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Calculated Confusion: Can O2 Get You High?

Anyone who’s dived to 30 meters on nitrox (we don’t do air here!) is familiar with what Jacques Cousteau eloquently termed “rapture of the deep”—the result of breathing high partial pressures of nitrogen. But what about the oxygen? As you may know, there are some convincing arguments that oxygen should be considered narcotic at depth as well, but there are also many qualifiers, anecdotes (ever feel narc’d on your 20-foot O2 stop?), and a broad swath of research and nuance that casts some doubt. Diver Alert Network’s Reilly Fogarty teases out what we know and what we don’t. Mind your ENDs!

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by Reilly Fogarty

Header image by Sean Romanowski

Hyperbarics is a tricky field to study — gas laws sometimes behave like suggestions, the effects of high-pressure gases in the body are highly subjective, and decades of research often end in what amounts to an educated guess. Our understanding of narcotic gases is a great example of this: we know a little about increasing partial pressures of nitrogen decreasing our motor function and cognitive ability, and a bit about some gases like helium ameliorating those effects, but not much else. The specific mechanisms of action, variability through human anatomy or interactions with other gases, and the range of those effects at various depths are the stuff of theory rather than proven science. There are some convincing arguments for the treatment of oxygen as a narcotic gas, but the qualifications are many, and a broad swath of research and nuance casts everything we think we know into doubt. Here’s what we know so far, as well as some best-practice recommendations. Understanding the narcotic effects of oxygen is by no means a clear-cut situation. 

A Primer on Narcosis

Before discussing narcosis, it’s important to cover what we know already. Narcotic gases (any gases that can cause narcosis, including nitrogen, argon, etc.) have a wide range of effects, all affected by depth. The general consensus is that these gases likely interfere with the release or uptake of neurotransmitters in the body or alter the postsynaptic response from those transmitters. Greater partial pressures of some gases increase this effect, which is why we see increased narcosis as we descend on a gas containing nitrogen. In short, much like the gases used for surgical anesthesia, common diving gases can interfere with the communication pathways in our body. 

The effects of these gases are understood by the Meyer-Overton rule, a holdover from anesthesia research in the early 1900s. *Updated: The rule predicts that the anesthetic potential of a gas is directly related to its lipid solubility (i.e., a gas that can be absorbed effectively by fatty tissue will be more narcotic than one that cannot) and ranks gases by that solubility. Helium exhibits extremely low lipid solubility and correspondingly little narcotic potential according to this rule, and this holds true to experience. WAS: The rule predicts that the anesthetic potential of a gas is inversely related to its lipid solubility (i.e., a gas that can be absorbed effectively by fatty tissue will be less narcotic than one that cannot) and ranks gases by that solubility. Helium exhibits extremely high lipid solubility and correspondingly little narcotic potential according to this rule, and this holds true to experience. The effects of oxygen, however, appear to be significantly more complex. 

Gas Solubility Coeficients of gases in water and oils - used by the Myer-Overton hypothesis to infer the narcotic potential of breathing gases, but can also be used to deduce tissue gas loading in disolved gas Haldanean decompression models
Fig 1: Solubility of gases in water and oil (Dueker)

Note: These units are permeability coefficients. A larger number represents a greater energy required to pass the same quantity of gas through a membrane or lipid tissue, indicating decreased solubility. Gases with smaller permeability coefficients (helium, for example) are more soluble and can permeate barriers more easily while gases with a larger permeability coefficient (like oxygen) are less soluble and require more energy to pass through a barrier. More information on gas solubility and permeability in specific tissues can be found here.

