-oxygen blend we usually call “hydrox”, or a hydrogen-helium-oxygen trimix which goes by the awkward name of “hydreliox”, depending on practicalities.  

Dive operations may even opt for a quad-mix including nitrogen.  The ultra-deep diving trials at Duke University found the narcotic properties of nitrogen helped to suppress HPNS, which was so problematic for their divers breathing heliox. However, the interaction is complex. Since we are still working out the exact mechanisms that make nitrogen and hydrogen narcotic under pressure, it remains to be determined if combining nitrogen and hydrogen for deep sat dives makes narcotic issues better or worse.  The issue deserves testing.

What oral supplements might look like. Photo by JESHOOTS.com from Pexels.jpg.

Regardless of the other gases in the sat diver’s mix, if there is hydrogen, then hydrogen biochemical decompression could be considered.  A couple of days before the end of the bottom time, the diver would prepare to biochemically decompress as a supplement to the physical decompression.  The basic process would be identical to that for our animal models, except for a gentler way of delivering the methanogens to the diver.  We would freeze-dry cultures of M. smithii and pack them into oral-delivery capsules designed to dissolve only under the conditions inside the large intestine.  It would take around 24-36 hours to have a capsule arrive in the intestine, dissolve, and re-activate the methanogens.  We would know that the M. smithii were on site and sufficiently active by chemically analyzing the sat chamber gases for methane output.  Then we would get to watch the diver not bend as he decompressed faster than divers in other hydrogen diving operations without biochemical decompression.  As I said, coolest job ever, or what?

But wait!  

There is one more really exciting finding to report.  We have evidence that even the quantity of methanogens native to the intestinal flora of a pig can provide sufficient hydrogen-scrubbing activity to reduce DCS incidence from a hydrogen dive (See Fig. 4 below).  Humans and pigs are similar in many respects, including basic intestinal flora.  It may well be that any human divers on a hydrogen dive, such as those at COMEX , have already benefited from hydrogen biochemical decompression without realizing it.  They have only to test for methane in their chamber gases to know.  

Figure 4.  Native methanogens in untreated pigs significantly reduced DCS incidence.  As untreated pigs were exposed to various dive profiles in hydrogen, increasing pressures of hydrogen elicited increasing quantities of methane released by methanogens native to the pigs’ intestinal flora.  Open circles represent pigs with subsequent DCS, closed circles represent pigs without DCS.  DCS incidence was significantly lower as the pigs released more methane.  

Skeptics have argued that the relatively small percentage of hydrogen scrubbing we have computed may be far too little to have any impact on DCS risk in human divers or to make a worthwhile reduction in decompression times. In addition to pointing to our DCS incidence data, we note that all divers are familiar with how important small differences in gas loads can be in DCS risk. If we dive within the time at depth limits of our chosen algorithms, we are confident to a very high level of probability that our dive will end safely. But exceeding our planned no-decompression limits by even a few minutes, and thus adding only a relatively small percentage increase in our inert gas load beyond what we think of as safe, makes our dive profile much riskier.  [Ed. Note: These are computational risks not necessarily operational ones i.e. small changes in times/depths are unlikely to result in DCI] Likewise, we are all in the habit of making what we term a “safety stop” in 3-5m/10-15 ft even from a low-risk, no decompression time-requiring dive. 

Sat dive operations currently using heliox and contemplating a shift to adding hydrogen will be dismayed to realize that hydrogen is considerably more potent at inducing DCS than is helium (Lillo R.S., E.C. Parker, W.C. Porter, 1997 Decompression comparison of helium and hydrogen in rats. J. Appl. Physiol. 82(3) 892-901). This would mean that costs saved by substituting relatively inexpensively manufactured hydrogen (by electrolysis of water) for increasingly expensive imported helium could be overwhelmed by the costs added in significantly longer decompression time. This is where hydrogen biodec may provide its greatest advantage: in shaving down the extra time needed for safe decompression from a hydrogen dive to something closer to that of a heliox dive.  Until someone takes the step of testing hydrogen biodec in human subjects, we will not know to what extent operational decompression times could be reduced.  

Nitrogen Biodec?

