Rick Inman:
I know very little about rebreathers, but I buddy with one guy who dives a SCR and another who dives a CCR. I know enough to be an OK buddy, I guess - the symptoms of O2tox and hypoxia, how to read the buddy computer on the SCR, how to do a bubble check, etc. I've done air share drills with both of them. One guy likes to do a few mins at 10' before descending and the other likes to breath off his at the trucks for a while. No problem.
Here's my question. Are there greater risks using a rebreather vs. OC scuba? How about SCR vs. CCR? Both of the rebreathers seem to have a zillion failure points. Does one have greater risk than the other? If so, how much? Or are rebreathers just as safe as OC scuba.
Rick,
You have gotten some good advice so far..
On the matter of risk vs OC, well that depends on the dive, the CURRENT experience of the diver (what is meant by this is how much diving has been done on the rig RECENTLY, even the most experienced diver gets rusty..) and how attentive a diver is to maintenence and predive checks..
OC is obviously the simplest, but not necesarily the safest.. The relative safety depends on the depth and if a direct ascent shallower (not necessarily the surface ) is possible.. When you are deep, any problem on OC is generally serious since gas supplies are limited..
SCR, scrs are a gas extension device, they offer no advantage on decompression over OC. Thedo have the benefit of being quieter and warmer gas.. SCRs are simple but without PO2 monitoring (which is NOT standard on any SCR rig), the rigs can be dangerous because the diver really has no way of knowing what they are breathing.. A po2 monitor goes along way on making things safer.. prett much any failure on an SCR means bailing to OC..
CCR, offer many benefits,, Deco, dive duration, war, ect.. They also offer the most options to get yourself out of trouble.. if the loop is intack the diver can usually fall back to run it as a manual SCR, then if this fails go to OC.. For a new or rusty CCR diver, I would say the risk is higher than OC but not significantly.. For some experienced and in practice in most cases I would say the risk is lower for most dives.. The deeper the dive the "safer"I would say a CCR is compared to OC since "time" is taken out of the equation in many cases.. If you are deep on OC you have to solve the problem quickly, on a CCR this generally isnt the case..
If you want to be a good buddy make sure you are familiar with your buddies rig.. ASK questions... Practice with your buddy flushing his loop.. make sure you understand how to open/close the dsv, and add diluent or oxygen.. Don;t disturb your buddy during his setup, distractions could lead to a check being missed if a physical checklist is not used.. Be aware that during ascents and descents the CCR diver will be much busier than an OC diver.. and as was pointed out remeber RB divers want to swim AROUND things NOT over them..
If you are diving deep, make it a point to know what gases he is using for his diluent and his bailout.. If hes using a hypoxic diluent you NEED to know this.. You need to know what depth its breathable at so you know the correct response should you have to add gas to your buddies loop..
A common hypoxic mix used by CCR divers is 50% helium 10% oxygen.. You have to be deepr than 6m (20fsw) if you are going to flush, otherwise you can make things worse.. 6m or shallower its best to flush the loop with oxygen but if ou know its air or normoxic a dil flush is ok..
Deeper than 6m/20fsw, in most cases if you saw your bussy having a problem and he seemd unresponsive to your querries, flush the loop with diluent would get a breathable mix in the loop..
