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Nitrogen Narcosis – Perceptions of Susceptibility

Is it really possible to gauge your susceptibility to nitrogen narcosis and make good judgements to manage it?

Nitrogen narcosis is a hyperbaric neurological phenomenon. Its existence, symptoms and onset are known, even if medical science has not yet explained the physiological mechanisms causing it. Individual susceptibility to the effects of nitrogen narcosis varies in severity. It is also inconsistent in onset for a given individual on a given day. A diving medical study also seems to indicate that nitrogen narcosis may be persistent, even when ascending from depth.

It has been shown that the level of narcosis potential for a particular inert gas stems from its lipid solubility; the efficiency of a gas in diffusing into fatty tissues (i.e. the brain tissue) in the body. The most recent research is studying the effects of lipid-dissolved inert gasses on neurotransmitter receptor protein mechanisms in the brain.

Meyer Overton narcosis nitrogen
Meyer/Overton proved that the narcotic potency of an anaesthetic gas can generally be predicted from its solubility in oil.

Variance in individual blood-brain chemistry and/or neurological make-up obviously play a role in nitrogen narcosis susceptibility. Nonetheless, it remains a known neurological occurrence that affects any diver subjected to an elevated partial pressure of inspired nitrogen.

Be under no illusions, narcosis affects humans as soon as inert-gas partial pressure begins to increase, from immediately below the surface and increases in severity as depth/ partial pressures increase. We all get narc’d…and that starts a lot shallower than many divers are inclined to believe.

Perceptions of nitrogen narcosis susceptibility

The greatest variation between divers is the individual perception of susceptibility to narcosis.  This is the person’s awareness of when, or if, they are suffering a decline in mental cognizance due to elevated nitrogen partial pressure.

One of the problems with gauging the perception of susceptibility to narcosis is that of misleading education. Nitrogen narcosis doesn’t really conform to the classical “martini rule” that many instructors use as an analogy to describe the issue. The ‘martini rule’ is a baseless lay theory that states that narcosis affects divers on a par with drinking a martini for each atmosphere (i.e. 10m/33ft depth) of pressure increase.

A weak or inaccurate analogy used by diving instructors to describe the symptoms of nitrogen narcosis causes divers to often fail in accurately diagnose its onset. If divers don’t feel ‘drunk’, then they don’t perceive that nitrogen narcosis is affecting them.


Nitrogen narcosis isn’t a form of intoxication (drunkenness); it is actually an effect of sedation or anaesthesia. The word ‘narcosis’ originates from the Greek word ‘narke’, meaning a “temporary decline or loss of senses and movement, numbness”. The currently accepted definition of narcosis is “a state of stupor, drowsiness, or unconsciousness”. At no point do those definitions indicate a propensity for giggling or donating your regulator to fish…

See my other article on the sedative impediment of narcosis on consciousness:

Nitrogen Narcosis – Sedation and Consciousness

That is not to say that nitrogen narcosis doesn’t amplify the moods or emotions of a diver. But these are just one distinct subset of a much wider, and more subtle host of symptoms. If divers actually believe that narcosis presents only through symptoms understood from the analogy of alcohol intoxication, then they will miss all of the more insidious signs and symptoms that otherwise indicate reduced mental faculty.

The Placebo Effect

There are, I strongly believe, also ‘placebo effects’ because of this alcohol intoxication analogy. I’ve seen divers ‘acting drunk’ underwater at mediocre depths; just as I’ve seen kids ‘acting drunk’ when unknowingly imbibing non-alcoholic beers at parties.

The placebo effect is well understood and researched in relation to alcohol.  I’d suggest the same effect occurs with some divers in relation to nitrogen narcosis.

American Psychological Society: Study Finds that Alcohol Placebo Impairs Memory

 BBC NEWS | Science/Nature | ‘Fake alcohol’ can make you tipsy

Nitrogen narcosis and autonomic competency

Placebo effects aside, nitrogen narcosis is insidious because the very effect of reduced mental perception inhibits the diver from being aware of the decline in their intellectual capability. It’s difficult to gauge a decrease in your IQ.  In short, dumb people don’t understand they are dumb.

What matters, from a safety perspective, is whether the diver remains functional at a given depth; regardless of reduced mental performance (noticed or not). By ‘functional’, I mean retaining sufficient competency to apply the necessary skills and protocols needed to sustain diver safety given the parameters and relevant hazards of the dive undertaken.

There has been a substantial debate on whether certain divers develop an immunity to narcosis, or a capacity to operate effectively even when nitrogen narcosis is present. Neither of these theories reflects the neurological imperatives of how narcosis affects consciousness.  I would suggest that the answer to differing performance levels under narcotic influence lies in what performance functions are affected, not which divers are affected.


I believe that retained functionality under the effects of nitrogen narcosis stems greatly from the degree to which diving skills, drills, protocols and procedures are ingrained to an autonomic (unconscious or involuntary) level. Reduced mental faculty impinges less on functions that are ingrained deeply as a second nature to the diver.

Often, only when the diver observes impairment to autonomic capabilities do they perceive the impact of narcosis.  The need to problem-solve, or the presentation of novel situations, brings a much more immediate perception of narcosis impairment. This, in principle, is a situation where the diver becomes aware that they should be able to achieve something but struggles to do so without obvious cause.

For a novice diver, with few ingrained second-nature capabilities, the perception of narcosis occurs quickly – at shallower depths. Mild narcosis exposes the fact that they are still problem-solving, rather than unconsciously performing, rudimentary diving functions.

