Nitrox in the deep dark south

[kasdeva]

So I am doing my Nitrox course. I struck gold by getting an IANTD cave instructor that enjoys teaching Nitrox and advanced Nitrox for kicks and very little money at my dive club. Needless to say, PADI Nitrox turns into the dive education of your life if you care to pay attention.

We are watching the PADI video where they go through the O2 clean cylinders, testing procedures and Nitrox logs required for getting Nitrox. Having watched all that, he turns nonchalantly to us and says: "In the USA perhaps, but let me tell how it works here...".

Here... being my beloved South Africa, you walk up to the fill station with Nitrox card, dump your oxygen unclean HP100 air cylinder down, point at your Nitrox card and say "Fill me up".

A minute later a kind person will hand you back your cylinder give you an analyzer and a piece of masking tape. You test, write the MOD and dive.

It seems most Nitrox is premixed and you can any mix as long as its EAN32 around here.

"Ah..." I argued, "My cylinder will never see 100% O2 then!".

"Well...." My instructor replied with a shrug. "If you walk up to Badgat and ask for EAN29.5, they will happily supply exactly that in your air cylinder". Badgat, is our premier deep cave diving site and not a little backward one. This is deep CCR cave trimix territory.

"So.. so, is that not dangerous?" I exclaimed.

"Well.... when is the last time you have heard of a scuba cylinder explode at a Nitrox filling station? If its less than EAN40, and its has a hydro/viz sticker, they will fill it."
my instructor retorted.

To be honest, if that cylinder gets to me in one piece ready to write my MOD on a piece of masking tape, it will dive just fine.

 

[sam1]

The LDS I go to has 40% O2 banked and they will mix any % you want (<=40%). Since the tanks they are filling never get O2 > 40% they do not require that the tanks be O2 clean.

 

[TSandM]

It's true that places that bank 32% or use membrane systems, don't need O2 cleaned tanks or gear. But if they are partial-pressure blending and not requiring things to be O2 cleaned, they are taking risks I wouldn't take. There HAVE been explosions at fill stations, and they're violent and have killed people.

 

[4sak3n]

I don't know about up there in Jo'burg (where the number of dive shops is inversely proportional to the number of dive sites) but down here in Cape Town there are only two places that continuous blend, none that bank Nitrox and all the rest do partial pressure blending. So, unless you want to limit yourself to one specific shop, then yes, you do need an O2 clean cylinder.

Things differ from place to place, even within a country. What is the norm up north might not be the standard down here along the coast.

 

[kasdeva]

In the PADI video, right before you are told in all seriousness about having O2 clean equipment, partial pressures of O2 is discussed.

Should the video not be a bit clearer about the difference between O2 clean and exceeding PP02 of 1.4?

I am happy knowing that if my cylinder did not explode while being filled, I am safe diving it regardless of its O2 clean status or method of blending. But... lets assume I am a bit more relaxed about all this diving science and stuff and argue that ah... O2 clean... O2 partial pressure is the same, just there to please the PADI police. It cannot be that serious, ignore the computer and dive!

Perhaps I wrote this post because I am bemused by the discrepancies between casual shallow reef diving and anything beyond that.

I had a very experienced and highly regarded instructor look at me earnestly when we met for drinks in the club after my lectures and remark: "All that partial pressure stuff, I don't care. I put 32 into my computer and go up when it complains."

This instructor is not flaky at all. She has taught thousands of OW students and I am sure that she could work out all the math if she was required to. But, you know. If you are taking pictures of a Nudibranch in 50 feet of water, Dalton's law does not matter much.

South Africa, the last wild west.

Regards
Kasdeva,
the murky pond diver that worries too much.

Ps. When I left my lecture, I had no doubt about the difference in danger between O2 clean and exceeding 1.4 PP02.

 

[kasdeva]

I don't know about up there in Jo'burg (where the number of dive shops is inversely proportional to the number of dive sites) but down here in Cape Town there are only two places that continuous blend, none that bank Nitrox and all the rest do partial pressure blending. So, unless you want to limit yourself to one specific shop, then yes, you do need an O2 clean cylinder.

Things differ from place to place, even within a country. What is the norm up north might not be the standard down here along the coast.

I know very little. This is the first time I am getting in contact with anything but air. I promise you, I was told with a shrug of the shoulder that the Natal sites (the closest coast to where I live) and Mozambique dive sites will happily fill any cylinder you bring.

I am looking forward to diving Cape Town, I will make sure to bring a dry suit and a O2 clean cylinder with me. Thanks for the heads up.