What comes next?  In an ideal scientific world, our research in animal models would be followed by equivalent studies in human divers.  However, for the time being in the post-Russian Cold War Era, the US Navy has expressed no further interest in hydrogen diving and has not offered to support human studies in hydrogen biochemical decompression.  To assuage my disappointment, I wrote a novel in which hydrogen biochemical decompression is used to help save the day in a submarine rescue scenario.  The novel is entitled “Operation SECOND STARFISH, A Tale of Submarine Rescue, Science, and Friendship,” available as a paperback and Kindle e-book on Amazon.  

But I am still dreaming bigger than that.  Since hydrogen biochemical decompression works, why not shoot for something everyone in the diving world could use?  Nitrogen biochemical decompression!  There are nitrogen-metabolizing microbes native to our intestinal flora.  But the problems of experimentally making nitrogen biochemical decompression work are staggeringly complicated.  One of many is that in nitrogen metabolism, usually referred to as nitrogen fixation, the end-products are molecules such as nitrites, nitrates, and ammonia, which are not gases that would just come bubbling out for us to measure.  

Susan submerged. Photo courtesy of Susan Kayar.

These fixed nitrogen compounds would stay dissolved in the fecal material and join many more such molecules already there from protein digestion.  (If you think the fart jokes are bad, consider the fecal jokes. “No shit!”-Ed.) The presence of fixed nitrogen products in feces (also known as “fertilizer” under other circumstances) suppresses the nitrogen-fixing microbes from fixing even more, since the process is energetically expensive to the microbes and done only by necessity.  It would take some genetic manipulation of the microbes to get them to work for us, and some form of special molecular labeling to measure how much end products they are making.  I leave those problems to future scientists to solve, while I enjoy my retirement in New Mexico, the Land of Enchantment, and go on dive vacations to Hawaii, Papua New Guinea, Tahiti, Fiji, and Raiatea to keep my vestigial gills damp. I may even write another novel. 

Additional Resources

Operation SECOND STARFISH, A Tale of Submarine Rescue, Science, and Friendship

References

Bennett, P.B., R. Coggin, M. McLeod, 1982.  Effect of compression rate on use of trimix to ameliorate HPNS in man to 686 m (2250 ft).  Undersea Biomed. Res. 9(4)335-51.

Fahlman, A., P. Tikuisis, J.F. Himm, P.K. Weathersby, and S.R. Kayar, 2001.  On the likelihood of decompression sickness during H2 biochemical decompression in pigs.  J. Appl. Physiol. 91:2720-2729.  

Imbert, J.P., C. Gortan, X. Fructus, T. Ciesielski, and B. Gardette, 1988.  Ch. 13.  Hydra 8: Pre-commercial Hydrogen Diving Project.  Advances in Underwater Technology, Ocean Science and Offshore Engineering, Vol. 14, pp 107-116.  

Kayar, S.R., M.J. Axley, L.D. Homer, and A.L. Harabin, 1994.  Hydrogen gas is not oxidized by mammalian tissues under hyperbaric conditions.  Undersea Hyperbaric Med. 21(3):265-275. 

Kayar, S.R. and M.J Axley, 1997.  Accelerated gas removal from divers’ tissues utilizing gas metabolizing bacteria.  U.S. Patent No. 5,630,410.  

Lillo R.S., E.C. Parker, W.C. Porter, 1997 Decompression comparison of helium and hydrogen in rats. J. Appl. Physiol. 82(3) 892-901

Kayar, S.R., T.L. Miller, M.J. Wolin, E.O. Aukhert, M.J. Axley, and L.A. Kiesow, 1998.  Decompression sickness risk in rats by microbial removal of dissolved gas.  Am. J. Physiol. 275 (Regulatory Integrative Comp. Physiol. 44):R677-682.  

Kayar, S.R., A. Fahlman, W.C. Lin, and W.B. Whitman, 2001.  Increasing activity of H2-metabolizing microbes lowers decompression sickness risk in pigs during H2 divesJ. Appl. Physiol. 91:2713-2719.  

Kayar, S.R. and A. Fahlman, 2001.  Decompression sickness risk reduced by native intestinal flora in pigs after H2 dives.  Undersea Hyper. Med. 28(2)89-97.  