Working solely from the Meyer-Overton rule, it would appear that oxygen should cause significant narcosis — it has twice the lipid solubility of nitrogen and thirty-eight times that of helium. Comparing just the lipid solubility of nitrogen and oxygen, it appears that saturation with oxygen would not only cause narcosis but would also result in stronger symptoms than those caused by nitrogen. The aptly named, Does Oxygen Contribute to the Narcotic Action of Hyperbaric Air?. a paper by hyperbaric researchers from 1990, attempted to confirm just that hypothesis. Researchers compared motor skills and mental performance with participants exposed to air and normoxic nitrogen and oxygen mixtures at 6, 8.5, and 11 bars ambient pressure. They found impairment of up to 40 percent at the highest pressures of all gases, but participants exhibited the same impairment on oxygen as gases with higher partial pressures of nitrogen. Their conclusion indicated that oxygen did not ameliorate mild narcosis and should, therefore, have some narcotic properties. 

A Case for Oxygen

A similar paper from a little more than a decade before found the same results. A rise in the partial pressure of oxygen to 1.65 ATA gave similar narcotic effects as a rise in the partial pressure of nitrogen to 6.3 ATA, or an end-tidal pressure of CO2 or 10mmHg. Again, these researchers came to the conclusion that while the specific contributions to narcosis from oxygen could not be exactly measured, it did appear to contribute to the narcosis of divers. 

Photo by David Rhea, 2004.

There’s an argument for the sake of safety here too. Oxygen may be narcotic, so by calculating our equivalent narcotic depth (END), by including oxygen in the calculations as we would nitrogen (more on how to do that later), we give ourselves an extra margin of error. If oxygen is, in fact, narcotic, we’ve planned for its effects at depth, and if it isn’t, then the worst thing that happens is we have a little less narcosis than expected.

Narcotic Nuances

When I said hyperbarics was a tricky field to study, I meant it, and not just because of the complexity of the issues involved. Understanding the effect of oxygen in the body is an incredibly nuanced balancing act that involves attempting to apply our limited understandings of oxygen metabolism, neurotransmitter function, metabolic dysfunction, inflammatory responses and more, all in the application of something that in the end will be almost entirely subjective. There are a few notable issues with the presentation of oxygen as a narcotic gas, and they’re easiest to work through in pieces: 

Meyer-Overton

Rules were made to be broken and Meyer-Overton is no exception, despite holding mostly true for more than a century. Not only does it lack a specific mechanism of narcotic action, but there are some explicit exceptions to the rule. It should be noted that even these exceptions are the source of some controversy, but it’s widely believed that several anesthetic gases work in exception to the Meyer-Overton rule, specifically anesthetics with long alkane chains in their structure. Some of these gases exhibit dramatically lower potency than would be expected based on their lipid solubility, and we have no way to know whether oxygen is one of these exceptions to the rule or just another narcotic gas. 

Environmental Concerns

The environment we’re concerned about, primarily deep open- or closed-circuit diving has a long list of restrictions for the application of oxygen. As divers, we carefully plan our exposures to keep oxygen in a narrow range of partial pressures while diving. This careful control of the PO2 of our gas means that we’ll never see a PO2 greater than 1.6. While a ride in a hyperbaric chamber may exceed that threshold, it’s unlikely to see in the water and brings to light another question — if oxygen is narcotic, at what partial pressure do you see the effects? No study available on the subject is able to define either the PO2 at which oxygen begins to have a narcotic effect or to even strongly correlate pressure and narcosis on oxygen alone. 

Photo from the GUE archives.

Compounding this confusion is the fact that oxygen is a gas that we constantly metabolize. Even if we were to breathe similar amounts of nitrogen and oxygen during a dive, the metabolic processes required to keep us alive and well constantly consume some of that oxygen. How much oxygen is consumed and at what rate is a complicated answer based on individual physiology and what a subject is doing at any given time, making it even more difficult to isolate the effects of oxygen from the metabolism of inspired gas. Until now, our understanding of narcosis has relied on our ability to estimate the partial pressure of nitrogen in our gas, but once oxygen enters the mix, a whole host of new variables become important to consider. While it’s true that we can estimate the effects of the gas based on theories and the research we do have, it’s not enough to definitively say that oxygen is a potent narcotic. 

