John Scott Haldane developed a method that allowed deep-sea divers to ascend to the surface without suffering decompression sickness.
It has long been known that individuals who have been subjected to high atmospheric pressure cannot be returned rapidly to normal pressure without risking painful symptoms. During the mid-1840’s, miners who worked in coal mines pressurized to keep out water frequently suffered muscle pains on ascending to the surface. These symptoms were first studied in 1854, when it was noted further that a return to compressed air alleviated the pain. In 1878, the French physiologist Paul Bert
Deep-sea diving had been plagued by decompression sickness (also known as compressed air disease or “the bends,” because of the slightly bent, limping posture of its sufferers) since diving attire for individuals was developed in the early 1800’s. By the beginning of the twentieth century, no safe method for retrieving a person from deep dives had yet been achieved.
England’s Royal Navy used divers in its routine operations. Intent on finding a way to spare these men the risks of pain, paralysis, and even death as a result of decompression sickness, the navy commissioned John Scott Haldane—a physician and man of letters who was famous for his studies of respiratory physiology—to develop a decompression schedule that could be written down in tabular form and distributed to its fleet divers. Haldane was a scientist with a strongly philosophical nature. He disapproved of the generally accepted line between “pure” science, or science carried out for its own sake, and applied science, or science in the service of useful technology. He was a laboratory scientist who envisioned the results of his labors as being linked intimately to the general welfare. As such, he was eager to apply his theories and insights to the human working environment. Already famous for his studies of the composition of the air in schools and dwellings and for his identification of carbon monoxide as the cause of death in coal mining disasters, he accepted the Royal Navy’s commission with alacrity and began his studies of what came to be known as stage decompression.
It was standard knowledge that as a diver descends through a body of water, every 33-foot (10-meter) increment of depth exerts an additional pressure of one atmosphere. A diver at a depth of 33 feet thus experiences two atmospheres of pressure (the pressure of the air plus the extra atmosphere of the 33 feet of water), a diver at 66 feet (20 meters) is subjected to three atmospheres, and so on. Haldane was aware that cases of decompression sickness never occurred, even with rapid decompression, when a diver suddenly ascended from two atmospheres to one. He reasoned that it must, therefore, be equally safe to decompress suddenly from four atmospheres to two, or from six to three, as long as the two-to-one ratio is maintained. Thereafter, in order to avoid the bends, a diver would have to proceed more slowly through the ascent to give nitrogen that had been dissolved in the tissues under pressure the necessary time to emerge from the blood and be vented by the lungs. Haldane’s method therefore consisted in an initial reduction of pressure to one-half as rapidly as possible, followed by continued, slower decompression in a series of stages designed to prevent the rapid bubbling of nitrogen out of the blood.
Haldane carried out his first live experiments on goats in a steel compression chamber at the Lister Institute of Preventive Medicine in London. He was assisted in this work by pathologist Arthur Edwin Boycott and by Lieutenant Guybon C. C. Damant of the Royal Navy. They exposed several of the animals for long periods to 6 atmospheres of pressure (equivalent to a dive of 165 feet, or just over 50 meters) and then decompressed them suddenly to 2.6 atmospheres with no ill effects. When the animals were dropped from 4.4 atmospheres to 1 atmosphere (far in excess of the two-to-one proportion), 20 percent of them died and 30 percent experienced the bends.
Immediately after the animal experiments, Lieutenant Damant volunteered to be the first human experimental subject. He crawled into the chamber, experienced rapid pressure differentials, and emerged with no symptoms. Haldane had proved conclusively that it was quite safe to halve the absolute pressure rapidly, regardless of the depth of the dive.
Haldane realized, however, that he had only part of the solution. The danger of decompression sickness lay in what remained of the ascent after the pressure on the diver’s body had been rapidly halved. This required the painstaking working out of decompression tables that took into account not only the depths to which a diver had descended but also the amount of time the diver had remained underwater. These factors taken together actually determine the degree of saturation of body tissues with nitrogen.
To appreciate the complexity of the task of formulating accurate decompression tables, consider that the various tissues of the body absorb nitrogen at different rates. The rapidity with which a given tissue becomes saturated with nitrogen is dependent on two factors: the solubility of nitrogen in that tissue and the rate at which nitrogen is transported to the tissue by the blood. Nitrogen is very soluble in fatty tissues, for example, but much less so in nonfatty, or aqueous, tissues. Conversely, fat is served poorly by the circulation, so the rate of nitrogen saturation of that tissue is slow, whereas aqueous tissues quickly reach their nitrogen saturation points because they are well supplied with blood vessels. Haldane therefore divided human tissues into two types: slow (those, such as fat, that are poorly vascularized but have a high capacity for storing nitrogen) and fast (those parts of the body, such as the brain, that are well vascularized and quickly become saturated with nitrogen).
In drawing up his decompression tables, Haldane realized that saturation rates for the various tissues vary from seconds to hours. Because the rate of saturation also changes as the individual tissues take up nitrogen, it was impossible to determine on paper when exactly a given tissue would be fully saturated. Haldane struck upon the idea of “half-time tissues.” A tissue half-time is the time required for nitrogen to reach half its saturation value. Because it was not possible to assign precise half-times to real tissues, he arbitrarily chose to designate five-, ten-, twenty-, forty-, and seventy-five-minute half-time tissues for mathematical convenience in predicting the uptake and elimination of nitrogen. Although he realized that the longest half-time tissue in the body is sixty minutes, it is typical of Haldane’s conservatism and his emphasis on safety that seventy-five minutes represented the longest half-time tissue in his decompression schedules.
