Herbert Nitsch back from the underworld

Record holding freediver Herbert Nitsch gave his first interview 9 months after a decompression accident that almost killed him on June 6, 2012 in Santorini, Greece. Herbert was trying to surpass his own 2007 record of no-limit freediving to 214 meters by aiming to reach 240 meters (no-limit is one of the freediving disciplines and consists of using a weighted sled to descend very rapidly, and an inflatable device to ascend even more rapidly, allowing for much deeper dives in a short timeframe).

Herbert Nitsch
Herbert Nitsch on his no-limit sled.

What seemed to have happened is that a nitrogen narcosis-induced loss of consciousness at 100 meters on the way up prevented Herbert from leaving the sled, which led to too rapid an ascent all the way to -10 meters, where the safety divers picked him up and brought him to the surface. The rapid ascent triggered decompression sickness (DCS), otherwise known as the bends, which consists of nitrogen leaving the body tissues too fast and, rather than being circulated back to the lungs, entering the bloodstream in the form of bubbles. The nitrogen bubbles caused strokes (technically, an arterial embolism shutting down oxygen supply to the brain), which led to brain damage in cortical areas related to motor control and memory. As a result, Herbert partially lost the ability to walk or use his right arm, and his language abilities and memory of names deteriorated significantly. While these symptoms subside over time, DCS victims typically never recover fully from such serious accidents.

DCS is a well-know feature among compressed air divers – whether recreational scuba divers who exceed no-decompression limits, or technical divers who miss a deco stop. But DCS is not routinely discussed within the freediving community as a threat – the dive times, rarely in excess of 4 minutes, are not considered to be sufficient to trigger excessive loading of nitrogen from the lungs into the tissues.

In the case of Herbert’s attempt, though, time was not the factor. The onset of DCS is a function of both time and depth – which, in freediving, are rarely extreme enough. But on June 6, 2012, Herbert did reach a planned depth of 244 meters – even a bit more according to his dive computer. At that depth, the air inside his lungs had a pressure of 26 bars (26 times the pressure of the atmosphere at the surface) – something no recreational or technical diver will ever experience (although some commercial divers who engage in saturation diving can go even beyond that). Anyone familiar with standard diving tables understands that at such a depth, the maximum bottom time for a no-decompression dive must be extremely short. But how much exactly?

I did a quick back-of-the envelope calculation. A standard PADI no-decompression limit (NDL) table indicates the following maximum bottom times:

  • 10 meters: 219 minutes
  • 20 meters: 45 minutes
  • 40 meters: 9 minutes

A crude extrapolation assumes that every time the depth doubles, the maximum bottom time decreases by 80%. At 240 meters, this would equate to 13 seconds of maximum bottom time – and keep in mind that bottom time, despite its name, is inclusive of the descent time. To do this dive without any decompression stop, Herbert would have had to go from 0 to 240 meters in 13 seconds. However given a 20-second stop at 30 meters to fill his famous Coke bottle with air from his lungs (to help future equalization), and accounting for a vertical sled speed of 3 meters/second, the descent must have taken about 100 seconds – almost 8 times the no-decompression limit.

Of course, Herbert and his technical team were well aware of that, and in fact they had planned a slow ascent from 100 meters up (without the sled), and a 60 second decompression stop at 10 meters. I have not plotted this profile into a compressed air decompression planning software to use as a proxy, but it is not hard to see that a 60-second deco for such a dive was already pushing the envelope. Herbert’s loss of consciousness and subsequent uncontrolled ascent to 10 meters was obviously not going to end well; but even without it, the dive profile looked like an extremely risky physiological experiment. I wonder, in fact, whether the technical team could have made Herbert breathe trimix (helium, nitrogen and oxygen), or even heliox (helium and oxygen) or hydreliox (hydrogen and oxygen) for the hour leading up to the dive. This would have possibly mitigated the risk of nitrogen narcosis at such depths, and would have avoided the loss of consciousness at -100 meters which was the main cause of the accident. But we all have 20/20 hindsight and it is easy to raise those considerations in retrospect. Notionally, other risks come on top of that – such as oxygen toxicity (the partial pressure of oxygen in standard air at 26 bars would be 5.46 bars, more than three times higher than the limit for onset of ox-tox) which cannot be addressed at the surface (breathing a sufficiently hypoxic mixture prior to the dive would be devastating to the freediver’s performance, and quite possibly cause immediate loss of consciousness!).

In the end, it is adventurers like Herbert Nitsch who improve our understanding of hyperbaric limitations of the human body. Without daredevils like Nitsch, and before him Mayol, Maiorca, Ferreras, Pelizzari and others, dive doctors would possibly still expect the human body to implode well above -100 meters. These world-class athletes have all furthered the science and understanding of deep dives. But at what price!

Thank you Herbert, and I wish you the speediest recovery.

8 thoughts on “Herbert Nitsch back from the underworld”

  1. Thanks teedeepee for your insightful reply.

    I think it is a concise description of the dangers freedivers face when these depths are being contemplated and then challenged.I would like to add perhaps the underlying qualification of why no technical intervention was made to Herbert’s freedive training process.

