** Diving History -- John Scott Haldane "Father of Modern Decompression"....and a bunch of other stuff **

** Diving History -- John Scott Haldane "Father of Modern Decompression".....and a bunch of other stuff **

STAGED DECOMPRESSION
In 1905 shortly after the publication of the first dive manual, British admiralty adopted decompression procedures to depths of up to 180fsw based on British Professor John Scott Haldane's staged decompression theory. Haldane's staged decompression model had a diver leave bottom at a relatively fast rate followed by decompression stops at shallower depths. This was in sharp contrast to continuous-ascent (liner) decompression procedures developed by French physiologist Paul Bert that was being used at that time. Bert's liner decompression model usually recommended a slow but continuous ascent in the area of 3 feet per minute. The problem with liner decompression vs. staged is the very slow/continuous ascent rate which allows the diver to still on-gas while at the deeper depths. While liner decompression works well for saturation type diving (because you cannot possibly on-gas anymore......you are saturated), it posed serious problems for non-saturation type diving.

ACCEPTANCE BY THE U.S.
The U.S. was slow to adopt Professor Haldane's stage decompression procedure, but had great interest. In 1912, George D. Stillson set up a program to test Haldane's diving tables and methods of stage decompression in the Long Island Sound. Prior to these tests, Navy Divers rarely went deeper than 60 fsw. Throughout a three-year period, first diving in tanks ashore and then in open water from the USS WALKE (DD 34), Navy Divers went progressively deeper, eventually reaching 274 fsw (all on air). Before this the believed safe diving limit was 120 feet but these experiments pushed that limit to around 200 feet. Mixed gas diving would not be discovered for another 27 years but would push this depth limitation well beyond that of air.

ASCENT RATES
Haldane's original staged decompression model recommended ascent rates between 5 and 30 feet per minute dependant upon depth. This was later modified to a rate of 25fpm which remained in effect from 1920-1957. Then in 1958, while revising the U.S. Navy Diving Manual, this rate of ascent came under review. Commander Fane of the U.S. Navy West Coast Underwater Demolition Team wanted rates for his frogmen of 100 feet 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 slowly (usually 10 feet per minute). Thus, a compromise was reached at 60 feet per minute, which was also a convenient 1 foot per second for time/record keeping. This 60 feet per minute rate lasted in the Navy from 1957 until 1993, based on this purely empirical decision, with many recreational diving tables and even early computers following suit. In recent years the ascent rate has been slowed to 30 feet per minute as research has shown this rate helped to better guard against illnesses associated with diving such as decompression sickness and gas embolism...it seems Mr. Haldane had it pretty close to start with.

Haldane's basic staged decompression model formed the basis for what all divers (military and civilian) use world wide for non-saturation type diving. Bert's liner decompression procedure became and remains the basis for saturation type diving decompression.

A few other notable FAQ about John Scott Haldane:

1. He was heavily involved in experiments involving the effects of certain gases on the body. One of these gases; Carbon Monoxide affected not only divers but miners and other workers. He was the first to research the effects of CO on the body by breathing it in himself until it saturated his blood, nearly costing him his life. "At the end I could hardly stand and could not walk alone without falling down" he noted. His research revealed the mechanics behind CO poisoning which became known and "the Haldane effect".

2. During the First World War (1914-18) Haldane was asked to identify the type of gas that the Germans had used in the first gas attack of the war. Haldane found it was chlorine. In order to protect the soldiers, Haldane designed the first gas masks, which proved better than the urine-soaked handkerchiefs that the soldiers had used at first. Haldane also demonstrated the value of oxygen in treating soldiers when they were gassed.

3. He introduced the use of small animals for miners to detect dangerous levels poison gases underground, using either mice or canaries. The reason for this (aside from their portability) was that they have a faster metabolism. This faster metabolism causes them to show symptoms of poisoning before gas levels became critical for workers, giving an early warning sign. The use of canaries was used until 1986 when the method was replaced by the electronic gas detector.

4. Haldane led an expedition to Pikes Peak in 1913 to examine the effects of low atmospheric pressure on respiration. His work here also revealed that decompression sickness was not limited only to divers and miners. He also discovered that the respiratory reflex is triggered by an excess of carbon dioxide in the blood rather than a lack of oxygen.

5. Like his experiments involving Carbon Monoxide, Haldane would routinely experiment with toxic and non-toxic gases on his own body. Despite all the benefits these experiments would yield, years of doing them would eventually take its toll on his lungs. John S. Haldane would die of Pneumonia in 1936 and is still remembered as the father of modern decompression theory.

Note: To learn more about John Scott Haldane and his work check out "Suffer and Survive: The Extreme Life of JS Haldane" by Martin Goodman.

H/Y

This Week in Diving History -- August 28, 1965 -- SEALAB II

** This Week in Diving History -- August 28, 1965 -- SEALAB II leaves surface **

On August 28, 1965, the first of three teams of divers moved into what became known as the "Tilton Hilton" (because of the slope of the landing site) also known as SEALAB II. This first day of the operation happened to be one of the divers involved birthday; Bob Barth, who turns 79 today-Happy Birthday Bob!

