Why 100 % OIs A Dive Site Necessity


Larry "Harris" Taylor, Ph.D.

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 This article is based on material presented in the authorís DAN O2 Provider Class.  

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The ability of oxygen to relieve the symptoms of decompression illness (Caisson's Disease) has been known since the mid 1800's. Much of this early work is summarized in Paul Bert's classic work, Barometric Pressure, written in 1877. The use of oxygen by recreational divers as a first-aid measure has been promoted for more than three decades. A training organization, DAN, was founded in the US with a primary goal of getting the message of on-site O2 delivery to the recreational community. Yet, despite all the effort of diving educators, there is still a major lack of understanding in recreational divers for the need to deliver the highest possible O2 concentration to the victim of a diving accident. Perhaps, this stems from an unfamiliarity of the reason behind the hyperbaric medical community's recommendation that those suffering from a diving malady be treated with100% O2

A decompression event can be envisioned primarily as a "bubble disorder." A bubble of inert  (not used in body metabolism, so it accumulates) gas has formed within the body. This bubble may impede nerve impulses, block circulation, or trigger a variety of cellular processes designed to cope with foreign-to-the-body molecular invaders. The symptoms seen in the victim will depend on how much gas has formed bubbles and where these bubbles are located. Our mission, at the first responder level, is to reduce, as much as possible, the magnitude of this "bubble trouble."  An understanding of simple gas dynamics gives us the rationale for the need to deliver 100% oxygen 

From a standpoint of "molecular psychology," gas molecules tend to ignore the presence of other types of gas and focus only on their own kind. Each element or compound present in the gaseous state will act independently, as if they were alone. If a gas-permeable barrier (like a cell wall or the interface between a liquid and a gas) is introduced into the system, then each type of gas will independently try, in terms of "molecular sociology," to acquire the same population of their type of molecule on both sides of this barrier. Gas molecules will freely move in both directions across the barrier, but the net movement into or out of the gas pocket will be directed towards making the concentration the same on the inside and outside of the bubble. The movement of each gas type will be primarily dictated by the DIFFERENCE in concentrations between inside and outside of the gas pocket for each type of gas present within the bubble.

So, let's consider a nitrogen (or any inert gas in the breathing mix) bubble inside a diver. In decompression sickness, the gas will be nearly all inert gas derived from the breathing mix that has percolated out of tissues. In an air embolism, the bubble initially will be about 80% nitrogen, but since oxygen can be used in cellular processes, the oxygen diffuses away and is rapidly consumed by metabolic reactions. So, for sake of argument, all DCI events can be considered primarily an inert gas bubble trouble event. 

Since the body's chemical machinery cannot utilize the inert gas, it just accumulates and interferes. If we want to "denitrogenate" (get rid of the offending inert gas bubble) the body, we must introduce an environment that contains NO NITROGEN (or whatever gas was used as the inert gas in the breathing mix). We could use ANY gas that was NOT nitrogen. Anything! Carbon monoxide, hydrogen cyanide, argon, or methane would do the job of removing nitrogen from the bubble. Of course, the gasses just mentioned are toxic to life, and, if, unused by the body, would themselves, accumulate in the bubble. So, although they would "denitrogenate," it is probably best, because of their toxicity, that we do not use them. Instead, consider oxygen.

If we could surround the offending nitrogen bubble with a ZERO nitrogen concentration atmosphere by introducing a 100% oxygen environment, we give rise to the scenario shown in figure 1.


Figure 1. "Denitrogenation" Scheme 

In terms of "molecular sociology:" when we surround the nitrogen bubble with 100 % O2

1.There is no N2 outside the bubble, so N2 moves out in an attempt to equalize concentrations on the inside and outside of the bubble.

2 There is no O2 inside the bubble, so O2 moves into the bubble.

Eventually, (from this simplistic static point of view ( reality is a bit more complicated with initial influx of O2 slightly enlarging the bubble before shrinkage becomes noticeable during a constantly changing dynamic process driven by changes in gas concentrations), the N2 moves outside the bubble and is transported away by circulation and the O2 moves inside. So, the bubble, near the end stages of this scenario is composed primarily of O2. But, the body metabolism uses O2. Thus, the bubble disappears as the surrounding cells consume the oxygen diffusing out of the bubble. 

Why all the hype about 100%?  Does it work? 

Examine the cat brain shown in figure 2. 

 Figure 2. An exposed cat brain

Pay particular attention to the red areas in the brain. They are blood vessels. From the simplistic point of view of a biochemist, "Blood is life!" So, wherever there is red, there is blood. Cells are receiving nutrients and oxygen. Waste products like CO2 are being removed. Now, let's embolize the cat brain with a bolus of air injected into the carotid artery. This is shown below in figure 3. 

