29. Feb, 2016

Facing the abyss: free diving and the risks

Free diving for commercial purposes already existed in ancient Greece when sponge divers descended in the Mediterranean to collect  sponges used for bathing.  This profession continued  for many centuries thereafter.

The early start Initially, the divers had no fins, diving mask or goggles and just jumped in the water with a heavy flat stone of 15 kg, called skandalo petra, to descend rapidly. The sponges were already spotted from the boat using a cylinder.  When sufficient sponges were collected the  basket with sponges and the diver with stone were pulled on board. Greek divers could remain underwater for around 3- 5 minutes at a depth of 20-30 meters. The skandalopetra method is still used in modern times  by free divers trying to break records. They are allowed to use a nose clip but no fins or diving suit. http://www.freedive-earth.com/learn-freedive/skandalopetra-CMAS  Sponge diving remained a typical Greek profession  carried out  up to the 20th century in Florida waters.  But then the divers  used  helmets and suits that received compressed air via an air hose  connected with a  motorized or hand  driven pump on deck  of the boats.  Another ancient form of free diving  was that of the Japanese Ama’s, young and  also older women diving for oysters with pearls along the Japanese coast.  Either in the nude or dressed  in white gowns. Many of these divers must have suffered from decompression illness,  since they had to do many dives a day to make a profit**. There are reports of ancient divers in the 13th century  that used  polished  tortoise shells as a lens in their self made goggles. Polynesians seem to have used wood or bamboo goggles that would trap air to create a viewing area while submerged. Once introduced to glass, they applied glass lenses to their goggles. 

Competitive  free diving Although modern competitive free diving is not commercial, it does force the diver to push the limits of the human body and sometimes overstepping these limits. In 1976  the Frenchman Jacques Mayol, became the first man to break the 100m dive mark. Mayol also introduced yoga and meditation into free diving as a means to prepare his body for the forthcoming physical stress.  There are several  categories  of free diving, each with its own records and champions.  There is static apnea  (in a pool),  dynamic apnea (swimming horizontally as far as possibe, with or without fins), vertical diving (with or without fins, using constant weights or variable weights) and no-limits apnea (any means allowed during descent and ascent). Most ‘natural’ seems the vertical apnea without fins or weights. But this will require a lot of  muscle power and consequently more oxygen  and carbon dioxide buildup.  Fastest way to get down and up is the no-limits apnea. Here the diver uses  a weighted sled to descend rapidly  and an air-filled balloon to return fast to the surface.  It resembles a bit  the skandalopetra method.  This method is certainly the most risky because if a slight detail goes wrong,  it could mean the end of the diver.  Ideally, a diver trying to break a record  in this category in the open sea should first practice the stages of descent and ascent in a controlled environment. For example a submarine escape tower, although these are often not higher than 30 meters. Even better would be a wet hyperbaric chamber allowing  to control the hydrostatic pressure and to monitor the divers physiology.  

Records  The skandalopetra free diving  record was set  at 112 m by Andreas Güldner in 2014. The current world records for static apnea are 11 minutes 35 seconds and 9 minutes and 2 seconds for men and women, respectively. The current world records for non limits apnea are 702 feet (214 meters) and 525 feet (160 meters) for men and women respectively.  Deepest man on earth  in this category is  Herbert Nitsch, with  214m. Deepest women in the same category is Tanya Streeter  with 160 m.  A tragic victim  in the same category was the beautiful champion free diver Audrey Mestre  who  dove 561 feet  trying to break the world record.  But the 28-year old French woman did not make it back up alive in October 2012. The lift bag that should have taken her back to the surface did not work, because someone  had forgotten to fill the connected air 

On 17 November 2013 Nicholas  Mevoli an American freediver in the category with fins and constant weights attempted a dive to 72 metres (236 ft) on a single breath in the Bahamas but later collapsed due to pulmonary edema. Current free dive champion in the same category  is  Alexey Molchanov who reached 128 m.   His mother Natalia Molchanova who held the women record of 101 meters  in the same category died in a diving accident last year in Spain (see picture of Natalia above).  bottle. https://vimeo.com/70997378