Valée, N., Weiss M., Rostain JC, Risso JJ, A review of recent neurochemical data on inert gas narcosis. Undersea Hyper. Med. 38(1)49-59


Susan grew up in the St. Louis, Missouri, area.  An early fascination with the films of Jacques Cousteau inspired her to become certified as a scuba diver while still in high school.  Her diving in Missouri was confined to artificial lakes with sunken rowboats, lost Coke bottles, and a few carp as the thrills.  She persevered in her interests in marine sciences and attended the University of Miami as a biology major, remaining at that institution all the way through to a doctorate.  After graduation, it did not take long to realize she would starve if she insisted on a job in marine biology, so she moved into studying physiology in extreme environments and exercise stress.  Postdoctoral research appointments sent her from Colorado to Switzerland to New Jersey.  Her dream job finally materialized in an appointment with the US Navy in the Washington, DC area, where she studied decompression sickness risk in animal models of ultra-deep diving.
Susan was inducted into The Women Divers Hall of Fame in 2001 in recognition of her Navy diving research.  When funding for her Navy program ended, she managed research funding efforts for the National Institutes of Health (NIH), Defense Advanced Research Programs Agency (DARPA), and the Office of Naval Research (ONR).  Now in retirement, she has written a diving-themed novel, “Operation SECOND STARFISH.”

Cave

Meet The British Underground

It’s cold, dark, you can barely see two meters in front of you, and you’re diving alone. Oh, and there’s a sump up ahead. Welcome to the British Underground! Not exactly a scooter-ride in the warm, clear, stalactite studded caves that lay beneath Riviera Maya. Here British caver and training officer for the Somerset Section of the Cave Diving Group Michael Thomas guides us on a tour of British cave diving and explains why it may not be everyone’s cuppa tea.

Published

on

By

by Michael Thomas 

Header photo courtesy Michael Thomas. Diver entering Keld Head in the Yorkshire Dales.

Recently someone approached me about British cave diving wondering what in particular makes it so very different from Mexican cave diving, for example, and why it’s so appealing to a select few. In the U.K. we have two types of underground diving. The first is the significant number of flooded mines that have given rise to some world-class mine diving that’s becoming very popular with technical divers from around the world. The second type of  underground diving is traditional British cave diving, which, due to the nature of U.K. caves, involves both dry caving and cave diving. The aim is to explore the caves underwater or in the dry underground following it as far as possible. We are now finding that technically trained mine and cave divers are starting to learn the art of dry cave exploration in order to further their knowledge and adventure, some even gaining enough experience to join the Cave Diving Group in the U.K. 

Firstly, a little about myself if I may be so bold. My diving career is now in its thirty-third consecutive year, from starting out as a trainee open water diver with BSAC to trainee cave diver within the CDG to becoming the Training Officer of the British Cave Diving Group Somerset Section in the U.K. Since 1996 I’ve had links to TDI and currently hold Full Cave Instructor, Sidemount and Tech Instructor status with TDI, active mod 3 CCR cave diver, and on the British Cave Rescue call out list as a diver. 

My diving life crosses all paths of British and worldwide diving, from open water to cave and tech. I’m actively involved with technical diving conferences and a fellow of the Royal Geographic Society of the U.K. My father was a cave explorer before me, and my son has also taken the same path. You could say, caves and diving are our lives. 

See The CDG 

To understand British cave diving we first need to understand the CDG.  The Cave Diving Group is the representative body for cave divers in Great Britain and Northern Ireland and is a constituent body of the British Caving Association (BCA). Its function is to educate and support cavers for recreational and exploratory operations in British sumps. The CDG also helps control access to numerous cave sites, including Wookey Hole and Gough’s Cave  in Somerset, and Keld Head And Hurtle Pot in Yorkshire, in conjunction with the BCA. The group was formed in 1946 by the late Graham Balcombe, and its continuous existence to the present day makes it the oldest amateur technical and cave diving organization in the world. Graham Balcombe arguably invented cave diving in the U.K. with his audacious dives in Swildon’s Hole cave and Wookey Hole cave in 1935. 

Now the huge difference between the Cave Diving Group and other cave diving training agencies is you can’t just sign up and pay to do a training course. From the very start in 1946, the prerequisite for joining the CDG was always and is a knowledge and experience base of dry caving skills, though in modern years we also require an open water certification. Once you have made yourself known to one of the four sections that make up the CDG—Somerset, Welsh, Northern, and Derbyshire—and proven you have dry caving skills and can get along with your new-found friends, you are voted in, hopefully to whichever section you approached. 

