Mistakes on Rebreathers

[Tienuts]

I'm a rebreather instructor in Grand Cayman. We see many rebreather divers come through here, and I see several common issues that are worrisome:

• Not understanding O2 sensors, their behavior, failure modes, and troubleshooting. This is the heart of the rebreather, you need to understand these backwards and forwards. I've had CCR divers tell me their brand new sensor is bad, because they installed it, and didn't understand they needed to calibrate it.
• Entering with gas turned off. Just in this thread, some have mentioned doing that. Sorry folks, that is inexcusable, and will lead to an issue one day when you don't pick up on it. Checking valves, and that all manual addition buttons work is part of the pre-jump check. Every student needs to tattoo this into their brains before I will sign off on them. Brian Buggee, and many others have died from hypoxic events from not turning their O2 on prior to jumping.
• Being overweighted. Many divers are using steel tanks when diving in warmer climates were the additional weight isn't required. The increased weight requires more air in the wing to offset and creates buoyancy issues.
• Bad configurations, sloppy rigging. I see many setups that are overly complex, and not much thought went into how the equipment is rigged. Many of these divers would be incapable of self-rescue should the need arise, because of their complex rigging. Your bottles and equipment should be streamlined, with no danglies, and you need to be able to don/doff the equipment unaided, both topside and underwater.

Tony

 

[rjack321]

In addition to the points raised above.
ONLY putting O2 in your unit on the surface and leaving your ADV shut off until you descend.

 

[davehicks]

Lots of good info about checklists and user error issues. I'll take a different approach and point out a few other possible mistakes you can make getting into rebreathers in the first place.

• Are you going to be diving frequently enough to build experience and get value from the RB?
• Do you have a community of other RB divers you will dive with to compare notes and support each other, especially as you are learning?
• Are you comfortable building, tearing down, and at least doing light service on your own gear?
• Have you spent time talking to other RB divers and researched what you liked about various units?
• Finally, are you comfortable and resigned to paying 10X the rational price for a customized plastic or metal widget that breaks or needs replacement?

I've seen lots of people, even very experienced divers, get into rebreathers and realize after a short time that it's not for them. I think the questions above will help to ensure that you are a good fit for this hobby and can enjoy it for a good long time.

 

[Mermaiden_RB]

Please share your experience, how do you do/teach weight check with a rebreather for different configurations and dives!

I do a weight check without my bailout tank(s) at 1 to 5 meters. This is the most difficult dept. Or I empty my bailout tank to 50 bars.

 

[kensuf]

I would love to see your SF2 checklist. Can you send it to me?

Of course!

http://www.divegainesville.org/wp-content/uploads/PreDiveSF2_edit_en.pdf

 

[silent running]

I am a new rebreather diver and would like to hear other people's recommendations for a new RB diver and what mistakes have you have made on such a machine?

Asking to become wiser and better.

English is not my native language, so sorry for that.

Mistakes will be made, hopefully you won’t make many and the few that you do make will hopefully not be a big deal provided your CCR is well designed and fault tolerant.

That being said, there is no substitute for real learning, comprehension and awareness. The more complete your understanding of how your CCR works, the more awareness you will have and the less likely you will be to make mistakes or have failures:

-If you understand how oxygen sensors work, you will never put them in your checked luggage because of shock and temperature extremes. Don’t leave your CCR in the hot tropical sun in between dives, put a towel over it if it’s not in the shade. Don’t let boat guys toss around/mishandle your CCR, even if you are tired.

-If you understand how mushroom valves work you will never store your loop in a hot, dry place like a garage, and you will learn to recognize the sound of properly functioning mushroom valves during the dive. I usually do a rapid in/out breathing test underwater to make sure I hear the correct popping and feel the gas pulsing through the loop hoses as it should when the mushrooms are opening and closing properly in rapid succession.

-If you are generally aware of your O2 metabolism and fully understand the principles of constant PO2 diving, you will learn to listen for the solenoid firing when it is expected to, like during ascent or when you are working harder. A solenoid firing too often or less than you expect is a leading indicator of big trouble.

