Where does the 60ft/minute ascent rule come from?

[rjack321]

I think you missed the point. Decompression procedures evolved from human testing. Tissue theories were evolved many years later and would have no basis without that body of work. Decompression theory is just that, theory. 60'/minute is scientifically valid only because there are massive amounts of quantitative data to confirm that 60'/minute coupled with the decompression procedures tested produced acceptably low hit rates. Other navies used different ascent rates at different times with equally good results.

Actually "acceptably low" for a Navy with chambers all over the place looks surprisingly high if you're at some remote atoll or just going to look at the fishies. Like close to 1% hit rate for maximal bottom times followed by direct 60ft/min ascents, this is for fit males Navy divers too. Thal can probably whip up some references off the top of his head.

The addition of the "safety stop", along with 30ft/min ascents, and the concept of "deep stops" are all newer concepts attempting to extend the ascent time in a logical manner and reduce the hit rate. Because dove to their "no deco" limits today Navy tables are generally considered unnecessarily aggressive if you don't have a national security mission.

 

[ptyx]

For the record, British (BSAC 88) and French (MN 90) tables go with 15m/min (50ft/min). Close enough.

I do not know about the BSAC tables, but MN 90 (Marine Nationale, 1990 revision) was established the same way the USN tables were (cheers for military divers!).

Edit: I stand corrected, MN90 is 15m/min, but it looks like older versions were 20m/min.

 

[Doc Intrepid]

The long version of the history regarding how the 60 fpm ascent rate came about (through a series of meetings and agreements) is also related by Brett Gilliam in his book titled: "Deep Diving (Revised) - Physiology, Procedures, and Systems" (find it here -- )

Amazon.com: Deep Diving, Revised: An Advanced Guide to Physiology, Procedures and Systems (9780922769315): Bret Gilliam: Books


As related above, it was a compromise between two different group opinions...

 

[Akimbo]

From the DAN site

Cdr. Francis Douglas Fane of the U.S. Navy West Coast Underwater Demolition Team wanted rates for his frogmen of 100 feet (30 meters) per minute or faster. The hardhat divers, on the other hand, considered this impractical for the heavily suited divers who were used to coming up a line at 10 feet (3 meters) per minute. Thus, a compromise was reached at 60 feet (18 meters) per minute, which was also a convenient 1 foot per second.

I saw US Navy diving manuals from mid 1930s and I am almost certain they were using 60'/Minute then — well before the UDT. The Naval Experimental Diving Unit was established in 1927 was first dedicated hyperbaric research facility in the US. Before that research was carried out most anywhere they could use a recompression chamber and get some funding.

 

[Thalassamania]

Rjack's right. For some square dives taken to the limit (as I recall 70 for 50 was a problem) the incidence was way too high. But the real problem in the sports community was lack of ascent discipline. Actual timing of sports divers' ascent indicated that they were where Fain had wanted them, 100 fpm and even 120 fpm. The safety stop was originated as a way to make up for problem schedules, lousy ascent procedures and loosing buoyancy control in the last 20 feet when targeting the surface rather than a stop. One procedure fixed all. Today, with ascent monitors built into almost every computer, deep stops (which have been shown to be very useful) and a 30 fpm ascent, safety stops are really rather irrelevant, except for the buoyancy control and targeting questions.

had something to do with navy vs commercial divers. the navy had chambers they were going to dump their divers in after a dive. or it was the speed at which a hard hat diver could be hauled up by a winch, or some such BS. I think it was set back wards, like that is the speed they could do it so that is what was written down.

either way slower is better.

No, Surface Deco is a commercial technique, begun (I believe) by COMEX that has been adopted for some limited Navy diving.

I saw US Navy diving manuals from mid 1930s and I am almost certain they were using 60'/Minute then — well before the UDT. The Naval Experimental Diving Unit was established in 1927 was first dedicated hyperbaric research facility in the US. Before that research was carried out most anywhere they could use a recompression chamber and get some funding.

I think the old rate was 25 fpm.

The long version of the history regarding how the 60 fpm ascent rate came about (through a series of meetings and agreements) is also related by Brett Gilliam in his book titled: "Deep Diving (Revised) - Physiology, Procedures, and Systems" (find it here -- )

Amazon.com: Deep Diving, Revised: An Advanced Guide to Physiology, Procedures and Systems (9780922769315): Bret Gilliam: Books


As related above, it was a compromise between two different group opinions...

It better be ... Bret was there listening to Ed's answer to the question.

 

[Akimbo]

[

For the record, British (BSAC 88) and French (MN 90) tables go with 15m/min (50ft/min)...

Yeah, and they use 50 Hz electricity too???

Actually I have seen old Siebe Gorman tables used for years by the British that only specified time to first stop rather than ascent rate. A cursory glance showed the rate varied a lot, but probably had more to do with the distance to the stop. If I recall correctly, they favored deeper first stops than the US.

 

[Akimbo]

Actually "acceptably low" for a Navy with chambers all over the place looks surprisingly high if you're at some remote atoll or just going to look at the fishies...

I totally agree. I think the saving grace for recreational divers is very few spend all their time at the max depth and don’t work as strenuously (talking averages here). The higher risk side is physical condition, age, and gender are far more diverse.

I guess that statistics have to be our guide until we know a lot more and can figure out how to apply the information in the real world.

 

[Akimbo]

… No, Surface Deco is a commercial technique, begun (I believe) by COMEX that has been adopted for some limited Navy diving.

I have a 1963 US Navy Diving Manual with SurD O2 and Air (Surface Decompression using Oxygen/using Air) tables. They allowed SurD-O2 on mixed gas dives as an emergency procedure only. .

I remember Cal-Dive was using mixed gas Sur-D before 1969 off Santa Barbara. I doubt Comex was sharing information with the US Navy. Diving company tables were closely guarded industrial secrets in those days and Comex was among the most secretive — for good reason, there was a LOT of money involved.

I think the old rate was 25 fpm.

You could be right, none of my manuals go back that far. I just looked in the 1963 manual and it was 25'/Minute for SurD-O2, 60'/Minute for the rest. No idea when it changed or how many times.

 

[Thalassamania]

My memory (which could be correct and the information wrong anyway) is that SurD was a COMEX technique that was used by COMEX as part of their Rapid Intervention Program, essentially doing quick jobs on scuba that, more traditionally, would have been Surface Supplied or even Sat jobs.

Sure, Tables have always been closely held, but the technique is pretty straightforward.

 

[Akimbo]

My memory (which could be correct and the information wrong anyway) is that SurD was a COMEX technique that was used by COMEX as part of their Rapid Intervention Program, essentially doing quick jobs on scuba that, more traditionally, would have been Surface Supplied or even Sat jobs.

Sure, Tables have always been closely held, but the technique is pretty straightforward.

Henri Delauze founded COMEX in 1961. There wouldn’t have been enough time for Comex to develop tables and convince the US Navy to include them in their 1963 manual.

I just found this reference in Sir Robert H. Davis' Deep Diving and Submarine Operations, Page 97:

During recovery operations of the Laurentic (1917) sunk in 132', Captain Damant, R.N., was frequently compelled by some accident or sudden change in weather, or for military reasons, to bring his divers straight to the surface. They were put into the recompression chamber as quickly as possible, the pressure was run up to the diver's working depth and, after a minute or so they would decompress by the ordinary tables for a normal dive.

The method was used as routine during the salvage of 250,000 dollars worth of silver from the Empress of Ireland in 1914, where several hundred dives we made at a depth of 170-190 feet.​

And you guys think we are flying by the seat of our pants because we can’t settle on an ascent rate! Those lads were tough.