Putting It to Practice

Academic review is one thing, but putting a new concept to practice is what brings it home for most divers. Here’s how you can calculate END with oxygen included as a narcotic gas (the most common decompression planning software also offers an option for this in their calculations):

(Depth + 33) X (1 – fraction of helium) – 33

Because oxygen and nitrogen are considered equally narcotic, END can be calculated using the total of a gas minus the fraction of non-narcotic helium.

Best Practices

Discussions of narcotic gases rarely provide rewarding moments of discovery. What we have as divers and as an industry is a best guess that indicates that oxygen is likely narcotic, but we don’t know what the mechanism of that narcosis is, nor do we know how potent the effects of oxygen are. The issue is deeply nuanced and requires some careful consideration before arriving at a conclusion, but your mental tribulations shouldn’t ruin your next dive. As a dive safety organization, Divers Alert Network has an interest in promoting safe diving practices, and the results in this case are promising and present little additional risk. Calculating your END with oxygen as a narcotic gas is a safe and conservative practice until researchers tell us definitively that it’s non-narcotic. Aside from a slightly higher gas bill there’s no downside, but you might just be safer for it. 

For more information on narcotic gases and advanced dive planning, visit DAN.org or contact the author at RFogarty@DAN.org.

Works Cited:

1. Scuba Diving in Safety & Health by Chris W Dueker, MD

2. Diffusion Coefficients for Gases in Biological Fluids and Tissues

3. DOES OXYGEN CONTRIBUTE TO THE NARCOTIC ACTION OF HYPERBARIC AIR?

4. Roles of nitrogen, oxygen, and carbon dioxide in compressed-air narcosis

5. THE CORRELATION BETWEEN CRITICAL ANAESTHETIC DOSE AND MELTING TEMPERATURES IN SYNTHETIC MEMBRANES


Reilly Fogarty is a team leader for risk mitigation initiatives at Divers Alert Network (DAN). When not working on safety programs for DAN, he can be found running technical charters and teaching rebreather diving in Gloucester, MA. Reilly is a USCG licensed captain whose professional background includes surgical and wilderness emergency medicine as well as dive shop management.

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Out of the Depths: The Story of British Mine Diving

If sumps and solo cave diving are, well, a bit too Brit for you, you may want to consider diving into the perfusion of flooded serpentine chert, copper, limestone, silica, slate, and tin mines that honeycomb the length and breadth of the Kingdom. Fortunately, British tekkie and member of UK Mine/Cave Diving (UKMC) in good standing, Jon Glanfield, takes us for a guided tour.

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By Jon Glanfield
Header image courtesy of Alan Ball.

When many think of the UK’s caves, with wet rocks and their penchant for darkness, often the images conjured are of tight, short, silty sumps, that can only be negotiated by intrepid explorers outfitted with diminutive cylinders, skinny harnesses, wetsuits and typically a beard. These are the domain and natural playground of the well-known, highly-respected, Cave Diving Group (CDG). 

In truth, much of our sceptered isle’s caves are of this ilk, but there is an alternative for the diver who favours a more conventional rig, extra room to manoeuvre, and perhaps a more team-orientated approach—one that is less than optimal in many of the true cave diving environments of the UK.

Holme Bank. Photo by Ian France.

Alongside our natural cave diving venues, we also sport a varied collection of flooded mines across the length and breadth of the Kingdom. In the south and southwest, miners have extracted metals such as tin and  copper, while in South Wales it was the mineral, silica. The Midlands Linley Caverns were a source of limestone before being converted to a subterranean munitions store in WWII. Sadly, access to these is no longer feasible. In the rolling hills of the Derbyshire Dales, flinty, hard chert strays close enough to the surface to be mined. In North Wales, the once-proud slate industry has left its Moria and Mithril redolent halls and tunnels beneath the landscape, while copper and slate underlay parts of Cumbria. Meanwhile, just over the border in Scotland, limestone was the resource that drove us to follow its veins into the earth.