SEALAB II rested at a depth of 205 ft 65 miles off the coast of LaJolla, CA. Whereas SEALAB I tested and proved the concept of saturation diving, SEALAB II provided evidence that useful work could be done. The Navy conducted physiological and psychological studies to determine man's effectiveness underwater for an extended period. Navy Divers not only evaluated the structural engineering of the habitat. They did things like working on a mock-up of a submarine hull, tested undersea tools, conducted salvage ops using syntactic foam; they set up a weather station, mined ore samples, experimented with plants, and studied ocean floor geology just to name a few things. They also experimented with a trained porpoise named Tuffy from the U.S. Navy Marine Mammal Program, to do courier work between the habitat and the surface.

Each team spent 15 days in the habitat, but aquanaut/astronaut Scott Carpenter remained below for a record 30 days. During that time, he was able to speak with astronaut Gordon Cooper who was in the Gemini space capsule, orbiting the Earth. Also a congratulatory telephone call was arranged between President Lyndon B. Johnson and Scott Carpenter while he was still under pressure. The fact that Carpenter was breathing Helium-Oxygen made him sound unintelligible to operators. Much was learned about working in the ocean and contributions were made to a large number of undersea science and engineering disciplines. SEALAB II was no doubt a success and represented another large step forward in enabling human beings to live and work in a hostile environment. SEALAB II was designed, built, and outfitted at Hunter's Point Naval Shipyard in San Francisco at a cost of $850,000. It was designed to house ten men at a depth of 200 feet for 30 days. The habitat was 50' long and 12' in diameter, and included four separate areas: entry, laboratory, galley, and living spaces. Entry while on the ocean floor was from below the habitat, with divers emerging into the pressurized habitat through an open moon pool.

Construction of SEALAB II's cylinder end bell used technology ahead of its time. The large dish-shaped cap was formed from a sheet of one-inch thick flat steel placed over a die. In order to shape it, one hundred pounds of C-4 plastic explosive were distributed on the side of the blank opposite the die. The whole package-die, blank, and charge, weighing 60 tons total-was lowered 30 feet beneath the surface of San Francisco Bay where the explosive was detonated. In approximately .004 seconds the end bell was formed. Explosive metal shaping on this scale had never been attempted before. If you would like to see this end bell, visit the Naval Undersea Museum in Keyport, WA.

Note: This photo entitled "Bob-Barth-Scott-Carpenter-Sealab.jpg"; is a picture taken at the dive station on the support barge of Sealab Two, Bob Barth is shaking Wilbur Eaton's hand as he and Scott Carpenter are making ready to swim down to the house (they were the first two to leave surface).

H/Y

This Day in Diving History - Treatment Tables 5 and 6 introduced into the U.S. Navy

** This Day in Diving History August 22, 1967 - Treatment Tables 5 and 6 introduced into the U.S. Navy **

The use of oxygen in recompression therapy in the Navy does not go back as far as many believe. In fact, it was not until the 1924 edition of the US Diving Manual that a standard recompression therapy was recommended at all; but these were all air tables. Treatment pressure was based on either the depth of the dive (or a multiple thereof) or the depth of relief, oxygen simply wasn't used back then. It wasn't that no one hadn't thought of using O2 however. The roots of using oxygen as therapy for diving illness can be traced back to Paul Bert's experiments way back in 1870. He first observed that when 100% oxygen on the surface was administered to animals after decompression, some of the signs would resolve. Surprisingly, Bert did not try hyperbaric oxygen, which was first proposed several years later. Initial results were actually disappointing, probably because the therapy was too brief.

In 1939, two US Navy medical officers (Yarbrough and Behnke) first published results of DCS treatment using compressed oxygen, but despite their success, the technique was not initially adopted. Instead for the next 20 years, the US Navy continued to recommend a variety of air tables despite long treatment duration and high failure rates. While these deep air tables provided a higher amount of oxygen, they also caused divers to take up amounts of inert gas in doing so. In the early 1960s, the US Navy instituted another series of investigations into low-pressure oxygen tables. Originally tests used 33 feet as a treatment depth; but due to a high recurrence rate, they were altered to use an initial recompression to 60 feet. This treatment depth not only dramatically improved treatment success, but did so in keeping the risk of oxygen toxicity at an acceptable level - the Navy had found "the sweet spot".

On August 22, 1967, Treatment Tables 5 and 6 were introduced into the U.S. Navy. These treatment tables marked the first time that 100 percent oxygen was used at relatively shallow treatment depths in comparison to the deeper air treatment tables (TT's 1-4). Two additional tables were also introduced (TT-5A and TT-6A) that began with an initial deep short excursion on air followed by treatment profiles identical to tables 5 and 6 (TT-5A was quickly abandoned). Because of the success of low-pressure oxygen treatment of decompression sickness, tables 1-4 are now rarely used. Continued experience with the O2 treatment tables revealed frequent reoccurrences of decompression sickness with the shorter procedures in Tables 5, which now sees limited use for treating diving related illness. TT's 7 and 8 were developed in the 80s to address a longer need for oxygen breathing at 60 feet or deep blow-up respectively; followed by TT-9 in the 90s mostly for non-diving disorders with great success.

Reading: Check out "Diving Medicine" by Alfred A. Bove and Jefferson Davis. This book is commonly referred to as The Bove ('Bo-veigh') and I guarantee that either your friendly neighborhood Master Diver, Diving Medical Officer or Diving Medical Technician has a copy.

H/Y