Recalculating Thirds

[Sludge]

Let me reflect on how many times I've seen anyone in training use cylinders smaller than 72s. Hmmmmmmm.

[floridabob]

That's pretty much the standards across most agencies. It was based on diving double 72s, which were the most common cylinder used when the standards were created. Basically the standards required a cave dive be started with a full set of double 72s.

Rob--I think you are probably right on the explanation.

I do find it strange that that particular standard has stood so long without update. That seems a bit remiss. Or I guess its possible it was not deemed necessary to change it.

Bob

[RN]

There are a few things that have continued to remain unchanged simply because people don't like change. Another such example is requiring deco training before getting full cave training. Before Nitrox cave dives were done on air and decompression was on bottom gas. Decompression was much easier and simply a matter of following Navy air tables. Since the introduction of Nitrox and accelerated decompression things have changed. It's not as easy as it used to be but we still have a lot of full cave divers whose only exposure to decompression diving has been during their 4 day apprentice/full cave class. They likely don't understand the theory, the planning, or anything else. But yet they are doing decompression dives using 100% O2 to accelerate decompression because their cave instructor said it's okay to just follow the dive computer.

[Sludge]

Decompression was included in my Open Water class in 1986. We didn't do any actual deco dives, but the calculations were on the test, and you had to pass all sections to pass the test.

[kensuf]

Decompression was included in my Open Water class in 1986. We didn't do any actual deco dives, but the calculations were on the test, and you had to pass all sections to pass the test.

I did a deco dive as part of my advanced training in 1982. They also made me do a scuba ditch and turned off my air at 50' during my openwater training in 1981. As an instructor I would never consider doing some of the stuff that was done regularly back in the day.

Having said that, deco theory should be discussed and covered in almost all levels of training.

[fishinmaniac]

I don't have nearly the experience of some on here but I'll put in my two cents.

Recalculating thirds on the exit to go check out a side passage seems dumb, it's unnecessary risk if you ask me. The math to do it isn't complicated but one mistake and one failure and your odds of survival take a major hit.

Recalculating thirds at a place like peacock to do the traverse I can understand. You HAVE exits you could use, I wouldn't want to but they are there.

The last thing I'll add is why not simply bring more gas with you instead of squeezing every last bit out of backgas? I'm apprentice right now but I have no problem and do carry a stage bottle with me on many dives. I don't breathe it, don't intend to breathe it, don't factor it in to my dive plan but it's there. If the silt hits the fan 80cf of gas adds a large safety margin and practice carrying extra bottles never hurt anything. I hardly notice a stage bottle that's rigged properly and riding well on too of my side mount tanks.

Again just my opinion, I'm still new, always learning but one thing I do know is there's no such thing as too much gas in a cave.

[twaldo]

I'm apprentice right now but I have no problem and do carry a stage bottle with me on many dives. I don't breathe it, don't intend to breathe it, don't factor it in to my dive plan but it's there. If the silt hits the fan 80cf of gas adds a large safety margin and practice carrying extra bottles never hurt anything. I hardly notice a stage bottle that's rigged properly and riding well on too of my side mount tanks..

Fish,
I'm in the same boat as yourself... new to cave diving.... and I agree totally... silly to recalculate, just carry (or stage) more air... On that note, where you trained with the stage or just chose to carry it on your own? As a NAUI Cave 1 diver, we are supposed to bring an extra tank and drop it in cavern zone (at stop sign, I guess) but not carry it with us... not doing this yet because I'm exiting the cave where I would normally be turning my dive... but will start as my penetration gets closer to 3rds....

Tim

[fishinmaniac]

Don't have formal training to carry a stage, always carry deco gas if it's needed on the dive and that's dropped either in the cavern or further in the cave depending on the dive site (theft).

Learning to carry a stage wasn't rocket science but it did take a fair bit of time to get right. I've done maybe 30 or 40 cave dives since I started training (not including training dives) probably 10 were carrying a stage, safety bottle, whatever you want to call it.

[sandy]

Decompression was included in my Open Water class in 1986. We didn't do any actual deco dives, but the calculations were on the test, and you had to pass all sections to pass the test.

Same here in 1980.

[MandM]

Fish,
I'm in the same boat as yourself... new to cave diving.... and I agree totally... silly to recalculate, just carry (or stage) more air... On that note, where you trained with the stage or just chose to carry it on your own? As a NAUI Cave 1 diver, we are supposed to bring an extra tank and drop it in cavern zone (at stop sign, I guess) but not carry it with us... not doing this yet because I'm exiting the cave where I would normally be turning my dive... but will start as my penetration gets closer to 3rds....

Tim

If you have a volume of gas sufficient to complete that part of the dive safely, what makes it silly? If you personally aren't comfortable doing the math underwater, I understand and that's ok, if we were diving together, I'd accept that. I agree its better to have too much gas than too little, but that doesn't mean you should carry a stage on every dive. Hardly Hogarthian. LP85's are more popular than 95's because they are more streamlined. What do you think carrying a stage does to streamlining? These are all tools. Use the ones that make sense for the dive you are doing.