Prof. Dr. med. Albert Bühlmann, University of Zürich
Published 1961 by J.R.Geigy S.A Switzerland «Der Weg in die Tiefe» in five bulletins
Diving, general meaning and difficulties
The collision of the «Andrea Doria» with a Swedish ship off New York harbor is still generally remembered as the biggest shipping disaster after the Second World War. Even today, four years after the sinking, the wreck of what was then the most beautiful ship of the Italian merchant navy lies at the bottom of the sea.
Although the «Andrea Doria» still represents a value of several million Swiss francs, it has not yet been salvaged. After the First World War, the English were already able to lift the valuable ships of the German Imperial Navy, which had sunk itself in Scapa Flow, and thus to supply English industry for years with the best and cheapest steel scrap.
Why have no serious attempts been made so far to salvage the «Andrea Doria»? The reason is very simple: the ship is too deep.
The keel of the ship sits on the sea bed at a depth of about 120 meters, and the uppermost deck structures are about 80 meters below the sea surface. It is possible for well-trained divers to dive 90 to 100 meters deep with a rubber suit and helmet and the usual equipment, to make observations there and to do light work for a short time. As a rule, professional divers rarely go deeper than 50 to 60 meters.
To lift the «Andrea Doria» they would have to be able to drill channels for hawsers through the sand under the keel, connect air hoses to the hull to displace the water with compressed air, and seal at least the coarsest leaks. The requirement, then, would be to dive 120 meters deep, stay there for at least some time, and do physical labor.
Armored divers, who are in partially mobile armored equipment and thus protected from water pressure as in a submarine, can descend to such depths without difficulty, but are unable to perform complicated manipulations because of the quite insufficient mobility in the armored suit. The freediver or frogman, on the other hand, whose rubber suit serves only for thermal insulation and has little restriction on mobility, would be able to perform even difficult work if he could descend to such depths without danger.
However, the wreck of the «Andrea Doria», which has not yet been salvaged, proves that this is not possible with conventional diving methods. However, the young mathematics teacher from Winterthur, H. Keller, in cooperation with the writer, succeeded in diving several times to a depth of 120 meters and once to a depth of 155 meters in various Swiss lakes in the summer of 1959 and 1960, and in withstanding a pressure in the overpressure chamber of the French navy in Toulon, such as prevails at a depth of 250 meters.
155 meters diving depth is a world record for free diving, and 250 meters (25 atm overpressure) has never been reached even in a hyperbaric chamber.
Nevertheless, since there are no international rules in this field, the term world record is not quite correct. More importantly, these successful deep dives are not sporting feats of strength combined with a bit of luck. On the contrary, they are intended to prove that it is quite possible to dive to such depths using appropriate methods, without any particular physical exertion, with a feeling of well-being, so to speak, but above all without any particular risk, and to come back up again without any damage to one’s health.
It was not about a one-time world record, which is occasionally improved like a sports record, but about the development of a method that makes it possible for every diver to reach the mentioned depths. The fact that Swiss divers, of all people, succeeded in finding new ways in this special field beyond the usual atmosphere is not least due to the fact that diving technology has been stagnating for about 30 years.
Although diving plays a major role especially for the seafaring nations in connection with ship salvage, harbor construction and geological investigations of the seabed off the coasts, technical development has practically come to a standstill. This is partly due to the mentality of most professional divers, who, unlike pilots, do not sit enthusiastically in the cockpit of ever faster and higher flying machines, but on the contrary are extraordinarily conservative and meet all new proposals with the greatest skepticism, if not usually rejection. After World War II, recreational diving for underwater hunting and photography became widespread. In the military field, too, the diver’s possibilities were recognized and teams of frogmen were trained for special tasks. This gave the interested industry many impulses for new developments and improvements in equipment.
But even with the best equipment it was not possible to dive deeper than it was 30 years ago, because the diving methods remained unchanged. Before the First World War, diving rescuers were developed for the crews of sunken submarines, but they were used only exceptionally in an emergency.
Even the systems in use now, which do not differ in principle from the old ones, do not allow rescue from a submarine 150 meters or deeper; if it is not possible to refloat the submarine, the crew is lost.
