Overfilling LP Steel Tanks -- How bad is it?

[TheScubaBOB]

why is that the right answer?

For the same reason the Right answer to "How bad is it to exceed the posted speed limit by 50%?" is "You should never exceed the posted speed limit by 50%"...

The agency which regulates the existance & safety of the cylinders says you shouldn't and knowingly telling someone to exceed those specs can make you liable in the event there is an incident involving overfilled tanks.

 

[H2Andy]

well, i know the dangers of exceeding posted speed limits by 50%

but what exactly are the dangers of exceeding max pressures in steel cylinders?

why is that a good rule to follow?

i operate on the belief that only reasonable and sensible rules should be followed; a rule shouldn't be followed just because it's a rule

you're basically saying, it's the rules, so follow them

i am saying, why is it a good rule? why should i follow it?

 

[SharkDiver36]

I've never been one to mix words.

The Department of Transportation sets the rules and regulations for scuba cylinders.

You can do as you please and ignore the law if you choose to do so, it is your right.

No Dive Professional should ever give any advice to break any rule or regulation - ever - period.

To do so makes the dive professional wrong and LIABLE if sued.

Speed if you want, overfill your tanks if you want.

The only answer I can give, or any other Instructor - SHOULD GIVE - is....

Never overfill your tank. Fill it to the stamped operating pressure on the tank - period.

 

[H2Andy]

you are not answering my question

how am i in danger by overfilling steel tanks?

if you want me to believe your assertion that the right answer is not to overfill, you need to do better than "because that's the rule," sorry

 

[SharkDiver36]

Check this link out.

http://www.eileenscubasite.com/Images/Explodedcylinders.jpghttp://images.search.yahoo.com/imag...&sigr=11lpjicqk&sigi=11k3cme76&sigb=13taej4df


It isn't an assertion - It's the Law.

 

[DA Aquamaster]

A freind of mine noted the max speed on my GPS history screen was 120 mph. At the time, I lived in a state with long straight, flat roads with no traffic for miles. Exceeding the 65 mph speed limit was pretty common, although admittedly 90 mph is more common than 120 mph. If the viz is good, I can see for miles and it is not hunting season, 120 mph on a straight road with no traffic is not exactly dangerous.

It is in any event a lot safer than trying to go the posted speed limit on a DC freeway in those rare moments when traffic is actually moving and everyone is going 10-15 mph over the posted limit. In that case all you are doing by not going with the traffic flow is just impeding traffic.

So again, rules don't always work so well when you look at them in only a black and white manner.

 

[AceszHigh]

Oh..look what I have started! So...it is quite clear to me now that DOT reg's stipulate that cylinders shouldn't be filled past their rated pressure values.

And, Sharkdiver -- I also understand your point and can agree to an extent..that professionals/instructors shouldNT advise others to break "rules."

However...I have yet to hear/see good evidence as to why overfilling a STEEL tank (not 72cf), particularly an 80 or 85cf one, is going to put me at great danger. Anyone know of a steel tank like this 'exploding' when being filled to 3000-3500 psi? Or exploding at depth, etc?

Another question -- can someone tell me, or point to one of those charts..that show the buoyancy characteristics of various tanks?

I live in florida and dive a 3mm suit...I don't need to be negatively buoyant by 14lbs + on a full tank of air.

Thanks for all the info this far guys..you all rock!

 

[SharkDiver36]

Ok, you two aren't getting it.

All I am saying is NO dive professional should EVER give any advice contrary to the Law, Regulations or Standards of their agency.

Giving any person the advice, as a Dive Professional, is WRONG and it's really not debatable. It's a fact. If any Instructor/DM/Ast.Inst is sued or and a complaint filed with their agency, they will be found liable and their agency could revoke their certification. This is a FACT not an opinion!

There is such a thing as a "RIGHT" answer. The "RIGHT" answer is to never overfill your tanks.

I know what I do, others know what they do, this guy can ask his buddy's about what they do, the shop can fill his tanks to 5,000 PSI for all I care.

As an Instructor who can be sued, found guilty and potentially lose my certification for giving anything but the right answer...once again...the ONLY answer a Dive Professional can give IS (sarcastic drum roll please!!)....

You can only fill a tank to the pressure that is stamped on the tank.

..and thank you AceszHigh for "getting it"....

 

[adelman]

DOT Regs are very specific and can only be filled to the operating pressure stamped on the tank - period - no exceptions.

There are two exceptions in 49 CFR 173:

The overfills permitted in 49 CFR 173.302a(b) (plus rated cylinders can go 10% over) and 49 CFR 173.301a(c) (The pressure in a cylinder at 21C (70F) may not exceed the service pressure...).

So you can fill a cylinder above the rated pressure if the temperature is above 70F, provided that if cooled to 70F it wouldn't be above rated pressure.

 

[DA Aquamaster]

The best guess at this point is that the force of the impact split the valve, allowing a rapid flow of gas through the dip tube, which caused friction heating on the thin lower edge.

A couple things to consider...

It is true that a high flow rate of gas will cause heating on sharp edges, protrusions, etc. due to the extremely high flow velocities that can occur. In general scuba valves are terrible candidates for O2 service as they have sharp bends, sharp edges and open very quicky, creating the potential for heating. But they are all we have, so we deal with it, handle them very carefully and open them very slowly, and keep the flow of gas through them as low as possible.

Removing the dip tube is not going to do anything to prevent a future occurrence of the accident that occurred. If what you suspect happend but the dip tube had not been present, the gas would have escaped past the threaded portion of the valve where the dip tube would have been. Consequently, with a high flow rate, the sharp edges of the threads would have heated as well. In fact, given that they are sharper and thinner than the end of the dip tube, and there are more of them, it is pretty obvious that they would reach a critical ignition temp sooner than the end of the dip tube itself.

Even if you drilled them out and properly radiused the edge of the hole, the gas is still going to pass over a sharp orifice on the way through the valve and it will also rapidly heat in a high velocity flow.

Even though you have the best of intentions, you are probably increasing the risk and your liability by removing them from tanks you prepare for O2 service.