    Air calculations and potential guesses at what the human body will or wont do are always great but, as with Enzo Maiorca, the scientists then advising he not go beyond 50m because his ribcage would implode, guessed wrong. There was limited knowledge available then about Bloodshift and the homeostasis achieved by the human body during breath-hold under pressure. Perhaps we musnt underestimate the ability of the body to gradually adapt to environmental stresses. What kind of adaptation and enurement to stress Herbert and his team made are only known to them a\at this point, and decisions to attempt that depth we hope, must have be borne out of a training regime that had programmed in gradual exposure to similar depths and that had shown positive results confirming his capability, or it would not have been attempted. Unfortunately things didnt go to plan. If they had done, the question remains as to what might this ,might have proven However, such is the nature of all the freediving disciplines, with perhaps, NO LIMITS FREEDIVING being the biggest challenge of all regarding the tolerance of the body to extreme pressure , that ANY ALTERATION TO THE NATURAL BREATH CHEMISTRY IS NOT TOLERATED AT ALL. Unfortunately to suggest that the support technical team could have advised him better to take a mixture of other gases before the attempt to help prevent the levels of toxicity and compression in the blood, would have meant that they would have had to contravene that rule.

    In specifying that freediving and moreover freediving records are about exploring human potential, it means exactly that; the man/woman, the mind and the human body must stand on their own. Curiously perhaps as each individual is so different we might not ever know exactly where that limit is. Of course another discipline might still be invented just because the human spirit is what it is, which would allow for some chemical or other kind of technical intervention just to enable the science to go further? Perhaps Herbert’s fellow countryman, Felix, might have an opinion about that!

    oh, and exactly… as your article COLOPHON, in TeeDeePees REDSHIFT, states COLOPHON states….” It means that the next evolution of man will be driven by technology, not (uniquely) biology””!

    1. Thank you Maria Teresa, those are all very good points, and I wouldn’t want to come across as underestimating the amount of preparation and care that the technical team and Herbert may have put into this endeavor (I’ve slightly edited the wording in my post to clarify this). In fact, the efforts into engineering the sled and the dive protocol were well publicized; I just don’t know enough about the other aspects of their preparation.

      You raise an interesting point about whether they could have changed the air mix. I’ll have to look into the rules for no-limit (but given that AIDA no longer validates no-limit attempts, I’m not even sure there is a rule book anymore). My first opinion is that as long as the mixture is not hyperoxic, but merely aims to mitigate the risk of nitrogen narcosis, it is still “no-limit” as it won’t improve the freediving performance but will only address safety. This is different, for example, from Tom Sietas breathing pure O2 prior to his 22′ STA attempt, which is almost twice the 11.5′ STA record held by Stephane Mifsud breathing normal air. In this case, the gas was clearly designed to enhance the performance, and as you suggested, this means it’s a different category of the sport altogether.

      Thanks for having shared your thoughts. It’s a hugely complex subject, being at the edge of human performance, and I hope Herbert’s Extreme 800 team will start sharing more info as time goes by. We can all learn from this.

    2. I did some further research into whether breathing a normoxic (21% oxygen) hyponitrogenic (less than 78% nitrogen) mixture prior to a no-limits (NLT) attempt would be acceptable. The answer seems to be positive:

      • Section 3.1.4 of AIDA’s competition regulations (version 12.0) states that “any inhalation of oxygen and/or highly oxygenated mixtures 60 minutes prior to the athlete’s performance is forbidden” (this regulation is enforced by section 10.2.5: “one judge must supervise the athlete at all times beginning 60 minutes before OT“). It explains why Tom Sietas’ pure-oxygen 22′ STA record is not homologated by AIDA. It does not, however, explicitly rule out trimix or heliox as long as they are normoxic.
      • Section 10.1.1 further states that “AIDA International does not recognize competitions in the discipline No-Limits” but still considers it an open-water discipline subject to homologation of world records. Therefore regulations that normally apply to competitions might be even more relaxed for NLT (AIDA’s website in fact indicates that “there are few rules” in NLT.

      I’ve sent an email to AIDA asking for clarification and will post the follow-up here.

  2. I received a reply from AIDA’s Medical and Scientific Committee today. They pointed me towards a decision made by the AIDA board in September 2012, following Herbert Nitsch’s accident and others’:

    Due to a number of incidents resulting in serious injury or death in connection with No Limits world record attempts, and concerns regarding additional safeguards that may be needed for athlete safety, the Board voted to temporarily suspend for a period of one year (until 30 September 2013) AIDA International’s sanctioning of No Limits world record attempts. During this period, AIDA International, in connection with AIDA Nationals, will review incidents, procedures and other matters relating to No Limits (in addition to other work being done regarding deep and sled diving), and take additional steps relating to No Limits risk management. (source)

    To my question of substituting helium for nitrogen in the pre-dive mixture, AIDA’s response was (emphasis mine):

    It should also be noted that helium might have detrimental effects during rapid ascend during a No Limit’s dive due an phenomenon known as high pressure nervous syndrome (HPNS), which limit the usability of helium for these dives. Trying to perform no-limit dives with helium mixtures would therefore be highly experimental and irresponsible without supervision of an dive-medical team. It is currently difficult to predict how helium would respond to no-limit dives, however data from technical diving suggest that the symptoms are more severe if the descend is faster, which would suggest it would not be a suitable solution for (deep) no-limit dives.

