How do divers die

The limits of the submersible

Records on the way down

In 1992, divers for a French company reached a theoretical depth of 701 meters. Theoretically, because the divers of the Hydra project were in a superlative experiment in a pressure chamber and not 700 meters below the surface of the water.

Nevertheless, this mark is still considered an absolute record low today. The strain on the body is enormous: at a depth of 701 meters there is a water pressure of 70.1 bar. The time to equalize this pressure, the decompression phase, was more than 550 hours for the test subjects.

The German Aerospace Center also conducted research into deep diving in the 1990s. The findings from these tests were of interest to the aerospace industry, as they were supposed to provide information about insulation, gas mixtures, developing spacesuits and working under pressure. The climax and conclusion of these attempts was a dive to a depth of 615 meters.

Deep diving research is not only complex, but also expensive. The results of the tests also showed that reliable work at this depth is no longer possible. That is why machines are now doing the exploration of the oceans or maintenance work at extreme depths.

Instead of manpower, science, industry and the military rely on remote-controlled underwater vehicles or diving equipment that protect people from the high ambient pressure. The exciting question of whether dives in the four-digit meter range would be possible will probably remain a theoretical one.

Falsified voice from the depths

The right breathing gas mixture is crucial on the way down. It doesn't work without oxygen - but there is a problem here: Depending on the temperature, ambient pressure and working conditions under water, pure oxygen has a toxic effect deep down and there is a risk of oxygen poisoning.

Without warning, the diver can be surprised by a seizure, which can best be compared to an epileptic seizure.

That is why the compressed air used by recreational divers is usually enriched with nitrogen. But this mixture also has its pitfalls.

With increasing pressure, deep intoxication can set in, a state that is perceived very differently from person to person. This high can be associated with anxiety or euphoria and lead to unconsciousness. Therefore, recreational divers should only go a maximum of 40 meters deep.

For professional divers, however, work often only begins below 40 meters. So if you want to go even deeper, Heliox, a mixture of oxygen and helium, is used.

Anyone who has ever inhaled helium knows the effect: the voice becomes high and distorted. This of course makes communication between the divers and the crew on deck of the ship extremely difficult.

In order to be able to understand the voices of the divers, unscramblers are used, electronic devices for speech equalization.

But despite the equalizer, the falsified voice from the depths can usually only be understood by professionals who have already been in use with these helium mixtures.

Under pressure for weeks

To stay at 100 meters for 30 minutes, a diver would have to decompress for many hours on the way up. Gases such as nitrogen or helium, which the diver ingests through his breathing mixture, dissolve in the body under pressure.

Those who emerge too quickly run the risk of paralysis or worse, because the gas then bubbles out and can block blood or nerve tracts. An effect like a soda bottle that is opened too quickly.

For example, to repair oil pipelines at a depth of 180 meters, saturation divers are used. Theoretically, they can stay at the same depth as long as they want, since their bodies are saturated from a certain amount of gas. The gas pressure in the body tissue and the ambient pressure are then identical, the risk of bubbles being eliminated.

A diver who is kept constantly under the same pressure in a pressure chamber can work for weeks. The dive is artificially elongated. And the time-consuming ascent is only due at the end of the work unit.

Without the pressure chambers, a diver would spend more time decompressing than doing actual work.

Body and mind at the limit

The danger for the diver increases with every meter of depth. Not only is the high ambient pressure a problem - the human body consists largely of water and can withstand the pressure comparatively well. The psychological burden is also enormous.

Breathing becomes more difficult, the conduction system of the nerves can fail and hallucinations occur occasionally.

Nevertheless, humans are capable of almost unbelievable records: In 2007, Austrian freediver Herbert Nitsch dived 214 meters in the "No Limit" discipline. With a single breath.

Five years later, Nitsch failed in an attempt to increase his own record to 244 meters. He lost consciousness and suffered from diving disease. After the accident it was decided not to set any more records in the "No Limit" discipline.

The depth at which a person can still do useful work underwater cannot be clearly determined: There are professional divers who regularly repair weld seams at a depth of 180 meters.

The duration is also unclear: a dive for professional divers should not exceed 28 days - the saturation dive of the German Aerospace Institute at 615 meters lasted even 40 days.