Likelihood of air supply failure?

[Lee Taylor]

Something I have often wondered about is the likelyhood of total air supply loss. I have had hose fittings leak, seen o-rings blow, had regulators free flow, etc. Some divers carry all sorts of back up air supplies. Has anyone out there seen any statistics on air flow failure. What I am speaking of is for instance if ones air-pressure-gage "hose" were to explode, one would quickly become out of air. Regulators can fail and hoses can fail. What is the likelyhood of finding oneself with no air? I use to dive with a back up air supply. I don't feel the need for a back up now days and I am wondering if there are statistics to back up my confidence in my regulator/hose/gage tank system?



Charleston SC Scuba Club

 

[Daz]

Total system failure is really not something I worry about. A HP hose failure woudln't cause a big issue, you should have plenty of gas to make a safe ascent - Yes, the pressure is high, but the orifice is so small that actual gas loss is not that rapid. I'd be more concerned with a full on free flow or failure of a second stage. You'll lose more gas that way.

While such cases do seem to argue for fully redundant systems, IMNSHO, the actual rate of failure is so low as to not make it an issue for the type of diving that I generally do.

 

[DA Aquamaster]

TDI published some test results for various failures.

I posted it previously several months ago.

short story is that that the big threat is a ruptured burst disc as it can drain an AL 80 in about 80 seconds. The good news is that with replacement evert 5 years when the tank is hydro tested, burst discs almost never fail.

A ruptured LP hose will dump a tank in 3-4 minutes, a ruptured SPG hose will take 15-20 minutes to drain the tank.

With proper inspection hose failures almost never sneak up on you.

In 25 years of diving and maybe 2000 dives I have never had a hose failure or burst disc failure in the water.

A freeze flow from a frozen first stage in cold water will dump air at perhaps 30 cu ft per minute so it can be a substantial threat.

Blown o-rings tend to be very minor leaks, that get your attention more than pose a threat.

For an OW diver, gas failure is not an issue to worry about. For a technical diver, you use a redundant equipment configuration to ensure that lost gas is not a problem.

 

[Lee Taylor]

Reference Recreational Diving 1ft to 130ft. From what I have been hearing and reading, it sounds like an absolute stop of air flow is for all practical purposes is almost unheard of. It appears that 99.999% of air flow failures will leave you with a little time (air) to grasp what is happening and to at least do a partial ascent before the tank drains completely. The technical information in the posts helps me understand and rationalize. Thanks for responding!

 

[leapfrog]

Lee. Interesting post. A few things you can do to lower the risk having a total OOA/OOG situation are:

Swap your standard hoses for Miflex hoses. This is a very inexpensive upgrade to your equipment. It won't only stop or lower the rate of the leak, it will allow you to breathe exactly the same with a knot in the hose.

Choice of regs for the environment you are diving in. You probably don't ned cold water regs but free flow tends to be caused by freezing. Anywhere under 38F you should go CWR.

Not all regs freeflow in "fail safe" mode. You want to consider your options. You seem to be an experienced diver. If you do opt for fail safe mode then practice freeflow breathing on a regular basis.

DIN connection.

When diving from a boat, make sure they have a full scuba tank of air or nitrox on a line at 15 ft.

Make sure you have the right dive buddy (the one that stays close).

Remember to turn on and check your air before you jump in (this happened to me once!).

Practice opening and closing the valve at different depths.