Use of the Halcyon Rebreather (John Todd)
WKPP Initiates Use of Halcyon Rebreather
by John Todd
While the Woodville Karst Plain Project is best known for precision teamwork that results in unbelievable scuba dives covering record distances in deep caves and for withstanding in-water exposures and decompressions not thought possible, they are also known for being on the leading edge of equipment and technique development. Along those lines the bar was again raised by the WKPP with the advent of the Halcyon rebreather.
This machine has been brought into the WKPP stable of underwater tricks the same way everything else was – by going to the smartest guys in a particular field and using their expertise to design equipment suited to the need. George Irvine was introduced to Jack Kellon and began diving experimental versions of the machine some time ago, and then Robert Carmichael of Brownies Third Lung in Ft. Lauderdale teamed up with Kellon to form a new company, PVR-BASC, to manufacture the unit with the WKPP as the ongoing beta testers,
Following extensive in-water testing by George Irvine, as well as chamber testing by PVR, WKPP began cave diving the unit and developed a complete open circuit bailout system that will take a (well-conditioned) diver 10,000 feet at 300, the limit of exploration so far. Obviously, safety bottles would be used to increase this margin significantly. A semi-closed circuit dive on the unit to 10,000 round trip takes a single 80 aluminum of gas, versus the 9 aluminum 80 equivalents it took to do just that dive in Wakulla by Brent Scarabin, Jarrod Jablonski and George Irvine this past summer.
Decompression is not a problem for the team on these dives, as they already have closely approached the maximum necessary with a 155 minute bottom time at 285 in Wakulla. For twice the time, the deco only rises by five hours max, not a problem for this team. Scooters are no problem as just one of the three used by each diver will go 20,000 round trip. Lights are not a problem as the exploration version of the AUL light burns five hours with a 50 watt bulb. Backup lights built by Barry Miller have a focused beam which extends for 100 feet.
The real advantage of the rebreather is that dives can be setup and executed simultaneously, as gas does not have to be used to set up gas – the full load of bottles can be taken to their destination unbreathed. With the limited windows allowed the WKPP due to operation of the State Parks and the weather, every opportunity must be taken advantage of to the fullest. Since team members have jobs and can not take endless time off to dive, we must become more efficient as the distances get longer. Also, as our favorite cave, Leon Sinks, has obvious stretches of up to five miles with no sinkholes as it travels south, we must be able to get in and get the job done without it taking weeks. WKPP plans to dive the resurgence as well.
WKPP has already begun working the Halcyon into its dives, and plans extensive use of its machines once the system clears. The real trick to doing this is the fact that we can already do it on scuba – this will just let us spend more time in the cave and do more things while we are there, bringing all of our potential work onto the same priority level.
The Halcyon is a passive semi-closed system which is keyed to respiratory minute volume. In other words, the diver’s breathing operates the addition and deletion of gas, and the diver breathes what the supply gas is, for all intents and purposes, and there are no electronics of any kind.