Ascent Rate History

[tursiops]

Where did the venerable 60 ft/min or 18m/min come from, and when?
Surprising account by someone who was there....
View attachment Ascent Rates - Lanphier.pdf

 

[OceanEyes]

From the depths of my memory the tale that I’ve found to be slightly frightening but still mildly entertaining is as follows:


The U.S. Navy adopted the standard ascent rate of 60’ per minute not due to any specific empirical research but rather as an easy to remember number. Initially devised before the advent of SCUBA, the ascent rate was out of the diver’s control, but was rather the pace at which the diver’s surface based tender was instructed to retrieve the line as he hauled the diver up from depth. Thus an enlisted man simply had to remember to recover a line at one foot per second.

 

[Akimbo]

One of my instructors in Navy Diving School was trained by a diver previously stationed at NEDU (US Naval Experimental Diving Unit) when Dr. Lanphier was there. According to his story, everyone understandably hated 25'/minute. A tender hauling up hose could “estimate” 5"/second (25'/minute) sort of OK. But the guy running a chamber had a low precision pressure gauge calibrated in FSW (Feet of Sea Water) and a stopwatch. The needle on the gauge was wider than the 1' marks so estimating .4166'/minute was insane. Similar story for the diving supervisor who had to calculate the ascent time to the second… before electronic calculators and it’s not like these guys could use slide rules.

As he told the story, the EDU divers were also lobbying to ditch the 25'/minute rate. None of them (all Mark V heavy gear divers) were thrilled about hauling up umbilical 4x faster or a 1.66'/second rate running a chamber that the UDT guys wanted though. Especially in the early 1950s, Navy divers weren’t math wizards or especially intellectual souls. I’m sure they lobbied hard for a rate that matched the ticks on stopwatches. It’s easy to imagine a grizzled cigar chomping Master Diver across the table from the medical officers pressing his point.

Having used 60'/minute most of my life, I still hate 30'/minute on Scuba. Estimating ascent rate was easy since the smallest pencil diameter bubbles ascend about 60'/minute. I have yet to find a 30'/minute bubble.

 

[Rick Murchison]

Where did the venerable 60 ft/min or 18m/min come from, and when?
Surprising account by someone who was there....
View attachment 201427

Dr. Lanphier's account is what I learned some 40 years ago. (only difference is that the way I heard it, the frogmen wanted 120FPM, not just 100...)

Rick

 

[Akimbo]

It would also be interesting to learn when the X'/minute rate morphed from “not to exceed” to an exact rate we are expected to strive for. I was taught the latter in my first Scuba class in the early 1960s and in the Navy in the early 1970s.

The UDT requesting a “not to exceed” rate makes a lot more sense than the stories I heard in the past. The UDT didn’t have any ascent rate restrictions when using pure oxygen rebreathers since they couldn’t get bent.

 

[Rick Murchison]

It would also be interesting to learn when the X'/minute rate morphed from “not to exceed” to an exact rate we are expected to strive for. I was taught the latter in my first Scuba class in the early 1960s and in the Navy in the early 1970s.

The UDT requesting a “not to exceed” rate makes a lot more sense than the stories I heard in the past. The UDT didn’t have any ascent rate restrictions when using pure oxygen rebreathers since they couldn’t get bent.

Don't know 'bout the "when" but certainly understand the "why?" - Since "bottom time" ended when the diver left the bottom, the nitrogen tissue loading calculations ceased at that time, and the tables depended on an ascent rate that minimized any additional time at depth - with concomitant tissue loading. The real question to me should be "what is the acceptable ascent rate window that will assure table calculations aren't blown due to spending too much time too deep while assuring no bubble formation?"
Rick

 

[ajduplessis]

Seriously scientific stuff......

 

[Akimbo]

Don't know 'bout the "when" but certainly understand the "why?" - Since "bottom time" ended when the diver left the bottom, the nitrogen tissue loading calculations ceased at that time, and the tables depended on an ascent rate that minimized any additional time at depth - with concomitant tissue loading…

I have to wonder if decompression theory was that sophisticated in the early 1950s. Dr. Lanphier’s account cast a lot of doubt if anyone thought the rate was all that important. Maybe it didn’t matter for the kind of diving the Navy was doing at that time. Except for training for the extremely rare submarine rescue, all the diving was pretty shallow in those days. It wasn’t very many years before that EDU developed the first treatment tables.

It could also be that the “not to exceed” morph was a result of simplifying training diving supervisors. It is a lot easier to teach sailors hard objectives than how to make reasonable judgments.

…The real question to me should be "what is the acceptable ascent rate window that will assure table calculations aren't blown due to spending too much time too deep while assuring no bubble formation?"…

True, but it is becoming increasingly academic since computers take it into account and so few people actually use tables anymore. I have left the bottom (deepest depth) many times on wrecks where the computer would complain about slowing ascent, and then fool around on the super structure for about half the dive. The computer took it into account and calculated decompression stops without missing a beat.

I have often thought of just making a more convenient 60'/minute ascent and see if the computer would dictate a deeper stop to compensate. The RGBM implementation on the Atomic Cobalt is biased toward short deeper than typical stops anyway.

 

[Rick Murchison]

... It is a lot easier to teach sailors hard objectives than how to make reasonable judgments...

HHhhaaaarrrr! Ye were one, eh? (I was...)

Rick

 

[Bob DBF]

It could also be that the “not to exceed” morph was a result of simplifying training diving supervisors. It is a lot easier to teach sailors hard objectives than how to make reasonable judgments.

Ah yes, the never ending battle to make equipment and instructions sailor proof.



Bob
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There is no problem that can't be solved with a liberal application of sex, tequila, money, duct tape, or high explosives, not necessarily in that order.