Smallest Rebreather Ever
by Dave Sutton
OK, Guys, here is my version of the worlds smallest CCR. Here's what it is,
and how it came to be.
I've been diving pure 02 rebreathers for a long time, doing photography,
observation, and occasionally shooting a fish for dinner. Naturally, I am
careful not to exceed PP02 limits for pure 02, which ends up limiting depth
to about 25 feet if the bag is fully purged with before use. When I was a
kid, I remember reading Hans Hass, writing about using 02 rebreathers for
photography before World War 2, and how they dive deeper by leaving some air in the counterlung before diving to let the PP02 be usable deeper.
Basically, he was using the 02 rigs as a nitrox rebreather by not fully
purging the loop with 02 pre-dive. This works, although it's a "blind"
method, and surfacing is fraught with danger, as PP02 is dropping as the
diver ascends. Back in the "Bad old Days" of rebreathers, circa 1950's,
sufficient number of divers died using 02 rigs that they got a reputation
for being extremely dangerous. Too deep, and you go into an 02 toxicity
convulsion. Let the loop get too lean on ascent and you pass out at 10 feet
and drown. No wonder rebreathers were essentially unknown for 30 of so years of diving history.
Fast forward to today: As well as being a technical wreck diver, using
rebreathers to dive deep and to dive long, I'm also a freediver. I enjoy
breath-holding diving and especially enjoy spearfishing while freediving.
It's a totally different sort of diving than technical diving, and is
extremely enjoyable. I use an 02 rebreather as an extension of freediving,
as it allows me to go and explore areas in shallow water for longer periods
than I can manage while holding my breath. To save 02, by not needing to
purge the loop with pure 02 several times to make sure no inert gas is left
in the 02 rig, I added a PP02 meter to an 02 rebreather about 5 years ago.
This allows me to watch what the loop is doing, and lets me play a bit by
not fully purging the loop with 02 at the surface, sort of like Hass used to
do, only this time with the ability to watch and know what the PP02 is.
After a while, I started playing to see how far I could go with this. The
bottom line is that I finally managed to master the technique of *fully*
inflating the bag with air, taking a *deep* breath (like I was freediving),
and the kicking hard to get down to perhaps 30 feet, where both my lungs and
the bag would be at half original volume, going onto the loop there (PP02
now 0.4-ish), and then adding only 02 as I continued to descend. Using this
method, I was successful in diving to about 60 feet or so on a regular
basis using nothing but an 02 rebreather, a freedivers wetsuit, long
freedivers fins, a mask, and a weightbelt. This was (and is) truly freedom
in silence, with no equipment to speak of, gracefully swimming around, one
with the sea in every way. I was always careful on ascent to do a full 02
purge at about 30 feet so the mix was good to go to the surface with, and
all was well.
But...... Deeper blue water beckoned.
Solution: A Spare-Air. I took to carrying a tiny little emergency SCUBA
bottle, and using the above method would get to about 40-50 feet. Pausing there, I would close the loop, exhale into the water, take a deep breath from the Spare-Air, and then exhale that air back into the loop after going back onto the DSV. Result? I just added diluent to the loop and could go deeper. I would repeat every 30 or so feet, and one day I managed to look up through the water at the surface 140 feet above me, still wearing nothing but fins, thin wetsuit, mask, weightbelt, and the tiny 02 rebreather, and thinking "Boy, this is really neat. Boy-O-Boy, I'm *really* damned deep without any backup. Shit! Nobody would believe me if I told them I managed to pull this off. I must be the bravest diver in the water today, or the dumbest. I better go back up......".
It worked, but was not "Clean". In fact, it was scary as shit. So, the challenge was set forth, and I sallied into the Little Diveshop of Horrors to again perform the unthinkable task of ripping apart entirely good diving equipment to once again produce a Frankenstein Monster
Here is the result of that challenge: I took the Spare-Air and turned it into a manual/auto diluent addition system for the loop. Basically, I stuck a P-connector into the counterlung of the rig, machined an adapter for the mouthpiece of the Spare-Air so it'll plug into the P-Connector, blocked off the exhaust ports, and plugged it into the counterlung. It works on demand as an auto-add valve system, and also manually by pushing the purge button.02 is added manually, using the original 02 add button from the 02 rig, and PP02 is monitored using a 2 cell meter that I made up myself using displays bought from Gordon Smith hooked to my own cell probe.
I even ran a quick-disconnect fitting into the system so I can actually carry offboard gas (a 13 on my back works fine, and can also fill my drysuit). Now the system is complete. By plugging in what I need, I've got a pure 02 system, a CCR for "reasonable" depths using just the Spare-Air and a CCR using offboard gas when I want to wear a drysuit.
How does it work? In a word, *GREAT*. I've had it to 25 meters for an hour and had a blast. It'll go far longer, I just got cold. You had better know what you are doing to try to dive equipment like this, and there is NO margin for error. With that said, I'm entirely comfortable on it. Bailout? Hah! I freedive to 25 meters all the time, and can swim for it. Rip a hose? Unplug the Spare-Air from the P-Connector, shove it into my mouth, and use it demand on ascent.
(1) OMG P-96 Oxygen rebreather
(1) Old spare air (the new ones don't have a shut-off valve)
(2) Gordon Smith PP02 displays
(1) Shop of Horrors 2 cell sensor probe
(2) Dreager P-Connectors
(1) Shop of Horrors adapter between Spare-Air and P-Connector
That's it for the basic rig.
For use with offboard gas:
(1) Quick-Disconnect for offboard gas and self-made adapter for same.
(1) Manual diluent add valve for offboard gas (not show, but made from a BC
That's all, folks. Kids, don't try this without adult supervision. It would
be a REALLY good way to get killed.
contact Dave Sutton