51 replies to this topic

[WreckWench]

Kimber is right. It is very important to understand the rules and also understand the safety issues both real and perceived.

As divers we must make decisions about our health when it comes to diving everyday. We choose who we give our business to and if they practice what we feel is an unsafe practice then we can choose to not give them business. OTOH...if we encourage a business to practice unsafe habits then we are guilty as well. But we must know what is fact, fiction, and common beliefs so we can make informed and educated decisions.

I know that I personally thought an 'overfill' or now adays called a 'cave fill' was great. WOW!!! Look how much more gas/air I have and how much safer I'll be with that reserve. Now that I know more about diving I realize that there is a reason that things like 'cave fills' and 'overfills' are a bone of contention. Many see them as harmless and others know in principal that they are harmful. The real trick is to find the appropriate middle ground.

And of course its all clear as mud!

I will say this...I got a 'cave fill' to 3600 psi in a tank last year on our annual Florida trip and it blew an o-ring in my first stage out. It ruined my dive...could have seriously hurt me if it had happened in the water and it almost ruined my second dive of the day. (I had to use borrowed gear which is never a preferred way of diving!) So in my book...serious overfills are not safe and they are not desired. I like my gear just as it is WAY too much to risk losing it over an 'overfill'.

I'd rather carry a bigger tank or a safety stage if I am worried about having enough air/gas to dive with.

[TekDiveGirl]

This is what I saw ---

The Department of Transportation (DOT) sets exact limits on the weight of hazardous materials that may be transported before vehicle placarding is required. Remember that when you are transporting cylinders, you are transporting hazardous materials. Vehicle placarding is required when the total weight (both cylinders and their gas contents) reaches a combined weight of 1,000 pounds or more. Placards are "signs" that tells others around you that you are transporting hazardous materials.

From the following website.

http://www.calaged.o...rticles/bk1.htm

It also says --

Transporting cylinders in cars, vans, or in any enclosed vehicle is extremely dangerous and should be avoided. Never transport flammable gases in the trunk or passenger compartment of a vehicle. Many persons disregard this warning each year, and there are many vehicle explosions as a result.

But that sounds more like a recommendation than a regulation.

[TekDiveGirl]

I will say this...I got a 'cave fill' to 3600 psi in a tank last year on our annual Florida trip and it blew an o-ring in my first stage out. It ruined my dive...could have seriously hurt me if it had happened in the water and it almost ruined my second dive of the day. (I had to use borrowed gear which is never a preferred way of diving!) So in my book...serious overfills are not safe and they are not desired. I like my gear just as it is WAY too much to risk losing it over an 'overfill'.

I'd rather carry a bigger tank or a safety stage if I am worried about having enough air/gas to dive with.

Well that is why we educate ourselves and make informed decisions. I don't like to go on -- my buddy/instructor/mom told me so -- so it must be true.

That said -- I don't know that you can really blame the o-ring failure on the high pressure fill. It was likely a coincidence. O-rings go when they go. And it could happen at 2640 as well as at 3600. You don't use special regulators for HP tanks and LP tanks -- other than DIN instead of yoke on HP of course - but the innards past that are the same.

[WreckWench]

I will say this...I got a 'cave fill' to 3600 psi in a tank last year on our annual Florida trip and it blew an o-ring in my first stage out. It ruined my dive...could have seriously hurt me if it had happened in the water and it almost ruined my second dive of the day. (I had to use borrowed gear which is never a preferred way of diving!) So in my book...serious overfills are not safe and they are not desired. I like my gear just as it is WAY too much to risk losing it over an 'overfill'.

I'd rather carry a bigger tank or a safety stage if I am worried about having enough air/gas to dive with.

Well that is why we educate ourselves and make informed decisions. I don't like to go on -- my buddy/instructor/mom told me so -- so it must be true.

That said -- I don't know that you can really blame the o-ring failure on the high pressure fill. It was likely a coincidence. O-rings go when they go. And it could happen at 2640 as well as at 3600. You don't use special regulators for HP tanks and LP tanks -- other than DIN instead of yoke on HP of course - but the innards past that are the same.

