Diving Rebreathers is being hailed as the future of Scuba Diving, The question is, why are Rebreathers becoming so popular? What are the benefits of using CR on a dive? How do they work and what do they do?

CCR stands for Closed Circuit Rebreather and essentially means that when you exhale, your bubbles are not released into the water as with normal scuba equipment. Instead, the gas you exhale is recycled back through a scrubber unit, containing grains of Sofnolime (I won’t go into the chemistry but there’s a chemical reaction), which ‘scrubs out’ the Carbon dioxide that you exhale, meaning that you can breathe it again… or re-breathe it!!

With most Rebreather Units, you must have a means of injecting Oxygen into your breathing loop. Back to Physiology basics…
Oxygen is the only gas in the air that humans use in the process of respiration. We breathe air in, and we metabolise the Oxygen in the air, which our bodies use to “feed” every cell in our body. The human body cannot survive without oxygen and in partial pressures of less than 0.18, we risk Hypoxia (lack of Oxygen). We then exhale the used air with a high concentration of Carbon Dioxide.

The end result is that the Oxygen in the Rebreathers breathing loop decreases as we use it up, so we need to add more periodically to maintain a breathable mix. This is done on the Megalodon by using Oxygen sensors that work on Voting Logic. They measure the partial pressure of the Oxygen in the loop to keep it at a certain set point, which you set manually. When the Oxygen levels drop below a certain point, the Rebreather fires Oxygen into the mix.

So what are the Benefits of Using a Rebreather?
Diving with a Rebreather is beneficial in a number of ways. As mentioned earlier, you can manually set your set-point to whatever you want on the dive (your Rebreather instructor will tell you more about this on your Training Course) but usually, it is set to around 1.2 PO2. The Rebreather will then give you the optimum mix of nitrox or trimix; depending on your diluents for whatever depth you are at. For example, with a set point of 1.2 PO2, Rebreather Diver using air diluents, at 30m will be breathing a mix of 30% nitrox. If that same diver ascends to 15m, the Rebreather maintains the 1.2 PO2, adds more Oxygen to the breathing loop and delivers a mix of 48% nitrox. This gives you an added margin of safety from narcosis and decompression and allows accelerated decompression, if you make a decompression dive.

Other Benefits of using a Rebreather over Open circuit Scuba include

• Extended bottom time.
• Minimized inert gas absorption for various dive profiles
• Maximized elimination of inert gas narcoses.
• Maximized gas conservation.
• Minimized oxygen toxicity problems
• Minimized equipment drag
• Looks cool
• Increase of over all safety

Prior to Diving

The big difference here is in the pre -dive checks that an Inspiration user MUST do. On your open circuit set, you’ll probably get away with just turning the gas on and going diving. This is not true on a rebreather. Each user will have a set sequence of tests they MUST do before entering the water, even if its only 5 mins since they come out (even more so in that case). Don’t worry they wont take long and are carried out in addition to the normal buddy checks which still need to be done. One of the myths of rebreathers is that they take ages to set up. This is not true

Positive Inflation Test. 

The units buoyancy compensator and breathing loop are filled to maximum pressure, sealed and left for a time. They must not deflate. This tests for air leaks. This test is often done well before kit up time. The lung dump valve is tested at this time also (Min 3 mins)

Negative Inflation Test

The units breathing loop is sucked free of gas and sealed for a time. Often a hose is crushed. The system must not draw air back in and expand for some time. There should also be an audible gush of air into the mouthpiece when it is opened after the test. Again this tests for air leaks. This test is often done well before kit up time (Min 3 mins)

Diluent side Checks

The diluent cylinder is turned on, the pressure gauge checked to make sure it has enough gas and the diluent injector tested (also the ADV if fitted). The fitted bail out DV should also be tested along with the buoyancy compensator and drysuit direct feeds. (30 seconds)

Oxygen Side checks

The oxygen cylinder is turned on (SLOWLY) and the pressure gauge checked to make sure there is enough gas. The Oxygen manual injector is also tested. (60 Seconds)

Electronics and initialisation

The master handset is turned on. There should be audible beeps to confirm the beeper works and then a click as the solenoid and batteries are tested under load. This test should always be done with the O2 on and pressurised to be meaningful. The slave handset is then tested in the same way. The user will then proceed through the electrics initialisation routines to get the handsets into dive mode. This may (and should daily) include a calibration check. They may also need to calibrate their computers (min 1 min, max 5 mins). This check is computer prompted and should involve another check of all valves

Pre-breath

The last and the most important test is to breath from the unit for at least 3 minutes prior to diving. This way if something is malfunctioning they will go unconscious while on the boat/shore and not in the water. This test is the most important and is a real lifesaver. Don’t dive with them if they don’t do it.

