80cu Tank at 800 Feet ????

[kanonfodr]

Wow, that's some serious chunk of stainless steel there! How long do you stay down when you go?

Ya, exactly how long does a tube trailer last down there??

Peace,
Greg

 

[Jax]

Serious, this gauge gets bolted outside the bell so you can see it through one of the view ports. Some certifying agencies, and diving companies as policy, don’t allow HP gas inside the bell except for bail-out bottles. Industrial gas bottles are wrapped outside the bell for normal oxygen make-up inside the bell atmosphere and emergency pre-mixed HeO2 in case the surface supply fails — like a blown hose or cut umbilical. That way, some hundreds to thousands of cubic feet of gas is available to get the dive(s) back into the bell without having to resort to the puny +/-80 Ft³ of gas in their bail-outs.

Remote-sensing pressure reducing regulators are also outside so only LP gas enters the bell (150-300 PSI). There was no other way to monitor pressure in the onboard banks. We used different gauges in the same housing for the 6000 PSI banks on deeper bells.

Is this making sense or way more than anyone wants to know?

Well, I find it fascinating but I'm weird like that! :blinking:

Do you have any pics? (Said before I go search your profile! :lol

 

[Akimbo]

Well, I find it fascinating but I'm weird like that! :blinking:

Do you have any pics? (Said before I go search your profile! :lol

Not many pix on my profile, I will try to find some good links for you.

Wow, that's some serious chunk of stainless steel there! How long do you stay down when you go?

I just realized I forgot the "how long" part of your question -- Typical is 14-30 days on the bottom, decom in the 2-14 day ballpark depending on depth. "On the bottom" means living in a complex of decompression chambers (not recompression) on deck pressurized to a holding depth, usually a little less than the minimum working depth. Typically, 3 teams of divers will swap for 8-12 hour shifts, 24/7. The actual time of day doesn't mean much. Topside crews are usually 12 (hours) on/12 off. Divers usually get every second or third run offshore in the barrel.

Teams are decompressed out on that 14-30 day cycle and new teams sent in to replace the next as needed. Compression to the 600' range is often in the 24 hour ball park to prevent compression pains and joint damage.

Decompression is continuous, though some operations stop during sleeping hours; at least during the shallower portions. The top secret schedule I see used most often is:

• 6'/hour, to 200 FSW
• 5'/hour, 200-100 FSW
• 4'/hour, 100-50 FSW
• 3'/hour, 50-0 FSW

That's about it. Straight out of the US Navy Diving Manual, Revision 6, 15 April 2008, Page 15-33. You can leave your dive computers home on this one.

Is anyone interested how we monitor diver depth?

Is this too much of a thread Hi-jack? Ask questions in the Commercial forum if you think it is.

 

[Jax]

Not many pix on my profile, I will try to find some good links for you.

I just realized I forgot the "how long" part of your question — Typical is 14-30 days on the bottom, decom in the 2-14 day ballpark depending on depth. "On the bottom" means living in a complex of decompression chambers (not recompression) on deck pressurized to a holding depth, usually a little less than the minimum working depth. Typically, 3 teams of divers will swap for 8-12 hour shifts, 24/7. The actual time of day doesn't mean much. Topside crews are usually 12 (hours) on/12 off. Divers usually get every second or third run offshore in the barrel.

Teams are decompressed out on that 14-30 day cycle and new teams sent in to replace the next as needed. Compression to the 600' range is often in the 24 hour ball park to prevent compression pains and joint damage.

Decompression is continuous, though some operations stop during sleeping hours; at least during the shallower portions. The top secret schedule I see used most often is:

• 6'/hour, to 200 FSW
• 5'/hour, 200-100 FSW
• 4'/hour, 100-50 FSW
• 3'/hour, 50-0 FSW

That's about it. Straight out of the US Navy Diving Manual, Revision 6, 15 April 2008, Page 15-33. You can leave your dive computers home on this one.

Is anyone interested how we monitor diver depth?

Is this too much of a thread Hi-jack? Ask questions in the Commercial forum if you think it is.

Da-emn . . . How long (career-wise) does a diver last? It sure seems like this should be doing a real number on your joints and connective tissues.