CDG rescue practice exercise after the Thailand rescue to update our rescue skills and standards. Photo courtesy of Michael Thomas.

As a trainee member of the cave diving group, the training is apprenticeship based and generally takes between 12-18 months. At the end of that, a written exam and an underwater test is completed, and as long as your section is in agreement, the qualified diver status is awarded. It’s a slow process but ensures adequate experience is gained in a variety of different sites and conditions, producing a cave diver that is capable of exploration cave diving, rescue work, and continued training of new members. 



The Solo Mentality 

Probably the one difference with most U.K. cave diving, that is a world away from agency standards, is the CDG approach to team diving. In all but a few sites in the U.K., the CDG considers solo diving the safest way to approach the dive. While divers might enter the cave together as a team, and dry cave their way to the dive base (dive site within the cave), once they are in the water they typically dive solo. This is because a diver is usually unable to help another diver in the water. Then they meet up on the other side if more dry caving is to be done. 

CDG trainee divers are taught from the beginning to be solo divers or work within a team as solo divers, something we call “team solo.” Most dive sites in natural caves in the U.K. are unsuitable for team diving. The few sites that are suitable for a team to operate together, such as Wookey Hole in Somerset, Hurtle Pot in the Yorkshire Dales, and Porth Yr Ogof in South Wales, should really be a team of only two divers. Passage size and visibility generally means divers can’t see the third team member if at the back or front of the team. The mine diving sites are much more suited to team diving with larger passages and clearer water. The links below offer more information on mine diving in the U.K. [Ed.note: Global Underwater Explorers does not sanction solo diving.]

Robert Thomas at Top waterfall sump dive base Ogof Ffynnon Ddu Cave Wales UK. Photo courtesy of Michael Thomas.

The article, “Solo Cave Diving,” on the CDG website explains why it recommends solo cave diving as the safer alternative for U.K. sump conditions. It lists some of the advantages of solo cave diving as follows:

  • There’s no one to get physically jammed in the passage behind you (thereby blocking your exit).
  • There’s no one behind you who may get tangled in the line and have to cut it—leaving you with no guide home.
  • There’s no one to accidentally disturb your ‘out tags’ at line junctions (e.g. in one cave there are 10 branch lines off the main line in the first 500 m/1640 ft of passage).
  • There’s no one to cause silt problems (but yourself).
  • There’s no chance of being called upon to share air—in small passages.
  • There’s nothing to get confused about—communication in sumps varies from difficult to impossible.
  • There’s no one to provide you with a false sense of security.
  • There’s no one to worry about but yourself, so you can concentrate on your own safety.

Equipment Configuration

Due to the generally small passage size of British caves and the sometimes energetic nature of transporting equipment to a cave dive base (station), sidemount diving is the normal equipment configuration. Sidemount started in the U.K. in the 1960s with a need for streamlined and lightweight diving equipment. U.K. cave divers today will have a choice of sidemount harness for the project they are involved with. In a short, shallow, or constricted dive, the diver will use a wetsuit and a lightweight, webbing-only harness with no buoyancy, as it’s not needed if your chest is on the floor and your back on the ceiling. 

 Diver leaving Dire Straits dive base Gough’s Cave Somerset UK. Photo courtesy of Michael Thomas.

In slightly larger cave passages, the modern British cave diver will use one of the now-common sidemount harnesses that are available. Many British caves require vertical cave techniques to reach the water, so the divers have modified the sidemount harness to be able to descend into the dry cave, do the dive, and then climb out. It’s very rare to find a British cave diver with an unmodified sidemount harness. For exposure suits, many short dives and some longer dives, if significant dry caving is expected before or after, the dive will be done in a wetsuit even though water temperature is on average between 7-10 degrees C/45-50 degrees F. This is for practical reasons, as it’s very difficult and potentially dangerous caving in a drysuit, so better to be slightly chilly during the dive and caving safely. 

For larger sites and when the diver is expected to be underwater most of the time, a drysuit is sometimes carried to the dive base and put on underground, to be utilized for the dive. As most divers are solo diving, having two short standard-length hoses on their regulators is normal, although for team diving or cave rescue, a standard long hose is used on the right. 

