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Dave
>
>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.
>
Exactly my thoughts Dave
>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.
Pete Smith used this system in 1980, he wrote it up for Diver mag in the
80`s, they rejected it as excessive and wouldn`t publish it.
>
>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).
Names written on them can help, and insistence on everyone putting their
own up and not sharing gives simple indication of numbers up. This would
allow a surface cover crew to act before anyone has surfaced and
possibly prevent a loss. We certainly had a death in Scapa which could
have been avoided with this sysem.
>
>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.
We now have a policy on board and I know that Al Wright is thinking
along the same lines that the first thing on long dives is to return to
a station on the shot line etc etc. The DSMB system is to be used as a
back up in case of non return to the shot.
>
>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.
Also to prevent fatally deploying into the vessel from shallow water,
depth gives you time.
>
>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.
We tend to suggest the non ratchet type reel as they need three hands
for operation.
>
>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.
this is becoming standard.
>
>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.
If you all float on bags how many of these do you have?
>
>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.
Because of the bulk a lot of guys still use an manually inflatable one.
>
John
Web site http://www.johnpt.demon.co.uk
John Thornton Owner/Skipper M.V.KARIN
Polrudden House scapa Flow Technical & Charters
Peerie Sea Loan Air & Nitrox Charters & Tuition To Trimix
Kirkwall
Orkney UK Tel 01856 874761 fax 01856 870950
KW15 1UH
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