And how can this be off-topic? We're still at 800' fsw, right?

 

[eponym]

I'm with Jax. Or split it off and move it to Commercial if you want to.

And curious. How do you monitor diver depth? Sonar?

-Bryan

 

[Akimbo]

Ya, exactly how long does a tube trailer last down there??

Peace,
Greg

We usually figured 1½ Ambient Ft³/minute as an average (screw SAC rates, these guys are working). Helium is expensive enough that most cylinders are pumped down to 100 PSI, or whatever minimum the supplier doesn't penalize for. Most suppliers credit back returned gas, but that doesn't cover shipping costs offshore.

Bigger operations use surface-based closed-circuit gear sometimes called Push-Pull systems. The diver has a demand exhaust regulator and hose to the bell. The gas then passes through a bell-mounted water separator/filter before the negative-biased back-pressure regulator. Think of it something like a backwards Scuba regulator with 2-300' of hose in between. A high purity compressor on the surface boots the pressure back up to 200-500 PSI OBP after it has been scrubbed by the same CO2 and odor absorbent chemicals used on the chambers. O2 is added to maintain a .3 PP02. From there it goes back to the bell/diver via a volume tank.

Bigger, usually ship-based, sat systems often also have helium reclaim systems. Gas from chambers, venting medical/equipment locks, bell mating trunks, and decompression empties into a big flexible bag. The gas is pressurized to 3000 PSI and passes through heat exchangers bathed in liquid Nitrogen. Water vapor, Oxygen, Nitrogen, CO2, and… "shall we say assorted human generated gaseous contaminants" precipitate out. Purified Helium goes back into storage flasks in the lower decks, usually 22-24" in diameter, 12-33' long, and around 3000 PSI.

It is fairly common for these systems to have 10-50 cylinders like these built-in. Ship based systems prefer not to have more than a couple tube trailers on deck at once for stability and deck space is needed for other stuff.

Based on these numbers; you can pick a depth, assume open circuit, one diver in the water, and get pretty close. Example: 1000' = (1,000'/33')+1 ATM = 31.3 ATA x 1½ SCFM = ~47 SCFM or 2,817 Standard Ft³/Hour. Figure you get 22 hours a day with the hatch open and that is ~62,000 Standard Ft³/day. Check my arithmetic but that sounds about right.

Figuring gas loss if you have Push-Pull and Helium reclaim systems is a harder calculation. It depends on how good your crews are, how lucky you are keeping all the machinery running, how much of a tight-arse the company rep is, and not exceeding reclaim capacities.

 

[Akimbo]

I'm with Jax. Or split it off and move it to Commercial if you want to.

And curious. How do you monitor diver depth? Sonar?

-Bryan

Sonar, we are talking commercial divers here! Calibration instruments are 4 Lb malls and adjustable wrenches are called Crescent Hammers -- and even the ends of those are sawed off and pointed rods called Spuds are welded on to align flanges and increase leverage.

Think about it. How would you reliably and simply find the depth a snarky 800 Lb Gorilla at the end of the hose? Use another hose and a precision pressure gauge in the dive shack of course! It is called a pneumo-fathometer. Honestly, it is the only system anyone has found that will survive the abuse. To be fair, these guys are paid to get the job done. Wasting time trying to protect equipment isn't part of the job description.

There is a 3/16 to ¼" diameter hose in the umbilical bundle. The dive super or gas shack operator opens a valve from the manifold that feeds breathing gas to the diver to blow the water out the bottom of the hose. You now have a column of air to the diver's depth. The pneumo hose basically plugs into the bottom of a precision pressure gauge calibrated in Feet or Decimal Meters of sea water. Several gauges can be cross-connected through valves to check for accuracy and as backup in case of failure. No batteries necessary.

Here is a link to a typical portable air box.

Amron International 2 Diver Air Control - Low Pressure

You would think that they would just blow air down a pneumo to save money, right? I did too until I realized that you can stuff the end of the pneumo hose past your neck dam or face seal and breath off it. Just because your gas supply umbilical fails doesn't mean your pneumo hose will. Besides, Air would contaminate bell atmospheres.