The regs had just been serviced for the trip and they are rated for 3000 psi. So 10% over that is 3300. I had a fill of 3600 and it was clearly the fill issue. When I took it in for servicing I was told that I must of had a overfilled tank as it blew the main body o-ring that seals around the shaft of the piston.

I do dive older regs but even newer regs are only slightly more capable of handling higher pressures but they are not rated that way for liability purposes.

[BradfordNC]

wow, i'd like to know where you guys get your "cave fills" from.

north of 4000 psi huh?? interesting. never seen that before.

in all the shops i've been to in cave country you'd be lucky to end up with around 3600 psi.

that will turn a LP 108 into a 150. so a set of doubles goes from 216 cf to 300 cf.

so basic math on that dive is 100 cf in, 100 cf out, 100 cf in reserve.


haven't seen any solid data on the practice shortening the life of a tank.
plenty of tanks down in cave country with Hydro stamps going back to the 60s and 70s.

and already on this thread there was mention of a tank that was never "overfilled" and yet it failed hydro.

another thing to look at, the tanks in europe are lasting just as long as the tanks in the US.
the factory is in europe. do you honestly believe they have two factories? one smashing out tanks for the US market, and another smashing them out for the european market that is using some completely seperate mix of metals?
its the same press smashing out the tanks. but the tanks being shipped to the US have DOT info stamped on the shoulder.

the 3442 tanks that are so popular now are the same tanks that were 2460 a few years ago, they simply got a DOT Exception (see, the "E" in PST's line of tanks stands for Exception) to the regulation. how did they do it? they took one of the 2460 tanks and put it through over 100,000 fills to over 3500 psi (more than any of your tanks will ever endure) and then hydro'ed the thing. DOT said, "damn, still holds up. OK, the approved pressure at 3442 will keep the cylinder from being rated as HP."

if the 3442 tanks don't destroy your regs, then the "cave filled" 2460s won't destroy them either.

there is no magic in diving. no witchdoctor dances around cylinders making this tank dangerous at a certain pressure and another identical tank safe at the same pressure.
its all simple science. far far far simpler than launching the space shuttle.

[Geek]

It's dangerous. It's illegal and it shortens the life of your tanks. If you do it, I don't even want to be near your tanks.

I'm afraid I have to agree with the substance of what Walter says here. Tanks are rated to specific pressures. While I am not concerned about the "tank police", I don't want to be near such tanks either. In fact, I don't want to be in the same county.

Tanks can explode. The more pressure, the greater the "boom". Burst disks letting go are no picnic either, so don't think of a blown burst disk that as an acceptable result. If you have overfilled, you are clearly the one responsible, and should be held liable. Note I did not say "could", I said "should" and I mean it. That includes manslaughter charges if someone is killed.

If you need more gas, get bigger tanks or learn to use a rebreather. With 150 HP tanks available, you really have to be doing some extreme diving to need to resort to cave fills.

[gcbryan]

I have to say that I've seen or read of no evidence that would support those arguing for exploding tanks and shorter tank life (steel only). There is a limit of course but most of the negative claims are not supported as far as I can tell.

Edited by gcbryan, 02 June 2006 - 01:22 PM.

[Geek]

I have to say that I've seen or read of no evidence that would support those arguing for exploding tanks and shorter tank life (steel only). There is a limit of course but most of the negative claims are not supported as far as I can tell.

Tank explosions are rare, but they do occur. If they did not occur, we wouldn't need VIPs or Hydros. I'm not sure what you would consider convincing evidence, but there are photos and stories on the Internet. I believe you could track them down by searching Scuba Stop or Scuba Board. If you spend a few bucks with PSI, they have a CD full of very impressive photos. From the pictures I have seen, steel tanks tend to rip rather than explode into shrapnel, but I still would not want to be in the neighborhood.

You might also want to read the book Shadow Divers, which is about Chatterton and Kohler's efforts to identify the U-Who. If I remember the book correctly, during the period they were trying to identify the wreck, Chatterton had a tank explosion in his garage. Fortunately, no one was there at the time, but the damage was considerable.

