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How Chrysler's Battery-Less Hybrid Minivan Works
thecarchik writes "Chrysler announced Wednesday that it would partner with the US Environmental Protection Agency to build and test prototypes of a different kind of hybrid vehicle, one that accumulates energy not in a battery pack but by compressing a gas hydraulically. The system in question, originally developed at the EPA labs, uses engine overrun torque to capture otherwise wasted energy, as do conventional hybrid-electric vehicles. The engine is Chrysler's standard 2.4-liter four-cylinder, the base engine in its minivan line. But rather than turning a generator, that torque powers a pump that uses hydraulic fluid to increase the pressure inside a 14.4-gallon tank of nitrogen gas, known as a high-pressure accumulator."
Yes, SCUBA tanks (in the U.S.) are supposed to undergo annual visual inspection (basically an interior/exterior idiot check for bad rust, chips, cracks, beat up valves, etc) as well as hydrostatic testing every 5 years*. The cylinders most likely to have a catastrophic failure (typically the neck) were a bunch of aluminum 80's manufactured something like 30 years ago. Back when I worked in a dive shop we would do an eddy-current test on the necks of ALL aluminum cylinders during the annual visual inspection even though it was only really necessary for the one batch. If you take halfway decent care of a tank and don't let moisture get in (by draining the tank too low), they'll last for ages. We had decades old steel cylinders in our rental fleet that had probably outlived many a valve!
The concern is probably warranted but I would imagine the auto industry's safety measures will be far greater than those of the average diver. If the vehicles only go in for maintenance once every few years, the tanks ought to be fine. I would worry more about them being punctured during a collision. Frankly though, assuming they've done at least a minor amount of planning with collisions in mind, the severity of a collision strong enough to puncture the tank would make a sudden release of pressure the least of your concerns.
* Disclaimer: I've been out of the dive industry a while, my numbers might be off.