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Looking Back On Innovating Decompression Protocols to Expedite Water Exits

by Bret Gilliam:
Bret Gilliam
The era of dive tables as the only method of calculating dive plans is one that is largely forgotten by many in the “modern” world of electronic diving computers and the plethora of algorithms and deco models that now are available.

I have long been an advocate for embracing innovation and new technologies, including being a prominent spokesperson for transitioning to dive computers, nitrox, mixed gases for deep diving, and rebreathers beginning in the late 1980s.

But my first involvement with deviations from standard practices was back in January of 1971 working on an experimental Navy deep diving project where we were assigned to film fast attack submarines in the open ocean at depths that eventually took us past 500 feet. At the time, all Navy diving was done on dive tables and there were very few choices.

We had “standard” single dive exposure, “repetitive” multi-dive exposure, “exceptional” exposure, and “heliox” that employed helium with oxygen to manage both narcosis and O2 toxicity issues. Of course, there were also tables to default to in the event of omitted decompression due to contingencies. But it was a short menu.

For the most part, these tables served us pretty well. One thing that is interesting to note is that the standard maximum oxygen partial pressure then was a PO2 of 2.0 ATA. This allowed air diving to 300 feet. Later the PO2 limits were reduced to 1.6ATA but that was derived from NOAA protocols that determined that some of the population could not tolerate higher PO2s.

In military diving when I came into the project, the governing protocols tended to be determined by the priority of the project as this was during the height of the Cold War era and making fast attack submarines as undetectable as possible was right at the top of the list. So we were encouraged to innovate as necessary to get the job done. In retrospect, it’s also worth noting that our dive team was probably considered to be “expendable” in the pecking order of achieving the outcome and we were very much aware of that in short order.

Most Navy divers were tethered and on surface supply breathing gas then except for shallow scuba work and some one atmosphere 100% O2 rebreather projects. (Of course, Sea Lab’s saturation project preceded us but the divers were basically confined within a restricted swimming range of the habitat.) We were some of the first teams that would work untethered, on self-contained multiple cylinder equipment packages and without the benefits of removal from the ocean for surface decompression. There is much to be learned from a variety of the departures from standard practice and some of the internal controversies that ensued, but the “bottom line” was the priority of the mission to get us below the deep scattering layer of ocean thermoclines (typically first encountered in the Caribbean below 500 fsw) and get the film work done for evaluation that would drive changes in nuclear submarine design to make them quieter and undetectable to the Soviets.

I was assigned to a team working in the Virgin Islands Trench, over 10,000 foot depths, while other teams were doing similar work off Andros Island in the Bahamas. Those teams included such pioneers as Jordan Klein who was also known for his Hollywood movie work on such films as “Thunderball” that featured Sean Connery’s secret agent James Bond in diving adventures.

When we learned that we would be deployed from surface vessels and would conduct our dives and subsequent long decompressions in the open ocean this initially did not raise any particular warning flags to our team. However, once we began operations we encountered a completely unexpected hazard that was off our “radar”. Everyone is probably aware of the prolific population of oceanic white tip sharks, a pelagic species known for their aggressive behavior. What we didn’t know then was that their aggressiveness was amplified by low frequency sound projections we introduced into the ocean caused by both the instruments used to calibrate various sonar devices and by the subs themselves with their own systems.

It wasn’t until many years later that the relation of low frequency sound, and other stimuli such as the noise made by sinking ships as the hulls and compartments collapsed and aircraft that crashed into the ocean, tended to drive the sharks into far more excessive threats and virtually ended any ability to thwart their aggressive attack behavior. At times, we would enter the water for routine dive system drills and encounter 10-15 oceanics and have virtually no problems with them other than curious close approaches that could be dealt with by a bang on the snout or similar actions. However, once low frequency sound and other stimuli were introduced, both their numbers and aggression tended to go off the scale.

Instead of a few sharks that generally behaved, we would now be faced with scores that could escalate into hundreds at a time. And all seemed hell-bent on biting anything they encountered. They bit the ship’s props, the prop shafts, equipment that was lowered into the water, cables that were deployed, and just about anything that entered their ocean universe. From our rather selfish perspective, we were not particularly concerned about rushes to bite the boarding ladders. But we did care about their tendencies to want to bite us… fins, tanks, camera housings, and most importantly: body parts.

