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).
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.