On the other hand, the hyperbaric chamber test in Toulon proves that ascent from a depth of 250 meters is possible without damage. Real improvements in diving technology must address the physiological and medical problems.
The relevant literature, including the more popular diving books, offers nothing more in the way of established medical facts than what was already known 50 years ago, thanks to the work of the great respiratory physiologists of the last century, such as the Englishman Haldane and the Frenchman Paul Bert, who had studied diving intensively. Besides, the same half-truths and unproven prejudices and misinterpretations of physical and biological phenomena are repeated again and again. The discussion about the so-called deep intoxication, which supposedly prevents deep diving or makes it a great risk, is characteristic of this.
With the desire to clarify the existence and cause of this intoxication, our diving experiments began. Various divers report that at a certain depth, of 70 or 80 meters, for example, they experienced a peculiar, exhilarating feeling that made them rush to ascend to a shallower depth. It has been observed how divers in this euphoria became uncritical, did all kinds of stupid things, even took off their breathing mask and drowned. Many fatal accidents are rightly or wrongly attributed to this ominous deep intoxication. The nitrogen solution in blood and tissue, which increases under overpressure, is always cited as an explanation.
Though, at least the medically educated experts should not have overlooked the fact that a specifically narcotic effect of nitrogen is not known at all. It should have been obvious that, according to the above-mentioned data, the deep intoxication disappears very quickly when going back to lower depths, and that, on the other hand, staying for hours at low depths does not produce intoxication. The additional nitrogen dissolved in the organism over and above the normal amount already present is, up to full saturation, the product of overpressure and the duration of exposure to pressure.
During a one-hour stay at a depth of 30 meters (4 atm total pressure), much more nitrogen is additionally dissolved in the organism in terms of quantity than during a descent to 90 meters lasting only a few minutes. Since pharmacological effects always depend on concentration, if the nitrogen theory is correct, the diver or caisson worker at 30 to 40 meters depth should have a deep intoxication after one to two hours. Since the additionally dissolved nitrogen is only slowly released by the organism during ascent, it is quite incomprehensible – again according to the nitrogen theory – why the symptoms of intoxication abruptly disappear when going back to lower diving depths. The depth intoxication, if the descriptions are correct, must be related to the current overpressure.
Since the human organism, with the exception of the organs containing air, consists of liquid and is therefore practically incompressible – at a depth of 1000 meters, at 100 atm, there would only be a decrease in body length of a few centimeters – it cannot be a direct effect of the overpressure on the human being.
What changes immediately with the respective diving depth and is adapted to the momentary pressure, however, is the pressure of the respiratory gases, be it oxygen, compressed air or other gas mixtures. To prevent the thorax from being compressed, the intra-alveolar and intrathoracic pressures must be equal to the external pressure, just as they are at the surface. The breathing valves of the diving apparatus therefore control the pressure of the breathing gases as a function of the water pressure. Of course, the pressure in the paranasal sinuses and middle ear must also be adjusted to the respective external pressure in order to avoid compression fractures of the cranial skeleton and rupture of the eardrum.
Pressure equalization with the middle ear is possible only by opening the eustachian tube if the eardrum is intact, which requires some practice and presupposes continuous tubes. Pressure equalization is most difficult to achieve at the beginning and at the end of each dive, as the following consideration shows: 10 meters of water column has a pressure of 1 atm. At 10 meters depth, the absolute pressure (water pressure and air pressure) is 2 atm, reducing a gas volume by half. If the volume is to remain constant, the number of gas molecules must be doubled. The next doubling occurs only at 30 meters depth at 4 atm absolute pressure, then at 70 meters, the next time at 150 meters and so on.
In other words, equalizing the pressure with the sinuses and with the middle ear is no more difficult when descending from 70 to 150 meters than when diving from the surface to only 10 meters depth. While the necessity for this pressure equalization is known to everyone who once had his head under water for a few meters or flew in an airplane without a pressurized cabin, or even just drove a car in the mountains in a short time to overcome larger differences in altitude and thus pressure, the special respiratory physiological problems of overpressure are unknown to most divers. However, deep exhilaration is nothing other than an overpressure effect on breathing, which will be discussed in more detail in a later bulletin.