-And of course, check lists before entering the water are important, but also specific to your unit/training and dive habits. Some units are more checklist intensive than others because of their designs. I personally like to begin a dive day/trip by imagining every step I will take between putting on my suit and stepping into the water, so I can be purposeful and eliminate as many X factors/distractions as I can. I find distractions are many on dive boats, especially liveaboards, and it’s easy to find yourself rushed if one step in your donning is interrupted by an untimely announcement, or the boat changing course into rough water while you are trying to stand up to grab the rest of your gear. Routine is very important to good safety habits, turn your gas on as soon as you get into your rig. Other little omissions of habit can screw up your whole dive, you don’t want to realize you left your SMB in the rinse tank the night before when you are just about to splash for the day’s fist dive. That kind of mistake can cause others, like jumping in without turning on your electronics...

 

[Gareth J]

I have always ensured I get everything ready for the next dive as soon as I've dekitted after a dive. (as long as I'm not in the way of others getting back aboard). This goes back to my O.C. days. Having everything ready for the next dive means I am not distracted or in a rush when I kit up for the next dive, so I can run through my checks in a relaxed manner.

My most recent 'error', was last year. I burned through my DIL.
A mix of complacency, poor conditions. It was a wash down dive, at a fresh water site, after a weeks diving. Using gas I had left over from the last dive.
The dive started OK, with a little bit of light relief, my buddies were inflating a storm trooper in 20m whilst I took pictures. Visibility was poor. Leaving our storm trooper attached to the bottom, we swam further into the site then dropped into the 35m area (diving as a three). Not only was it dark but the suspended matter made it feel like we where diving through sand. I had a mask leak, and was intermittently clearing. We messed up our navigation and did a little loop - this was obvious when we passed a waypoint for the second time.
It made no sense to press on, so we ascend back to the 20m lip. At this point I realised I had used a lot of DIL. I continued swimming, having a mental discussion. It was divable, - as long as i didn't need to bailout, or continue mask clearing.
Sensibly I decided I was being foolish,so opted to plug the 80 bailout cylinder back into the loop. Solving bailout, mask clearing, and gas issues immediately.
I paused to do this, realising that the whip was not easily accessible, I released the rear stage clip, flipped the stage in front of my and pulled the whip free. Re clipped the stage and unplugged the counterlung from the onboard cylinder, preparing to plug the whip in.
My buddies appeared, a little concerned (both OC divers), and decided to 'help'. It was easier to let them assist, than try to explain anything. They unfortunately plugged the onboard cylinder in. I then unplugged it and plugged the off board in, closed off the ADV feed. At this point they got a bit stressed and I chilled out.
I was ready to continue the dive, I had gas for mask clearing, bailout and buoyancy, and we where shallow.
My buddies where now very stressed and opted to abort - so we started to ascend.
At this point we got a deep stop warning on one of my buddies computers. So we stopped and each sent up a DSMB. then we ascended to the shallow stops. Once these cleared. we opted to swim back to shore at 6m (its easier, and less embarrassing at the busy inland site).

Lessons learned.
1. Mask clearing at depth uses gas quickly (we all know that), especially out of a 3litre cylinder!
2. A leaking mask is very distracting.
3. Poor vis = high task loading
4. OC buddies do not always understand what a CCR diver is doing (even when you dive together regularly).
5. On a rebreather, generally, you have time, so nothing is a rush to resolve. (not something OC buddies understand).
6. Work the problem calmly, and there is no crisis.
7. Despite bailout cylinders being a pain, even on the easiest dives, they can prove to be very useful. (I was carrying it more for the OC buddies than myself, and it's almost a habit to have an 80 bailout cylinder, as much as carrying a torch or SMB. )
8. Having a contents gauge on your DIL can prove very useful.
9. Things go wrong, even on the easiest of dives.
10. If a buddy is unhappy, then aborting in a non-issue.

Gareth