Decompression Chamber-homemade

Discussion in 'Do It Yourself - DIY' started by Lawman, Jan 21, 2005.

  1. Lawman

    Lawman Senior Member

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    Here in Central Michigan we don't have a decompression chamber. Our dive club would like to build our own. We have a 2000 gal fiberglass septic tank and an 8 hp aircompresser. We thought with a few fittings and a larger hatch we could adapt our tank and save a ton of $$$$. Does anyone have any ideas that might help?
     
  2. roakey

    roakey Old, not bold diver ScubaBoard Supporter

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    Does anyone know where the link is to the homemade decompression chamber that blew up that killed someone?
     
  3. String

    String Scuba Instructor

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  4. jbd

    jbd Scuba Instructor

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    I remember that thread, but IIRC the explosion was linked to the use of 100% O2.
     
  5. jbd

    jbd Scuba Instructor

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    I took the post as being serious. Conceptually a deco chamber is quite a simple appartaus. The only thing I wonder is how long will it take them to pressurized a tank that size with the compressor they have? Curious also if they intend on using O2?
     
  6. Gary D.

    Gary D. ScubaBoard Supporter ScubaBoard Supporter

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    Check the NASA web site. They are always looking for more efficient ways to get items into orbit.

    Go buy a used one. They're affordable.

    Gary D.
     
  7. miketsp

    miketsp Great White

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  8. simbrooks

    simbrooks Snr LayZboy Meteorologist ScubaBoard Supporter

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    There was one on ebay recently, although i cant find the thread, but i know there was one on here! ;)
     
  9. fdog

    fdog ScubaBoard Supporter ScubaBoard Supporter

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    It would be cheaper to buy used, than build from scratch and meet the ASME pressure vessel (for human use) specs, have the redundant gas supplies, paint off-gas requirements, keep OSHA happy...windows...

    Not to mention installing a medical director (M.D.) and a training program so you can actually use the thing. Since putting someone in is "medical treatment" under order of a physician.

    IIRC, test pressure has to be around 2.5 times working pressure. To run a Table 2A that'd be 185 psig. So the septic tank would have to pass this (questionable), and I'm not sure fiberglass is even a permisable material under ASME.

    All the best, James

    PS Besides there's just something wrong about it...."Here ya go, we'll fix you up in this sh*! tank"
     
  10. rmediver2002

    rmediver2002 Scuba Instructor

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    Are you planning on using this chamber for treatment or some type of familiarization dives?

    It is doubtful the tank will have enough integrity to hold the pressure required for treatments (around 100 psi for TT-6A) and 26.7 psi for standard treatment tables (TT-5 and TT-6)

    Your compressor (8 HP) is more than likely only going to provide between 6 and 8 cubic feet a minute so your decent time is going to be very slow and the compressor is going to be running at 100% duty cylcle so the air is going to be extremely hot (this temperature is going to be a big issue with your compressor especially if it is oil free / teflon rings)

    Once the chamber is at depth your flow from the compressor is not going to be enough to allow venting of the chamber, this is going to cause a build up of CO2 from the exhaled air from the divers inside. Another more serious issue would be a build up of O2 if you are having the patients breath O2 during the treatment.

    If you do decide you want to try and see if the vessel will hold pressure, first fill it with water. You can increase the internal pressure slowly using a pressure washer, having the container filled with water will greatly decrease the amount of energy released in the event of a rupture but you really need to be careful...

    Before considering putting any human being inside of any pressure vessel make sure you consider all of the possible hazards (rapid depressurization, O2 toxicity, CO2 toxicity, decompression sickness, hyperthermia, dehydration, waste elimination, etc...) you also need to consider the legal ramifications of any such endevor...

    The advice above about begining a collection for a refurbished chamber or looking into government surplus is the best advice so far. Even new your only looking at between 25,000 and 35,000 for a decently equiped double lock chamber.
     
  11. Brandon

    Brandon Banned from the LDS... ScubaBoard Supporter

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    I imagine you might have some success with this...

    Until the accident.

    Then I wouldn't want to be in your shoes.

    This just doesn't seem to be the kind of thing to homebrew... safety/liability issues all around that may be very difficult to work around.

    -B.
     
  12. roakey

    roakey Old, not bold diver ScubaBoard Supporter

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    With over 700 posts by the person establishing the thread, I took the post as being serious too. So, given that we're discussing a fiberglass septic tank, I felt my response was appropriate.

