Underwater off-gassing equivalent to a surface interval on air

[Wibble]

We traditionally do our stops in 0.3atm/3m/10ft increments.

If we could change that to, say, 0.1atm/1m/3'4" increments, would the SAME dive require less decompression time?

 

[rongoodman]

I thought the old VR-3 had a continuous ascent mode, but I haven't been able to find a reference to it.

 

[boulderjohn]

Here is an old thread on the topic: Continuous Decompression AND Staged Decompression

 

[inquis]

In particular, @EFX ran the 1-foot schedule resulting in a whopping 12 seconds difference on a ~14 minute deco.

 

[boulderjohn]

Back when people were trying to help miners suffering from caisson disease, the idea that excess nitrogen was the cause was born, and people advocated for a slow, continuous ascent. In his studies, John Haldane specifically compared a slow continuous ascent with a staged ascent, and those studies indicated that the staged ascent was better. That eventually became the norm.

 

[dmaziuk]

We traditionally do our stops in 0.3atm/3m/10ft increments.

If we could change that to, say, 0.1atm/1m/3'4" increments, would the SAME dive require less decompression time?

With a database of a few million real-life deco profiles, we could run them through the ascents with different increments and see if there is a trend. Or perhaps several clusters depending on max depth, or gas, and so on.

 

[Duke Dive Medicine]

@Duke Dive Medicine (or anyone else that knows), we're taught that one of major reasons to take air breaks during lengthy O2 stops is to reduce mucus buildup (improving subsequent gas exchange). Does partial pressure drive that buildup or is it more tied to the fraction of O2 breathed?

I've honestly never heard that before. Pulmonary O2 toxicity is a concern during long O2 breathing periods but that's not so much mucus buildup as it is oxidative damage to the lungs.

Best regards,
DDM

 

[Duke Dive Medicine]

@Duke Dive Medicine: could two staged decompression dives per day at a depth of 165 ft per dive over ten to fourteen subsequent days resulting in high CNS toxicity as a consequence. Would those types of dives prevent you from using a hyperbaric chamber if you were to get bent?

I'd be more concerned about pulmonary O2 toxicity at that point, but no, it would definitely not be a contraindication to hyperbaric O2 therapy for DCS.

Best regards,
DDM

 

[Wibble]

Picking a sample open circuit dive of 50m/165ft for 60mins with 21/35 bottom gas with 50% and 100% for deco using 50:80 gradient factors.

Throwing this at MultiDeco for three scenarios (omitted all stops below 9m/30ft for clarity):

• 3m/10ft stops with last at 6m/20ft
  • Stop at 9m 13:00 (98) Nitrox 50
  • Stop at 6m 44:00 (142) Oxygen
  • Surface (144)
• 3m/10ft stops with last at 3m/10ft
  • Stop at 9m 13:00 (98) Nitrox 50
  • Stop at 6m 15:00 (113) Oxygen
  • Stop at 3m 29:00 (142) Oxygen
  • Surface (143)
• 1m/3'4" stops with last at 3m/10ft
  • Stop at 9m 4:00 (89) Nitrox 50
  • Stop at 8m 4:00 (93) Nitrox 50
  • Stop at 7m 4:00 (97) Nitrox 50
  • Stop at 6m 4:00 (101) Oxygen
  • Stop at 5m 5:00 (106) Oxygen
  • Stop at 4m 6:00 (112) Oxygen
  • Stop at 3m 29:00 (141) Oxygen
  • Surface (142)

Observations:

• The time from 6m to 3m is the same 44 mins for all three scenarios
• The 3m final stop means it's quicker to the surface at 3m/min

Basically there's no significant difference except that holding 3m/10ft intervals is a lot easier and that the option of having a shallower than 6m/20ft final stop makes life easier.

As ever the CCR version of this dive is a few minutes longer:

• Stop at 9m 12:00 (98) Diluent 15/35 1.30 SetPoint
• Stop at 6m 51:00 (149) Diluent 15/35 1.30 SetPoint
• Surface (151)

 

[Alaskan Scuba Dude]

I'd be more concerned about pulmonary O2 toxicity at that point, but no, it would definitely not be a contraindication to hyperbaric O2 therapy for DCS.

Best regards,
DDM

Thanks for clearing up a hypothesis that was brought up in a conversation years ago.