Scuba Cylinder Common Sense

by Bill High
President of PSI, Inc.
(Professional Scuba Inspectors)

The Scuba cylinder, that clumsy aluminum or steel tank that we all strap on, is the most basic piece of equipment we own. The technology used to make it is over 40 years old. As a matter of fact, many of the parts in today's valves can be interchanged with valves from the 50's.

Because the tank is such a low-tech device, many divers feel that it can be totally overlooked - some feel that it can even be modified. You probably remember the "exploding tank" scare from a few years ago. A diver painted and heat-treated his aluminum cylinders. When filled, the cylinder exploded. This resulted in a flurry of safety notices, and many shops refusing to fill tanks with custom paint jobs. There are a few things about the dive industry that many divers either ignore or just don't realize.

Visual Inspections

These are suggested by the CGA, or Compressed Gas Association. It's not a law. A correct inspection takes more than a cursory peek inside the tank with a light. It is supposed to include a careful inspection of the tank's exterior for dents, corrosion and other damage. A mirror has to be inserted into the tank so the underside of the neck and threads can be inspected. The threads should also be inspected. The boot has to be removed and this area inspected. Does your dive shop do all this? I took my tank for a visual inspection to four different dive shops in the Chicago area, as well as a hydrotesting facility.

Only one of the shops did a complete inspection. Of the remaining three, one removed the tank boot, two used a mirror, and node did a good job of inspecting for dents and damage. I even stuck a small yellow "dot" inside my tank, at the base of the threads. Only the first shop spotted this!

The hydrotesting facility used a mirror, and removed the boot (it had to as part of the testing.) A cursory inspection for damage was done.

None of these facilities checked the burst disk. All the shops automatically sold me a new neck and face O-ring.

The overall feeling of the shops way "hey it's aluminum. It lasts forever." Not true - that's why the manufacturers even have inspection guides. For example, several years ago a problem with some tanks came to light. Some were developing cracks at the base of the threads, where only a mirror could be used. Yet some shops still don't use a mirror!

Burst discs should be inspected every time the tank is inspected. Some agencies say they should be replaced yearly, others only if they show signs of corrosion. There are four major problems with burst discs:

  1. Age and corrosion
  2. People stacking burst disks, i.e., butting two or three in the valve so it will not pop
  3. Plugging the burst disc (unfortunately a regulator LP plug is the same size as most burst discs)
  4. Older style "lead plug" burst discs - these are literally bullets and should be replaced. Is should be common sense that you don't mess with burst discs and don't plug them - why would anyone want to carry around a potential bomb?

Hydro Testing

This is a regulation set by the Department of Transportation. It's not a law, but a federal regulation that carries stiff fines if not followed. Any place that fills a cylinder that does not have a current hydro-test can face huge fines and penalties. Scuba cylinders require a test every five years.

Bottom Line

Don't play games. A Scuba cylinder contains a great deal of kinetic energy. I have seen the damage an exploding tank causes. It can literally destroy a dive shop, blow apart the roof, and cause serious - even fatal - injuries.