There were times when it was necessary for the deck crews to hang over the working dive decks on the vessel’s sterns to push away the sharks with boat hooks just to make a “hole” in the ocean that we could jump into. It was not for the faint of heart. Once our descents were initiated, we found that the sharks would lose interest in the divers as we passed about 80-foot depths and return to abuse the vessel and its equipment. But when we came back up from deep exposures, we entered long decompression cycles that forced us into a constant war of evasive protective behavior that was more than a bit nuts.

So we began to experiment with anything that would get us out of the water faster without compromising our inherent risk and tolerance of inert breathing gas uptake that dictated our long decompression hangs to out-gas. The first thing we did was initiate contact with some civilian physiologists in Canada at a company called BioLab that were fascinated to have human subjects to beta-test some of their theories about the then largely unproven methods of changing decompression by innovations in usage of both pure oxygen and what they called “oxy-air”. This gas would later become known as “nitrox” or “enriched air”. Hell, they could have called it “magical mystery” gas as far as we were concerned if it got us out of the water faster and away from the munching predator sharks that never ceased trying to eat our equipment… and us… during the long hangs.

The first deviation from Navy protocol was to begin switching to oxygen as deep as 60 feet… a PO2 of 2.8 ATA. That exceeded the allowable maximum oxygen exposure for working divers but was exactly the same as what divers breathed if removed to the safety and comfort of a decompression chamber. We adopted a practice of as little physical exertion as possible to minimize carbon dioxide production (CO2) that was known to be a triggering influence for O2 toxicity and seizures. Our methods worked and that cut our deco hangs by as much as 50%.

The next innovation was to switch to “oxy-air” or nitrox mixes in deeper depths while adjusting the PO2 levels to our tolerance. This even more dramatically cut our deco times.

Also remember that this was January 1971, over 44 years ago. There were no cell phones, no Sat-Phones, barely any land phones on St. Croix and calling Toronto in Canada was absurdly expensive. There was no email or fax to quickly communicate the results of our daily dives and deco results so sometimes our dialogue was accomplished by “snail mail” and it could take weeks for our feedback and BioLab’s suggestions to be exchanged.

On occasions when we could get access to phones, we’d call in following a new beta-test of a suggested aggressive deco schedule and when the phone would be answered on the other end we’d detect obvious surprise that we had somehow managed to survive. But that quickly moved on to a conversation about the next suggested evolution. It was an interesting process but ultimately effective. It laid the foundational groundwork for major changes in diving.

But most importantly to our dive teams, it got us out of the water faster and away from our antagonist shark partners that we shared the ocean with.

Later, NOAA picked up where we left off and when the first generation of computers allowed algorithmic experimentation on deco models using early electronic “real time” diving computers, the revolution really took off. Much credit is owed to the late Dr. Bill Hamilton in the U.S. and the late Dr. Albert Buhlmann in Switzerland for their pioneering work in underwater physiology and deco modeling. I was pleased and proud to have known both men as friends and professional colleagues. Their work forever changed how we dive today.

Looking back on how we arrived where diving technology is today is revealing. For our dive teams nearly 45 years ago, it was prompted by adaptions aimed at self-survival and the methods worked. That’s a “bottom line” that increased our “bottom time” at depth while dramatically reducing our “hang time”.

I’m sure the oceanic white tip sharks missed us. But we were not missing our prolonged time with them…


Bret GilliamBret Gilliam was the founder of TDI and the other agencies of International Training. He began diving in 1958 and his professional diving career in 1971 with the Navy project. Since then he has been involved in every segment of the diving industry including retail and resorts, military and commercial operations, filmmaking, publishing, manufacturing, diving ship and liveaboard design and operations, as well as legal consulting in litigation procedures. Along the way he has logged over 18,000 dives. He was inducted into Diving’s Hall of Fame in 2012 by the AUAS as the Recipient of their NOGI Award for Diving Sports/Education. After nearly 25 years of living in the Caribbean and equatorial regions of the world, he now makes his home in Maine and travels internationally on diving projects.

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