These are truly awesome numbers (and accidents), as are those in the other competitive categories. Some scientists believe that free divers have learned to ‘push evolutionary buttons coming from a period earlier in evolution'. Probably still functional during the birth process,  when it’s important for the fetus to slow down to survive a perilous passage through a birth canal that restricted blood flow.*

Physiology The physiology of the  free diver is well investigated. There  are several effects working  in succession on the body of the diver during the descent. The dive reflex comes first, after the face touches cold water. This implies that  heart rate and metabolism slow down.  The effect of this reflex is greater in cold water than in warm water. The arteries in arms and legs constrict, pushing more blood  back in the body and  vital organs like  lungs and liver.  Decrease of heart rate and blood pressure also lowers cardiac output. At 20 meters  divers without weights usually reach negative buoyancy. With increasing depth  the pressure around the thorax increases  dramatically, and so the lung volume. At 100 meters lung volume is only 1/10 of its surface volume.  The smaller volume will increase the partial pressure of nitrogen, carbon dioxide (CO2) and oxygen (O2) in the lungs.  Miraculously, the lungs do not collapse, probably  because blood plasma forced in the thoracic cavity compensates the decreased volume of the lungs.  During the descent the free diver must resist the trigger point: the moment when he/she feels a strong urge to breath, even when the  diaphragm that separates the thorax from  the abdomen, starts to contract. During the ascent there are two factors working on the divers physiology, time and volume increase of the lungs. The resultant rapid change in the pressure of gasses in the body and brain are essential to survive in the relatively short period to reach the surface.

Risk factors The main hazard of repetitive free diving, as it was carried out by  the old commercial divers  is  the  build up of nitrogen.  Although their bottom times are short and their dives rather shallow, there is a buildup of nitrogen with each dive that may cause the bends **. Competitive divers sometimes experience euphoric and ‘spaced out’  feelings, probably the result of  the higher pressure of nitrogen but also the lack of oxygen. The same factors can lead to a black out or difficulties with carrying out simple motor acts like opening a valve,  at greater depths.  Hyperventilation is also a risk  factor. It does not increase the amount of oxygen in the blood, but washes out the carbon dioxide, which is the major trigger  of the need to breath. Shallow water blackout is one of its greatest dangers. It is most likely to occur  during ascending in the last 10 meters, when air in the lungs  expands rapidly. This may cause the O2 level to drop  into the diver's blackout zone before the CO2 can rise enough to force the diver to resurface to breathe.  Being fit, a large lung volume and  having learned how to bypass the urge to breath, are factors that can extend the time that one can hold his or her breath. Some divers  also practice meditation prior to a deep dive to relax. But competitive free diving  remains a very dangerous sport where the line separating a safe dive and a fatal accident remains very thin. The  experienced  divers are aware of the dangers and have found ways not to cross that line. But they or their team members remain humans, and likely to make errors of judgment.

Sources

https://en.wikipedia.org/wiki/Freediving

https://en.wikipedia.org/wiki/Alexey_Molchanov 122 meter

http://freedivingexplained.blogspot.nl/2008/03/basics-of-freediving-freediving.html

http://divewise.org/education/freediver-blackout/

*http://nautil.us/issue/22/slow/the-impossible-physiology-of-the-free-diver

 **Wong, R. M. (1999). "Taravana revisited: Decompression illness after breath-hold diving"South Pacific Underwater Medicine Society Journal 29 (3). ISSN 0813-1988

**Schipke JDGams EKallweit O. Decompression sickness following breath-hold diving. Res Sports Med. 2006 Jul-Sep;14(3):163-78.

http://edition.cnn.com/2015/08/06/opinions/pollock-free-diving/