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What is PSI?   What is Visual Plus?   Altitude Dive Tables

What is PSI?

PSI (Professionsal Scuba Inspectors) is the training and certifying agency for visually inspecting high-pressure SCUBA and SCBA cylinders. PSI procedures follow an 18-step inspection format, adhering to CGA standards, which also includes filling out an inspection report for the customer.

An active SCUBA diver may, in one year, subject his cylinder to conditions not encountered by most other cylinders in their entire service life. We divers submerge our cylinders in both salt and fresh water. Water may enter the cylinder during air compression, air filling and, potentially, by back flow through the regulator when the cylinder is near empty. Cylinders are dropped, banged against one another and struck against a wide range of other hard objects (such as rocks). Because cylinders appear to be hardy and, of course, they are, owners (and users) tend to view them as indestructible. Often, little thought is given to the care of our cylinders. There are many things a cylinder owner can do to extend the life of their cylinders; poor care, on the other hand, may reduce a cylinder's life considerably or may cause a near-new cylinder to rupture explosively, endangering lives of anyone in the vicinity at the time.

While a few cylinders do explode each year, most dangerous cylinders are removed from service by visual or hydro inspectors.

We now have a new tool to help find those cylinders which may be subject to explosions:

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What is Visual Plus?     Click the image for a larger view, click your 'back' button to return here.

Aluminum cylinders can develop a fault within the neck area, called Sustained Load Cracking (SLC) - this causes, in some cylinders, a crack to develop within the aluminum in the neck area that spreads with time, resulting, eventually, in an explosive rupture. By its molecular nature, aluminum may not exhibit any warning signs of the impending explosion and the developing fault may not be visible to the naked eye. There have been many explosions of aluminum cylinders over the past several years with many lives lost and/or serious injuries as a result. The most recent in Canada was in a dive shop in Campbell River, B.C. a short time ago. Fortunately, there were no injuries or deaths during this explosion, but there was devastating damage to the building. An exploding SCUBA cylinder has the explosive potential of many sticks of dynamite - a sobering thought, indeed.

A test procedure, called eddy current testing, can detect these faults deep within the neck material of an aluminum cylinder before they become serious enough to cause a catastrophic explosion. We use the tester called Visual Plus, manufactured by Advanced Inspection Technologies, to detect these faults during an annual visual inspection.

Our normal annual visual inspection on aluminum cylinders includes the testing of the cylinder neck material using the Visual Plus eddy current test equipment. The cylinder owner receives a print-out of the results of the Visual Plus test and a special sticker is affixed over the normal PSI inspection sticker to indicate the cylinder has been tested for sustained load neck cracks. As a safety concern, we will not fill any cylinder more than 5 years old that does not carry a current visual inspection sticker and a current eddy current test sticker. I recently discovered, by using the Visual Plus eddy current tester, a 6-year old cylinder that had a serious neck flaw - the cylinder manufacturer replaced the cylinder for the customer, free-of-charge.

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Altitude Dive Tables

For those of us divers who do much of our diving away from the ocean, we often dive in lakes and rivers that are well above sea level. According to the typical dive tables, any dive in water above 1000 feet above sea level is considered an altitude dive and special considerations must be taken when calculating the nitrogen uptake, maximum dive depths/times and the repetitive dive profiles. To make all this easier, I am including a set of Altitude Dive Tables that divers can use to help them calculate differences between sea level diving and diving at altitude.
The tables are provided here without any warranties or promises of accuracy or applications. Should you use these tables, you assume all and any risks associated with altitude diving and the calculations of depths and times. As there is little research on the body's responses to diving at altitude, each diver is urged to dive very conservatively when diving at altitude, keep well within the allowable times and keep dives as shallow as possible - always less than 100 feet (30 metres) deep. There is quite a bit of information on these tables, although we usually will only want to calculate our nitrogen uptake and repetitive dive designator to use with the standard sea level dive tables. The easiest method of doing this is to refer to the table that covers the altitude at which you are diving (always use the next higher elevation if you fall in-between), then select the column for the type of depth guage you are using (usually bourdon tube type), then follow down that column until you reach the depth (or next greater depth) that you expect to dive, then follow that row across to the right hand column where you will find the equivilant ocean depth you should use on the standard sea level dive tables to find your equivilant nitrogen saturation and, therefore, to calculate surface intervals, repetitive dive depths/times, etc.
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