Sign up for our monthly newsletter so you never miss the latest from InDepth!
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.
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.
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.
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:
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.
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.
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.
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.
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.
Preserving Florida’s Springs: The Bottled Spring Water Problem
There’s no doubt that Florida’s Springs are imperiled. Most are flowing 30% to 50% less now than their historical average and are suffering from eutrophication. However, as veteran hydrologist Todd Kincaid explains, the problem is not spring water bottlers like Nestlé, in fact they could be allies in the fight to preserve the springs.
By Dr. Todd Kincaid
Header photo by Florida DEP of Wakulla Springs in April 2008.
Florida’s Springs are imperiled. Most are flowing 30% to 50% less now than their historical average. Some don’t flow at all except after big storms or abnormally wet periods. Nearly all have become overwhelmed with algae and bacteria (eutrophied) due to excessive nutrient pollution. The causes are straightforward and increasingly hard to ignore: groundwater over pumping, the overuse of fertilizers by agribusiness and homeowners, and insufficiently treated wastewater. Solutions exist, can be widely implemented, and would significantly improve spring water flows and spring water quality, but they require major investments and diversions from status quo: caps on groundwater extractions, tiered fees for groundwater usage applied to all users, tiered taxation on fertilizer usage, advanced wastewater treatment, transition away from septic systems, etc.
Existing policies have failed to even bend the steep downward trajectory of Florida’s springs. “Minimum Flows and Levels” (MFLs) appear to protect spring flows but, in reality, they open the door to continued declines while people argue over the difference between natural and human causes. “Best Management Practices” (BMPs) pretend to reduce nutrient loading, yet are not only unproven and unenforceable, but not even conceptually capable of the needed nutrient reductions. Even as more and more attention and resources are directed at the condition of Florida’s springs, most continue to degrade: less and less flow, more and more nitrate and algae.
In the face of these declines, it’s easy to become disheartened and jaded. It’s even easier to become focused on reactionary measures aimed at what we don’t want and be rooted more in emotion than in facts. This is, I believe, epitomized by the highly publicized reactions to a permit renewal application filed with the Suwannee River Water Management District (SRWMD) by the Nestlé Corporation (Nestlé) for a bottled spring water plant down the road from Ginnie Springs.
The application requests that the SRWMD renew a standing permit that was first issued in the 1980s for the extraction of 5 million gallons per day (MGD) of groundwater from the Floridan aquifer to support spring water bottling. This same permit was voluntarily reduced to 1.1 MGD by the property owners to prevent the possibility that it could be incorporated into one of the many groundwater pipeline schemes that are persistently proposed to transport water from relatively rural north Florida to the substantially more populous cities in central and south Florida. Through the years, several different companies have leased the property and had access to the water, one of which was the Coca-Cola Company, and the most recent being Nestlé.
My perspective on this issue is a product of 30 years of work on karst hydrogeology in Florida, more specifically from my work for Coca-Cola on mapping groundwater flow paths. Specifically, we mapped the pathways to the springs on the western Santa Fe River, including Ginnie Springs, and identified the threats to the quality and quantity of flow to the springs. Even more, my perspective reflects the evolution of my understanding of what it’s going to take to sustainably manage groundwater (synonymous with spring flow) in Florida.
The problems facing Florida’s springs are not technical and not a consequence of any one particular use or user. The real problems are instead failures of the established policies to take the necessary steps to put concrete limits on groundwater consumption and pollution. If we are to achieve sustainable spring flows, limits on groundwater consumption must be established and enforced and, in reality, must be lower than current levels.
From a quantity perspective, who gets the water is irrelevant. All that matters is how much is taken. At present, not only is too much being taken, but there are no established limits. Conservation measures enacted by one user simply opens the door for new or larger allocations to other users. This is accomplished when users of the water claim a “beneficial use”. So, while we can and should be proud of those engaged in conservation, the reality is that spring flows will continue to decline.
If we are to restore and preserve spring water quality, nutrient pollution, specifically the input of nitrate and phosphorous into Florida’s groundwater that stimulate the explosive algae growth in Florida’s springs, rivers, lakes, and estuaries that nobody wants, must be dramatically reduced from current levels. Some experts state that nutrient discharge levels will need to be cut across the board by 70% or more in order to meet water quality targets for Florida’s natural waters. That would mean 70% less nutrient loading from agriculture, 70% less nutrient loading from households, and 70% less nutrient loading from wastewater treatment and disposal.
At present, and for the foreseeable future, there is insufficient political will to achieve any of these needed changes given resistance from corporate and special interests. Year after year, proposed legislation calling for the types of sweeping changes needed fails to receive sufficient public support for passage. While the political efforts that would result in real and positive change continue to fail due to lack of support, the public’s attention focuses on perceived impacts from individual users without regard to the actual impacts those users and uses have on the springs.