 Figure 3. Cat brain following injection of air into the carotid artery.

Notice the lack of red in the brain region. The blood vessels are blocked by air. There is a "vapor lock" in the brain's circulation and cells not receiving nutrients are beginning to die from lack of necessary fuel and oxidizer while drowning in their own waste. Within minutes, neural tissue will start to die and once dead, most likely will never function again. 

Now, let's put the cat on 100 % O2.

 Figure 4. Cat brain with circulation restored by oxygen administration.

 It is clear that O2 shrinks bubbles. This process has been described as miraculous!  

Microscopic examination (see references, below) of animal tissue that has been rapidly decompressed to generate a massive bubble population revealed that in the presence of a 100% O2 atmosphere the bubbles shrink and disappear from view in about 2 hours. This "denitrogenation" is something YOU CAN DO on the dive site and the reason why delivery of 100% O2 is so emphasized in diving first-aid management classes. 

So, why all of the hype about demand valves? 

The rate of gas movement out of the bubble is primarily determined by concentration of inert gas on the outside of the bubble. ANY NITROGEN IN THE BREATHING MIX WILL SLOW DOWN THE REMOVAL OF NITROGEN FROM THE BODY! (Remember, this process is driven by DIFFERENCE in concentration, the greater the difference between inside and outside of the bubble, the more rapidly the nitrogen will move outward) The best possible first responder scenario is for the patient to breathe 100% O2  (0 % N2.). This promotes "denitrogenation."

Most oxygen delivery equipment is meant to deliver lower than 100% O2. This is because most O2 delivery equipment is DESIGNED to treat shock-associated hypoxia that occurs from trauma or disease. This is NOT the same as using O2 to "denitrogenate!"

In diving, since our mission is primarily to "denitrogenate," our O2 delivery devices MUST address this need. That is why the demand inhalator (only device available that delivers 100% O2 to a breathing patient while meeting the patient's full respiratory needs) is considered the best device for treating a decompression illness incident and should be the delivery device of choice in the on-site first responder management of a dive malady.

On the Site

Remember our primary task on the site in the management of a diving malady is to "denitogenate" the body of the diving accident victim. Thus we should seek to deliver the highest possible concentration of O2   available and to use it until the gas supply is exhausted or relieved by a higher medical authority. If a demand system is NOT available, use whatever is the highest possible concentration delivery device on the scene.

Bottom Line:

Our mission ("denitrogenation" vs. shock associated hypoxia) in a diving accident is different from that of most every other use of oxygen administration by first responders. Since our mission is different, we must use the tools designed specifically for our task.


With respect to "denirogenation," nothing works better than a demand system. This is why our dive accident management equipment should include a demand delivery system and a supply of USP Oxygen sufficient to supply a diving accident victim for the time it takes to get assistance from the emergency medical community. 


The cat brain slides were a kind gift from Lee Somers of the University of Michigan.

 References On Bubble Shrinkage

Hydlegarrd, O. & Madsen, J. Influence Of Helox, Oxygen and N2O-O2 Breathing On N2 Bubbles In Adipose Tissue, Und. Biomed. Res.16(3), 1989, 183-193.

Hyldegarrd, O. Moller, M. & Madsen, J. Effect of He-O2, O2, and N20-O2 Breathing On Injected Bubbles In Spinal White Matter, Und. Biomed. Res. 18,(5-6), 1991,  361-371

Hyldegarrd, O. Moller, M. & Madsen, J. Protective Effect Of Oxygen And Heliox Breathing During Development Of Spinal Decompression Sickness, Und. Biomed. Res. 21,(2), 1994,  115-128.

Hydlegarrd, O. & Madsen, J, Effect Of Air, Heliox, And Oxygen Breathing On Air Bubbles In Aqueous Tissues In The Rat, Und. Biomed. Res. 21(4), 1994, 423-424.


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Article History

This article was originally written at a time (mid-1980's) when some in the recreational dive community was resisting the suggestion that dive site oxygen was of potential use in treating a dive accident malady. One major training agency even stated that demand oxygen devices were too complicated for diver's to use. (The fact that the scuba second stage regulator was a demand device was, of course, irrelevant). The article was expanded in the mid-90's with the publication of Hydlegarrd's bubble measuring articles.

 About the Author:

Larry "Harris" Taylor, Ph.D. is a biochemist and Diving Safety Coordinator at the University of Michigan. He has authored more than 100 scuba related articles. His personal dive library (See Alert Diver, Mar/Apr. 1997, p. 54) is considered by one of the best sources of information in North America.

  Copyright 2001-2022 by Larry "Harris" Taylor

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Use of these articles for personal or organizational profit is specifically denied.

These articles may be used for not-for-profit diving education