Bailout procedures

Bailing out is a term used by technical divers to refer to a backup system to get the diver back to the surface. When I teach divers how to use rebreathers, I define the rebreather as the primary SCUBA system and the OC SCUBA as the secondary system. It doesn't necessarily have to be a rebreather (CCR) and an open circuit (OC) system, it can be two OC systems or two CCR systems. Then we have to ask ourselves, why just two? Why not three? It’s quite easy to get buried in the weeds, but in the end divers have to balance what is reliable with what is practical.

Open Circuit bailout is 1.5x the amount of gas you need from maximum penetration to return home. It is not gas for your buddy, unless the dive team plans to utilize a “team bailout” strategy. Whether you carry all of your gas with you in case you get blown off the wreck or stage cylinders nicely in the cave, you have to plan it and carry it yourself.

CCR bailout or a bailout rebreather is a second rebreather that is utilized to return home in the event of a failed primary rebreather. This is often utilized in conjunction with some additional OC gas that acts as a transition gas and drives the diluent of both primary and secondary rebreathers. A Bailout rebreather must be able to independently function but does not need to be transferable. Transfer of a bailout rebreather in a team bailout setting is a particular strategy that must be planned for before the dive. The rebreather is also a backup decompression system because the primary focus will be for the diver to get back to the door quickly and begin decompression as soon as possible.

Team bailout is often scrutinized and is associated with divers individually not carrying enough OC gas but are required to depend on a buddy to get home but that does not necessarily have to be the strategy. When a cave undergoes a period of lots of diving, such as the exploration of P3, or Weeki Wachee, divers will stage safety cylinders that are placed throughout a system to supplement the diver in the event of an equipment failure and make sure the diver has enough gas to safely get to the surface. Team mates do not depend on this gas but it does create a nice and cozy margin for project divers. Habitats with staged decompression gas are a critical piece of the bailout strategy along with Habitat rebreathers and redundant power sources.

At NASA, during EVA operations there are three types of egress scenarios; 1st being standard, we have reached the end of our objectives and to adhere to the timeline, time to pack up the worksite and make our way back to the door. 2nd, there is a pressing problem and we need to organize ourselves efficiently, pack up the worksite, end the mission and begin to make our way back to the door. 3rd, the emergency scenario where we leave the worksite immediately and all priorities are to egress to the airlock.

In rebreather diving, the parallel is the 1st scenario of staying on rebreather the entire dive, the ideal dive. 2nd, would be the rebreather has encountered a failure and PO2 monitoring/control has failed or the scrubber is no longer usable. Going beyond the obvious SCR and other strategies to extend our gas, this scenario means for us to make our exit quickly and efficiently. 3rd, the diver has encountered a caustic event or an injury, requiring a rapid egress towards decompression and to the door. In the #2 scenario would the diver remove things placed into the system? Say a guideline or jumps? The technical diver should have adequate gas planning to calmly end the dive and perform the planned decompression with no emergency because the gas requirements should be more than adequate to end the dive. #3 scenario is under extraordinary circumstances such as a caustic burn where the diver’s gas consumption is much higher than anticipated thus the diver is consuming more gas. Combined with the elevated gas consumption and the diver’s injury, the diver will require that the exit be as efficient and quick as possible, while performing all required decompression obligations.

Bailout systems are the backup system so that in the event of a failure a diver can safely exit back to the surface. Technical divers are trained from the beginning to always have a backup system in the form of a redundant gas delivery system combined with conservative gas management strategies. For OC tech diving in caves we follow the rule of 1/3rd gas management which is arguably not conservative enough in the event of a system failure but is still quite standard practice. The 1/3rd of gas is typically never used unless an emergency occurs. With Rebreather divers they are all often technical minded and the secondary OC system referred to as “bailout” is often untouched unless incorporated as a diluent gas through offboarding which is quite common practice in cave diving.

Planning for our bailout in rebreather diving is not an overly complicated endeavor. We calculate how much gas is required for our planned range and decompression obligation, simple enough, right? The biggest problem is that most divers like to let their ego get in the way and base their gas planning on an ideal gas consumption on a normal day ( I know I’ve had to learn this the hard way). Oftentimes we don’t practice OC diving enough for us to maintain our good practices and good gas consumption, isn’t that the reason why we got into CCR diving?? Then in the event we do have a rebreather failure and have to go on OC it’s often not in the best conditions and we need to get our butt back to the door.

Breathing is elevated, a flooded rebreather is throwing off any and all trim, stress, kicking yourself thinking how could you have taken the loop out of your mouth! All of this brings up the wonderful RMV that you were once so proud of. This scenario is just an example of making a mistake and flooding the rebreather. Now if this was a flood on a SM unit - this could quickly lead to a caustic event, now you’ve got an entire myriad of problems, throat spasms, coughing/gagging just to name a few.

The reality is you need to plan for an “Oh S***” moment, bailout and get your butt back home. Let's put some numbers down and say I normally plan for a .7 cuft RMV, then what I will do is plan for that initial bailout moment at a 1.5 cuft RMV, for 5 min, maybe 10 minutes, then I will settle down (all while moving towards the door) and bring my rate back down to a .7 RMV until I get to my decompression gas.

Bailout procedures are very site specific and mission specific. Daily conditions can often have a significant impact on the divers' bailout strategy. This could mean an additional buffer of gas, perhaps using an Al80 for oxygen rather than an Al40 but it should always be scrutinized and constantly be reevaluated, especially when things have never been a problem, because that's when we should practice a bailout and see how we do. The old adage of practice makes perfect is good, but perfect practice makes better. Remember, every day we have an opportunity to be a better diver!

Author: Joseph Jonathan Bosquez