Scuba Tank Explosion - Myth or Reality?

[PSFlyer]

Just wondering if scuba tank explosion due to tank overheating is a reality. I had students ask that question as it relates to transporting tanks in a car. For years I've given them a standard answer that was given to me years ago by my instructor: "well, yeah, it could happen, so shield the tanks from the sun in the back of your SUV, etc. etc." Now that I have done a bit of research into the topic, I feel kind of dumb...

1. Through my research I found out that the highest temperature ever recorded inside a vehicle sitting in the sun was 170F.

2. According to my son's High School physics book, gas laws would dictate that for every 1F temp rise inside a closed container filled with air, you can expect a 5PSI pressure increase.

3. Assuming the tank is put into the vehicle at room temp 70F, and the temp rises to 170F, the temp rise is equal to 100F. This causes the pressure to rise by 500PSI.

4. OK so now my 3000 PSI tank is, at the most, at 3500PSI.

5. Burst discs are rated at 140% of rated pressure so on a 3000PSI tank they would not blow until 4200PSI.

That leads me to a conclusion that even a burst disc blow is a very unlikely event at 3500PSI (170F) not to mention the actual tank exploding.

Am I wrong here. What am I missing? Can you guys and ladies shed some light on this. I searched the SB but could not find any info on this topic. Thanks.

 

[VooDooGasMan]

Well you can seach tank suppliers, and psi testers.

One thing for sure is the higher and hotter, and possible movement in trunk could explode or kill if in accident, there shoud be a plumbed ac unit in divers trunk.(now thats a way to make money in the scuba industry)

Also when disk fails it now as put a freeze on your valve which is not good either.


Happy Diving

 

[Saudi-Diver]

I have seen burst discs go. Tanks left in the shade in the open air, temps around 45 C (113F). It was really noisy and drilled a nice deep hole in the sand! Suspect the Burst Discs may have been fatigued due to expansion and contraction from heating, cooling, filling and emptying.

 

[Ghanguss]

Tank exploding should only occur if the tank is rusted or cracked. Otherwise the burst disk will go.

I keep my tanks on the floor behind the front seats of my car. The lower they are, the cooler.

The trunk gets hotter than the floor Ive found especially if you have the windows down half an inch.

I also lay something over the tank if its likely to be in direct sunlight.

I recently left my pony bottle on the floor of the car while diving for the day on a hot summer day (Covered). When I checked it at 2pm it was a bit warmer than after a fill

 

[PSFlyer]

thanks for pointing that out Saudi-Diver. Physics aside, life is life... and worn out discs, improperly maintained tanks etc, will render all calculations useless. I, of course know that, and the point I was trying to make, is that as a general rule, a properly serviced tank should be able to withstand 3500PSI easily. On the other hand, let's face it, reaching a temp of 170F is not something that would happen as you drive to your destination.. So overall, if my calculations are correct and tanks properly maintained - I would lean towards a conclusion that tank explosion in the back of my SUV should be written of as a MYTH... I think

 

[DA Aquamaster]

Well you can seach tank suppliers, and psi testers.

One thing for sure is the higher and hotter, and possible movement in trunk could explode or kill if in accident, there shoud be a plumbed ac unit in divers trunk.(now thats a way to make money in the scuba industry)

Also when disk fails it now as put a freeze on your valve which is not good either.


Happy Diving

That's an equally "chicken little" response and one that does not focus on the more serious dangers involved.

First, when the "higher and hotter" we are talking about is about 150 degrees and 450 psi, it's not significantly higher or hotter from either a material strength standpoint or a pressure standpoint.

Second, it's highly unlikely a tank will explode due to being crushed in an accident, and if it did, the accident would have to be incredibly severe - to the point where the tank explosion was an issue in an already non surviveable accident.

Third, many of the actions you might take to keep the tank cool (carry the tank in the passenger compartment, etc) will actually increase the much more serious risks the tank creates if you are in an accident.

Let's stay with reality here and address the real threats involved in transporting tanks in a car:

1. It is very possible that a valve could be sheared off of a tank,

2. In addition, even if the valve does not shear, a 30 pound tank makes a very dangerous object to have rattling around inside the car.

3. Consequently, securing the tank in the car is important to prevent the tank from impacting the people inside the car in an accident, or from impacting something that may shear the valve off.

4. If the valve does shear off, you want the tank to not be propelled toward the passengers and the valves are probably better protected if they are near the center of the car. (However that makes them more difficult to load and unload and it requires a fore/aft placement of the tank and both have risks of their own that need to be considered.) If you look at cars that have been in accidents, you will note that very few are ever compressed sideways in the area of the rear axel, due to the axel itself, the frame structure and the dynamics of most front or rear collision accidents. That suggests that is not a bad place to lay tanks sideways.

5. Storing tanks vertically and securely strapped with the valves up is ideal - and is required for commercial transport of tanks. However is something that is hard to achieve in many vehicles used by divers.

So....storing/transporting a tank in the trunk makes more sense than carrying it in the passenger compartment of the average sedan, simply because it will not be rattling around in the passenger compartment in an accident, rollover, etc. In this case any heat concerns are clearly secondary as they pose an exponentially lower risk than carrying the tank in the cooler passenger compartment.

The same is true with a valve shearing scenario. I'd much rather have the tank in the trunk with the valves facing the passengers or facing to the side in the event one wer to be sheared in an accident.

Conseqently, the best option for many cars is probably to carry the tanks in the trunk laid sideways and secured - ideally with cargo straps and if not, at least secured so they are not rolling around. If possible pack stuff on top of them so they they are not free to move around in an accident.

SUVs pose different problems as the cargo compartment is not separate from the passenger compartment - but most also have cargo tie downs. For for a small number of tanks I will strap them down sideways, but on a cave country trip with several sets of tanks, stage, deco bottles etc, that usually is not practical from a space efficiency perspective. In that case they are carried for and aft, but are securely strapped down.

 

[vladimir]

2. According to my son's High School physics book, gas laws would dictate that for every 1F temp rise inside a closed container filled with air, you can expect a 5PSI pressure increase.

Volume is constant, so P₂=P₁(T₂/T₁). Let's use 540〫Rankine as T₁, 541〫R as T₂, 3000 psi as P₁, and let's solve for P₂. P₂=3000 (541/540) = 3005.5555 The physics book is correct! (Although it's sad that it's using units of Fahrenheit and psi.) I think the rest of your post is also correct, and I agree that neither tanks in a trunk nor their burst disks will explode from the midday heat if they aren't drastically over-filled or somehow flawed.

 

[Doc Harry]

Explosion in a car secondary to cylinder corrosion. Don't think a cylinder could explode in a car just from the heat alone.

 

[String]

A healthy tank isn't going to explode in a car.

Burst disks are unlikely i guess unless flawed themselves which apparently isn't that uncommon.

No tanks here have burst disks and im not even sure they're legal at all on valves so no danger of that here.

All the tanks here are 232 (3410psi) bar working pressure and a test pressure of 348 bar ( 5115 psi) so there is substantial extra capacity in that tank to withstand overpressure.

You'd need a temperature increase to push that tank to at least that pressure provided the tank is healthy. In a car that simply isn't going to happen.

 

[CAVDVR93538]

I agree, but I think the operative word here is HEALTHY tank. Usually stress cracks in the neck and threads are the culprit, unless the tank has sustained other issues or oxidation has weakened the material that caused the failure with other forces acting upon it.
I've seen the photo above and others from inspector class where a tank exploded and tore up the inside of a car. What I think about is other than a burst disc that is very startling, is if something happens, it's not going to be pretty. Let's eliminate as many of the possibilities as possible.