We know that nitrogen in particular gets intoxicating at greater depths than
approximately 100 feet. Pure or 100% oxygen gets toxic below 15 - 20 feet. This
has led to the development of mixed gases, known as "breathing cocktails" in order
to obviate the danger. In 1945 Arne Zetterström of Sweden reached 164 meters
(535 feet) on a mixture of oxygen, nitrogen and hydrogen. That mixture is a lot lighter and
easier to breathe than oxygen-helium mixtures that were commonly used at that
time. Remember, these were the war years of WWII and helium was hard to come by.
Great care must be taken to avoid the risk that the hydrogen reaches a
limiting point (thundering gas). From a diving standpoint this was a great success.
However, the 28 year old Zetterström lost his life owing to two military service persons misinterpreting the signals, continued to hoist
the suspension cable.
1) from the surface down to 30 meter - standard air
2) from 30 meter to 40 meter 4% Oxygen and 96% Nitrogen
3) from 40 meter to 160 meter 4% Oxygen, 24% Nitrogen and 72% Hydrogen
In 1948 the English diver William Bollard reached a depth of 164 meters
(535 feet) on oxygen-helium. It was not until 1956 that the English diver George
Wookey reached 180 meters (580 feet). But after spending only a few moments at
that depth, Wookley had to undergo nearly 12 hours of decompression.
In 1959, a 26-year-old Swiss mathematician Hannes Keller, with only two
years experience in diving, decided to tackle the problem of decompression, and
had the idea of combining different mixtures of gas for diving at different depths.
He began diving and shattered all depth records for deep diving. Now the single
hose regulators were starting to be used and Keller used a U.S. Diver "Calypso" for several of his record dives.
In 1962 he reached the depth of about 300 meters
(1,000 feet) off the California coast.
Hannes Keller's dive was accomplished employing a 7' x 4.5' "submarine" with a hatch to get out to the sea-floor outside.
Not really a dive by normal standards.
John Bennett reached 1,000 foot 301 meter on open circuit scuba in 2001.
We have talked a little bit about regulators. In general there are two types;
one hose and two hose. With a two hose regulator, you inhale through the one
hose and exhaled through the other. There was no "need" for a purge button. A
disadvantage was it would free flow when rolling over on your back, or really any
time the mouthpiece was above the regulator in the water. This was more prevalent
in the U.S., as we used larger cylinders here. This in turn forced the regulator
further up toward the head. The greatest argument for the double hose regulators
were "No bubbles in front of the mask." That argument kept the double hose alive
for many years, beyond when it should have been retired. A major problem with the
two hose regulators was, if you had to vomit underwater. One could possibly roll
over on the back to make the regulator free flow, but nobody was supposed to get
sick. So don't do it. To address the problem, non-return valves were added to the
mouthpiece in 1954. Although this made clearing the regulator easier, it was still a
problem. So under these conditions, the single hose with a purge button is far
superior. Purge like crazy, let it free flow and hang onto the regulator while you do
your thing.
Dacor came along in 1953 with Sam Davidson Jr. He wanted to circumvent
the patent that Cousteau had. He took apart a U.S. Diver regulator and found one
diaphragm separating the inlet valve from the outlet ports. He figured he could
out date the whole thing by putting two diaphragms in it instead. Thus, he would
not have to pay the royalty to U.S. Divers. And that was a great thing. Today there
is only one manufacturer of Double Hose regulators. Nemrod of Spain. They are
particularly interesting for re-breather training and for photographers.
