USN decompression 30fsw/9m with 100% O2

[tbone1004]

I disagree. 70% gets me out of the water faster than 100% O2 on dives in the 150ft range that require 30-45min of deco. I can get on my deco gas at 40 ft instead of breathing backgas all the way up to 20ft. Has nothing to do with being cheap or making a poor selection.

do you get out any faster than with 50% which is easier to blend and gets you on deco at 70ft? While you may not have any deco down that deep it has the safety advantage of being able to hop on it

 

[tursiops]

do you get out any faster than with 50% which is easier to blend and gets you on deco at 70ft? While you may not have any deco down that deep it has the safety advantage of being able to hop on it

This has been my preference. Go on 50% at 70 ft, then switch to 100% at 20 ft. No reason (on my dives) to do any deco on backgas.

 

[Duke Dive Medicine]

Tangential question for the hardhat divers / medical folks - I know that humans seem to inexplicably tolerate far higher PO2's in dry chambers than on wet dives. Is that also true for hardhat dives?

That's a great question. It's not entirely inexplicable - immersion causes changes to the vascular system, including to cerebral blood flow. Diving can increase circulating levels of CO2 depending on a number of factors. CO2 is a vasodilator, which also increases cerebral blood flow, which in turn increases risk for CNS O2 toxicity. Warm, dry patients breathing 100% O2 at pressure in a hyperbaric chamber are at much less risk of O2 toxicity than divers breathing a comparable pO2 in the water.

Also, what @TeamBubbles said. If someone does seize in the hyperbaric chamber, they're not at risk of drowning, so a marginally higher risk of seizure is usually tolerable and can be mitigated by air breaks and closely monitoring blood sugar in diabetic patients (hypoglycemia is another risk factor for CNS O2 toxicity).

Best regards,
DDM

 

[Wibble]

I'm not aware of any agency that does not advocate 100% deco gas at 6m and certainly not one that advocates 80%. 70-80% gases are only used by cheap divers that don't want to buy a booster *note that filling 70-80% is convenient because an O2 bank bottle comes in at 2000ish psi and if you top it off to 3000ish psi with air then the mix is in the 70-80% range. It has nothing to do with decompression efficiency.

Yeah, tightwads not wanting to use a booster…

Or people who use a gas that is safer AND can be used at 9m/30’ AND doesn’t need air breaks AND doesn’t blast up the CNS and oxygen clock AND is available in high pressure fills AND makes little practical difference to deco times.

Yay 100% 80% rocks

 

[grantctobin]

Yeah, tightwads not wanting to use a booster…

Or people who use a gas that is safer

lol

 

[tbone1004]

Yeah, tightwads not wanting to use a booster…

Or people who use a gas that is safer AND can be used at 9m/30’ AND doesn’t need air breaks AND doesn’t blast up the CNS and oxygen clock AND is available in high pressure fills AND makes little practical difference to deco times.

Yay 100% 80% rocks

If it is that much better why isn't there any agency that advocates for its use? 50% is much better.

 

[kensuf]

Personally, I'm a "Standard Gases" kind of guy for deco gases, but sometimes things don't work the way one would hope and the ability to have some flexibility is important. At one point it was actually nearly impossible for me to get 100% for decompression in the Cayman Islands due to CITA regulations, but it was really easy to get 80%. Now it's just impossible for me to get into the Cayman Islands...

One of the agencies I'm an instructor with has a long history of advocating 80% as a deco gas. I disagree with them, but whatever, the point is it's actively being taught out there and to this day there are several IT's in that agency that would tell you that 80% is better than 100% for most deco.

Another one of the agencies I'm an instructor for actually used to require 100% for their single gas decompression program, even on dives where 50% was a better choice. Something like 140' for 30 minutes I'm going to prefer 50% over 100% as my deco gas almost every time. Thankfully I helped talk sense into them and they changed their S&P last year to allow any deco gas up to 100%.

Here's another mind-bender. I've got friends (really, I have friends, I'm a people person!) that regularly use 63% as a deco gas when doing single deco gas dives. Their normal profile (130-150 for 30) has their first stop at 50' and it gets them out of the water quicker, so that is the gas they standardized on for decompression. They've been doing this successfully for years and haven't exploded or died yet.

 

[Degenerate]

Yeah, tightwads not wanting to use a booster…

Or people who use a gas that is safer AND can be used at 9m/30’ AND doesn’t need air breaks AND doesn’t blast up the CNS and oxygen clock AND is available in high pressure fills AND makes little practical difference to deco times.

Yay 100% 80% rocks

If I could dislike a post on this forum, this would be the one.

 

[Akimbo]

Some members may find this thread helpful:

Info - Oxygen Toxicity Limits & Symptoms

Oxygen Toxicity Limits & Symptoms Oxygen toxicity limits can be very confusing, especially for PPO2 (Partial Pressure of Oxygen) levels above 1.6 ATA used in chamber-based hyperbaric treatment (recompression) and decompression tables. For example, here is a chart of one of the most common DCS...

scubaboard.com

 

[rjack321]

Hello,

I do not try to adapt. I try to understand and out of interest These are tables that are publicly available and even regular sport diving agencies like PTRD are ‘using’ them. But rarely or even never you see diving examples (scenarios) in the theory lessons that use deco with 100% oxy at 6, let stand 9m or propose an alternative for the 9m ‘issue’

Thank you all for your answers. It helped a bit.

Sorry you'll need to help me out here...
1) Why is an Italian training agency using US Navy tables? Are they teaching deco in English with all the caveats and details behind those tables explained and translated?

2) This is the first I have heard of any agency teaching the US Navy tables (for deco or even the no-deco tables) in over a decade. At least not in an official capacity, although some instructors might hold them up as an example.

What was the scenario in class and how were the US Navy deco tables being used?