Bailout is the alternate path to the surface in case our rebreather is not working propperly. Issues such electronic failure, hyper- or hypoxia as well as a flooded unit or Hypercapnia might cause us to go off the loop. Signs and symptoms of hypercapnia may include warm fuzzy cotton mouth feeling, slight feeling of something is not right, with slightly elevated breathing as well as confucion or dizziness.

Open circuit, a SCR or CCR can be used as bailout to bring us back to the surface in case of unit malfunction.

-Bailout Valve or BOV

It has happened that a diver managed to get in the water without Co2 absorbent in his unit, despite checklist and all that. As they went down at about 20 feet / 6 meters the diver was breathing uncontrolled due to exertion and higher PCo2. The dive partner realized what is going on and urged the student to switch to o/c. The unit was not equipped with a BOV. The diver was not able to make the switch as he was not able to hold his breath for even a split second to do the switch over. They went to the surface and they lived to tell the story.

With a BOV the diver would have been able to switch from his CCR to his o/c bail out without a problem. Additionally the other diver could have intervened and help the affected diver.

I believe that if I decide to go off my CCR then I am off and want to go to something that is not connected at all to my CCR. Most BOV are connected to the inboard dilluent tank. With the limited volume offered by the onboard diluent tank the BOV is just a step in-between, to get off the loop and then onto the seperate bailout tank. Take a breath or three then go on to your o/c bailout stage, which is a completely separate life support system with precalculated po2 and gas volume, and you know it’s going to work.

I have seen some divers who had there BOV plumed via disconnect into their o/c bailout stage tank and this way going onto your BOV you will not need to take the BOV out of your mouth to go onto your off board bailout tank, keeping your mouthpiece in your mouth to do a easy switch over and yet go off your CCR onto a separate tank at once.

When doing that last switch over to your complete detached and separate gas supply, you as well have decided you are not going back onto the CCR as you have decided you do not trust it anymore, other then providing buoyancy. And you stick with it. And while you at it change your set point to a low one and open the over pressurization valve from your counter lungs as you will go up. The BOV could be a life saver if used properly.

Something else I have witnessed with BOV equipped divers is that they tend not think about what gas they have in their BOV supply tank and use the BOV freely on the surface, and why not. It is that I just always imagine as they go on with their diving career and coming to trimix diving that this habit will have them killed on the surface, due to hypoxia breathing a low o2 content mix on the surface and exerting. As one habit might be good in one diving situation it may kill you in another.

Deep diving with higher pata and with it higher pco2's and a faster need to switch over might warrant the use of a BOV with the added ability of your team mates to help and intervene if you are possibly incapacitated already hy hyper- or hypoxia or hypercapnia..

What I have witnessed over and over again is that divers do hesitate to long, way toooo loooong before they decide to go to  bailout ( either o/c SCR or CCR ) when they think something is not right. They start thinking about it, are not sure, they feel something is or was not right, don't want to be embarrassed or think the process of bailing out without a BOV is just to cumbersome and time consuming. The installation and use of a BOV can be a live saver.

If you just think about going off loop and to bailout but can not even put your finger on what or why, that very thought of just thinking about bailout is the very reason to bail out, now. Do not hesitate a split second and go to o/c bailout, because that might have been your last chance to do so.