As a diver gains experience and undergoes (effective) training, a wider spectrum of competencies is made second nature and performed unconsciously. More skills are ingrained. More problems are encountered and overcome; becoming planned reactions rather than novel issues to be solved.

However, diving competencies fall into two categories; fundamental and specific.  Fundamental competencies are things like buoyancy, trim, situational awareness and gas management.  Specific competencies are those necessitated by the respective hazards of the dive environment and/or the tasks to be completed on the dive. Examples of these might be guideline procedures in cave diving or gas-switching procedures for decompression diving.

As such, diving competency must be considered relevant to the level of diving undertaken. An Advanced Open Water diver with weak foundational competencies can be just as narcosis compromised as a cave diver with weak specific competencies. Where the novice recreational diver might forget to check their air supply, the novice cave diver might deviate from proper guideline protocols. The same effect occurs, regardless of the level of skills compromised.

Routinely employed dive functions don’t expose narcosis impairment until that impairment reaches a very severe level, whereby the narcosis degrades actual autonomic dive functionality. In contrast, novel problems arising during the dive expose narcosis impairment more obviously.

Perceptions of narcosis impairment vary greatly.  I believe that diver experience and competency play a major role in that perception.

See also my articles

Nitrogen Narcosis – Sedation and Consciousness

Does Nitrogen Narcosis Persist?

Narcosis and the impact of CO2 retention.

There is increasing debate on the impact of CO2-increasing narcosis. I don’t doubt that CO2 retention significantly increases the severity of narcosis and reduces the depth of onset. CO2 has the effect of increasing blood flow to the brain, which exaggerates the effects of other inspired gasses. By itself, CO2 also has a very high narcotic potency;  20x higher than nitrogen, due to its much higher lipid solubility.

   Relative narcotic potency

Again, the effects of CO2 retention favour those with more diving experience and skill. Within the parameters of a given dive; skill and technique can modify the need to resort to physical exertion. Workload decreases. Breathing techniques are better.  Stress management is improved. Experience acquisition tends towards better self-awareness; in particular, the recognition that respiration becomes elevated and the wisdom that exertion needs to be reduced or stopped.

An experienced, skilful, diver is more likely to manage their CO2 retention more effectively than a less experienced, less skilled, diver.  This might play a large role in deciding the severity and perceived onset depth of nitrogen narcosis.

Nitrogen narcosis management

All of the preceding issues factor into a very personal decision needed on narcosis management.

The competency to make decisions on narcosis management becomes clearer as experience and skillfulness develop; relative to a given level of diving. To the casual observer, deep air diving may seem like a very “do as I say, not as I do” attitude by higher-level divers. Indeed, even the definition of what constitutes ‘deep air’ diving is subject to great debate – for the reasons outlined already in my article.

Setting mandatory maximum narcotic depths (max ppN2) under-estimates the very real relationship between narcosis impairment and the level of autonomic dive skill acquisition. It is, however, a logical approach for diving agencies that have to consider a cross-spectrum of divers and diving competency levels.

The most prudent advice remains:

  1. Dive within the limits of your training and experience
  2. Respect your comfort zones
  3. Practice acquired skills diligently and routinely
  4. Minimize exertion and workload on dives
  5. Limit your depth until necessary dive competencies are ingrained

In addition, I’d suggest the following points are considered:

  1. The hazard of narcosis is relevant to the degradation of competencies necessary to preserve safety on a given dive.
  2. Fully understand the skill competencies necessary for the dives you undertake.
  3. Consider the degree to which you have ingrained competencies into autonomic functions.
  4. Experience acquisition precludes the need for problem-solving.
  5. If you perceive any impairment to your expected diving competency, assume it is narcosis.
  6. Abort the dive if diving functionality is compromised by narcosis.
Nitrogen Narcosis – Perceptions of Susceptibility
Nitrogen Narcosis – Perceptions of Susceptibility

The greatest variation between divers is the individual perception of susceptibility to narcosis. This is the person's awareness of when, or if, they are suffering a decline in mental cognizance due to elevated nitrogen partial pressure.

Read More
Does Nitrogen Narcosis Impairment Persist?
Does Nitrogen Narcosis Impairment Persist?

A new study on nitrogen narcosis challenges the long held presumption that nitrogen narcosis impairment dissipates immediately on ascent from depth.

Read More
Nitrogen Narcosis Sedation & Consciousness
Nitrogen Narcosis Sedation & Consciousness

The commonly taught model of alcohol-like intoxication fails to describe the nuanced cognitive effect upon the diver and, at worst, promotes divers towards a dangerous misbelief that they aren't mentally impeded by narcosis

Read More

Andy Davis Technical Sidemount Wreck Diving Subic Bay Philippines RAID Courses Training

About the Author

Andy Davis is a RAID, PADI TecRec, ANDI, BSAC and SSI-qualified independent technical diving instructor who specializes in teaching sidemount, trimix and advanced wreck diving courses.

Currently residing in Subic Bay, Philippines; he has amassed more than 10,000 open circuit and CCR dives over 27 years of diving across the globe.

He has published numerous diving magazine articles, designed courses for dive training agencies and tests/reviews dive gear for scuba equipment manufacturers. He is currently writing a series of advanced diving books and creating a range of tech diving clothing and accessories

Prior to becoming a professional technical diving educator in 2006, Andy was a commissioned officer in the Royal Air Force and has served in Iraq, Afghanistan, Belize and Cyprus.

Originally posted 2018-03-07 23:55:40.

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