To give you an idea, deeper gauges are 16" in diameter, 0.1% accurate, have a mirrored strip and the end of the needle twisted so you can correct for parallax, and the needle rotates 660°. 0-1800 FSW in 1 foot increments is no problem to read.

I tried uploading some photos but the board isn't liking it (yeah yeah, slang I know). I'll try later.

Edit: I just looked at this again. Hope it comes across as "conversational" rather than rude in any way

 

[Jax]

I tried uploading some photos but the board isn’t liking it (yeah yeah, slang I know). I'll try later.

The board's been having problems with uploading pictures lately. I opened a thread in support.

So, is my question next?

 

[Akimbo]

Da-emn . . . How long (career-wise) does a diver last? It sure seems like this should be doing a real number on your joints and connective tissues.

And how can this be off-topic? We're still at 800' fsw, right?

Sorry, had to run off to dinner.

Career-wise, it varies a lot. I know a few guys in their 50s that make it in the barrel now and then while others are out at 30. Saturation divers probably suffer the least from long-term medical problems than any other type of deep diving. There was a lot of concern over aseptic bone narcosis in the mid 1970s, but it appears to have been more related to better diagnostic equipment seeing problems from previous bounce dives than from sat. It isn't often a diver gets hit on a sat run and then it is very mild and immediately treated.

As you can imagine, commercial diving is a pretty physical activity -- as in moving heavy crap to get the job done. No doubt, working smart is key sign to success, but sometimes brut force and ignorance has its place. From my observation, the life-style causes more accomplished divers to leave the industry than anything else. Of course, a lot of people leave at the beginning phases either because the life-style, competitive pressures, and/or simply loose patience before they "break out".

Picture a younger guy who makes a lot of money, has a month off at a time and can't spend anything for the 30 days at work. Alcohol gets to some guys, meeting a mate who would rather have them home doing something less risky, and just wanting a "normal" life are all factors that count far more than medical complications of the profession.

By far, the most common injury among commercial divers is loosing fingers. A lot of the work involves installing some fantastically heavy thing suspended from a crane, guiding the divers verbal commands... did I mention that acoustics in the hat are worse than a toilet bowl, made a little more understandable by a Helium speech unscrambler (Helium = Donald Duck voice), relayed by the diving supervisor, to some guy in the crane's cab who is maybe 60' off the water, on a moving vessel, with a 60 to 300' boom? Add bad visibility to the mix and accidents happen. BTW, even if you could actually find what's left of the finger, which is was probably smashed like a grape, who would sew it back on?

There is a well know early saturation diving accident that happened at Taylor Diving & Salvage in the 1970s, a pioneering and primitive time in the industry. A diver was in the chamber sitting on the stainless steel toilet bowl tending to his business. Normally the diver would finish, stand up, call for a flush, someone outside manually opens a pretty large dump valve, and the diver flows water into the bowl while the chamber operators makes sure pressure doesn't drop.

If I recall, they were around 250' or 111 PSI. Anyway, somebody "thought" they hear the order to flush, the diver is still sitting on the pot, and 10-15' of his intestines are gone. By some miracle it didn't just suck all his soft tissues out the crapper and drop the chamber by 100'.

Needless to say, the entire industry reduced the diameter of their dump valves, installed mechanical interlocks so it was impossible to sit on the pot when the valve was even slightly open, and moved all control to the diver. It is amazing how accidents are so obvious in hind-sight. I can't remember a recent major injury to a saturation diver that wasn't basically a heavy construction accident rather than a system or operation failure.

 

[Jax]

Thanks for explaining all this, Akimbo!

I have lurked the "Commercial Divers" a little, but you seem to speak your own language in there. Thanks for the basic-diver version.

The industry sure went through some horrific accidents in their learning curve.

BTW - there's a story running around the Internet about 'a bad day at work' where a diver talks about water being pumped into his suit. There began an itching, then stinging feeling, and he realized that the pump had sucked up a jellyfish and the tentacles were being blown down his back and buttocks.

Is that true? Seems like you'd have a better filter on your pump.