[captsteve]

I have to say that I've seen or read of no evidence that would support those arguing for exploding tanks and shorter tank life (steel only). There is a limit of course but most of the negative claims are not supported as far as I can tell.

Tank explosions are rare, but they do occur. If they did not occur, we wouldn't need VIPs or Hydros. I'm not sure what you would consider convincing evidence, but there are photos and stories on the Internet. I believe you could track them down by searching Scuba Stop or Scuba Board. If you spend a few bucks with PSI, they have a CD full of very impressive photos. From the pictures I have seen, steel tanks tend to rip rather than explode into shrapnel, but I still would not want to be in the neighborhood.

You might also want to read the book Shadow Divers, which is about Chatterton and Kohler's efforts to identify the U-Who. If I remember the book correctly, during the period they were trying to identify the wreck, Chatterton had a tank explosion in his garage. Fortunately, no one was there at the time, but the damage was considerable.

If i read the book correctly, that was an old emergency escape cylinder off the U-who that exploded. it had been submerged for over 50 yrs and i believe that many of the alloys used later in the war to make those things were inferior.
also, thats what burst discs are for.... if i didnt have enough faith in a tank that was filled at 3600psi, then im getting rid of it or giving it a lower fill. A new Lp faber rated in europe for 4400psi should be fine with 3600psi and a 5000lp burst disc.
JUST FOR THE SAKE OF THE ARGUEMENT....... there is no doubt that lower pressures are safer and better on the regs. that is common sense. Is it safe enough to operate a good steel tank at higher pressure? I think it is no worse than some of the other thing we do in everyday life. how many people here every break the speed limit? the speed limit may be 55mph, but does your car fly apart just because you are doing 70mph?...... yeah....I know that is a poor analogy.

[ScubaHawk]

do you honestly believe they have two factories? one smashing out tanks for the US market, and another smashing them out for the european market that is using some completely seperate mix of metals?
its the same press smashing out the tanks. but the tanks being shipped to the US have DOT info stamped on the shoulder.

Why not believe that? Factories all over the world make different grades of the same product for different markets. If they can get away with using cheaper materials or a cheaper process to make goods for one country they do. IE: baby clothes have to be flame retardant to a degree in the US, not so in Mexico I know from first hand experience that plants will run a different line of material to make the baby clothes for export.

Edited by ScubaHawk, 02 June 2006 - 03:13 PM.

[Geek]

I have to say that I've seen or read of no evidence that would support those arguing for exploding tanks and shorter tank life (steel only). There is a limit of course but most of the negative claims are not supported as far as I can tell.

Tank explosions are rare, but they do occur. If they did not occur, we wouldn't need VIPs or Hydros. I'm not sure what you would consider convincing evidence, but there are photos and stories on the Internet. I believe you could track them down by searching Scuba Stop or Scuba Board. If you spend a few bucks with PSI, they have a CD full of very impressive photos. From the pictures I have seen, steel tanks tend to rip rather than explode into shrapnel, but I still would not want to be in the neighborhood.

You might also want to read the book Shadow Divers, which is about Chatterton and Kohler's efforts to identify the U-Who. If I remember the book correctly, during the period they were trying to identify the wreck, Chatterton had a tank explosion in his garage. Fortunately, no one was there at the time, but the damage was considerable.

If i read the book correctly, that was an old emergency escape cylinder off the U-who that exploded. it had been submerged for over 50 yrs and i believe that many of the alloys used later in the war to make those things were inferior.
also, thats what burst discs are for.... if i didnt have enough faith in a tank that was filled at 3600psi, then im getting rid of it or giving it a lower fill. A new Lp faber rated in europe for 4400psi should be fine with 3600psi and a 5000lp burst disc.
JUST FOR THE SAKE OF THE ARGUEMENT....... there is no doubt that lower pressures are safer and better on the regs. that is common sense. Is it safe enough to operate a good steel tank at higher pressure? I think it is no worse than some of the other thing we do in everyday life. how many people here every break the speed limit? the speed limit may be 55mph, but does your car fly apart just because you are doing 70mph?...... yeah....I know that is a poor analogy.

