Before retiring from the Royal Navy this year to join Gas Services Offshore Ltd, I spent my last two years as a Project Officer at the Navy Experimental Diving Unit (NEDU) in Panama City, Florida As part of my duties there, I was responsible for the test and evaluation of diving equipment for potential US Navy use During the latter part of 1986, I evaluated a wide range of military and commercial diving equipment, looking for a new saturation diving rig As a result of that evaluation, we saw that there had been some very significant advances in breathing apparatus technology, particularly with the arrival of the Gas Services Ultraflow 500 Demand Regulator This led us at NEDU to take a fresh look at our published unmanned acceptance criteria (NEDU Report 3–81)

At the same time Dr Clarke, at the Naval Medical Research Institute at Bethesda, Maryland, was conducting a review to see what acceptance criteria they would like to recommend for future procurements or designs of underwater breathing apparatus Shortly, we shall see how NEDU and NAMRI arrived at similar recommendations

But first let us discuss how unmanned testing is done, how we measure the results, and how to interpret those results Then we shall look at some test results and consider NEDU's recommended new performance goals Then briefly we shall see what has made the Ultraflow 500 the super performer that it is.

In conclusion I would like to introduce the secondary life support system (SLS) that Gas Services has developed to provide up to 15 minutes' bail-out duration at 500 MSW, with gas supplied to the diver at a safe minimum inspired temperature even with total umbilical severance


Figure 1 shows a basic breathing simulator A variable speed motor drives a piston with a variable stroke length to ‘inhale’ and ‘exhale’ from the breathing apparatus fitted to a manikin head In this way we can simulate various breathing rates and tidal volumes and so RMV

Figure 2 shows the standardized RMVs and how they relate to diver work rate I have highlighted 62 5 RMV and 75 RMV because they will be significant in our later discussion of US Navy acceptance criteria(Fig 1 and Fig 2 are available in full paper)

Figure 3 shows a schematic of a typical unmanned test facility. This facility would automatically record differential (or changes) in pressure at the oral nasal or mouthpiece and plot a loop against tidal volume as the breathing simulator inhales and exhales The result is the loop shown in Fig 4. From the loops, which are taken at various depths and at each of the RMVs (or diver work rates) that were shown earlier, we can measure the peaks of inhalation resistance and exhalation resistance. The total differential between these peaks is known as the breathing resistance of the UBA The total areas of the loop represent the total additional work that the diver would have to perform to breathe the UBA This is known as the rig's work of breathing

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