Scrubber Duration

So would 6 or 7 hours be feasible during "normal" diving conditions then?

Again, I'm asking as a comfort blanket in case I outstay my plan/go deeper than planned in an emergency...

Bear in mind that I and at least one other bought RBs having been strongly influenced by DrMike's post on being trapped at 65m for 30 mins...

Got a link to it? This post sounds like it might be an interesting read!

Stuck in a 60m wreck for 20mins
This happened a few months back on a CCR dive - good learning experience (I certainly learnt something) anyway thought it may be of interest -


We went over the structural plans we had of the wreck we were to dive deciding where we would explore and exit/entry points. Me and Chris agreed that we would penetrate the wreck near the sea bed at 60m then along inside before swimming up one deck level then back along a gangway, through a narrow door, up another hatchway and into the target room. We should be inside the wreck for 10 minutes or so all being well. Chris was careful to calculate his gas requirements for the dive as I did for my bail-out gasses (assuming rebreather failure at worst possible time, ie deepest point inside the wreck)

Chris wanted to do 25mins on the first what would be a warm up dive so we agreed that when it came time for him to turn back I would continue alone. As we would be moored over the wreck for three days we had plenty of time. The currents was very strong and I decided to use my scooter to bring us down to the wreck. Chris held on and I scootered us both down the line. With the added drag and strong currents it took us longer than expected to reach the penetration point, by the time we had unclipped the scooter and his stage tanks in preparation to penetrate it was already 12 mins into the dive. Chris with his planned 25min bottom time and associated gas volume didn’t have enough time to enter the wreck so I signaled to him that I would go in solo and return to the entrance point in 5 mins where we would meet up and ascend. I had to really squeeze to get into the wreck. The opening was very narrow and I could hear the cover of my unit scratching against the rusty hole edges as I dragged myself in. As I didn’t have much time I just wanted to verify the route we would take on the next dive and be back to met Chris after 5 mins. I swam along thru the wreck at quite a pace then literally flew up the small hatch to the second deck level skirted along the corridor another tight squeeze through a doorway and that brought me to a room that was to lead to my target destination. This had taken me about 2 mins so I figured Id just stick my head into the room a little. I swam to the left entrance and it was a VERY tight squeeze to get in. I had to twist and turn and drag myself through the narrow opening. This kicked up quite a bit of silt and the viz dropped but it was still manageable. Once through the opening I immediately realized I had made an error it just led to a small room little bigger than a cupboard. Due to the shape of the room it was very difficult to turn around with my stage tanks hanging on me. After a lot of scrapping and tank banging I managed to half turn around then I attempted to make my way out of the room. Clunk! I tried again, clunk! Ok this is tight, Ill try moving more to the left....Clunk!..more to the right...clunk! Ok don’t worry drop down a bit and try again...clunk! a bit higher?..clunk!

Ah....do I have a problem here? I started to feel my normal calmness evaporating and immediately checked the feelings inside as concern grew. I tried again...clunk! My repeated efforts had stirred up the silt and now visibility was rapidly approaching zero. This added to the stress levels and I had to work a little on my feelings to remain calm. I was very glad I was breathing trimix. I used my normal technique of visualizing and checking what is OK in the situation to retain stress levels. Can I breathe? Yes - good. Do I have any gas concerns? No, I can last more than 3 hours here provided my rebreather is working correctly. Is my rebreather working ok? Yes - good. OK That’s all good so my only real problem is the fact I’m stuck. (inside a 60m deep wreck on my own in zero viz ) I have maybe three hours before my scrubber fails I’m sure it wouldn’t take that long to work my way out as I had after all managed to get into this space.

With renewed calmness I inched forward in the now zero viz...clunk! I couldn’t understand how if I could get in - then why It was so proving so damn hard to get out!

I thought about Chris and checked my watch. I couldn’t see it. Heck I couldn’t even see my arm. I couldn’t see anything. As Chris was on open circuit and had a limited gas supply I knew he would have no choice but to leave the hole where he was waiting anxiously for me once the 5 mins was up. It would be another hour for him to mull over the possibility that I was already dead or possibly trapped somewhere deep inside the wreck before he would break the surface after his deco was complete to raise the alarm and a further half an hour or so before assistance would reach me. But how could they help? I didn’t need gas - I didn’t need more fins kicking up more silt or other no doubt stressed divers around trying to communicate in zero vis adding to the stress levels. I found myself hoping that I would be able to sort this out before 'help' arrived. I was by now doing a very good impression of a calm person. The alarm bells that had been ringing in my ears with increasing volume since the first clunk! had now been silenced and with my heightened senses the only sound was the seemingly deafening rush of moving gas as I breathed in and out. I knew I was not in immediate danger and I knew sometime in the next 3 hours of my scrubber life I would find a way out.

I turned now thru 90 degrees and inched slowly anxiously forward...clunk!

I had long since given up trying to retain a fins up position or any other attempt to prevent silting - we were beyond silt-out this was like being burred in mud. Nothing I could do now would make the silt out worse or better so there was little point trying to keep trim or prevent careless fin movements. I was totally blind. I closed my eyes. This technique is reported to be of assistance in zero vis conditions as with eyes closed your mind is apparently not distracted or confused by the hideous dancing shapes in the swirling silt that you create in your imagination - being blind keeps you calmer and heightens your other senses…allegedly.