    Roak
     
  13. Brandon

    Brandon Banned from the LDS... ScubaBoard Supporter

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    Well... the other problem is that a septic tank isn't a pressure vessel.

    I couldn't google a PSI rating for a fiberglass septic tank, but I imagine it isn't much, if it's even computed.... I found some info about the water holding tanks, which are very similar in terms of construction, and the tested pressure was very low, far below what you'd need for a deco chamber.

    Think about the application these systems are used for: residential or small commercial water/septic holding tanks. The contents are rarely under much pressure... maybe just a little bit more then your tap water is... max.

    All the deco chamber pictures I've seen look like the chamber is made out of steel... and fairly thick steel at that (judging from the viewing portals). Just compare the weights... a normal deco chamber weighs in somewhere around 5500 - 6500 pounds... that 2,000 gallon fiberglass septic tank weighs about 550 pounds. That'd make the wall thickness of your septic tank what.. 1/2" thick? Doubtful you're going to hold much pressure with that, considering the real chambers are made out of several inches of steel...

    There's no way... I'd say they're similar in cylinder size only.

    Maybe I'm way off... there's plenty of more experienced folks on this board who are better versed in these matters... but this is what common sense and a little bit of reason is telling me.

    -B
     
  14. simbrooks

    simbrooks Snr LayZboy Meteorologist ScubaBoard Supporter

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    Lets just say that septic tanks are for use with hydrostatic pressure upto only 15-20 deep, really not meant for pressure.
     
  15. fdog

    fdog ScubaBoard Supporter ScubaBoard Supporter

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    Lawman, just like Roakey, I assumed you were serious by your history.

    So, here's were the start: $165 to buy the "bible of chamber construction" .

    Best of luck!

    All the best, James
     
  16. rmediver2002

    rmediver2002 Scuba Instructor

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    just some more information for those interested:

    Recompressions chambers are low pressure vessels, but since they are used for human occupancy they are signifigantly over engineered for safety.

    Chambers are built from steel, aluminium (most common), lexan, and more recently synthetic cloth.

    Most systems are designed to operate to 165 FSW (73.425 psi) or 60 FSW (26.7 psi)

    This is an example of a portable system we used in the military, it is quite expensive since it was designed to military specification not produced for sale.


    http://www.hqmc.usmc.mil/factfile.n...b6bb2f0c31edc4f28525628a004fba06?OpenDocument

    This is am example of a cloth / transport chamber, the US Navy has also purchased several of these and already successfully used it to transport a sick fisherman / diver in Hawaii

    http://www.nautilussystems.com/chambers/chamber-frame.htm

    This shows a typical 220 cubic foot double lock chamber, the most commonly used military and commercial diving chamber. For military and commercial operations the chamber is used as a tool to facilitate surface decompression as well as a device for treating diving injuries.

    http://www.ambergriscaye.com/pages/town/hyperbar.html

    Here is one of the most extensive types of systems you will find, a saturation diving system. These systems include pressurized bells for transporting the divers under pressure to and from the work site as well as pressurized living quarters.

    http://www.nut.no/html/saturation_diving_systems.html

    Here is a photo of the ocean test facility at the Navy Experiemental Diving Unit, a floodable chamber allowing equipment to be tested in a controlled environment at simulated water depths at a variety of temperature extremes.

    http://www.supsalv.org/nedu/images/Photos/Osf10.jpg
     
  17. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

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    Even with only an 8 cu ft per minute compressor, you could still use an airbank to provide the air required to blow the chamber down to the required depth and to ventilate the chamber as needed. With a big enough air bank and enough time between cycles, you could do it with 3.5 cfm compressor.

    The pressure vessel itself is the big issue. The 75 psi needed to reach 165 ft. is no big deal with a small pressure vessel, but the stresses involved could pose a real challenge for a 2000 gallon septic tank. The effects of rapid decompression (ie. a near instaneous ascent from 165 ft) if it failed would be a real killer even if it did not explode.
     
  18. diversteve

    diversteve Moderator Staff Member

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  19. Robert Phillips

    Robert Phillips Loggerhead Turtle

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    Come on guys, Lawman is the Troll King, but you all took the bait!
     
  20. Rick Inman

    Rick Inman Advisor ScubaBoard Supporter

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    Hey, I got a good name for your new chamber:

    Darwin Hall! :D
     

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