When the autopsy was performed on the diver in 1900, they found bubbles in his brain and heart. There were so many bubbles, in fact, that when examiners lifted the heart, it gurgled with froth. The cause of death was decompression sickness. And while doctors knew the cause of the condition, they desperately needed a way to prevent it. For the Scottish physiologist tasked with finding a solution, it would take multiple tests—and 85 goats—to find a method to avoid the excruciating condition.
Any person working under compressed air is subject to decompression sickness–this is especially true for divers, who in order to dive deep need to breathe higher levels of compressed air in order to overcome ambient sea pressure. As divers on the bottom breath compressed air, they notice nothing–the air seems the same as it would on the surface. However, as a diver surfaces and the water pressure lessens, the gasses of compressed air the diver imbibed come out of solution forming bubbles, much the way a bottle of soda water does when the cap is opened.
Of the various gasses inside the bubbles, oxygen is easily absorbed by the body, carbon dioxide is readily expelled, but bubbles of nitrogen linger. These travel through the body and lodge into joints, the spinal column and organs. Those afflicted with decompression sickness experience a variety of symptoms including dizziness, double vision, severe pains, blindness and paralysis. Death was common. Decompression sickness was also known as diver’s palsy and caisson’s disease, since it was first diagnosed among workers who were building the Brooklyn Bridge under compressed air. But it is most commonly called the bends, due to the contorted position victims often took.
In the early 20th century there was no known way to prevent the bends. If divers surfaced and showed symptoms, they were often sent back down to the bottom or placed into a recompression chamber, nicknamed a “diver’s oven,” to breathe compressed air which forced the nitrogen bubbles in their bodies back into solution. Then they were decompressed by trial and error. The most common advice of the day was to gradually raise a diver by one atmosphere of pressure every 20 minutes, which hardly ever worked.
In 1905, the British Admiralty commissioned the Scottish physiologist John Scott Haldane to solve the problem. Haldane at that time was known for his experiments in combating noxious gasses in mines and his studies on respiration. Not one to shy from practical experimentation, he and a colleague sealed themselves in an air-tight box they dubbed the “coffin” and recorded their reactions as they ran out of breathable air. The Haldane family motto, was “Suffer.”
Haldane coordinated test dives with the Royal Navy, reviewed the medical literature, and interviewed divers. He learned that decompression sickness never occurred when a diver stayed above 33 feet. The compressed air that was delivered to divers at that depth was at a pressure of about two atmospheres, double the air pressure on the surface. Haldane reasoned that if a diver can surface after being exposed to double the air pressure with no ill effects, then any human could withstand an immediate drop in air pressure by half no matter the depth.
For example, if a diver descends to 300 feet, the volume of compressed air necessary to overcome the water pressure is just over 148 pounds per square inch (psi). Instead of coming up gradually, a diver may ascend immediately to 134 feet where the pressure is 74 psi, half. Then after waiting for a time to allow the body to adjust and dissipate bubbles, the diver may ascend to 51 feet, where the pressure is just over 37 psi, wait, and so on until he was able to surface. Haldane dubbed his theory staged decompression.
To test his hypothesis, Haldane ordered experiments to be performed at the Lister Institute of Preventative Medicine in London by Lieutenant Guybon Damant of the Royal Navy, an expert diver and amateur scientist, and the physiologist Edwin Arthur Boycott. The researchers first experimented on mice, rats, guinea-pigs and an old hen by placing them in a large experimental air tank, filling it with compressed air, then evacuating the air. The results were inconclusive since these smaller-bodied creatures exchanged gas more rapidly than humans.
The researchers considered alternatives such as monkeys, dogs and pigs. But these were either too small, difficult to obtain or had respiratory exchange rates far different from humans. At last they settled on goats which they calculated had a respiratory exchange rate 1.7 times that of an adult human male.
A herd of 85 goats was assembled at Lister for some grim experiments. The researchers put groups of up to eight goats inside the chamber, delivered compressed air, waited, and then normalized pressure before releasing them into the institute’s yard for observation.
Just as in humans, the goats had different kinds of symptoms indicating the bends. Some refused food. Others bleated in pain. Some became paralyzed (both temporary and permanent). Others showed injury in the knees (a common occurrence of the bends as bubbles would lodge in the joints). Some suffered shortness of breath and labored breathing. Others died. The researchers were not completely devoid of compassion. They attempted to limit experiments to what they deemed would not outright kill the goats, and those that were in great distress were euthanized. At the conclusion of all these experiments there was one surviving goat, which was adopted by Lieutenant Damant as a pet. It was in this way that the researchers confirmed that those goats which were staged decompressed did not suffer from the bends.
The next step was human testing. Lieutenant Damant and Warrant Officer Andrew Catto, an expert diver, volunteered for the job. Like the goats, they entered the experimental chamber and subjected themselves to bouts of compressed air of up to just over 94 psi from which they were staged decompressed. After repeated trials, there were no signs of the bends. Now it was time for real world experiments.
In late August 1906, Haldane, Catto, and Damant sailed the torpedo boat HMS Spanker to the deep waters of Loch Striven, a finger off the Firth of Clyde. Damant and Catto suited up into the bulky diving dress which in air weighed nearly 200 pounds. The divers were connected physically to the Spanker by an air hose and lifeline, the latter of which was threaded with a copper wire that allowed for telephone communication with the surface.
Tests dives were conducted by Catto and Damant who stood knee deep in the muck of the loch for up to an hour. When the time was up, Damant, who descended to 90 feet, was raised to 30 feet which was calculated to be the shallowest depth he could safely decompress. He held a shot line and waved about his limbs vigorously with the idea that this would help disperse nitrogen bubbles faster. Five minutes later, he was hauled to 10 feet. There he waited another 10 minutes before he was raised to the surface. There were no signs of the bends.
Testing continued for over a week, but not all went as planned. On the afternoon of August 28, Catto dove to 180 feet and worked on attaching a weight to a hawser for 12 minutes in order to simulate realistic conditions. As he ascended he found that his lifeline had become entangled. It was not a terrible tangle, but this was at an unprecedented depth and the pumps, which were hand cranked affairs, had trouble delivering the appropriate amount of air. This made Catto particularly sluggish.
Catto ultimately was able to untangle his line. By the time he was untangled, he had been on the bottom for 28 minutes. No human had ever been exposed to such levels of compressed air (over 90 psi) in real-world conditions for so long. When raising Catto, the researchers took great care and stage decompressed him with nine stops. It took Catto 90 minutes to reach the surface. The diver showed no sign of the bends, just exhaustion. Catto dove the next day, and three days later, Damant descended to an unprecedented depth of 210 feet, a world record. He surfaced with no signs of decompression sickness.
Testing was a complete success. Haldane published a series of diving tables which were quickly adopted by Britain and soon after by divers worldwide. These tables formed the basis of the essential rules of how to safely raise deep sea divers.
Staged decompression is still used today. On September 18, 2014, Egyptian diver Ahmed Gabr dove 332.35 meters (1,090 feet) in the Red Sea, setting a world record for deep sea scuba diving. The ambient sea pressure was over 472 psi. While it took Gabr 14 minutes to reach that depth, he spent 13.5 hours decompressing to the surface.
Joseph A. Williams is the author of The Sunken Gold: A Story of World War I, Espionage, and the Greatest Treasure Salvage in History and Seventeen Fathoms Deep: The Saga of the Submarine S-4 Disaster.