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All I know it is common practice in the USA to use lift bags under which to decompress. This seems to me to be a poor option with all the inherent problems that have been exposed by the recent tragic events. A while back there was a thread on drift decompression diving but I thought it may be worthwhile to mention the system the group that I dive with use. I'm not sure who invented this process but Nick Jewson was instrumental and introduced me to it, so I do not wish to claim any credit for myself. We use lift bags to lift artefacts and Delayed Surface Marker Buoys (DSMBs) for decompression. My lift bags are all yellow with the intent of making the skipper's job of recognition easier although this has not been universally adopted (yet). Firstly due to the UK conditions, we usually do drift decompression diving - typically about 60 minutes of deco. This is under a DSMB that is deployed from the wreck. The DSMB has a small cylinder that will self inflate the bag and is simple to deploy underwater. The cylinder can be recharged from an A-Clamp (yoke) pillar valve. As it is self inflating, there is no change to the diver's buoyancy whilst the gas is injected as would be the case with a manual DSMB or lift bag. As a result I deploy immediately on leaving the bottom i.e. on-the-fly whilst ascending. The bag is sealed with an OPV so there is no chance of the DSMB toppling over and deflating. The product is sold by Advanced Diving Products although there are others on the market now. Its is red in colour. The reason the DSMB is deployed from the wreck is to ensure that the current does not drift us a significant distance away from the wreck to an area where the skipper may not be focusing his attention. We carry a reel with sufficient line to allow for deployment on the bottom. There is a section of about 12-15 metres of stronger rope at the SMB end to take the strain of the longer duration of hang. I also insert a length of about 1 foot of bungee to further cushion any impact of wave action. The line is *not* cut but tied top and bottom to the bungee. However, between the two knots the line is coiled around the bungee so that the it can stretch (this is my only claim to fame on this system). Doing it this way, the bungee can be wound into the reel keeping the setup clean and allowing deployment without snagging. In the event of a failure of the primary DSMB or reel we discard it and switch to a secondary. This is a small red DSMB which is self inflating using a CO2 cartridge and sealed to stop gas escape. Again sold by Advanced Diving Products. These are really small and easy to deploy but require an additional reel. Some people use smaller reels which means that the secondary cannot always be deployed at great depth but at least from about 50m (165'). We assume that there has been a buddy separation hence the redundancy. Red DSMBs mean that the diver is decompressing normally. However, we also carry what I refer to as the signalling DSMB which is a day-glow lime green. This disgusting colour signals the boat that there is something wrong and spare gas or a support diver can be dropped in this event. The signalling DSMB is attached to the primary or secondary line an sent to the surface so that the boat sees a red and green SMB together. Our emergency bottles are pre-attached to 1" webbing and a float. The regulator is fitted so that the whole setup is ready to rock and roll in the event of it being required. We use steel safety bottles which ensures that they sink. The main problem with the primary is that it is bulky - I carry mine in a pouch on my waist section of my harness, pushed to the rear to ensure minimal drag. The other SMBs are not a problem due to their small size. AP Valves sell a nice inexpensive DSMB that is manually inflated and seals itself when inflated. This is a cheap alternative but does not have the advantage of simple deployment that does not affect the buoyancy. David Shimell Project Manager, Sequent Computer Systems Ltd, Weybridge, UK Email: shimell@se*.co* -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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