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Excerpted from The History of Oilfield Diving: An Industrial Adventure
by Christopher Swann (Oceanaut Press)
by Christopher Swann (Oceanaut Press)
In 1965, after chamber dives to 600'/183M and 800'/244M at the Royal Naval Physiological Laboratory, the diving vessel HMS Reclaim steamed to the Mediterranean for a series of dives off Toulon. The purpose of the exercise was to prepare for the pending 600'/183M submarine escape trials, for which it was considered necessary to station a safety diver outside the escape compartment. Eighteen divers went to 600'/183M for one hour, at the time the longest dives made to that depth. The series was preceded by trials in Norway to 400-600'/123-183M, and two separate trials off Tenerife in the Canary Islands to 600'/183M for periods of less than one hour.
The Submersible Decompression Chamber (SDC) was put into the water with the bottom just below the surface, the hatch open. The divers started the dive breathing the air of the SDC, then blew in helium to lower the partial pressure of oxygen and keep out the water as the bell plummeted down the shot-line at 120'/36M per minute. They knew the helium had displaced the air when a helium-filled condom dropped to the bottom of the SDC.
At 600'/183M, helium tremors complicated the otherwise simple task of putting on the wraparound full-face masks. Each diver worked in the water for 30 minutes, breathing through an umbilical, with two bottles of emergency gas on his back. Television cameras inside and outside the SDC monitored the dive. The divers wore Avon dry suits with two layers of thick underwear, one of wool, the other of fur. One diver, who discovered that French pharmacies sold small hot water bottles for babies, bought a supply, filled them with boiling water and strapped them round his waist.
The chamber on Reclaim being rated to just 300'/91M, the divers took their initial decompression in the SDC, starting with the first stop at 400'/122M.
"We had to fiddle the tables to get up to 300 feet as quickly as we could without doing too many in-water stops, but we had to do some," said Cyril Lafferty, one of the divers. "There was no heating in those days so we were really cold."
At 300'/91M, the divers sealed the SDC. It was then winched on board and mated to the chamber, and the divers transferred under pressure for the remaining 36 hours of decompression. The conditions were primitive. A French doctor who visited the ship with Cousteau remarked that the goats he used for his chamber experiments enjoyed greater comfort.
Although the subjects at RNPL had spent four hours at 600'/183M, the trials team limited the offshore dives to one hour. It proved a wise decision. Despite the success of the four-hour schedule in the laboratory, in the sea the one-hour schedule produced numerous bends. Originally, diving physiologists thought it would be unnecessary to carry out a recompression to greater than half the depth of the dive. But in the Toulon trials, Petty Officer Charlwood, suffering from a serious bend which did not respond to recompression to 300'/91M, had to be put back in the SDC and lowered to 455'/139M before he obtained relief — communicated to the surface over the video-link by a thumbs-up and a big grin. Given the extreme risk of an even deeper in-water treatment, the incident put paid to any idea of extending the trials to 800'/244M.
In another incident, a diver reported a bend immediately after a dive. He was put in the standby chamber, which was large, and as was routine in those days was recompressed to 165'/50M on air. He had of course been diving on helium. The deeper he was taken, however, the worse he got, until eventually he lost the use of his limbs and began to vomit.
Dr David Elliott, the medical officer, then decided to take the diver from 165'/50M to 300'/91M, with the diver breathing helium-oxygen from a mask. But because the diver was still vomiting, this did not work. Accordingly, Syrl Williams and Mike Kettle of the Admiralty Experimental Diving Unit took the ingenious step of rigging a supply hose and an outlet hose to one of the chamber locks, with the supply at the top and the outlet at the bottom. By slowly piping a 10% oxygen, 90% helium mixture into the lock, while simultaneously monitoring the oxygen percentage of the exhaust gas as it dropped from 21% to 10% and watching, through a port, the slow descent of a helium-filled condom that floated on the surface of the air, they replaced the air with helium-oxygen. The diver recovered.
As Lafferty recounted, Dr Elliott then had to work out an ad-hoc saturation decompression for him. "It was really hairy, but it has been a very useful case in that a lot of work has been done around it since. We realised that if you have a helium bubble and you then breathe nitrogen, the nitrogen will diffuse into the bubble and make it larger and the symptoms will become even worse; whereas the reverse happens if you’ve got a nitrogen bubble and you treat the man on helium: you decrease the size of the nitrogen bubble. That’s why we’ve now started using helium for treatment of most air bends."
In the end the submarine escape trials went ahead without the divers, on the ground that they would be running a greater risk than would the escaping submariners. Although escape trials were carried out in July 1965 from 450'/137M, the 600'/183M escapes did not take place until 1970. The submariners were compressed with air, presumably because by then it was known that rapid pressurisation with helium would produce severe HPNS. In effect, the escapes were no-stop air bounce dives, the exposure being so short that nitrogen narcosis, while present, did not have time to exert a debilitating effect. Wearing escape suits fitted with a hood, a plastic faceplate and a buoyancy stole, the submariners compressed to 600'/183M, locked out of the submarine and ascended to the surface, all in the astonishing time of 104 seconds.
