Keeping skills fresh

Diving like any other physical activity requires training and after the courses and certifications are under one's belt it is good practice to keep skills fresh ... Personally I tend to practice my skill circuit when I'm doing easy relaxing dives such as the familiar shores dives at Cirkewwa and Zurrieq as well as during long decompression on more demanding dives ... Repeating the skills outside the course framework and during normal dives keeps muscle memory tuned in.

A lot can go wrong when diving on a closed circuit rebreather, knowing how to handle issues that crop up before and during a dive will end the dive with a happy face. During TDI training it was drilled into my skull that before getting in the water I must run a series of tests, these test cover all the steps involved in the setup of the unit, so if per chance a step is incorrectly executed or omitted, when going through the pre dive checklist the error is caught and resolved.

There are three main tests;

Pressure Test

­    With the cylinders open, I run gas through all the buttons, counterlungs, ADV (Automatic Diluent Valve) and both the wing inflators (primary and secondary, since I'm using a double bladder wing)

 

The Electronics Test

­     The cylinders are opened, the unit is switched on and the software runs a number of checks;

o   the temp stick (Sofnoline duration),

o   batteries life, and

o   cell reliability (the cells check the partial pressure of Oxygen),

o   this test also gives the option of calibration which I opt to do every time before a dive, the unit calibrates the three cells and gives an average reading.

Positive & Negative Test

­     Closing the cylinders and the mouthpiece, the air is purged into the counterlungs which are further inflated to their maximum capacity orally through the mouthpiece, this tests the counterlungs and connections under positive pressure.
    After a few moments if the pressure remains unchanged the air is vented from the over pressure relief valve &/ the mouthpiece and any air left inside the lungs is sucked out orally, at the same time squeezing the breathing hoses, this tests the counterlungs and connections under negative pressure.

­     If either of these tests fail, all the connections are checked to make sure they are finger tight closed properly.

Once the unit passes all the tests then it is good to dive.

What if I encounter a problem during the dive?

During any type of dive, recreational or technical I always carry enough bailout gas that will enable me to abort and end my dive safely, should something go amiss on the Rebreather.  On recreational dives I normally carry two cylinders one with 21% - Air and the second with a Nitrox Mix, usually 60% or 70%, on technical and more demanding dives I carry a third tank with a Trimix mix suitable for the bottom depth of that particular dive.

There are a number of skills, which once mastered can get any diver through different situations.  Similar to knowing how to remove and replace a mask underwater gets a diver through, partially, fully flooded mask or lost mask.

Mouthpiece removal/replace

Knowing how to safely and comfortably remove a rebreather mouthpiece is a key skill when diving on closed circuit. For those that are not familiar with rebreathers, the mouthpiece must be closed before being removed from the divers’ mouth.  Failing to close the mouthpiece properly will cause water to enter the unit and flood and damage the electronics.  Once the mouthpiece is closed and removed it naturally floats above the divers’ head, since it is positively buoyant.

One starts to breath through the bailout gas, open circuit regulator.  Retrieving the loop and returning it to the mouth before opening it is very important for the same reasons mentioned earlier.  Once the diver has the loop safely in his/her mouth then it is safe to exhale, any water lurking in the mouthpiece will be purged and the diver can start breathing normally.

Gurgling sound in the breathing loop

Sometimes condensation or a little water in the mouth piece can create an annoying gurgling sound, which can be easily cleared, this is done by closing the mouthpiece, extending the loop above the head, stretching the arms as much as possible and tilting slightly to the right, any water lurking in the loop will be safely drained into the counter lung.

Practicing this skill when there is no water in the loop keeps it fresh for when diving at depth and the skill needs to be performed quickly and effectively.

Bailing out at depth

     

Whilst diving the diver switches to the off board gas, whilst breathing from the bailout tank that way one can identify and resolve most situations that arise. The procedure; Close the mouthpiece and remove it from the  mouth, open the bailout gas suitable for the diving depth, trimix, air or rich nitrox, purge the regulator and breath ... Check the cell readings on the Vision handset and if all is in order, prepare to go back to breathing the CCR ... ahhhh silence at last.

Should the situation not be resolved, switching the rebreather to open circuit, immediately changes the setpoint from high (1.3) to low (0.7), diver should remain on open circuit bailout gas, switch the back up computer to open circuit, check decompression status and begin a safe ascent to abort the dive.

Closing the on board cylinders

Being able to reach the on board cylinders is also a key skill, which is not easy to master especially when carrying one or more bailout tanks.  However with patience and practice it becomes second nature to reach behind and feel for the cylinder knobs and turning them closed.

The manufactures' advice is that the Oxygen cylinder valve is only open by one or two turns max to enable quick closure in case of emergency.

High Oxygen also known as the “Oh Shit !!!” Moment

Several reasons why there could be a High Oxygen warning, these include; an Oxygen Spike, which happens when the descent is too fast, slowing down the descent should resolve the issue.  Another reason could be that the partial pressure of Oxygen (ppO2) is rising quickly, if this happens, the steps to follow are;

Switch to bail out, close the oxygen cylinder, check that the pressure gauge goes to Zero, flush the loop with diluent (this reduced the existing ppO2 in the loop), by pressing  the diluent button and at the same time, pull the overpressure dump valve cord (this is done to avoid a rapid ascent to the surface). Open the O2 Cylinder slowly, check the readings on the handset and check the pressure on the pressure gauge, return to breathing from the loop and monitor the readings on the handset.

I must admit it is an unpleasant experience to hear the buzzer going and see the heads up display flash bright red, the moment I look at the handset and notice a high oxygen warning I’m never happy, but keeping the “Oh Shit” drill fresh gives me confidence that I can perform the skill and solve the problem safely.

In the four years I have been diving Closed Circuit I have encountered very few problems which couldn’t be solved – I am very happy diving my AP Rebreather and if I had to recommend Closed Circuit Rebreather diving to my buddies I would say;

1. Make sure you follow instructions, checklists and manufacturers' warnings.

2. Do not sign up for Rebreather Diving if you’re planning on cutting corners and saving money on batteries, Sofnoline & cells – you’re cutting corners with your life!

3. Take care of the unit, it will take care of you.  Maintain the Rebreather, rinse the unit and lungs after every dive, service it as per manufacturers' instructions & replace consumables as and when necessary.  Send the electronics for periodic servicing to the manufacturer.

4. As in Open Circuit Diving - Know your equipment, set it up diligently and always use a check lists.