So the Tank Explodes - What's the Big Deal???, the first place to look for a dive instructor

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Posted by Ken Kurtis on October 22, 2001 at 15:03:48:

Hopefully that get your attention . . .

To continue on Jeff's thread and to more directly deal with the underlying issue which is NOT "are boats underfilling tanks" but is more appropriately . . . Why is it that divers insist on over-filling tanks, and don't realize there's a danger to the practice?

A few years ago, there was a rash of tank explosions ("rash" being about five, all within a relatively short period of time). The explosions were happening mainly in Florida. The significance is that, due to the number of caves and caverns there, and the need for as much air as possible when exploring those, over-filling tanks is a common and somewhat-accepted procedure in Florida. (Whether it's individuals or stores doing it is a moot point).

Unfortutanely, frequently filling the tank beyond it's stamped & rated pressure causes the tank to expand beyond it's design specs, which over time produces metal fatigue. Now the tank is now ready to explode and does so on the next over-fill.

(And for those who might think an exploding tank is no big deal, or that the explosion will be contained by a shed or vat in which the tanbk is being filled, understand that a tank explodes with a force somewhat equivalnet to two sticks of dynamite. Needless to say, this can kill, or at least severely injure, anyone standing nearby. The force could also sink a boat.)

So with all this in mind . . . why do people keep asking for overfills? I'd be curious to hear from anyone reading this who thinks that overfilling is a safe practice.

DOT regs are pretty clear. We cannot fill a tank beyond it's stamped & rated pressure. If there's a "+" after the hydro, we can go 10% over the stamped pressure, but that's only on steel tanks. If the pressure cannot be read (becuase than tank's been painted), technically we're not supposed to fill it at all.

The stamp is pretty easy to find and understand. It's found on the neck and will usually be 2250 (for a steel), 2400 (for an LP steel), 3000 (for an aluminum), and 3500 (for an HP tank). You may also find some older small steels rated to 2015 or 1800, and some aluminums rated to 3300. But the bottom line is that EVERY tank is stamped.

So why are divers willing to (literally) risk life and limb by over-filling the tank. If you need more air, why don't you jsut get a bigger tank?


Ken Kurtis
NAUI Instr. #5936
Co-owner, Reef Seekers Dive Co.
Beverly Hills, Ca.

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