The P1SS Rebreather

There were smiles on everyone’s faces when I slipped into the water for the first ever dive on my homemade rebreather. For one thing the device looked like a vacuum cleaner with its scrubber made out of a piece of yellow plastic gas pipe and a counterlung made from a car inner tube. The smiles turned to laughter as the diver emerged a few minutes later with the rebreather in two pieces, counterlung in one hand and the rest of the unit – leaking an alkaline solution – in the other. Back to the drawing board…

Before going any further it should be stressed that making your own life support apparatus is very hazardous. Messing around with rebreathers can leave you looking stupid, dead or both. Futhermore, it might not actually save you any money. Look upon it as a form of adult entertainment. My closed-circuit rebreather is not, however, a toy and has seen some useful service.

Of course, rebreathers are not new, having been around for over a hundred years. The Italian Navy caused great consternation to the Allied forces by scootering up on ships and placing limpet mines on them. The British copied them and these early rebreathers fell into the hands of the Cave Diving Group who used them in places like Wookey Hole as a means of exploring underwater caves. Some of my friends had rebreathers (both homemade and commercially available units like the KISS and Inspiration) and I wanted one. The easiest place to start was to build a simple pendulum style oxygen rebreather for shallow water diving and also for decompression. With no means of monitoring the partial pressure of oxygen one is breathing it is important to purge the loop of air before using. Furthermore, on pure oxygen one’s depth is limited by considerations of oxygen toxicity when are the diver descends. A practical limit for such devices is 6 m. A problem particular to pendulum rebreathers is that the space between the mouthpiece and the scrubber is not cleaned of carbon dioxide. By fitting a power inflator with a bayonet on/off switch I could breathe from this and add oxygen ahead of the dead space thus sweeping any carbon dioxide back into the scrubber. The design is hardly original but it is surprisingly effective.

Before I go any further I should add that I only ever dive in caves or mines. All the testing of my creations has been done underground. It’s a steep learning curve…

Back at our HQ near to Peacock Springs a spare horse collar buoyancy compensator was pressed into service as the counterlung. Trials in the entrance to Peacock Springs under the watchful eye of the Park Ranger were successful. A couple of days later the P1SS (as it became known) was moored in the entrance to Manatee Springs while we scootered a mile into the cave and back. This was the first serious trial of the unit as a decompression tool. On reaching the rebreather I had to figure out a way of breathing from it without flooding it. This was achieved by opening the inverted mouthpiece while injecting oxygen and shoving the bubbling end between my lips. Fine. I then made the mistake of trying to put the horse collar over my head. This involved dislodging my mask and nearly drowning. Not good.

The second test was in some caves near Tampa. This time everything worked well and I learned that it was easier to stick my arm through the head-hole of the life vest and carry the rebreather around over my shoulder. Back in the UK the P1SS was used for some short, shallow caves dives in the Yorkshire Dales and at Wookey Hole. A careful watch was kept of the diver’s depth to make sure that the operator strayed no deeper than was allowed. The unit could also be used as a conventional buoyancy compensator by having more oxygen in the counterlung than was required to breathe. This feature came in handy when I rescued another cave diver who had lost a fin and was severely overweighted. I also learned not to exert myself too hard otherwise the little scrubber could not cope with the rate of carbon dioxide generation. It was very good for decompression and slow swimming though.

Its next foreign trip was a ten-day excursion to the Lot and Dordogne areas of France. I’d got a 3 l steel cylinder dedicated for oxygen use. This ended up lasting me the entire time I was there (in addition to a few changes of sodalime carbon dioxide absorbent) – being used for several decompression dives as well as one 500 m cave penetration solely on closed circuit. As always, I carried adequate open circuit bailout, which included fitting a second stage to the oxygen cylinder driving the rebreather. This came in handy for another diver whose computer had locked out on him – I simply unplugged my rebreather (when I’d done with it) and passed him the open circuit regulator and oxygen tank to use up. An amusing incident occurred when I returned to my rebreather (having left it securely moored at my 6 m decompression stop) to find it missing. Suspecting foul play or a trick by my buddies I spotted it on the surface floating above me. An emergency ascent to collect it and a return to my stop and all was well. A second incident of that nature taught me to securely fasten the rebreather to something solid when leaving it for later use.

Since then the P1SS has seen sterling service in the UK during explorations of a flooded mine complex near to Birmingham. The limits of exploration lie over a kilometre from the entrance at depths approaching 60 m. The rebreather can often be seen moored to a collection of rocks some 50 m into the mine and gets used for hour-long hangs in cold water. The benefits of breathing warm gas from the rebreather are apparent as well as the cost savings (1/2 the price including the cost of the sodalime) over using oxygen in open circuit mode.

Unsurprisingly, my antics have generated some interest amongst my colleagues and there are a number of homemade closed-circuit rebreathers in various states of construction. I’ve been working on a fully closed, mixed-gas rebreather which has seen field (cave) use on a number of occasions. More about the thrills and spills of that some other time…mind how you go!

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