It finally happened - my CCR tried to kill me

[KenGordon]

Anyway, that dive being relatively shallow and knowing the other guys were not going to be doing a long dive, I only took one BO gas with me. An AL80 of TX18/45. It was plenty to get me out. But, I also knew that if I did my deco on that it would take a lot longer than if I stayed on the loop.

On top of what @rjack321 says about sensible bailout choices, letting your spare deco gas swim off was a mistake.

125 ft is not shallow. 40 minutes at that depth is not a short dive. Just because you are not banging up against the limits of your qualification doesn’t make it a trivial enterprise. Give the dive due respect.

it seems Ross has broken multideco so it will not do bailout calculations today. I can’t see how long that bailout would have taken on the trimix and whether it would actually be enough.

I am either doing essentially no stop dives to 40m with OC single gas divers and have 32% bailout or I have a deco bailout, trimix bailout and a suit bottle. If am doing a week of diving and some are no stop and some are deco I just stick with the two bailouts. If I am doing a weekend of no stop/short deco I use the 32% for an easy life but will not have a TTS of more that 15 minutes.

 

[KenGordon]

it seems Ross has broken multideco so it will not do bailout calculations today. I can’t see how long that bailout would have taken on the trimix and whether it would actually be enough.

looks like he fixed it. When I looked in the App Store before the post it didn’t offer an update, now it does and bailout works.

40 at 35 bailout using 90/90 adds half an hour of deco and used 1500l of gas, so it would have been ok but no fun.

by contrast bailing to 32% only adds few minutes to the deco and uses half the gas.

 

[Tassi Devil Diver]

@stuartv jumping in with a single bailout of TX18/45 was not ideal, needed an additional NX50 or 100, I never just carry a single TX bailout when diving TX dill, you were probably taught this during your training I certainly was, a bit of complaisance creeping in there.

completely whacked out cell readings is clear sign of water interference you now know this after a partial flood, I learnt this after a full flood (not on the loop, practicing bailout in shallow filled the rEvo to the brim when I did not properly close BOV).

I always put the lid on before cylinders, and take note of number threads exposed when the lid is secured properly with retaining nut for me it is four, and if I can't get four threads exposed when screwing down the retaining nut I investigate why.

Your unit did not try to kill you, I see a a bit of complaisance creeping in.

 

[lermontov]

If you look at the mv when drawing a vacuum in your loop it will drop proportially. If there is a leak the mv reading will increase as the PPO2 increases in the loop.

this a great check - ive never been taught this -certainly will be building it into my routine

 

[Heat Miser]

On the Millivolts reading the rEvo holds a very very good neg.

So the problem is that in testing the neg, the ppO2 can drop below 0.21-0.22, to say 0.18. This of course fires the solenoid because the surface setpoint is fixed @ 0.19, so if you leave your shearwater on and walk away, you come back with a flat external solenoid battery. I turn my shearwater off after I have done the neg and turn it back on just before releasing the neg.

The other little stupid thing I learn't is that I used to test a positive, with my bailout gas, rather than my tx dil, in order to save helium. Leaving the low pressure inflator disconnected from the wing and trying to get a neg is a no-no. It took me hours to work that one out. Now I just use the dil I have whether tx or air.

 

[DiverDiverRUOK]

The other little stupid thing I learn't is that I used to test a positive, with my bailout gas, rather than my tx dil, in order to save helium. Leaving the low pressure inflator disconnected from the wing and trying to get a neg is a no-no. It took me hours to work that one out. Now I just use the dil I have whether tx or air.

For the positive test, just orally inflate the loop until the OPV fires and close the DSV/BOV while the OPV is still venting to trap the overpressurisation. This saves gas and actually makes sure the OPV is working properly.

 

[kensuf]

What BO gas I was carrying was somewhat irrelevant - as long as it was enough (per my training).

I would argue that anytime you're doing a planned deco dive on CCR, you should bring a deco cylinder as one of your bailout cylinders.

 

[kensuf]

A lot of people perform pos/negative tests that only last 1 minute each. This may not be long enough to catch smaller leaks. We perform 5 minute each pos/neg pressure tests. This has caught a few leaks that were still passing at the 3 minute mark. As mentioned, noting the mv/PO2 will also show something is leaking.

Caveat emptor. If you pull a 5 minute negative on an old KISS Classic you run the risk of damaging the ADV diaphragm.

 

[tbone1004]

Can you explain this in more detail? I've not heard of using the sensors to monitor pos/neg during check out.

Electrochemical sensors actually measure the partial pressure, not the percentage, of oxygen in the gas stream they are exposed to. So the output of the 5 sensors while under either a positive or negative pressure should remain constant unless there is a leak.

incorrect. When you pull a negative you are creating a partial vacuum which reduces the ppO2 in the loop. When you blow a positive you are creating a slightly high pressure environment in the loop. If you both after an O2 flush, you'll see the ppO2 go from 1.0 down to .9x during the negative and if it holds a good negative it won't rise back to 1.0. When you perform the positive it will go up to 1.0x and if it holds a positive it will stay there, if not it will fall back to 1.0
They can function as ambient pressure sensors when in a fixed fO2. The Liberty has actual ambient pressure sensors in the head and it uses those for its positive and negative checks, but the good CCR instructors teach you to use the O2 sensors to check whether your unit is behaving for those two.

 

[flymolo]

A planned deco dive on ccr definitely requires open circuit bailout deco gas