SATURATION DIVING - BRIAN COOPER
The early days of the North Sea oil industry created a series of demands on the then burgeoning diving industry and it was necessary to develop a technique where you could dive regularly in deep water without hurting people, or hurting people as little as possible should I say. So what they came up with was a technique called saturation which was developed in the 60s and 70s. And basically you live in a chamber for 30 days or more sometimes at a time, under pressure. Transfer to a diving bell such as this one here and then that’s lowered, perhaps even through the deck of the ship, through the hull (a moonpool) into the deep water to a depth obviously of the job that you’re going to do.
The diver then leaves the bell, goes off to do the work, maybe working for some 8 hours at a time, comes back to the diving bell, the doors are shut, sealed at that pressure.
Statfjord on Magnus Field STEVE WELSH
The diving bell is then recovered, back through the moonpool, locked onto the chamber and the diver then enters the chamber and takes his rest period, where he can get food, a shower and go to sleep. There’s always at least two divers in the diving bell.
In order to extend the depth capability beyond 50m, which was required for early commercial diving, helium was introduced as the diluent gas in breathing mixtures. Apart from the Mickey Mouse voice, dealt with by a helium speech unscrambler, helium is absorbed into tissues more quickly and can require a longer decompression time.
A further problem is the rate at which heat is dissipated from the body through breathing denser gas mixtures at depth. As the body is unable to replace the lost heat just by working, hypothermia now becomes a problem.
Today, what’s actually happened is that they’ve extended the period people can spend on the sea bed, whereas obviously in the past it was much reduced; they’ve extended the depth that you can reach, significantly. There have been dives taken place in 2000 feet for experimental purposes and I think one working dive at that kind of depth, but at the frontier you really are in some danger in reality: similar to divers in the seventeeth and eighteenth century.
CURRENT COMMERCIAL SET - IAIN MIDDLEBROOK
HSM Engineering Technology
Bringing us up to date we have a selection of diving equipment in front of us that brings us quite nicely into the 90s. We have a straightforward diving helmet, a band mask and a diving bale-out set.
We’ll start off with the bale-out rig to begin with. It consists of a cylinder, first stage regulator and harness assembly. Incorporating in the harness assembly is the lead weight. In addition you have various lifting points and various anchorage points to be able to put tools or the umbilical harness itself.
COMMS & DIVER
("And clear also.") "Ready for off. Ready for water. All clear. Ready for bubbles. Right, moving myself apart."
These two units are both in current service in the North Sea, both for air and mixed gas unit. The heliox is generally speaking used as a bellman’s hat, the superlite 17A or B is generally speaking used as the main diving hat.
To look at them in a bit more detail. The diving band mask consists of a hood and spider arrangement with a neoprene face seal at the front of the mask. Inside here you can clearly see the oral/nasal cavity. This unit here is a nose clearing device and on either side are the two earphones and in the oral/nasal is a microphone for communications.
Second stage regulator very similar to what a sports diver would use, but has the advantage of a ‘dial a breath’ so the diver, on depth, can change the pressure in the unit. And it has two forms of air inlet: there’s a standard air inlet from your umbilical; there’s a secondary air inlet point which is connected to your bale-out cylinder.
DIVER & COMMS
"The control is working." ("Is it an open flange or a blind flange?") "It’s a blind flange." ("Yep, how many bolts on the flange?") "Yes, there are bolts on the flange and I’m just trying to count, about... I’d say there are ten bolts on the flange."
This is becoming a more popular system for commercial divers: it has the advantage that being a helmet, you don’t get a wet head. The component parts manufactured in this unit are very similar to the hat we saw before. Second stage regulator, ‘dial a breath’, nose clearing device, main on/off valve and emergency valve at the side. Under normal diving conditions we now have a system whereby an emergency pin has to be placed within the system to disengage the ability of the diver to be able to take his own helmet off underwater.
The maximum diving requirement on this particular set-up would be 50 metres.