Checks for you to do

Do check up on your Inspiration equipped buddy
1) Ask to see his contents gauges and make sure the gases are switched on and their is enough. Query him if they are not both full
2) Listen to hear if there are any warning beepers sounding. If they are then something is up and the unit is NOT divable. Do not accept any excuses
3) Check if he is carrying sufficient Open circuit bail out gas to abandon the dive at any point and complete the required decompression
4) Learn how to close his mouthpiece. if you have to rescue him you must close this if you remove it from his mouth as otherwise the loop will flood and loose buoyancy
5) Most importantly. Is he pre-breathing from the unit and has he been doing it for at least 3 mins. Don’t dive if he isn’t (this most simple check would have saved many lives if carried out)

During the Dive

Descending

This is a time of high task loading for the rebreather diver. As well as clearing his ears and filling the dry suit, he will need to monitor his handsets, inject diluent into the lungs and at some time swap from his low set point to high set point. He should also perform a stop at around 6m to check for bubbles and leaks (a good practice on OC). The main risk here is descending so fast that the O2 level raises too quickly. Most rebreather divers are slower on descent than OC divers

Bottom

Once on the bottom the rebreather diver will settle down. The unit works best at constant depth and so the only differences will be that a) your buddy swims around object rather than over and b) they should be checking their handsets regularly (about once a minute). There should be no bubbles from the unit at constant depth. Most rebreather units will practice some drills at some time on most dives. Make sure that your buddy does check his handsets much more regularly than you check your contents gauge

Ascending

OK, now you will see some bubbles. As you ascend the rebreather diver will need to vent some of the expanding gas. he may do this several ways 1) through the lung dump valve (uncommon), 2) breathing out through his nose (common) or 3) breathing out through his mouth around the mouthpiece (common). He also needs to keep an eye on his gauges as as the pressure drops the PPO2 will lower. This is again on top of decompression and normal ascent constraints. So again this is a time of high task loading. On the surface he needs to continue to monitor his handsets

Post dive

The unit must be kept upright or laid on its lungs. Never on the yellow back. This keeps the internal condensation away from the Sensors. The buddy may need to turn off the electrics and gases if there is a wait before diving again. If its the last dive then he may remove the scrubber contents and dry the electrics. If it is being dived again on the same scrubber contents the mouthpiece is left shut to stop airflow. The exhale lung may be drained of fluid that has collected.

Some advanced points

THINGS AN OC BUDDY SHOULD KNOW
How to open and close the CC mouthpiece, the operation of the diluent and O2 manual inject valves, (but normally leave the latter well alone), and recognise the terms and symptoms of hypoxia, hyperoxia and hypercapnia. This is within the skill-set of BSAC Sport Diver and above, but would probably not be appropriate for anything less than a PADI Rescue Diver.

There are numerous modes of failure of a rebreather. Most are simple to spot if the checks are done. But if not the first warning you may get as a buddy is hearing a warning beeper. If this happens you must ensure that the rebreather diver takes steps to rectify the problem. He should at least inspect his controls and analyse the situation. Give him an OK while pointing at the handsets and expect one back. Unfortunately the second symptom of failure is normally unconsciousness. What can you do in that case

a) Get him on a known gas supply. If conscious swap him to his bail out system and begin an ascent immediately. Make sure his mouthpiece is closed. If unconscious then flush his system with diluent while venting and begin to surface immediately

b) If you can inspect a handset check to see if the O2 is high or low. If low make sure his oxygen is turned on. If high continue on the diluent or bailout.

If in Doubt Bail him out!

Rebreather divers can suffer from decompression sickness, burst lung and all the other diving injuries. Treatment is exactly the same as for an open circuit diver

BSAC Recommendations (Fairly Sensible)

It is important to ensure the rebreather diver is partnered with a buddy who can assist them in the event of a problem. Therefore, the BSAC recommends that the;

The buddy should be preferably another rebreather diver diving the same rebreather,

If the buddy will be an open circuit diver then;

A buddy of a rebreather diver (whether SCR or CCR) should be, as a minimum, an experienced Sports Diver with their DO’s consent
The DO (or DM acting on behalf of DO) should ensure that the Sports Diver who will buddy a rebreather diver is;

    experienced under the current diving conditions (i.e. site and weather)
    capable of recognising the conditions of hyperoxia, hypoxia and hypercapnia
    capable of performing a rescue (CBL and surface support) on the rebreather diver in the case of an emergency

The buddy of any rebreather diver should wear a redundant configuration if diving deeper than 20 m.
The capacity of this redundant supply should suit the depth of the dive being undertaken.
The buddy should carry a D-SMB (or SMB as appropriate) and at least one other surface detection aid
The buddy check procedure must be modified to accommodate the rebreather layout especially the shutdown operation of the mouthpiece.
Buddies should have preferably attended a BSAC Rebreather Awareness Course,

Dive Marshal
The dive marshal or deputy dive marshal should have:

Minimum qualification of Nitrox Diver / Advanced Diver
Preferably attended BSAC Rebreather Awareness Course

Must know the following information:

Dive plan (i.e. time and direction)
Max ppO2 setting and planned MOD
Surface detection aids carried
Size and content of all tanks (diluent, oxygen and additional bailout)
Remaining duration of scrubber material
Maximum duration of Nitrox tank (excluding 50 bar reserve)