It was these carefully worked-out calculations of the rates at which fast and slow tissues eliminate their nitrogen that made Haldane’s tables so valuable. With them, divers were able to regulate the rate of decompression so that no parts of their bodies were at any point so supersaturated with nitrogen that bubbles would begin to form in the circulation. Haldane’s method of ascent by stages replaced the previous method of continuous decompression, which took much longer and seldom left divers fully decompressed by the time they reached the surface. Haldane, Boycott, and Damant coauthored a report on these findings, and the Royal Navy immediately adopted the Haldanian decompression tables.
After Haldane’s experiments at the Lister Institute, Lieutenant Damant made numerous deep dives at sea with the use of the Haldanian decompression tables. He achieved a maximum depth of 35 fathoms (210 feet, or about 64 meters). Following stage decompression, he showed no symptoms of the bends.
Haldane’s method of stage decompression immediately altered diving practice, and his schedules were universally adopted. After the Royal Navy published his tables, decompression sickness virtually disappeared among the navy’s divers. One of the most notable tests to which the tables were put involved the recovery of an American submarine off Honolulu in 1915. The diving crew descended to a depth of 50 fathoms (15 fathoms more than Lieutenant Damant’s deepest test dive) and completed the salvage operation without any cases of decompression sickness.
Stage decompression can be a lengthy process, a slow ascent in stages after an initial rapid decompression being its underlying principle. Bodily nitrogen that has been subjected to high pressure must be given adequate time to leave the blood and be exhaled from the lungs as a diver ascends to the surface. Even after it is gone from most areas of the body, nitrogen tends to linger in the fatty tissues, where it is especially soluble. A diver who has been at a depth of 190 feet (about 58 meters) for sixty minutes, for example, must be decompressed for about three hours before being brought to the surface. Although primitive decompression chambers existed in Haldane’s time, they were often difficult to control, so Haldane favored resubmergence to appropriate depth in those cases where divers were experiencing symptoms of the bends.
Because decompression was such a lengthy process, questions were raised about ways to cut down on the time involved. “It appears that the times cannot be cut down without risk of trouble,” wrote Haldane in his monumental book Respiration (1922),
Haldane’s original schedules were found to be highly accurate over their middle range, but divers soon learned that they could cut corners on short, shallow dives without risking the bends. Conversely, they found that Haldane’s schedules were not conservative enough on longer, deeper dives. The schedules have therefore been modified through experience over the years to resolve these difficulties.
Haldane’s spirited commitment to the constructive application of scientific principles for society’s well-being characterized his investigations not only in deep-sea diving but also in mining and tunneling. The fact that his method of stage decompression has allowed humans to persist in these environments has earned for Haldane a reputation as the prime mover of modern times in respiratory physiology.
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Douglas, C. G. “John Scott Haldane.” Obituary Notices of Fellows of the Royal Society of London 2 (December, 1936): 115-139. Given Haldane’s accomplishments and his stature as one of the foremost scientific movers of his time, it is surprising that this is one of very few sources of detailed biographical information on him. A fitting and comprehensive tribute to Haldane, the scientist and the thinker. -
Guyton, Arthur C. Textbook of Medical Physiology. 6th ed. Philadelphia: W. B. Saunders, 1980. The classic text for students of animal physiology. Contains a detailed chapter on aviation, space, and deep-sea diving physiology. Clearly written and detailed, and with abundant references, it is an invaluable source of information for the reader desiring a grounding in the principles of diving physiology. -
Haldane, John Burdon Sanderson. Adventures of a Biologist. New York: Harper & Brothers, 1940. Son of John Scott Haldane, J. B. S. Haldane was an accomplished man who made major contributions in widely disparate areas of knowledge. Provides the most personal portrait in existence of his father, including his routine participation as a human subject in his own experiments. -
Haldane, John Scott. Respiration. New Haven, Conn.: Yale University Press, 1922. Haldane’s monumental work on the physiology of respiration, a compilation of lectures he gave at Yale in 1916. Provides a detailed account not only of what was known about respiration in Haldane’s time but also of the author’s pioneering experiments. Still considered a classic of respiratory physiology. -
Norton, Trevor. Stars Beneath the Sea: The Pioneers of Diving. New York: Carroll & Graf, 2000. Norton, a marine biologist, presents brief portraits of thirteen scientists, inventors, archaeologists, and others who pioneered in the field of deep-sea diving, including both John Scott Haldane and J. B. S. Haldane. -
Strauss, Michael B., and Igor V. Aksenov. Diving Science: Essential Physiology and Medicine for Divers. Champaign, Ill.: Human Kinetics, 2004. Written by two experts in diving medicine and physiology and designed for use by sport divers. Presents information on the physical, physiological, and psychological stresses that divers encounter. Includes detailed equipment recommendations. -
Strauss, Richard H. Diving Medicine. New York: Grune & Stratton, 1976. A highly readable textbook, valuable for its clear presentation of both the history and the physics of diving, including Haldane’s contributions. Although intended as an introduction to the medical aspects of diving for physicians, this work assumes little prior knowledge of human biology and is accessible to the interested reader.
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