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I've never used a chest mounted switch block but I have seen them in use. They are *not* widely used by eastern states (of Australia) divers and they are essentialy for switching supplies without changing regulators. I only know of two divers who used them. One of these divers described an incedent to me where he was on one gas, thinking he was on another, (he was switched to the wrong cylinder) He was on his O2 stop and spent 10 minutes on bottom mix rather than O2. He discovered his mistake, and simply disregarded his time on bottom mix and did his full deco again, this time on O2. (he hadn't surfaced so no harm was done) Shortly after this discussion he died on a 48 metre (160 fsw) dive. It has been speculated that he was switched to his deco gas on the bottom (50/50) but I have no evidence of this one way or the other. I would not recommend any diver use a switch block to change from one cylinder to another. In the commercial world, decompression gas is not even attached to the panel (gas distribution device) untill the diver calls that he is on his stop and his depth has been checked by the diving supervisor. Cheers Jason (not the Scottish one) O-) > > >Dr. Ali Lawrie asks for field experience of manifolds vs two independent > >cylinders. > > > >I dive in Lake Superior; water temps are just above freezing to about 50 F. > > I, like Dr. Lawrie, could never reach a manifold isolator valve because of a > >drysuit and thick underwear. A valve block in front of the diver would help, > >if one exists. > > Home made chest mounted air blocks are used in the eastern states of > Australia for wreck diving, these have been previously described on the > list, two first stages, air block, one second stage, block selects for > either or both first stages. I'll let someone who actually uses one > describe it better. > > > >Problem with 2 independent cylinders: A friend of mine nearly died of the > >bends in Lake Superior some years back as a result of not opening the valve > >on his second cylinder. A small but critical error! He ran out of air at > >140 during an ascent from a 190 for 20 exposure. Lots of permenant damage > >resulted. Buddy was below by 20 feet or so and didn't realize the problem in > >time to reach him. > > This doesn't sound like a problem inherent in the equipment. > > > regards, > > David Doolette > ddoolett@me*.ad*.ed*.au* > > -- > Send mail for the `techdiver' mailing list to `techdiver@opal.com'. > Send subscription/archive requests to `techdiver-request@opal.com'.
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