Bottled spring water is only one example. Though the entire industry uses only around 1/100th of 1% of the groundwater extracted from the Floridan aquifer and produces absolutely none of the toxic nutrient loading that is killing the springs, it holds a disproportionate grip on the public’s attention to usage, impacts, and solutions. If tomorrow the entire bottled water industry in Florida were to shut down, there would be effectively zero improvement at the springs in terms of either flows or quality. The little amount of water gained would very likely be quickly and quietly allocated to other users.
If, on the other hand, the roughly 400 bottles of water needed to produce a single bottle of milk were put to better use, say returned to the springs, and the associated nutrient loading to groundwater due the fertilizers used to grow the feed, were thereby eliminated, there would be a near immediate improvement in both flow and quality of water at the springs. Milk production uses far more water and produces drastically more nutrient pollution than the production of water. The water saved by eliminating milk production would, therefore, take longer to re-allocate to new users and eliminate a huge portion of the nutrient pollution that is killing the springs as well.
Far more water is used for that purpose, and much more nutrient pollution is caused.
Eliminating the production of milk, for example, would also require more time to re-allocate to new users and would eliminate a substantial portion of the nutrient pollution that is killing the springs.
Nearly every drop of water extracted from the Floridan aquifer and not returned reduces spring flows by an equal amount. Certainly from the entirety of the state north of Orlando and Tampa, and regardless of what it’s used for, from water from household taps, watering lawns and golf courses, car washes, crop irrigation, production of milk, soda, energy drinks, and bottled water. Similarly, all the nutrient loading to groundwater west of central Orlando and Gainesville and south of Tallahassee flows to the springs and contributes to the explosive algae infestations, which no one wants to see become normal.
The problems plaguing Florida’s springs stem from these realities, regardless of whether the springs are enshrined as State Parks or privately owned. Florida’s springs need allies not rhetoric—allies who help to build the public support necessary to achieve the only actions that will restore and preserve spring flows and spring water quality: caps on groundwater consumption and dramatic reductions in nutrient loading.
Regardless of corporate culture, spring water bottlers’ economic self-interest is directly aligned with springs protection. Spring water cannot be treated and cannot be captured if there are no more springs. Spring water bottlers, therefore, rely on access to sustainable, high-quality spring water. It then follows that they, along with other like-minded entities, can be strong allies for springs protection. It’s time for Floridians to stop focusing on rhetoric that fails to yield even as little as a diminished rate of springs degradation. It’s time to start working toward real solutions anchored in the realities of water and nutrient budgets. The bottled water industry is not sucking Florida dry, but denial and political inaction are.
As an organization focused on sustaining the environmental quality and required to support healthy underwater ecosystems, our task must be to confront environmental problems from a perspective grounded in the realities of what will be needed to achieve our goal. We must work for what we know we want rather than against what we think we don’t want. And to be successful, we’re going to need as many allies as we can muster.
At Project Baseline, we should and will seek to engage with the people and organizations who share our goals, even if doing so is not palatable to some of our fellow conservationists. We should work with those entities and use our voices, our votes, and our wallets to foster the policies and the actions that are needed to restore and preserve the type of underwater world we want to dive in, be awed by, and pass along to the next generation of underwater explorers.
Project Baseline is a nonprofit organization that leverages their unique capacity to see how rapidly the underwater world is changing to advance restoration and protection efforts in the local environments we explore and love. Since 2009, Project Baseline has been systematically documenting changes in the underwater world to facilitate scientific studies and establish protection for these critical underwater environments.
Todd is a groundwater scientist, underwater explorer, and advocate for science-based conservation of water resources and aquatic environments. He holds BS, MS, and Ph.D. degrees in geology and hydrogeology, and is the founder of GeoHydros, a consulting firm specializing in the development of computer models that simulate groundwater flow through complex hydrogeologic environments. He has been an avid scuba diver since 1980, having explored, mapped, and documented caves, reefs, and wrecks across much of the world. Todd was instrumental in the founding of Global Underwater Explorers (GUE) in 1999 and served on its Board of Directors and as its Associate Director from its inception to 2018. Within the scientific and diving communities, Todd advanced the use of volunteer technical divers and the data they can collect in endeavors aimed at understanding, restoring, and protecting underwater environments and water resources. He started Project Baseline with GUE in 2009 and has been the organization’s Executive Director from its beginning. More on Todd at: LinkedIn and ResearchGate
The Thought Process Behind GUE’s CCR Configuration
GUE is known for taking its own holistic approach to gear configuration. Here GUE board member and Instructor Trainer Richard...
The Joys and Challenges of Teaching Kids To Dive
We all lament the fact that we don’t see more young people getting into diving. British instructor and content creator...
Decompression Series Part Four: Finding Shelter in an Uncertain World
In the final of this four-part series on the history and development of tech decompression protocols, GUE founder and president,...
Understanding Oxygen Toxicity: Part 1 – Looking Back
In this first of a two-part series, Diver Alert Network’s Reilly Fogarty examines the research that has led to our...