As a full service scuba shop, we at West End Divers have looked a little sideways when the subject of rebreathers is brought up. Seemingly a bit on the “weird science” side of things, and assuming it to be new untried technology that needs to have the bugs worked out. Our attitude has changed.
After much study and soul searching our part-time instructor Tom, decided to embrace this form of diving and purchased a rEvo (brand) rebreather, and has been using it diving here with us. Mike, tech diver and longtime friend of the shop suffered exposure to this form of diving here on his last trip, talking to Tom and seeing the unit in action. Mike was already considering rebreather diving, and this may have sealed his decision because he rocked up this week with his own rEvo rebreather. Strange demographics immediately developed in the shop. We now have Open Circuit divers, and Closed Circuit divers (each with their prides and prejudices).
Open Circuit divers are the Scuba divers with a mask and a tank on their back who enter the water breathing compressed air from the tank and exhaling into the water in a cloud of bubbles, and diving until the tank is nearly empty, having to surface to avoid ailments like drowning. Think; James Bond, Jacques Cousteau, and Mike Nelson.
Closed Circuit diving and Rebreathers are a little more complicated, although automatic. The unit is closed-looped, and the diver must fill a small internal bladder by breathing into the unit prior to the dive. During the dive the diver’s exhalation travels through filters or scrubbers which extract the carbon dioxide from the used breath, and this scrubbed gas moves on to a bladder. The diver’s inhalation then draws from this bladder, completing the “closed loop”. The all-important oxygen that is consumed by the diver is monitored by computers attached to sensors, and is replenished from a small tank as needed.
Surprisingly Rebreathers are not new; the first commercially practical closed-circuit scuba was designed and built by the diving engineer Henry Fleuss in 1878, whereas it wasn’t until 65 years later that Emile Gagnan and Jacques Cousteau came up with the Open Circuit Scuba in 1943.
Rebreathers were originally designed as a means of escape from disabled submarines and for military applications. Due to the military importance of the rebreather, amply demonstrated during the naval campaigns of the Second World War, most governments were reluctant to issue the technology into the public domain. It wasn’t until after the Cold War that recreational diving rebreathers started to appear.
There are distinct advantages to Closed Circuit diving. Rebreathers are virtually silent, allowing the diver to observe underwater life without the roar of exhaled bubbles scaring the fish off, a huge plus for photographers. There is also extended bottom time. The rebreathers carry a 19 cubic foot capacity tank of pure oxygen to replenish used O2 during the dive. Because it is monitored, and because only the O2 needed is added to the system, this small tank less than a quarter the size of a normal Open Circuit tank, will allow the diver a six hour dive at a depth of 60 feet, compared to one hour on Open Circuit in the same conditions.
There are always disadvantages, and from casual observation I notice that there is lot more maintenance. These models have 5 oxygen sensors, two computers, and two scrubber cartridges which have to be maintained and in the case of the cartridges re-packed. The oxygen bottles, although small have a capacity of 3000 psi, and to support these units we have installed a high pressure gas booster pump. We are also importing the media for the cartridges which comes in the user-friendly 50 lb. canisters the airlines love so well.
The Closed Circuit guys; Tom and Mike, were accompanied by the Open Circuit guys; Mickey, Kal, Bugs, and myself, to everyone’s favorite Nitrox dive site Texas to see what all the hub-bub was about.
The dive site Texas rarely disappoints, and this day was no exception. There was zero current and making our way down the spectacular Pablo’s Wall after 40 minutes we came to the end of the universe. This is the Southwest-most point of the island underwater. It is at about 100 feet deep, and juts out into the abyss covered in corals, huge barrel sponges, and surrounded by the bottomless deep blue. This was it for the Open Circuit guys, as we were limited to 111 feet deep by the Nitrox we were using, our Nitrogen loading was approaching its limits, and we were running low on air (Nitrox). With no choice left but to ascend, we all surfaced and were picked up by the boat. A seriously incredible dive was had by all and amongst the woo-hoos and high fives Mickey (open circuit guy) offers a little lament in the form of “If only we could have stayed a bit longer...”
“Whaddaya mean?” Mike (closed circuit guy) says, “We had four hours left!”
OK, we have the Oxygen booster pump, the scrubber media, and I am having alarming thoughts of a major retail purchase.