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What is Saturation Diving?

Discussion in 'Commercial Divers' started by Akimbo, Oct 13, 2013.

  1. Akimbo

    Akimbo Lift to Freedom Volunteer Staff Member ScubaBoard Supporter

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    A lot of divers are not sure what Saturation diving is so I thought a quick summary might be useful.

    Saturation diving was developed by the US Navy's Captain George F. Bond (affectionately known as Papa Topside) in the 1960s. All divers know that the deeper we go and longer we stay, the longer decompression will be. That is true until we stay long enough for our tissues to become fully saturated, as they are normally at sea level. At that point decompression times no longer increase.

    Theoretical saturation time is about 24 hours. As a result, it does not matter if you stay 24 hours, 24 days, or 24 months, the decompression time is the same. In practice, dives deeper than a few hours at 300' will often push you onto a sat decompression table. Typical sats are 2-4 weeks on the bottom (plus decompression) or until the job is done. Many jobs last much longer so crews are swapped out through various chambers connected to the complex.

    Recreational divers are probably more familiar with habitat-based scientific saturation dives, but they are relatively shallow and rare. Commercial sat crews live in chambers on deck pressurized to their holding depth, typically at the shallow range of their working depth. They transfer to the work site via a diving bell, lock out, and typically spend 6-12 hours between crew changes. They all wear lightweight hats and hot water suits breathing HeO2 mixtures typically from 0.3 to 0.8 ATA O2, almost always using a closed-circuit surface-based recirculating system to conserve expensive Helium.

    I am often asked by recreational divers how to figure out decompression from a saturation dive. Most are shocked when I rattle off the table to them:

    US Navy Diving Manual Rev. 6 with Change A, Table 15-9. Saturation Decompression Rates. Page 15-33

    full.jpg

    The US Navy and some commercial supervisors will stop decompression during sleeping hours to prevent joint hits caused by compromised blood flow from sleeping in odd positions. Some will make divers wake up during the night to limber-up. Some ignore rest stops entirely. Bottom line is decompression from a 1000' sat can take 182½ hours decompression (travel) time or a little over 7½ days. Most that I have seen are closer to 10 days.

    Divers don't mind decompression that much because they are still getting depth pay. Diving operators don't want to stop the whole crew from decompressing in order to treat a diver that slept on his arm (how cute) since it holds up the whole parade. Often a new sat crew is standing by to press-down within hours of the crew decompressing out.

    What surprises even more people is how slow sat divers descent:
    Table 15-6. Saturation Diving Compression Rates. Page 15-24

    full.jpg

    The reason for slow compression rates is to prevent or limit HPNS (High Pressure Nervous System) symptoms. It also prevents tissue cushioning joints from compressing to the point that it hurts like a 90 year old with severe arthritis (compression arthralgia).

    This "summary" could go on forever but another important thing to understand is temperature. Helium not only makes your voice sound like Donald Duck but it conducts heat away from the body much faster. As a result, shirt-sleeve comfortable in the chamber is around 90° F. You would literally catch pneumonia after as little as half an hour when deeper than around 600' breathing unheated gas. The Navy has a table for that too, see Table 15-1. Guidelines for Minimum Inspired HeO2 Temperatures for Saturation Depths Between 350 and 1,500 fsw. Page 15-10.

    There are other tables out there but this will give you the idea. I am sure a lot of divers on this forum can add tons of information to the overview, and I hope they do.

    This is a fairly decent BBC documentary:
    BBC Real Men Series Saturation Diving - YouTube


    Edit: Tables updated for XenForo BB standard
     
    Last edited: Jun 14, 2017
  2. j2s

    j2s Loggerhead Turtle

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    When your finger tips are all wrinkly and your mother tells you, you have to come out of the water !!!!! ;P
     
    dberry likes this.
  3. 69jme69

    69jme69 Angel Fish

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    Location: Stonehouse Scotland
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    The company I work for has compression rates at 1 min per meter with a 10 min hold at 10msw ,then 1 hour hold at 100msw followed by 1hour holds for every 50msw thereafter down to a max of 360msw
    decompression rates are fairly similar to usn7
    360msw to 60msw 32 mins per mtrn,60msw to 30msw 32 mins per mtr, 30msw to 15msw 49mins per mtr and 15msw to the surface 65 mins per meter
    storage ppo2 is .40 to .45
    diving is .6 to .8 Heliox conducts heat approximately 7 times faster than air and the divers in sat can feel 1 degree difference in temperature as sated in the post above
    the body also metabolises quicker therefore sat divers need a higher intake of calories ..5-6000+ per day isn't unheard of .. It only takes 2 1/2 days to get back from the moon whereas a dive to 75msw takes 3days 10 hours to reach the surface
     
    Blasto likes this.
  4. Carlos Danger

    Carlos Danger Manta Ray

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    Fascinating video; truly amazing stuff!!! Much respect to those who do this work; hope they are getting paid well. Wonder if these guys go rec diving when they are on vacation?

    Welp, guess I'll just go back to feeling small and insignificant now... :frown:
     
    Last edited: Nov 6, 2013
    John C. Ratliff likes this.
  5. DCBC

    DCBC Banned

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    Welcome aboard 69jme69.

