By Peter Steinhoff

Breathing the wrong gas at the wrong depth will kill you
This is a simple procedure yet it can cause big problems for those trying to do it fast and mess
it up. Remember, slow and deliberate is always fast. Also keep in mind that all deco and stage
tanks are turned off when not in use. That prevents us from loosing gas without knowing it
and is also an additional safety step preventing us from breathing the wrong gas.
Common mistakes

These are the most common mistakes for those relatively new to this:
- It’s easy to float up or down while changing regs. The solution is to check the depth
between each step of the procedure.
- It’s easy to get the hoses wrong. Make sure you have a clear mental picture of where
everything goes and what is behind or crosses when you switch.

Switch to stage or deco tank
1. Wait until you reach the switching depth.
2. Hang up you primary light (turned on, pointing down).
3. Choose the proper tank by looking at the MOD label and show it to your buddy who
verifies it with an OK (depth and gas is correct).
4. Grab the second stage with your right hand and route the hose around your neck.
5. Open the valve and purge the second stage.
6. Remove the long hose (with left hand) and put the stage/deco reg in your mouth and breath.
7. Clip the long hose on the right chest D-ring.
8. Unclip your light and signal you buddy that you are ready with an OK.

Switch back to the long hose
1. Hang up you primary light (turned on, pointing down).
2. Unclip the long hose and hold it in your right hand.
3. Remove the reg from your mouth with your left and pull the hose over your head.
4. Put the long hose in your mouth and start breathing.5. Close the valve on the tank you were breathing.
5. Close the valve on the tank you were breathing.
6. Lift the inner tube with your left hand (thumb) and push the hose in there.
7. Pull on the hose and make sure the second stage is secured under the inner tube.
8. Unclip your light.

Switching between multiple tanks
If you need to switch from one stage to another, from a deco tank to another or any
combination, you go to the long hose first. Like this:

1. Switch back to the long hose and stow the tank you are breathing.
2. Move tanks around if it makes things smoother.
3. Switch to the new stage or deco tank.
And you can have the light clipped off until you have completed the whole process.
If you are switching deco gases, let’s say from 50% to Oxygen, you switch to back-gas (long
hose) at 9m/30ft for the last couple of minutes. That gives you time to stow the 50% and
move things around. Then ascend to 6m/20ft and deploy the oxygen. This is the cleanest and
safest way to do it.

Gas breaks
When doing more than 20 minutes on oxygen you have to do a gas break to keep the gas
exchange effective. When you go to breathe the long hose you can stow the reg on the oxygen
tank just by clipping the second stage to one of the bolt snaps or the handle. Anyway you
chose to stow it, you NEVER let regs hang around your neck. Why? Because when something
happens you will not know what you are breathing or even if it is turned on.
Team switching
When you switch deco gases it’s best to do it one at a time, especially if you’re not very
experienced. The chance of something going wrong is always bigger at the gas switches so it’s
a good idea to supervise each other. I have stopped people from breathing oxygen at the
wrong depth or choosing the wrong tank several times. Also it’s easy to get something into the
second stage, like small sticks, sand, clay and if you breathe that you may need some help to
recover. By the way that’s why you need to purge the second stage before breathing it. But we
all make mistakes, right?

Stage diving
When you are using stages in the ocean you often suck them dry or almost dry. Then you
switch to the back-gas (unless you have several stages which is uncommon). If you want to,
you can signal your buddies, show them the switch sign and everybody can do the switch.
Nice if you have similar gas consumption since everybody’s stages should be getting close to
empty. If you are experienced you can switch on the fly though.

Source

Gloucestershire based Severn (7) Shipbuilders has designed and developed an innovative rigid inflatable boat that is able to submerge and operate underwater.

Inflatable boat designed as underwater vehicleThe primary use of this form of vessel is for carrying maintenance workers and their equipment to undertake underwater repairs and routine maintenance of underwater structures, such as oil rigs, production platforms and bridge supporting structures.

The primarily operating profile would have the vessels launched from a surface maintenance vessel, where they will quickly travel on the surface to near the designated working area, and then completely submerge to operating depth using electric motors for propulsion and manoeuvring.

The outer tubes will normally be open, and can be closed with simple valves and vents. Contained within these tubes will be an inflatable inner tube that will only be inflated underwater to provide positive buoyancy for re-surfacing. An underneath compartment will contain the main fuel tank and powerful lightweight batteries. This will be capable of being flooded to assist submerging and to maintain stability underwater.

The crew will all be wearing scuba and breathing equipment, and will also be carrying the necessary tools and equipment necessary for the task in hand. All crew will be trained as helmsmen, and will be able to carry out any function in the use of the vessels at all stages of its operational profile.

Means of exit and egress: The vessel is designed to allow the occupants to easily enter and exit through the open canopy roof and is constructed entirely from marine grade aluminium, with standard transverse and longitudinal framing

Author:
Justin Cunningham