The CDBA (Clearance Diver Breathing Apparatus) was
and still would be a safe, practical and operationally capable set, if
we had spent some time evolving the set like the fore-mentioned
engineering designs. While I have a high regard for the scientists and
engineers who design and build new and high tech sets, I don’t believe
new is always better. I retired as Chief Diver/Unit Chief Warrant
Officer from DCIEM (Defense and Civil Institute for Environmental
Medicine) during the CUMA (Canadian Underwater Mine countermeasures
Apparatus) and the CCDA (Canadian Clearance Diver Apparatus) development
program. While not having much input into the program I did share my
concerns with the diver friendly application of the sets. Not forgetting
what it is like diving out of a Zodiac, crawling about the beach at
night, swimming, looking at a compass, depth gauge and looking after
your buddy, seemed like enough things to do whilst diving. This is where
I reflect, at the potential missed using the CDBA.
Some times Engineers get it right! This works for
me when I remember the CDBA. If only we had used the available O2 and
CO2 monitoring technology, which was available in the 60’s and 70’s and
changed the way we used the set, we might still have the Ole Reliable
CDBA set with us today. It is my hope that this article will stir up
some good memories, comments and debate with all the levels of
participants in the worlds diving community.
Now, to get to where I want to go with this and
generate interest, please allow me to go back in time when I first dove
the set and see how a few changes would allow this old diving set to
evolve and be as practical today as any other diving set.
1966 when undergoing training for the CD2’s course
(TQ5A) divers did an 8-week phase with CDBA rigged for O2. This was
followed by a 2-3 week phase using mixed gas. It was during this period
we learned? About the gas laws and how they effected the diver. I think
most of us memorized the laws instead of understanding them. This was
certainly the case for me. Remember this was still a “do as we say
navy”. We followed the BRCN 5350 to the letter (most of the timeJ). And
if we paid attention to what we were doing we usually had an uneventful
dive. Now to appreciate where I am going with this .It would help to go
through a typical O2 dive using the CDBA set. This would allow the
reader to appreciate the physics and the physiological effects to the
diver. Also, during this part we won’t do any of the engineering
changes, only, operational procedures will be changed. Maybe another
article with engineering modifications would be interesting.
With the set charged and the diver dressed, the
sequence would go like this:
1. Purge the (CL) counter lung, turn on O2 using
the by-pass valve, and fill the CL. Breath pure O2 for one min. Set was
rigged for O2 to flow at 1.5 Liters per min.
2. Purge the CL again, by-pass to inflate with pure
O2 and enter water. Note: diver at this time is exposed to O2 at a PP
(partial pressure) of 1 ATA (atmosphere Absolute).
3. Diver descends down to the long jackstay at 33
ft. or 10 meters keeps the CL full using the O2 by-pass valve. Note: The
diver is now exposed to O2 at a PP of 2 ATA.
4. During this dive, the diver would swim
underwater around the jackstay (for me it was about 9-11 Min’s J) the
depth would range from 33 ft to 15 ft so the diver would be exposed to a
PP O2 of between 2ATA to 1.5 ATA. Most dives were uneventful. Some were
not. One of my students during the same type of training experienced an
O2 hit, as did others over the years.
So! What do we know from all this?
The average amount of O2 consumed by a moderately
working diver is approximately 1.5 liters per min. We also know that
this rate does not chance. Example, A diver working at 165 ft still uses
approximately 1.5 liters per min. surface equivalent. So the counter
lung stayed at 100% O2 no matter how hard or little they worked, or
The reason we stayed on O2 for one min ranged
from,(Lwe were told) This will see if you have a negative reaction to
O2, or, to, this will remove some of the N2 still in your body and set.
Today the only operational people I know who pre-breath O2 is Astronauts
and Pilots of very highflying spy aircraft. Thus avoiding altitude
bends. I have never heard of any one having a negative reaction to
breathing pure O2 on the surface. One has to remember this is what the
Diving Manual BRCN5350 dictated, so, this is what we did. Ours was not
to reason why? Ours was just to do and whatever!
Since those days we have developed the PPO2 / Time
/Depth Exposure tables, so now we can better understand the effects of
gasses on the diver. So let’s do the same training dive, changing only
the way we dive the set, and instead of O2 in the emergency bottle we
put in air.
Note what happens!
With the set charged and the diver ready, the NEW
dive sequence would go like this:
1. On Gas, reducer set for 1.5 liters per min.,
inflates CL with air, enter the water, and dive to the jackstay @ 33 ft
/10 Meters. Diver inflates CL with emergency bottle to compensate for
depth. Diver swims around jackstay runs out of gas returns to the float.
SO! What happens to the diver, with the changed
The diver turns on the set and starts in-putting
1.5 liters of O2 per min. The diver inflates the CL with air. This is
made up of approximately 20%O2 and 80% N2. Now the diver is exposed to
O2 at a PP of .2 ATA. Every thing is OK!
Diver enters the water and goes to 33 ft, filling
CL with air to compensate for depth. At depth diver is now exposed to O2
at a PP of .4 ATA. As long as the diver swam using the 1.5 liters per
min the PPO2 would remain the same. The only thing, which would change
the PO2, would be the physical absorption of the N2 into tissue. All the
rules pertaining to swimming to fast or to slow would apply.
This may seem all so simple. And maybe it really
However, think about it, if, we dive using this
same scenario there would be no depth restrictions, except for
decompression, (theoretically). As long as the diver uses the gas and
bypasses with air. The PPO2 should not change; at 132 ft. or 4 ATA the
PO2 would be .8ATA. At 297 ft or 10 ATA the PPO2 would be 2ATA, which is
the same as pure O2 at 33 ft.
Using the gas laws to demonstrate the increased
effectiveness of the CDBA set is only the beginning of how to improve
what the engineers got right away, back when. I have a swim set in my,”
I Love Me Room” and it always challenges me to look at what we did not
do with a set, which done me proud. I also believe that there would be
more divers still diving today, had we evolved the set as it should have
evolved. When I think about the LARV1 A5800, CCR1000, CUMA, CCDA, MK5
modified, SL 17 and KMB9 I think they are all great technical advances
for the diving community. The CDBA Modified would have kept them all
honest and harder to fund, because SOMETIMES ENGINEERS GET IT RIGHT.
This is just a quick overview of what I believe the
CDBA could do had we understood it or tried to improve it. It would be
interesting to hear the views of others who dove and appreciate the CDBA
set. I am quite confident that divers can develop diving sets just as
well as engineers. If there is any interest, please drop me a line at:
firstname.lastname@example.org Submitted by Milt
Published with permission.