    It is interesting to note that, while HPNS is known and relatively well understood, the onset can be facilitated by a rapid descent – which is of course typical of NLT more so than of technical scuba diving.

    In conclusion, freedivers may mitigate the risk of narcosis by breathing a hyponitrogenic mixture containing helium (either trimix or pure heliox) before an NLT attempt, but at the expense of an increased HPNS risk (the DCS and oxygen toxicity risks remain unchanged). That in itself is a dilemna.

    Unless, of course, we consider hydreliox (oxygen-helium-hydrogen) or pure hydrox (oxygen-hydrogen) – in which case the nitrogen narcosis and HPNS risks are both mitigated, but at the expense of a new risk, hydrogen narcosis, which typically occurs below -300 m. Perhaps that’ll be the new NLT limit (it was actually Herbert Nitsch’s long-time objective). But it will require a lot more experimentation, and comes at a huge risk for those willing to experiment.

  3. A very correct description of the case, thank you. There is one technical statement which is not correct. The 26 bar pressure in the lungs is actually not a problem. You forgot about the followning mammalian diving reflex: “Blood shift that occurs only during very deep dives. When this happens, organ and circulatory walls allow plasma/water to pass freely throughout the thoracic cavity, so its pressure stays constant and the organs aren’t crushed.”
    What I have learned but do not understand: why is actually deco needed when we just use the air breathed in on the surface? I understand why it is needed when we breath in the air on higher pressure with scuba gear underwater, in this case there are more (nitrogen) particles in it which get more absolved in the blood.

    1. Thanks Tom. Actually the mention of 26 bars was not in reference to a risk of thoracic damage, but purely to estimate the increased exposure to both nitrogen narcosis (approx. 20 bars of partial pressure of nitrogen at 250 meters, when it is commonly accepted that narcosis starts occurring at approx. 3.2 bars of partial pressure of nitrogen) and to oxygen toxicity (approx. 5.5 bars of partial pressure of oxygen at 250 meters, when it is commonly accepted that oxygen toxicity starts occurring at approx. 1.6 bars of partial pressure of oxygen over a sufficiently long period of time).

      A deco is needed in very deep freediving because the great depth and pressure gradient causes the tissues to load up nitrogen quickly. To your question – in fact, the density of nitrogen atoms in the lungs of a freediver and of a scuba diver will be the same. If I can explain:

      Both body tissues and lungs at the beginning of a dive (whether freedive or scuba) are loaded with a partial pressure of nitrogen (a.k.a. PPN2) of 0.78 bar (atmospheric pressure of nitrogen at the surface). As the freediver descends, the air pressure in his lungs increases (as the volume of the lungs decreases) to be equal to that of the water pressure around him (that’s why freedivers equalize, just like scuba divers. The only difference is that the lung volume of scuba divers remains constant, and more air is pumped from the tank to fill up the space). The partial pressure of nitrogen therefore increases too, up to approx. 20 bars at 250 meters. Because there is such a difference (called gradient) between the nitrogen partial pressure in the tissues (0.78 bar) and in the lungs (20 bars at the deepest point of Herbert’s dive), the nitrogen is forced quickly from the lungs into the tissues. This happens over a very short period of time compared to scuba diving, however the pressure is also much higher (in recreational scuba diving the nitrogen partial pressure would not exceed 4 bars at 40 meters). So the tissues can end up being so loaded in nitrogen that a rapid ascent would cause them to come out of solution as bubbles (DCS). Hence a deco stop is needed.

      I hope this clarifies – if not let me know!

      1. Thank you for your explanation. It seems obvious that nitrogen more nitrogen gets absolved, and the problem is than the quick ascend. I am not sure from which depth use free divers deco stop at all. On the other hand, I also understand, that we can just guess at these levels, as not all bioligical processes are observed accurately. For example, as the lungs gets filled with plasma/blood when it contracts to its approx. 1/5 of its original size, what happens with the remaining air in the lung? Will there be fluid + a high pressure bubble? (1/26 of lung volume at 250m) Can the compressed, fluid filled lung also absorb gasses with the same effect from this bubble? May the remaining air also resolve in the plasma fluid as well and when by ascend the body pumps out/back this fluid too quickly it may still have too much dissolved gas? Many questions to be answered in the future, but we may just be able to observe the limits if people take their lifes to risk…

        1. Tom, this is a very good question – I do not know either how the bloodshift impacts the function of the gas-exchange alveoli in the lung, or how the plasma plays a role in carrying nitrogen as it withdraws from the lungs upon ascent. As you pointed out, this is at the far edge of diving knowledge 🙂

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