Q4_Fall_2016_AlertDiver

RESEARCH, EDUCATION & MEDICINE

ADVANCED DIVING

FALL 2016

bell and take over doing compressions and maintaining an

open airway, while the dive team transitioned to the ROV

downline. The bell, along with a support diver, would be

lifted out of the water and the injured diver treated, after

which the bell would be returned to the water for the

remaining dive team’s decompression phase.

Further protocols covered separated- and lost-diver

scenarios as well as out-of-gas emergencies. When in

doubt, all a diver had to do in an emergency was swim

back to the bell, which would be located just above

the wreck.

The bell was loaded with built-in cylinders filled

with the gases required for the dive. Each cylinder

was equipped with multiple regulators on long hoses.

Additional cylinders of deep and intermediate gas

mixes were also available.

ALGORITHM SELECTION

Because of the very strong surface currents that can

occur over the

Britannic

, decompression model safety

factors were considered, and the best protocol was

determined to be one that would promote completion

of as much decompression as possible at deeper

depths where the currents would not be as strong.

Thus we were on the hunt for bubble-based deep-stop

protocols. The varying permeability model (VPM-

B) and reduced gradient bubble model (RGBM)

algorithms used to dictate the deep stops on previous

expeditions were configured with a 10 percent increase

in the “nominal” critical radii of helium and nitrogen

bubbles. These models generated an initial ascent rate

and a deep-stop profile fairly close to a Bühlmann

model with a low gradient factor (e.g., 5 percent). Since

these models were based on real bubble mechanics

and not fudged to Bühlmann, we figured them to

be physiologically better. As a sensibility check we

compared the total run times of these profiles and

found them to be fairly similar to those generated

using the Drogon Dive Planner (DDPLAN) with 5/85

gradient factors, which had been used reasonably

successfully on previous deep projects.

With rebreather scrubber durations taken into

consideration, run times were capped at 40-50 minutes.

Both the Inspiration and JJ scrubbers had been shown

to be good for at least five hours on deep warm-

water dives, due to their efficiency in warm water in

conjunction with the divers’ work rate, which was very

low except during the first 30-40 minutes on the bottom.

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