Using Carbon Fiber Tanks for SCUBA Diving?!

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FukoChan

FukoChan

Member
Jun 14, 2015
798
27
Georgia, United States
I am a fan of killing two birds with one stone, except im guessing here it is done with pellets ;). So is it possible to use the huge 4500 PSI 100 CuFt tank for scuba diving? I've been searching on google and it seems it might be possible but I thought it would be a good idea to get a straight answer before I hop in my lake with a airgun tank and regulator and die from anemia. Based on my estimates, using Airgun CF tanks would provide enough air to stay submerged for possibly 2 hours depending on your body weight and measurements. This is HUGE difference compared to traditional steel and aluminum which would be about thirty minutes in comparison.

I was thinking it would be a good post in this section as it will provide just another reason to get a airtank. We would be able to get more into airgunning AND Scuba diving! I called people who sell airtanks and they don't think it would be possible as the carbon fiber tank is so light that it would float. However, im sure that if you just add more weights (as divers use weights made out of lead to submerge faster), it will let you sink even with the light CF bottle. Another thing to keep in mind, is that there are regulators that convert high pressure air into low pressure air, so that you can safely breath it in. These regulators are sometimes rated for 3000 psi. Although im sure there are high rated ones on other sites.

So what do you think? Do you think I could use my 100 CuFt bottle for scuba diving? Do you guys know anyone that scuba dives with CF tanks? It'd be nice to know I can get into scuba diving without buying a brand new scuba tank.

 
Being a retired Master Scuba Diver Trainer, I will just tell you straight up. Dont think I would ever even think of trying this option. There are so many reason not to even consider this but let me give you the first reason I would pass on the idea. The CF tank buoyancy is equal to the water that it displaces minus it's own weight. Fresh water weighs in around 62.4 pounds per square foot, salt water is about 64.2 if memory serves. Most aluminum and steel tanks weigh in around 35 to 40 pounds, depending on the cubic foot choice, but typically my 100 cubic foot steels at 3500psi weigh in around 41.4lbs (just went out and weighed one for you). You would have to have so much weight on to even get below the surface. I can tell you I typically dive with no weight on in fresh water using a steel tank that is a couple of pounds negatively buoyant when full and about 2 pounds positive when it is at 500PSI. Very comfortable and safe. Safe because should I lose my weights ( I add weight based on the thickness of my wet suit or if I am wearing a dry suit) while diving I am not going to shoot to the surface in an uncontrolled ascent. (very unhealthy if not death). On the other hand should my tank come lose from my BC (buoyancy compensator), the jacket that you wear that holds the tank, I am not going to have 40+ pounds strapped to my body without an air source to breath from. So in other words you would sink to the bottom while your tank and regulator are at the surface.

Now with that said, would I rather lug around a CF tank than a steel 41 lb tank all day? You bet! But for diving, I think I will stick with my steel tanks, comfort and enjoyment are what scuba is all about! Have fun! Hope this helps.

 
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Wow that seems brutal. So basically since my CF tank is so bouyant, worst case scenario: The CF tank could pop off my buoyancy compensator and float quickly to the surface. while all the 40lbs of weight is still on me and I sink to the bottom? Would it take too long to drop the weights as fast as possible and get back to the surface? What about the extra time underwater by using a CF tank? Its not worth a life thats for sure but is there any way to make this work? Would it therefore be relatively safe at shallower waters 30 ft max? And thanks for weighing everything for me you really helped me out. 
 
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Hey FukoChan I have to applaud your ingenuity and creative thinking but maybe these are two sports that should not be combined?

Two points I think are worth noting. First the CF tank that is 100cubic foot would have the same theoretical volume of air as a 100 cubic foot steel or aluminum tank. So the amount of bottom time would be the same based on available air. Your bottom time is more of a function of two things, your personal air consumption and the absorption of nitrogen based on your depth and time. Assuming you are following recreational dive tables or a dive computer.

Second point: If you use enough weight to offset the buoyancy of the CF tank, you are going to be limited in your freedom of movement under water. Think of it as a fishing bobber and a lead weighted hook on a fishing line. You are going to have to pretty much remain in the same position during the entire dive. Your tank will be the highest point of your body, pulling up on you. Your weights are going to be the low point on your body and always pulling down. Not very comfortable and not much fun I wouldn't think. Just a little insight, I once owned a set of full face mask OTS underwater communication system like the one shown. 218 × 150 - scubacenter.com


Just the extra air space in the mask was so buoyant that if your were not careful about keeping the mask pointed down when underwater, it would literally lift off your face or try to twist your neck sideways. Not very comfortable. When your under water you want to be as neutrally buoyant as possible so you can maneuver and position yourself with little to no effort. To answer your question about dropping the weight, yes that would be the procedure, but if you had a scuba tank that was closer to being neutrally buoyant, it simply slides out of your BC strap and usually goes unnoticed that it is loose till your dive buddy sees it. A CF tank would rip the reg out of your mouth and pop to the surface. oops, there went your air source. 

The most dangerous depths to make rapid ascents is from 30 feet and up. If you hold your breath from 30 feet (2ATM) to the surface (1ATM) after taking a breath of compressed air, your lungs would be about twice their normal size. Not good. Don't want to get into a scuba lesson here but get your certification and talk to your instructor about your ideas. You also always want to breath scuba quality air, not just compressed air we use in airguns. Please get your scuba certification before you try any of this. Scuba diving is safe, when you know what your are doing with the proper training, otherwise it can be deadly. On a personal note I would not ever use a tank that had not always have been filled with filtered, tested Grade E air. The compressors we use in scuba clean the air and are tested on a regular basis for contaminants. If you were to fill a scuba tank using only an airgun style compressor, without the Grade E filters and proof of testing, you very well could contaminate your lungs with oil from the compressor. This can really mess up your lungs, even worse when breathed at depth.
Sorry to get off the subject of airgunning but this is life and death and quality of life and I would hate to see anyone get hurt. 
FukoChan you have a great creative mind but maybe you could find a second use of your CF tank that does not involve breathing air from it underwater, like airing up tires? Airing up basketballs? Blowing up airbeds? I even use my scuba tanks to blow out water lines in my RV. Have fun!
 
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