If a tank is rated for 4400 psi, then go for it, but I am not aware of any such tanks being available in the US. HP tanks are rated to 3442. I wouldn't call 3500 or 3600 a "cave fill". Cave fills as I understand the term are boosted way beyond the rated capacity.

You may be right about Chatterton's garage. I'd have to check the book. Nonetheless, tank failures do happen on rare occasions.

As for burst disks, the same idiots that go for cave fills tend to double the disks. Even if that hasn't been done, you don't want to be in the way if a burst disk goes.

[gcbryan]

.....

As for burst disks, the same idiots that go for cave fills tend to double the disks. Even if that hasn't been done, you don't want to be in the way if a burst disk goes.

Other than being startled it's not a problem.

In addition one could argue that burst discs are a product for dummies. The burst dics are to prevent dummies from filling tanks to extremes at the cost of one going off underwater which would result in an empty tank. I believe any caver that choose to double the discs would be choosing to fill the tank within limits and do away with the possibility of a dics blowing underwater (not likely but possible).

There are choices everywhere and the choice one makes is rarely the result of being a dummy (I'm only speaking for myself of course).

Edited by gcbryan, 02 June 2006 - 04:58 PM.

[Lubold8431]

If a tank is rated for 4400 psi, then go for it, but I am not aware of any such tanks being available in the US. HP tanks are rated to 3442. I wouldn't call 3500 or 3600 a "cave fill". Cave fills as I understand the term are boosted way beyond the rated capacity.
(snipped)
As for burst disks, the same idiots that go for cave fills tend to double the disks. Even if that hasn't been done, you don't want to be in the way if a burst disk goes.

As far as cave fills goes, what we are talking about are LP tanks being overfilled. So, a 3500 psi fill would be way beyond the rated capacity.

Burst disks blowing is not that bad. I had a few let go on me as I was filling tanks. Just a big gush of air and the tank gets knocked down and starts to push itself around a little depending on the pressure. Just hold it down for a little while...

Just another FYI, the Faber cylinders are guaranteed for 10,000 cycles at 4000 psi. Their rated pressure is 2640.

[intotheblue]

At a previous PSI update, I don't recall them talking about a weight limit. I recall them mentioning carrying more than about 15 cylinders or so. I really can't recall the number exactly since I knew that it would be beyond what I would potentially carry in my car/truck at any time.

Aw heck... there goes my trips to cave country in Florida without needing gas fills...

[intotheblue]

Burst disks blowing is not that bad. I had a few let go on me as I was filling tanks. Just a big gush of air and the tank gets knocked down and starts to push itself around a little depending on the pressure. Just hold it down for a little while...

Just another FYI, the Faber cylinders are guaranteed for 10,000 cycles at 4000 psi. Their rated pressure is 2640.

Good... then with the number of cylinders I use and rotate in use, I figure I have a good 9,600+ filles each to go!

Actually, overfilling tanks for no valid reason doesn't make a whole lot of sense. It does cause extra wear and tear on your compressor too. I will routinely "cave fill" my appropriate cylinders for cave diving. There is a reason they are called "cave fills"... I also understand that the LP tanks that are manufactured for sale here are the same as those in Europe and that the hope in so doing is that the DOT will eventually allow a higher pressure rating on the cylinders already in production for sale here.

Incidentally, I would not boost an old steel 72 you might have laying around, but if properly cleaned they make a good cave diving oxygen deco tank. You can fill them close to capacity without significant risk associated with higher pressures of oxygen, whereas an Al 80 will be filled significantly lower than its volume capacity at the same pressure. Also, the steel "72's" have better buoyancy characteristics (or lack thereof) for laying on the cave floor...

For recreational "no-deco" diving, "poking" around the reefs, snapping a pic or two... an aluminum 80 with the typical 2700 to 2900 psi you get at the LDS is just fine.

Of more concern is the speed at which my tanks are filled... and how hot they get in the process.

Interesting assortment of reactions on this topic...