Interesting in-depth information, Sean. I just use welding oxygen, but now I’m asking myself whether I should have a new checklist item, testing the O2 bottle to make sure what is in there is in fact oxygen. Would this just be a matter of sampling it through my O2 meter? If I get a reading of 99.9% or 100% O2 concentration, then go ahead and put the bottle on the sub. If I got something lower, I might not know what it was, but I would know to skip that cylinder. Back when I learned to dive in 1980 Argentina we didn’t have any gas monitors of any sort, but we did a quick test on every SCUBA cylinder. You’d hold a handkerchief or some such white thing in front of the tank valve and give it a quick squirt of air. The theory was that if the tank was contaminated with oil, you’d get a stain. I never got a contaminated tank, so I’m not sure how good the method was. Best, Alec From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Sean T. Stevenson Scott, I have been dealing with issues like this with gas suppliers for years. The purity issue is nonsense. The medical grade oxygen is filled from the same bulk cryo storage as the industrial stuff. The difference is that medical grade is periodically sampled and analyzed for compliance with USP specs, which adds a cost overhead, and on the medical grade, the filling procedure is slightly different - vacuum is pulled, O2 is flushed at low pressure, vacuum is pulled again and then the cylinder is filled. Industrial cylinders either have one or no vacuum steps before filling. The idea is to avoid any kind of hydrocarbon contamination, but such risk is small. I have been using industrial helium and oxygen (run through my own physical and chemical filters) for years without issue. If you can do so, it will probably be cheaper. If not, just explain your situation to your GP and you can probably get a prescription. Another option to look for is so-called aviator's oxygen, which is certified to have minimal moisture content (prevents freeze-up issues), but may not track other impurities and so may be cheaper than medical. For submarine breathing media, industrial grade gas is fine provided you confirm the analysis (make sure it's actually O2 in the tank at 99.5+ %). The breathable atmosphere in your sub is exposed to external contaminants anyway from your body, clothing, equipment and any dirt you may have tracked in. Since you are conditioning the air anyway (via CO2 scrubbing), for peace of mind you could include other media stages in your filter for scrubbing hydrocarbons, CO, etc. I was at my local welding and gas supply the other day and they were asking me how my sub was doing and we got on the conversation about the life support system and how it works. They told me they could not sell me medical grade oxygen with out a prescription from a doctor which I thought was kind of weird. They said I might be able to use oxygen that you use for welding, but it is not as pure. Does anyone on psubs have any ideas on what to do? Also I had asked a question a while back about the tubing in the K-350. I have decided to go with stainless steal, but was still wondering what wall thickness to go with and how do you connect them (flair fitting, compression fitting, or something else?) Thanks, Scott Waters |