Mike Greathead descending the stairway to heaven. Photo by Ian France.

Undeniably, here in the UK, mine diving has a much shorter documented history than that of its close cousin cave diving, but some of the luminaries of this dark world were, and are, active in both. Some of the initial dives in sites like the Cambrian slate mine were undertaken by the incomparable Martyn Farr, Geoff Ballard, and Helen Rider in 2006. But it wasn’t until 2014 that it was further explored and lined by the likes of Cristian Christea, Ian France, Michael Thomas, and Mark Vaughan amongst others. 

Both Rich Stevenson and Mark Ellyatt, who were part of the vanguard of the technical diving revolution in the UK, had personal dramas on trimix dives in the deep shaft of the Coniston Copper Mines, the depth of which runs to 310 m/1012 ft. Ellyatt made his dive at 170 m/555 ft in the early 2000s in a vertical 2 m/6.5 ft square shaft, dropping away into the 6º C/43º F frigid blackness.

Mines Over Matter

As was alluded to, the differences in cave and mine diving are significant. Conventional, redundant open and closed technical rigs can be employed in mine diving due to the predictably larger tunnels, passages, and chambers. Water movement is negligible, so often regular braided lines can be used, lines which would not endure the flow in many of the UK’s upland cave locations. Small teams can dive in safely. 

No Exit. Photo by Chris Elliot.

In general, it is not common to surface and explore the sumped sections of the mines, due to often dangerously contaminated or hypoxic air quality. Also, in some cases, oils and other contaminants have leached into the water. The ever-present risk of collapse—both in the submerged sections and in the dry access adits or portals—haunt divers’ thoughts and is far more common in mines than in the smooth, carved bore of a naturally-formed cave. Casevac (the evacuation of an injured diver) is complex, long-winded, and often dangerous for those involved, and in the event of an issue involving serious decompression illness (DCI), almost certainly helicopter transportation would be necessary given the remote locations.

Landowner access—or, more commonly, denial of access—is an ubiquitous spectre in the underground realm, dry or wet, and much effort is directed at maintaining relations with landowners to safeguard the resources. Some of the most frequented mines are accessible only via traverse of private property, which could be agricultural, arboreal, and in one case, bizarrely on the grounds of an architectural firm. Careful management of these routes into the mines is critical, as is demonstrating respect for the land owner and complying with their requirements when literally on their turf.

At the more prosaic level though, simply getting into some of the mines is a mission on its own, necessitating divers’ decent levels of fitness, the use of hand lines, and sometimes as much consideration of dry weight to gas volume as the dive planning itself. Careful thought and prior preparation are also required in terms of both accident response and post-dive decompression stress, given the exertion expenditure simply to clear the site.

A passageway in Aber Las. Photo by D’Arcy Foley.

Many of the mines are relatively shallow, mostly no more than 30 m/98 ft with exceptions in the notable and notorious Coniston, and the almost mythic levels in Croesor, extending beneath the current 40 m/130 ft galleries that are known and lined. Though, what the mines lack in depth, they make up for in distance and grandeur. 

Aber Las mine survey. Courtesy of UKMC.

Aber Las, or Lost, is more accurately a forgotten section of Cambrian that extends nearly 600 m/1961 ft from dive base at the 6 m/20 ft level, and a second level 300 m/984 ft long at 18 m/59 ft. The section features no less than 35 sculpted chambers hewn off the haulage ways with varying dimensions and exhibiting differing slate removal techniques. Cambrian’s chambers less than a mile away are larger still, and a lost line incident here could be a very bad day given the chambers’ cavernous aspect.

In The Eye of the Beholder

Beauty is—as they say—in the eye of the beholder, but it would be disingenuous to try to draw comparisons between the UK’s mines and the delicacy of the formations in the Mexican Karst, the light effects through the structures in the Bahamian sea caves, or the sinuous power tunnels of Florida. In mines, the compulsion to dive is due in part to the industrial detritus of man, encapsulated in time and water.

