Diving with a Closed Circuit Rebreather Diver

As the club evolves there will be divers who will take their diving beyond the basic open circuit single cylinder no-decompression diving. They will move on to Extended Range Diving (ERD) and Closed Circuit Rebreather (CCR) diving. These types of diving involve different techniques and styles of diving. To help the club's divers get a better understanding I will post some useful links and information in this section on rebreather diving.

How a rebreather works:

http://en.wikipedia.org/wiki/Rebreather

 What you need to know about diving with a rebreather buddy:

http://www.divernet.com/cgi-bin/articles.pl?id=5221&sc=&ac=d&an=

What can happen when it goes wrong:

http://www.hse.gov.uk/diving/video/co2video.htm

CFT Rebreather Safety Recommendations (from www.CFT.ie)

 The following recommendations have been produced in a bid to promote the safe integration of Semi Closed and Closed Circuit rebreathers within the club and C.F.T. as a body. The most important thing that must be remembered is that no matter how well qualified a diver is on open circuit, a new rebreather diver becomes a diver under training and must again build and practise skills progressively, and be fully aware of all the dangers involved in going beyond the limitations of theirtraining and experience. All diving activities expose us to an element of risk and rebreather diving increases that risk, therefore it must emphasised very strongly that the guidelines laid down by the manufacturers and C.F.T. must be adhered to rigidly when diving a rebreather. 

Rebreather Divers 

C.F.T. prerequisites for rebreather training are minimum Club Diver, Rescue Diver, Extended Range Diver or international equivalents recognised by C.F.T.  The types of rebreathers currently approved for use by C.F.T include 1)      A.P.D Inspiration – classic2)     A.P.D Inspiration with vision electronics3)     A.P.D Evolution4)     Drager Dolphin   All training must be completed by a recognised Technical Training Agency (C.M.A.S, I.A.N.T.D , T.D.I , P.S.A, I.T.D.A or B.S.A.C). On completion of the course the diver should register their qualification with Head Office. 

Skills Practice 

A rebreather diver should regularly practise skills taught on their rebreather training course. Most importantly, shut down, gas switch i.e. bail out skills.     

Pre-Dive Checks 

Pre-dive checks should be conducted in accordance with the unit specification and training, this includes breathing from the unit for at least two minutes before entering the water.   

Cylinder Pressures 

The same rules apply to rebreathers as with open circuit scuba equipment. The dive should begin with a  sufficient amount of gas in all cylinders to carry out the planned dive. Divers shall return to the surface with sufficient reserve in accordance with unit specifications and manufacturers recommendations. Contents gauges and pPO2 levels should be regularly monitored throughout the dive.

 Buoyancy 

Rebreather divers must ensure that they have sufficient buoyancy to support them on the surface and at depth with full configuration of kit i.e. redundancy cylinders etc. Sufficient redundancy must also be considered in the event of a flooded breathing loop. 

Buddy Diving 

It is recommended that while a rebreather diver builds up experience on their unit (at least 100 hours dive time), their buddy should be at least an experienced club diver.It is important to ensure that the buddy of a rebreather diver is familiar with the unit so that in the event of a problem the buddy can assist their partner. Although not essential, it is preferable if the buddy has trained as a rebreather diver or has completed the try dive on the unit in a swimming pool.Proper buddy checks on gas and pPO2 levels must be maintained throughout the dive     

Breathing 

It is strongly recommended that rebreather divers breathe freely and normally, i.e. keep the flow going in the loop, this will increase the CO2 scrubbing and help to avoid hypercapnia. 

Alternative Gas Source 

It is recommended that all rebreather divers should carry sufficient open circuit gas to allow a safe return to the surface in the event of a complete rebreather failure.An open circuit regulator may be connected to the oxygen cylinder of a Closed Circuit Rebreather. If one is attached then the second stage must be clearly marked and have an isolator device fitted, i.e. slider shut off valve or similar.Gas supply should be worn on a “rich right” and  “lean left” basis. 

Diluent Gas 

The diluent gas may be air, nitrox or a helium mix (depending on a diver’s qualifications and the rebreather type)Air diluents should not be used below C.F.T’s maximum depth recommendations or in accordance with the diver’s qualifications (whichever is the shallower)  

Oxygen Gas 

All oxygen used in rebreathers should be of the correct breathing grade. 

Descent 

The recommended set point of O2 must be set prior to entering the water, and again on reaching target depth when diving CCR. When diving with a rebreather, in order to prevent task loading and oxygen spiking it is important that the descent is done slowly.  

Bubble Check (Leak Check) 

Bubble checks must be performed to identify any source of leakage and must be carried out no deeper than six metres. Note: Semi closed rebreathers will emit a trickle of bubbles throughout a dive.  

Ascent 

As with scuba, the recommended rate of ascent is 10 metres per minute.A slow controlled ascent is important in order to avoid a drop in the pPO2 in the breathing loop, which can cause hypoxia. (CCR only)It is also important to allow proper venting of the breathing loop in order to avoid becoming positively buoyant.  

Delayed Surface Marker Buoy 

C.F.T. recommend that an S.M.B.  be carried by all rebreather divers (two for extended range dives one red and one yellow) Boats cannot track bubbles, so the deployment of an S.M.B. is a clear indication of position and intent to surface.The S.M.B. if possible should have an independent means of inflation. 

Repetitive Diving 

It is important for rebreather divers that particular attention is taken regarding their O2 uptake. It is essential to ensure that the National Oceanic and Atmospheric Administration’s oxygen exposure table is strictly adhered to as with Nitrox Diving. 

Cover Divers 

It is recommended that divers covering rebreather divers  be familiar with rebreathers. It is also recommended that they be qualified to at least Club Diver level. 

Dive Planning and Organisation 

When a rebreather diver(s) is in the group it is very important that the dive plan and emergency plan are gone through thoroughly so that in the event of an accident/incident everyone knows exactly what to do. This should be normal practice but more attention is required because of the nature of thegroup.   

Stage Decompression 

Stage decompression diving should not be practised unless the diver has completed C.F.T.’s Extended Range Diver course or  a recognised equivalent.If stage decompression is planned it must be carried out using a recognised decompression computer and/ or decompression software.The diver must have a bail out plan and carry with him an adequate bail out supply of gas to enable him to cope with any foreseeable emergency situation that may arise.This type of diving should be carried out in accordance with Extended Range guidelines. 

Dive Site 

Diving involving hard work by the diver i.e. heavy seas, strong tidal conditions must be avoided by rebreather divers. This is because of the danger of a CO2 build up in the breathing loop of the unit. 

Boats 

When covering divers on rebreathers the boat cox’n must pay particular attention when manoeuvring the boat as rebreather divers produce very few bubbles if any. Rebreathers are “Life Support Equipment” and must be treated with respect on the dive boat. 

Care and Maintenance 

Particular attention must be paid to O2 cells. It is important that these must be dried off, removing any condensation build up after every dive. The manufacturer's recommendation regarding the changing ofO2 cells at intervals must be followed.  

CO2 Absorbent material 

It is imperative that the manufacturer's recommendation regarding the type of absorbent material and duration is followed to the letter. 

Hygiene 

It is important to disinfect the breathing loop in accordance with the manufacturer's recommendations using the proper solution.The breathing loop must be thoroughly washed and disinfected after each use to avoid lung infection.  

Rebreather use during courses and tests 

Rebreathers can be used in all C.F.T courses and tests (except rescue tests) by either the instructor and / or candidate, provided both parties consent. This should be arranged in advance of the course/ test.If a candidate in any way feels intimidated by an instructor using a rebreather during a test, then the test should be carried out on open circuit.