omitted decompression after a VERY long exposure time at 2,57 bars

[Duke Dive Medicine]

Hi, I’ve a question for the hyperbaric doctors of this forum which concerns omitted decompression after a VERY long exposure time under pressure.

I suppose that a person that was submitted during 14 hours to an absolute pressure of 2,57 bars and is then decompressed within less of an hour to the atmospheric pressure has very little chance to survive. But what I would like to know is how long it would take to that person to pass away. Is it a question of hours or minutes?

Thanks in advance for your reply.

An ascent from 15.7 meters / roughly 51 feet of sea water, decompressing over the span of an hour, would likely be survivable. +1 on analogies to old-time caisson workers.

Best regards,
DDM

 

[Akimbo]

I suppose that a person that was submitted during 14 hours to an absolute pressure of 2,57 bars and is then decompressed within less of an hour to the atmospheric pressure has very little chance to survive. But what I would like to know is how long it would take to that person to pass away. Is it a question of hours or minutes?

I seem to remember a habitat-based air saturation accident in the 1960s where someone surfaced from around 60'/18m/2.8 ATA and survived with some serious neurological problems, but can't guarantee it. Obviously, there is enormous human variability and not much data for survivability.

The US Navy's Table 9-9 for Exceptional Exposure at 55'/16.7m only goes up to 330 minutes/5.5 hours with 122:50 minutes of decompression.

For all practical purposes, 14 hours at depth would be treated as full saturation today. Treatment for omitted decompression would probably start with a Treatment Table 6 and extend from there if a small deck chamber (non sat) was available.

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This thread needs @Akimbo insight

Thanks but I am confident that @Duke Dive Medicine is more knowledgeable in this area.

 

[Papyone]

With nearly an hour of deco time, this could absolutely be survivable. This is not that far from the old Haldane critical ratio of 2:1. Assuming someone could control the deco speed, take a minute up to 4-5 meters and leave it there until you have 3 minutes left and then slowly surface.

The slowest tissues would still be supersaturated, but not fatally. There should be time to get the victim to a chamber for treatment.

An ascent from 15.7 meters / roughly 51 feet of sea water, decompressing over the span of an hour, would likely be survivable. +1 on analogies to old-time caisson workers.

Best regards,
DDM

DDM, thank you for your reply.

As I said to Akimbo, it’s hard for me to imagine that one hour of decompression was probably enough to keep him alive despite the very long decompression time prescribed by a decompression table.

What do you mean with “+1 on analogies to old-time caisson workers.”

 

[Papyone]

I seem to remember a habitat-based air saturation accident in the 1960s where someone surfaced from around 60'/18m/2.8 ATA and survived with some serious neurological problems, but can't guarantee it. Obviously, there is enormous human variability and not much data for survivability.

The US Navy's Table 9-9 for Exceptional Exposure at 55'/16.7m only goes up to 330 minutes/5.5 hours with 122:50 minutes of decompression.

For all practical purposes, 14 hours at depth would be treated as full saturation today. Treatment for omitted decompression would probably start with a Treatment Table 6 and extend from there if a small deck chamber (non sat) was available.

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Thanks but I am confident that @Duke Dive Medicine is more knowledgeable in this area.

Akimbo, that’s true, 330 min is the maximum available time in the Rev 7 usn manual.

Just to verify I’ve done a simulation on excel to see what the decompression time would be for a dive time of 840 min. It gives a decompression time equal to about 1320 min (22h).

At Comex we had the same politic that you describe, that’s to say decompress following a saturation profile as soon as the exceptional exposure time is exceeded.

Which in this case means 33 hours of decompression if I follow the CX profile for an air saturation decompression?

So it difficult for me to imagine that one hour of decompression would likely be survivable.

But as I’m not a doctor I’m certainly not going to contest what is said by the DDM.

 

[Duke Dive Medicine]

What do you mean with “+1 on analogies to old-time caisson workers.”

Sorry... SB shorthand for caisson work being a good analogy - many caisson workers were pressurized to similar or greater depths for long periods of time (though perhaps not 14 hours) and decompressed quickly.
Best regards,
DDM

 

[goldfishtornado]

This is not that far from the old Haldane critical ratio of 2:1

I think the parameters here are very close to the trials he did on goats to get that ratio. From the 1908 "The prevention of compressed air illness." It looks like they tried to avoid killing an excessive number of the goats and there aren't any trials that exactly match. Without actually reading the experimental procedures... It looks like the pressures are in "Pressure in lbs. positive" which I would guess is the pressure above atmospheric. In Table X and XI there are trials at 20 and 25 (psi above atmospheric??) for 240 minutes with decompression within 2 minutes. It looks like only one or two goats got bent in those trials, and none died of 40ish. Someone would have to read the article and make some extrapolations to see how that would translate to humans. From reading the description of caisson disease in the same article it looks like it would likely be more of a matter of hours rather than minutes based on the presentation for at all similar circumstances.

tedious work of going through them your self and try to verify sources, exact bottom times, rate of bends and rate of fatality.

many caisson workers were pressurized to similar or greater depths for long periods of time (though perhaps not 14 hours) and decompressed quickly.

From "Caisson disease during the construction of the Eads and Brooklyn Bridges: A review" It looks like there were caissons that were comparably deep, but people did start to understand the need to at least shorten shifts when working deeper. On the Brooklyn Bridge the workers were working eight hour shifts at up to 45 ft (~14 m), with no scheduled decompression, as far as I can tell. I think the article implies there were no deaths from this. A second caisson did have deaths working at a depth of up to 75 ft (~23 m). It's unclear to me if they were still working 8 hour shifts though. That review article does have references to the original sources if someone does want to look at the originally reported circumstances. Again, the descriptions seem to imply hours rather than minutes in terms of time to ultimate death from extended exposure in these pressure ranges.

 

[Akimbo]

Which in this case means 33 hours of decompression if I follow the CX profile for an air saturation decompression?

So it difficult for me to imagine that one hour of decompression would likely be survivable.

Keep in mind that saturation decompression is VERY conservative because it is so easy and there is no reason not to take time in a sat complex. There are a lot of reasons to be in a much bigger hurry to get a diver on deck when decompressing in the water or even a small deck chamber for surface diving opps.

 

[dmaziuk]

As I said to Akimbo, it’s hard for me to imagine that one hour of decompression was probably enough to keep him alive despite to very long decompression time prescribed by a decompression table.

What do you mean with “+1 on analogies to old-time caisson workers.”

Haldane's tolerable overpressure ratio, derived in part form observing caisson workers, was 2:1, which is "not that far" from 2.57:1. In fact by modern standards it would be closer to 3:1 for fast tissues. The problem here is after 14 hours you're looking at slow tissues that are not nearly as "forgiving" and are associated with worse DCS types -- but they're also slower to off-gas, giving you more time to get to the chamber.

Them being slow is what likely drives the deco times you're seeing in the planner.

 

[Papyone]

Thanks a lot to everybody for your replies. It seems that I’ve to revise my opinion about the survival time of this (these) diver(s) after this relatively rapid decompression. For your info, this case concerned the accident that happened in Trinidad & Tobago in 2022 where 5 divers were sucked into a pipeline. One of the divers managed to come back at the top of the riser on his own.
For the other four divers this unfortunately was not the case because they died on the spot following a very PISS-POOR POST INCIDENT MANEGEMENT.
(More info can be found in the Accident & incident section).