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US Navy Mixed-Gasses?

Discussion in 'Advanced Scuba' started by Trace Malinowski, Aug 25, 2018.

  1. Trace Malinowski

    Trace Malinowski Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Alexandria Bay, NY
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    @Akimbo, @Capt Jim Wyatt, or any other US Navy diver:

    What gas mixtures did you most often use in the US Navy for diving between 200 and 300 feet? I'm interested in how a US Navy dive may have compared with technical diving today. Suppose you were looking at a typical advanced trimix/tech 2 depth and duration of 250 feet for 20 - 30 minutes to complete a simple task. What kind of job might that be for you guys? What gas would you select? What sort of schedule might a diver do?

    Most of us who have used US Navy tables have only used them for air diving. Beyond air, we don't often hear about naval mixed gas diving. Is there anything tech divers might find interesting from your experiences as military divers?
     
  2. Akimbo

    Akimbo Just a diver Staff Member ScubaBoard Supporter

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    Except for some training dives in one of these semi-closed Mark V Helium Hats all my navy mixed gas dives were in sat where we shot for 0.3-0.5 ATA.

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    Commercial bounce dives generally shot for between 1.6 and 2.0 PPO2 (open circuit, surface supplied) in the early days of the offshore oil industry -- but 2.0 ATA was the operational limit then. I saw one French company going up to 3.0 surface supplied, but never worked for them.

    You can find the current US Navy recommendation in the Diving Manual, Rev 7A which is online.
     
    northernone and Trace Malinowski like this.
  3. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

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    @Akimbo all heliox for ease of mixing though right?
     
  4. Wookie

    Wookie Curmudgeon Apprentice ScubaBoard Business Sponsor ScubaBoard Supporter

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    There is a procedure for trimix diving on closed circuit, but for surface supply, heliox is correct.

    Scuba allows for air and nitrox.

    Edit: My bad, misread the table. HeO2 is correct. Trimix is not allowed in any breathing mode.
     
    tbone1004 likes this.
  5. Akimbo

    Akimbo Just a diver Staff Member ScubaBoard Supporter

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    To be accurate, it is more complicated (some of this @TBone already knows but I'll go over it for others). Historically, I would "guess" that HeO2 was chosen over Trimix due to unknown (unproven) physiological concerns. The investigation into using Helium-Oxygen to prevent Nitrogen narcosis was first suggested during the salvage of the submarine F-4. She sank in 1915 off Pearl Harbor Hawaii in 306'/93M of water. See: US Navy Experimental Diving Unit

    I imagine that analysis was a relatively minor consideration because their understanding of ingassing and outgassing rates for Helium was unproven and decompression calculations were based on assumptions from animal studies. The calculations were entirely manual (probably aided by slide-rules). Helium was not nearly as expensive for the US government since there was more supply than demand. Significant Helium reserves were discovered in natural gas wells in the US in 1903. The Helium Act in 1925 banned exporting Helium. As a result, it was impractical for other countries to experiment with it.

    The vast majority of Helium used for diving today is by commercial diving companies providing services to the offshore oil industry. Of that, the vast majority is used in saturation diving and related work including subsea pipeline welding operations. The quantities required are so vast that helium reclamation and surface-based recirculating systems for diver's breathing gas was implemented decades ago.

    Today, the main reason for using HeO2 in sat is to reduce WOB (Work Of Breathing). Remember that divers are working at depth much harder and longer than recreational rebreather divers. The cost savings would be relatively minor considering that Helium loss rates are typically in the low single digit range (as a percentage). It is also true that mixing and analysis required for Trimix would be much more complex on sat systems because the gas is recycled many times and removing large volumes of Nitrogen for deeper work is slow and expensive.

    From personal experience, I can say the the WOB on HeO2 around 900'/275M is quite noticeable. Just getting geared up and out of the hatch was much more difficult. To me, WOB on HeO2 didn't seem any different around 300'/100m than air at the surface.

    Mixing for open-circuit surface supplied diving (today) is not a problem since industrial gas suppliers can easily provide very precise and complex gas mixes (when relatively large volumes are ordered). Trimix is used commercially by some companies for the small amount of surface supplied mixed gas work done today. Most deep water oil and gas fields have DSVs (Diving Support Vessel) on contract with sat systems onboard so all but the smallest mixed gas jobs are done by them.

    With that background, using Trimix for very shallow sat dives would be possible -- like less than 50M/165'. However, the additional analysis and controls required make it between rare and impractical. It would also make banking gas much more complicated. Removing Nitrogen from breathing mix gas banks for deeper sat dives would also be difficult and expensive when shifting to deeper water. It is much less expensive to run HeO2 with surface-based closed circuit systems than even the lowest Helium content in Trimix on open circuit.

    The first open sea use of Trimix for deep diving that I am aware of was on the Hannes Keller's 1,000' dive in 1962. Keller used Trimix a year or two earlier in lakes and chamber dives.
     
    Trace Malinowski and tbone1004 like this.
  6. Superlyte27

    Superlyte27 Cave Instructor

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    Location: Florida
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    I wasn't in the Navy, but the commercial dive schools were still using Navy protocols in their teaching. My mixed gas dives in the GOM in the late 90's and 2000's were HeliOx at 1.6

    Same reason as above. Trimix wasn't well known or understood and costs didn't matter.
     
  7. Akimbo

    Akimbo Just a diver Staff Member ScubaBoard Supporter

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    Same added perspective for ScubaBoard members would probably help. A lot of factors are involved that are not obvious. First, the vessels to support surface-supplied diving are much larger and have bigger professional crews than most recreational dive boats. Small dive spreads often include a small double lock chamber, two fairly large LP air compressors, umbilicals, HP 6-12 packs for mixed gas and Oxygen, and a small gas control shack.

    full.jpg

    full.jpg

    Then you add hydraulic power packs, large water pumps, welding machines, and more umbilicals for the diver's tools and you are looking at several semis (truck loads) and tons of equipment. Add the deck space and handling machinery required to support the work, plus some means of multi-point mooring -- suddenly the minimum vessels are the 80-120'/25-36M range for small jobs where seas are calm. Now add the cost of the dive team, in$urance, fuel, plus amortizing mobilization and demobilization. The operating cost/hour suddenly makes the price of Helium much less important.

    All of these costs are NOTHING when a platform is offline waiting for the diver to make repairs. I was on a sat job in the 1970s when the operating cost for several vessels was over $2 million/day -- all of it waiting for a single diver to complete a repair.
     
    Trace Malinowski likes this.
  8. Superlyte27

    Superlyte27 Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Florida
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    The small operations only have 1 100 Ton Crane. :)

    We were doing a three man dive team at a power plant in Florida on the way to the real job in the north east of United States. A chain had jumped track on a traveling water screen on the intake. It took us less than 40 minutes to resolve the issue. The bill the company gave me to hand to the plant super was $17k. Inland.

    I can’t imagine what it costs to be idle on a jack up rig in the GoM as every one is in standby mode waiting for some giant issue to get resolved. I loved getting paid for it though.
     
    Trace Malinowski likes this.

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