I decided I would try removing some of my gear to reduce my profile before trying again. I unclipped my 5L stage and pushed it through the opening being careful to keep it close to the opening in case I needed to breathe the gas at some point. There’s always a danger of tearing the rebreather lungs - that would immediately reduce my option to one - to breathe from my stage tanks. That gas volume would only last less than 20 mins at this depth with normal non stressed breathing leaving nothing for deco so that was a major concern.

I inched forward again...clunk! changed orientation and tried again..clunk! tried feet first ...clunk!
Tried one leg at a time…clunk!

I then decided to unplug and remove my 11L tank. This one is plugged into my rebreather so removing it is a bit more involved but I felt I had little choice. I pushed it through the doorway and placed it next to my other stage tank. I now offered a much smaller profile so with renewed hope and anticipation I eased myself slowly forward...scrape...scrape...clunk!


I pulled back twisted thru 90 degrees and tried again scrape scrape woooshhhh! I sh*t myself. Suddenly there was a rush of escaping gas. Bubbles filed the small space and the deafening sound vibrated through my head. My 11L tank was on the floor so this must be coming from my on-board 3L rebreather tank that empties real fast at this depth and was currently all that was keeping me alive. I pulled myself back into the room and ran my hands feverishly over my unit. I soon realized my Auto-air was free flowing as the valve was being pressed against the opening. I unplugged it. It stopped. I calmed myself down again for a few moments. I couldn’t see my gauge in the viz so I just had to assume there was enough left, as it was not an oxygen leak it was not life threatening.

I pushed forward slowly inch by inch...scrape, scrape...clunk!

Damn this was no long scary - now it was starting to get annoying!!!


Sod it now I’m getting mad. I’ve had enough of this pi**ing around I want to get through this damn opening.

Had I been on open circuit with the associated increased rate of breathing that comes from being stressed I would have been dead by now after this time.


There was only one last thing to do - to remove my rebreather. This is quite a drastic thing to do and not done lightly its a lot more involved than removing open circuit gear especially due to the fact there’s no long hose on a rebreather. Drop a reg on open circuit and you just purge it again. Drop a rebreather mouthpiece and you can flood the unit rendering it incapable of life support.

I tried to check the handsets but in the zero viz I couldn’t see them I had to trust that it was working correctly as I couldn’t hear any alarms. I unclipped the harness and flipped the unit slowly over my head keeping the mouthpiece in. This was very had to do inside the cramped space. I then turned it sideways and pushed forward towards the door. I got the unit through (actually it amazingly didn’t even touch he sides!) but the breathing resistance was very high I wouldn’t last long breathing like this I had to get the unit back on properly and fast before I passed out. I started to feel light headed and I knew I could pass out any moment. Holding the buoyant unit in front of me I was now negative and was actually crawling with my knees I pushed myself through the door catching my wetsuit in the upper thigh area on the jagged edge and in a surprisingly fluid motion I was out and into my rebreather. In the proper orientation the breathing resistance disappeared and I felt a rush of relief – and gas. The loop gas was thick and real hot to breathe - for a moment I wasnt sure if I was breathing gas or sea water, I couldnt tell.

I took a moment to calm myself and check my status. I still had zero vis but I couldn’t hear any alarms so I figured as long as my unit was still switched on it should be ok. I waited in silent anticipation then I heard the solenoid opening as it does periodically to inject oxygen into the unit so I knew it was still turned on so that was nice. I crawled around looking for my stages and reclipped them on. I inflated my wing turned and headed out following the line. I exited the wreck and collected my scooter. I had been stuck inside this 60m deep wreck for over 20 minutes. I felt like a prisoner who had just been released from prison after 20 years. The grass would have been green the sky blue and birds would have been singing had there been any at 60m. I would be out of gas and dead now if I had not been using a rebreather. Before heading for the line I re-checked my handsets and gauges. Everything was normal calm and fine. The only sign that remained of the incident was the fact I was covered from head to foot in red rust and my unit had a few more scars to add to its growing collection.

I had a deco schedule for 40 mins at 60m so I followed that with some padding to account for the higher CO2 levels I’m sure the incident created. Chris must have been relieved to see me below him join the line.

After going over the plans and revisiting the room on my next dive it was clear that I had made a mistake in taking the left hand opening. The correct room opening was to the right - not that it was much bigger.

Lesson learnt? Just because you can get through an opening from one direction doesn’t mean you can necessarily get back through it from the opposite direction. The position and shape of the small room (little more than a cupboard) meant that to enter it was relatively easy if you approach it diagonally as I had done to get in. But once in it was very hard to orientate properly to get out. The only way would have been to have backed out.

I hoped the next dive 4 hours later would be better……but that’s another story – it wasn’t a good day for diving!!

Hah! I lied - it was 60m for 20mins




Nicked from YD - link to thread here...

http://www.yorkshire-divers.co.uk/fo...ad.php?t=10175

Mdemon, those profiles are achievable but depend on work rate, as Dr Mike has said, deco is not hardwork (normally), and is conducted shallow for the longest stops (obviously) so the scrubber can be pushed.

But do not take my word for it nor believe what I am saying, just because it works for me does not mean in anyway that it will work for you and as an Instructor I strongly advise you against exceeding the manufacturers limits for the scrubber duration. Ignore this advice at your own peril.

Cheers,

Dave Cooper.