    It's common for a company involved in saturation diving to have their own decompression schedule. Like Akimbo stated, as far as the USN is concerned they advocate a compression rate of:

    0 – 60 fsw 0.5 – 30 fsw/min
    60 – 250 fsw 0.5 – 10 fsw/min
    250 – 750 fsw 0.5 – 3 fsw/min
    750 – 1000 fsw 0.5 – 2 fsw/min

    and a decompression rate of:

    1,600 – 200 fsw 6 feet per hour
    200 – 100 fsw 5 feet per hour
    100 – 50 fsw 4 feet per hour
    50 – 0 fsw 3 feet per hour

    Traveling is only conducted for 16 hours in each 24-hour period. Table 15‑9 is used for Saturation. Table 7 is a Treatment Table.

    Most companies are much more conservative than this. It would appear that your company is more conservative with the compression rate than the rate of decompression when compared to the USN schedules.

    PPCO2 is kept below a limit of 0.005 (equivalent to 0.5 per cent at 1 ATA). For shorter periods a higher limit, 0.015-0.02 ATA is tolerable.
     
    Last edited: Nov 6, 2013
  6. 69jme69

    69jme69 Angel Fish

    # of Dives: I just don't log dives
    Location: Stonehouse Scotland
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    I forgot to say that we also only travel for 16hrs in any 24 hr period with a 6hr hold after 8hrs of travel followed by a 2 hr hold after a further 8hrs of travel and that cycle continues until the surface ,most companies I have worked for have tables loosely based on USN tables ( there was no other bench mark)..in the North Sea everything is fairly conservative where job constraints are offset against a increased safety regime
    Carlos Danger I know a few divers that dive recreationally but I think the vast majority think its like work with out the pay packet :wink:
     
  7. TSandM

    TSandM Missed and loved by many. Rest in Peace

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    Fascinating! Thank you for starting the thread. It had never occurred to me that a helium atmosphere would require a higher ambient temperature, but it makes sense.
     
    Compressor likes this.
  8. DCBC

    DCBC Banned

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    When breathing Helium, optimal working temperature (thermal comfort) can always be problematic. Temperatures may increase between 25°C and 33°C. Any deviation may cause hypothermia/hyperthermia. This can occur rapidly and can easily be missed at the early stage.

    A high carbon dioxide level will lead to hypercapnia and a reduced work capacity. When considering carbon dioxide levels, humidity can be a problem. When using soda lime to remove the CO2, a relative humidity (RH) of over 75 per cent gives better perform­ance. Other absorbents may require different optimal percentages. A higher RH reduces the risk of static sparks (a source of igni­tion in the fire risk zone). The problem with accepting a high RH is the increased risk from certain bacterial and fungal infections, which can be a problem during Sat, so the range chosen is a compromise. With water from wet gear and showering, it's often difficult to keep humidity down to the 60-75 per cent RH range recommended.

    Temperature, humidity, partial pressures, breathing mixtures, equipment and decompression profiles are just a few of the things that are part of the dynamics involved in a productive and safe saturation dive.

    ---------- Post added November 7th, 2013 at 06:51 AM ----------

    On the other hand many of us love to dive and be free of the umbilical... Work is work, fun is fun. [​IMG]
     
  9. Akimbo

    Akimbo Lift to Freedom Volunteer Staff Member ScubaBoard Supporter

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    There are other factors at play than the simple increase in thermal conductivity of Helium. As a reference, pure Helium is 5.9 times as thermally conductive as air. Nitrogen and Oxygen are very close to the same. Water is 24.2x as conductive as air.

    The amount of helium also increases as a percentage because the PPO2 is more or less constant. The 21% O2 in air becomes about 1% Oxygen and 99% Helium at 1000'. I didn't mention it in the OP but the "shirt sleeve comfortable" ambient temperature in the chamber actually increases with depth as the O2 percentage decreases.

    Another factor is that about 50% of heat loss is through respiration. As a result, core temperature is very rapidly lost when breathing HeO2 at depth. This makes people think the heat loss is much higher because we compare our experiences to immersion in water which is much more conductive. The difference is we don't have our lungs full of water.

    Not only does the temperature range go up, but the comfortable range becomes very narrow. A few degrees can make the difference between sweating like a sumo wrestler and shivering. Maintaining +/- ½° F seams to keep the complaining to a minimum.

    It is not an exaggeration to say the saturation diving on a commercial scale could not exist without hot water heated wetsuits. A typical diver gets about 2½ gallons/minute of salt water at 110° F when it hits the suit. That same hot water is used to heat the diving bell and the diver's breathing gas.

    There is a fascinating thread on a sat diver whose umbilical was severed and these factors actually saved his life: http://www.scubaboard.com/forums/ac...20-umbilical-severed-80-meters-north-sea.html
     
    Last edited: Nov 7, 2013
    Compressor and John C. Ratliff like this.
  10. Akimbo

    Akimbo Lift to Freedom Volunteer Staff Member ScubaBoard Supporter

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    That is exactly how I felt when I saw the new Mark I Deep Dive System in 1969. I was a senior in high school and a group of us were invited to FMC near the San Jose (California) airport to see it before it shipped to the Navy. I had dreams of becoming a saturation diver and left with the thought that I could never learn how all that stuff worked. Diving was my life and in a fit of teenage drama I thought it was over.

    ddsmk101.jpg

    --------------- Edit ---------------


    Fast-forward to about the 10:50 mark if you get bored for video of the Mark I DDS.
    The Mark II DDS that I was assigned to a couple of years later is at the 16:15 mark.
     
    Last edited: Oct 12, 2017

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