British cave divers always use helmets, as they provide protection from the environment in the dry caves as well as underwater, and are a great place to carry lights. Hand-held primary lights are used in larger, clearer passages with the helmet lights in reserve. For dive lines, we use 4 mm thick lines as permanent dive lines and we have fixed junctions in all caves— no jumps or gaps. Standard line arrows and cookies will not fit on a U.K. line. Pegs are used, or permanent markers on junctions to show the way home. It’s very unlikely you will see another dive team in the cave on the day you are visiting, and following a thicker line in sometimes low visibility and cold water is much safer and more comforting than trying to follow a technical diving line. 

Exploring U.K. caves 

The raison d’etre for the Cave Diving Groups formation was and still is the exploration of caves, including the surveying and reporting of that exploration and the training of new divers. The CDG publishes a journal four times a year with exploration reports and many books on the subject of U.K. caves and techniques. If it’s not surveyed and reported, it’s not explored. Now, it would be extremely tedious to the reader if I listed all exploration in underwater caves in the U.K.—we have thousands of reports—so I’ll mention a few of the classics to set the scene, and remember all exploration can be researched in the CDG journals. 

If visiting, most U.K. cave divers are happy to show you around or even get you involved in projects, although they will be of a very different style of exploration than found in Bahamas or Mexico, for instance, where swimming into hundreds of metres of new cave is possible. Big breakthroughs in the U.K. are rare, and if a diver explores 10 m/33 ft of new cave with ongoing passage seen, they will be happy. 

Wookey Hole Cave Somerset, Somerset 

Exploration in the home of British cave diving started in 1935 and carries on to this day. Slow and determined work by some of the great names in cave diving, including Balcombe, Martyn Farr, Rob Parker, Rick Stanton, and John Volanthen have seen this multi sump cave reach 90 m/294 ft depth beyond chamber 25 in extremely committing passages. Smaller side passages throughout the cave are still being explored. 

Michael Thomas surfacing in Wookey Hole after Recovering a 3rd 4th Century Roman pot ! Photo courtesy of Michael Thomas.

The Llangattock Cave Systems, South Wales 

Under Llangattock mountain lies many kilometers of caving—two caves, Ogof Daren Cilau at 27 km long and next door Ogof Agen Allwedd at 32.5 km, provide access to many cave diving sites that have provided incredible exploration over the years and will hopefully provide more in the years to come. One of the longest dives in the system is the Pwll y Cwm resurgence at 630 m/2066 ft long, surfacing in the downstream end of Daren Cilau. 

Kingsdale Master Cave and Keld Head, Yorkshire Dales 

One of the true classics of world class cave diving is the Kingsdale to Keld Head system. Graham Balcombe, of Wookey Hole fame, conducted dives in 1945 in Keld Head, and in 1978, Geoff Yeadon and Oliver Statham broke the world record with an 1829 m/6000 ft dive between Kingsdale Master Cave and Keld Head, connecting the two caves. In 1991, the underwater system was further extended, linking it into King Pot cave access to the valley floor, a traverse of 3 km in British conditions. Today, divers continue to explore and extend this system. 

Speedwell Cavern Main Rising, Derbyshire Dales 

This dive site requires a reasonable amount of dry caving effort to reach the dive base. The dive itself is multi-profile with a descent to 36 m/118 ft then up to 2.5 m/8 ft via a constricted rift, then finally down to 71 m/232 ft at the end. In the 1980s John Cordingley and Russel Carter worked the site and finally, 71 m/233 ft was reached by Martin Groves in 2002. The way on was lost in boulders and boiling sand with the water surging upwards. This was confirmed by John Volanthen in 2006. A change in geology and future technologies await. 

The Green Holes of Doolin, Ireland 

In the years leading up to the 1980s, open water divers reported cave entrances in the sea on the Doolin coast. These completely submerged caves are extremely weather dependent due to taking the full force of the Atlantic Ocean. But after experience gained in the Bahamas’ Blue Holes, British divers tried their luck exploring what became known as Green Holes. Several sites including Reef Caves, Hell Complex, Urchin Cave, and the longest Mermaid’s Hole have had successive and continued exploration. 1025 m/3350 ft penetration being reached in Mermaid’s Hole by Artur Kozlowski. Exploration continues when the weather allows. 

Robert Thomas demonstrates vertical caving skills needed to reach many cave diving sites in the UK. Photo courtesy of Michael Thomas.

