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On Sun, 25 Aug 1996 heyydude@pi*.co* wrote: > > AGA. The U.S. Navy Diving Manual (Vol. II) indicates that only Heliox is > used for deep dives with the Mark 15 & 16. They also set a bottom limit of > 200 fsw for both rigs. I don't know if that has something to do with > density of gas, or just the standard Navy safety crap, but the gas did feel > pretty thick (trimix) at 260' a few weeks ago. The depth and gas selection limits used by the Navy are set for their use only. These limits do not mean that these are the limits of the units themselves. Under ordinary circumstances Navy divers use surface supplied gas for deep operations and would not use rebreathers at all. The U.S. military uses rebreathers for two basic purposes, neither of which would ordinarily require heliox nor 200 foot dives. These are 1. clandestine infiltration and 2. EOD. This is why the MK 16 is silent and has a low magnetic signature. The military has a different agenda for the use of rebreathers than the sport diving market. The MK155 has been used by commercial divers in Europe to 1200 feet (deco was in a chamber) and has been used by non-military divers to depths in excess of 200 feet using air, trimix and heliox (a waste of good helium). I have dived my unit to 330 feet or thereabouts with trimix and never noticed any breathing problems related to gas density. If you are working hard at that depth there are certain body attitudes that make it more difficult to breathe, but if you change position in the water, the difficulty goes away- which it would not do if it were density. One of the biggest differences between OC and CCR diving is how each provides a breath for the diver. In OC -once you have sufficient experience- breathing is effortless, smooth, easy and you get as much gas as you want, the instant you want it. In CCR diving, it don't feel anything like OC. It is not harder or easier per se- it's different. It is not as effortless as OC, you don't necessarly get as much gas as you would like at times (when you bottom out the counterlung), it doesn't feel as smooth as OC, but it is easy to breathe and it is quiet. Throw in FFM and the differences are magnified mega-fold. FFM with OC means just a flicker of your nostril will deluge the mask with gas; FFM on CC. you have plenty of time to reflect on how hard it is to breathe while you are sucking in that first breath because it takes longer to get a lung full. The Navy diving regulations for salvage, construction are as or more stringent than OSHA Commercial diving regulations. Tethered divers, surface comm., diving bell for ops deeper than 200 feet, chamber on station. I don't know what the depth limit for OC scuba is but I'll bet it is around 120 feet. (In Ontario, it is 100 feet for commercial dives). If CCR op and one of three sensors goes out, the dive is scrubbed- I would still dive the unit. The death of the Sea Lab guy back in the 70's (?) on a RB really tightened the screws for RB diving in the Navy and the recent two deaths on the Mark 16 have the Navy standing down the use of the units right now unless it has been lifted. The US Navy Diving Manual is really good for when you are in the Navy- they won't let you dive without it. Out in the real world of YOYO diving where a little knowledge is a dangerous thing, the Navy Manual doesn't have much application except for Great Lakes divers to rationalize their fears of rebreathers. > > When you get your rigs, just go out and dive 'em. Get acquainted with it, > learn all its tiny nuances, talk to guys like John and Rod about theirs, > and most of all, have fun. I spend an hour last week on the bottom on a > shipwreck, just screwing around - it was great. I could have spent a > couple more hours down there, without a care in the world. That's what > makes these machines so cool for diving. The compressed air dudes I was > diving with had to bail after 40 minutes. > > Just thought I'd throw my two cents in... > > Kevin > HeyyDude > -- > Send mail for the `techdiver' mailing list to `techdiver@terra.net'. > Send subscription/archive requests to `techdiver-request@terra.net'. >
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