By Robin Battley

The photos were purposefully taped near the door of the air filling station. Holes in cinder block walls, a hole in the concrete floor, jagged pieces of metal, large cascade storage bottles out of place. Images from a recent Eastern bloc war? No, this is a recreational dive store. Why'd they do that? Why would anyone want to put the face of a "war zone" onto an accepted recreational leisure activity? What purpose can this serve the store's customers and potential customers? There can be only one answer - education. Serious, but education nonetheless.

Problems with scuba tanks was a topic seldom heard about among experienced divers. Lack of proper maintenance, chronic overfilling and recklessly increasing the burst disc capacity of tanks were reasons heard years ago to explain accounts of scuba tanks rupturing. But it was always Florida, or California, or somewhere else. Never here. Never close to home, right? That is sadly changing.

Let's take a "tank test", shall we? What capacity is your scuba tank? What is the working pressure? What inspections need to be regularly conducted to ensure the safety of your high pressure cylinder? How long is the shelf life of a scuba tank? When should I "retire" my tank or replace it?

Scuba tank capacities have ranged from the original 71.2 cu. ft. steel tanks of the 1960s and 1970s to the 80 cu. ft. capacity aluminum standard of the 1980s and 1990s. Many other tank sizes have come and gone to accommodate the smaller diver, the larger diver, the technical diver, the mixed gas diver... any unique diving industry target market. Original steel cylinders used at the dawn of recreational diving had a working pressure of only 2250 lbs per square inch (psi). Today a newer 190 cu. ft. capacity steel tank may have a working pressure of over 4000 psi. Newer alloys allow larger tanks, more pressure and longer diving. Good news for divers, right? Mostly, yes.

Unfortunately, not all divers are aware of the destructive power stored in a scuba diving cylinder. An 80 cu. ft cylinder has the same explosive energy as several sticks of dynamite. The statistics show that at least two scuba tanks fail during filling each year. That's not a high ratio considering all the scuba cylinders in circulation on the continent but even one accident is cause for concern.

"But I take my tanks in to my local store every year for their annual visual inspection," you say. Excellent, and your dive store technician has a significant burden to fully inspect and approve your cylinders. What are they looking for? Basically they are examining the cylinders for any alteration from the original condition including metal discoloration, rusting in steel cylinders, oxidization in aluminum cylinders, pits creating small holes into the metal on both the inside and the outside, and hairline cracks in the threads and neck of the cylinder. Things that hinder this inspection include your tank boot, the plastic tank mesh, the years and years of previous VIP and/or club stickers, a new paint job or vinyl coatings on the tank.

In addition to the inspector's skill, several new tools are available to detect potentially dangerous tanks and remove them from active use before a problem occurs. Bright strings of lights illuminate the insides of tanks much better now, enabling technicians to more readily identify discolouring or corrosion. Also, more accurate probes and gauges are available to detect and measure any surface anomalies. Electronic gauges thread into the cylinder neck and identify cracks or structural alterations in that part of the tank. As a result of these more aggressive visual examinations, most of the tanks that could subsequently explode are caught and condemned.

And now the hardest question of all what is the shelf life of a tank? There is no perfect answer. Manufacturers of steel and aluminum scuba tanks also offer no definitive answer. In 1994, the DOT issued a Safety Alert Bulletin regarding tanks made of the aluminum alloy 6351-T6. This alloy was identified by the markings "DOT 3AL" and those tanks are now well over ten years old. I am personally examining this issue since I own two tanks with the "DOT 3AL" markings, both of which are over twenty years old and a third tank recently started leaking air through the shoulder during a recent air fill. That's right, the shoulder of the tank just alongside one of the hydrostatic stamps. This incident mirrors an unfortunate accident in Florida this spring where a tank started leaking. The dive store staff thought it was a leaky valve and was in the process of checking when the tank exploded. He received disfiguring injuries and significant damage was done to the store. I was one of the lucky ones. No one was injured. No property was damaged. The air was released from the tank safely. The annual visual inspection was only nine months old and had been performed electronically. The hydrostatic test still had two years remaining. No, I would never attempt to use that tank again.

Technical knowledge and metallurgy have advanced light years over the twenty years since my tanks came out of their new cardboard boxes. Aluminum alloys contain less lead and are significantly stronger. Purer methods of refining provide us with a better steel alloy. There are even composite materials including a fibreglass/epoxy overwrap allowing neutral buoyancy and more air capacity. Wow, what will they think of next?

Really though, I think a combination of diver common sense and consistent quality inspections by trained technicians will keep the scuba tank accidents to a minimum over the up-coming years. The price of a new scuba tank is small relative to the inconceivable cost of personal injury and property loss.