In mines, the compulsion to dive is due in part to the industrial detritus of man, encapsulated in time and water.

Parallels are frequently drawn between wreck diving and mine diving, but often the violence invoked at the demise of a vessel—the massive, hydraulic inrush of fluid and the subsequent impact on the seabed—wreaks untold damage and destruction upon its final resting place. In contrast, nature reclaims her heartlands in the mines by stealth: a slow, incremental and inexorable seep of ground water, no longer repulsed by the engines from the ages of men, gradually rising through the levels to find its table. The result is often preserved tableaus of a former heritage with a rich diversity of artefacts left where last they served.

A leftover crate in the Croesor mine. Photo by Alan Ball.

Spades, picks, lanterns, rail infrastructure, boots, slowly decomposing explosive boxes, battery packs, architectural joinery, scratched tally marks, and, even in some cases, the very footprints of the long-past workers in the paste that was cloying, coiling dust clouding the passages and stairways, can be picked out in the beam of a prying LED.

Spades, picks, lanterns, rail infrastructure, boots, slowly decomposing explosive boxes, battery packs, architectural joinery, scratched tally marks, and, even in some cases, the very footprints of the long-past workers in the paste that was cloying, coiling dust clouding the passages and stairways, can be picked out in the beam of a prying LED.

Underpinning, protecting, preserving, and improving these gems of the realm is the UK Mine and Cave Diving Club (UKMC), which formed as mine diving intensified in the mid 2000s. So it was that Will Smith, D’Arcy Foley, Sasha London, Jon Carter, Mark Vaughan, and Ian France, all of whom are respected and experienced cave divers in their own right, forged the club to foster and engage with a community of like-minded divers. 

Sadly, in 2014, Will Smith fell victim to the insidious risks of contaminated air in the Aber Las mine system, which he had been lucky enough to re-discover and in which he conducted early exploratory dives as the club gained traction and direction.

As new members filter into the ranks, new ideas, new agendas, and new skill sets re-shape the club’s direction. At present, we are rebooting the club with a remastered website, focusing on new objectives and seeking opportunities to improve, catalogue, and document the resources we husband.

Lines laid in the Cambrian slate mine. Photo by Mike Greathead.

Exploration continues: the club is laying new line in some areas. What’s more, through our demonstrable respect and care for existing sites, the club is facilitating exploration in previously inaccessible sites, and lost and forgotten sites will resurface. Meanwhile, we’re improving the locations we frequent weekly for the benefit of trainees, recreational (in the technical sense) divers, and survey divers alike. Archaeological projects are rising from the ennui of lockdown; we’re establishing wider links with mine diving communities elsewhere to share techniques, data, and ultimately hospitality.

In Welsh folklore, a white rabbit sighted by miners en route to their shifts was believed to be a harbinger of ill fortune, but for Alice, following the rabbit into its hole led her to a whimsical and magical place. Be like Alice, and come visit the Wunderland!

Additional Resources:


Jon Glanfield was lucky enough to get his first puff of compressed air at the tender age of five, paddling about on a “tiddler tank,” while his dad was taught how to dive properly somewhere else in the swimming pool. A deep-seated passion for the sport has stayed within him since then, despite a sequence of neurological bends in the late 90s, a subsequent diagnosis of a PFO, and a long lay-off to do other life stuff like kids, starting a business, and missing diving. Thankfully, it was nothing that a bit of titanium and a tube couldn’t fix. He faithfully promised his long-suffering wife (who has, at various anti-social times, taken him to and collected him from recompression facilities) that “this time it would be different” and that he was just in it to look at “pretty fishes.” So far, only one fish has (allegedly) been spotted in the mines. The ones Jon has encountered in the North Sea while wreck diving just obscured the more interesting, twisted metal.

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