HPNS Test

[CraigAClark]

Ever wonder how you can determine how a new Dive Store employee would react to a ruptured burst disc when filling? Back in the mid 80's, I was working at one of the larger stores in my area. I was the service manager. This question had always intrigued me, so I took the title of a problem that sometimes showed itself in Sat divers
being pressurized to depth in a chamber, HPNS (High Pressure Nervous Syndrome) and applied it to a simple test. The store had a built in filling bath that tanks being filled were completely submerged in.

When the store hired a new employee, their main job was "fill-boy/girl" (I was an equal opportunity tester). My simple test was to take a 3000 psi rated cylinder and replace the burst disc with one rated for an 1800 psi cylinder. The victim, err new employee, was then directed to fill this cylinder while I, waited with anticipation, err observed. The reactions were priceless! One really sticks out in my mind though. One fellow started screaming "It broke, it broke, what I do!" then ran out the front door. However his statement had a cajun accent which was extremely hilarious.

You don't have to say it, I know I was an evil SOB.

Craig

 

[Isaac-1]

Craig your message reminds me of two seperate incidents I had the chance to see, or at least walk in just after it happend. Both happend back in the late 80's early 90's in the period after a number of tanks had exploded in Florida severvely injuring/killing a number of people (due to improper repainting of tanks). The first was while a tank was being filled at a shop in a strip mall, they had a water bath fill station located in the public part of the shop, I was in there shopping (wasting time) as it was within walking distance of my apartment when a burst disk blew. The interesting part was this shop had a suspended ceiling, and when the burst disk blew all the panels lifted up about 3-4 feet and almost everyone one dropped back into place. The second incident happend at another shop that I was instructing for around the same time period, this one I did not see, but walked in just afterward. I walked in to find the guy that had been filling tanks soaking wet and saying how he was never going to fill tanks again, he had been filling some tanks that were fresh back from hydro testing, when the valve blew straight out of one of the tanks. This is one of those things you don't tend to believe unless you see it yourself, and I still have no idea how it happend. Maybe the tank was bulged, regardless of how the valve came out without visibly damaging the threads on either the tank or the valve after being filled to around 1000psi (the valve would screw in hand tight at least, valve and tank were sent to the manufactuer for inspection, I never heard what they found). In case your suspecting a VERY fast fill, this shop filled straight from a 7 cfm compressor with no storage bank.


Ike

 

[CraigAClark]

Ike,
You're right, that second one is a little hard to swallow. In the 5 years that I worked at that store, I must have personally hydro tested a couple thousand cylinders, both scuba and scba. It's hard to believe that a cylinder that was actually tested, would fail as you describe. However it was possible to re-test a failed tank and have it pass, which is why I would never accept tanks that had failed elsewhere. You wouldn't believe how many people actually tried having failed tanks re-tested. My personal HPNS test came with the new composite scba bottles of the day. I was filling one and noticed air leaking near the valve (we couldn't completely immerse these), so I lowered it a little further in the water, then realized the leak was coming from the bell portion of the cylinder through a crack. I could have won an olympic sprint at the speed I was moving to throw that cylinder in the dumpster. Scared the crap out of me.:11:

Craig

 

[pescador775]

A burst disc blew out on a cylinder which was riding in my Suburban and located directly behind my head. My bad, I should have checked. I bought three of those 3000 psi steel tanks from an outfit in Chicago. They were a popular mail discount store in the early days called "Berry Dist". Anyway, only one of the tanks had the correct burst disc. Heck, I had used those tanks for years before that 2250 WP disc blew. Gave me quite a start. Funny thing is I was on my way to a dive shop when it happened, and they replaced the parts before the hour was out. I wanted to buy a simple disc but times had changed and I had to fork over some green for the module and gasket.

Good thing that the window was open (pop).

 

[Isaac-1]

There are worse places to have a burst disk let go, I once saw one blow at 85 feet on a wall dive on Roatan. I was about at about 55 feet and 20-30 feet over when it blew, the bubbles were spectacular.

Ike

 

[Jimmer]

I didn't see this, but a friend who owns a store was working late one night cleaning some rental gear. He was using his water bath tank with a little bit of detergent in the water to dunk the gear into as part of his cleaning. Well some guy came in wanting a fill, so he hooked up the tank, dropped it in his water bath as he always does, and the burst disc blew mid fill. I'm told it took him a couple hours to get rid of the bubbles and dry things up.

 

[rjack321]

I was helping out with a entry level tech class last month and the instructor was discussing manifolds and failures. He's from out of town and was using locally borrowed doubles, the only set available for him that day. Lecture is happening here on a pickup tailgate. He shifts the tanks pointing out different pluses and minuses to dual regs and hissssssss, leak. We shut everything down including the isolator. Still leaking. Burst disk was loose, crap he needs these tanks for today's shallow skill dives.

I cranked the little guy a hair tighter (no torque wrench around) while they all waited on the other side of the parking lot

 

[JKPAO]

By the way HPNS is an effect of mixed gas (helium) on the nervous system. Not that you would know!

see you topside! John

 

[CraigAClark]

By the way HPNS is an effect of mixed gas (helium) on the nervous system. Not that you would know!

see you topside! John

Actually it is an effect of the lack of a "narcotic" gas in the mixture. Minute quantities of argon have been used successfully to counter HPNS, because of its greater "narcotic" effect at much lower partial pressures than nitrogen.

Craig

 

[underboats]

We carry our tanks in a rack on the back of a pick-up. While I was stuck on a bridge waiting for a ship to pass the disk burst on one of the tanks. I knew right away what it was but the people in the cars beside me were ducking for cover. I just sat there like I didn't hear it until it quit, then I looked around at everybody like I didn't even know anything happened. I still laugh when I think about the look on peoples faces. Chuck