Swildon’s Hole Cave, Somerset 

A true classic sump diver’s cave with long sections of active wet streamway takes the visitor down to a series of eight short sumps that require diving and more caving to reach the terminal sump and end of the cave at Swildon’s 12. Wetsuits and lightweight sidemount harness and small cylinders needed. A grand day out. 

Porth Yr Ogof Cave, South Wales 

One of the finest and reasonably easy physical-access cave dives in the U.K. The dive starts from a small pool after a short climb down between boulders. A shallow and comfortable passage winds its way up the valley passing Rawlbolt Airbell 150 m/492 ft from base and Four Ways airbell around 200 m/656 ft from base. At 250 m/820 ft from base, a cobble squeeze can be passed to the surface in the dry upper cave. The flow in this cave can be very high and the passage size varies from 1 m wide to 3 m wide, making progress upstream interesting and downstream on the return exciting. 

Hurtle Pot, Yorkshire Dales 

Probably the most dived cave in the U.K. due to its easy access and the possibility of longer dives upstream in a large passage towards Jingle Pot Cave and an area called The Deep reaching 35 m/114 ft depth in a low complicated passage towards the end around 460 m/1508 ft from base. Downstream a 400 m/1312 ft long traverse can be made to surface in Midge Hole cave reaching 20 m/65 ft depth on the way. This cave floods dramatically in bad weather, and constant line repairs need to be made by local CDG divers. 

Peak Cavern, Derbyshire Dales 

Peak Cavern is an extensive dry cave with several significant cave diving sites located within the system. The resurgence is a classic training dive in a lovely bedding plane style passage reaching the surface in the main cave. Ink sump within the cave, nearly 200 m/653 ft long, leads to Doom’s Retreat, an area worked by Jim Lister and the most extensive digging project to find a new cave beyond a sump in the U.K. Far Sump at 385 m/1263 ft long leads to an extensive dry section of cave with some extremely technical caving that can now get you to surface on the hills above. 

Pollatoomary Resurgence, Ireland 

Not many easy surface access cave diving sites that go deep are to be found in the British Isles, but this one in Ireland is one. A resurgence site that reaches 103 m/336 ft but in dark, unfriendly waters. Original exploration by Martyn Farr in 1978 and taken to 103 m by Artur Kozlowski. 

Divers leaving surface in Wookey Hole on a practice cave diving rescue.  photo courtesy of Michael Thomas.

In summary, British cave diving is historically one of the oldest branches of the sport of cave diving. The Cave Diving Group’s knowledge and standards and procedures evolved over the years to the safest method to explore or dive in U.K. style caves. It is not diving in Wakulla Springs and does not pretend to be, although several CDG members got involved in the early Wakulla expeditions. It is at times cold, wet, and unpleasant, but also can be extremely rewarding, with new caves found or just a superb dive in excellent conditions. U.K. style conditions can be found all over the world—think of the Thailand Rescue in 2018—and it’s in these conditions that the CDG system is at its best. If you’re wanting more information on the CDG or sump diving and vertical access sump diving, please give us a shout. Just remember—a pint of English beer is supposed to be warm. Stay safe and dive well. 

Additional Resources:

Website: The British Cave Diving Group

From GUE’s membership magazine QUEST: “British Cave Diving: Wookey Hole and The Cave Diving Group” by Duncan Price

Books about British cave diving:

A Glimmering in Darkness by Graham Balcombe 

The Darkness Beckons by Martyn Farr 

Interview with Cave Diving Legend Martyn Farr

Historical British cave diving films:

Trailer for documentary film ‘Wookey’ by Gavin Newman

The Underground Eiger (1980s)

Articles by Michael Thomas:

Slow Down Young fellas-Attitudes in Technical Diving

The Difference Between Caves and Mines

Mine Diving in the UK


Michael Thomas’s diving career is now in its 33rd consecutive year, from starting out as an open water diver then a trainee cave diver to becoming the Training Officer of the British Cave Diving Group Somerset Section. He is also a Full Cave Instructor, Sidemount and Tech Instructor with TDI, active mod 3 CCR cave diver, and on the British cave rescue call out list as a diver. 

Thomas is heavily involved in U.K. diving projects and training, plus overseas diving and caving. Diving is life or is life diving? 

Continue Reading

Subscribe

Submerge yourself in our content by signing up for our monthly newsletters. Stay up to date and on top of your diving.

Thank You to Our Sponsors

Education