Propane overfill by a "professional"

westend wrote:

RJsfishin wrote:
I don't understand the tanks blowing up. All the valves are designed to vent slowly. Tanks cannot blow up if the valves are operating properly.

The fill valve is built to allow the displaced air to exit the tank slowly. The over-pressure relief valve opens instantaneously and it is not slow. When they open there is a release of liquid propane and is it not a small release.

We had a bad event close to me a few years ago at the local farm co-op. A customer brought a 100 lb.. cylinder to be filled. Within moments of starting the fill, the tank exploded, killing the young guy filling the tank. The shrapnel from the explosion ruptured a nearby bulk tank and nearly burned the building to the ground. A couple of others were also injured.
The cause of the tank exploding was later found to be that the cylinder had acetylene in it at some point and the acetylene residue combined with the introduction of propane caused a reaction.

This unfortunate result is caused by the effects of 'partial pressures'. What this means is that when two (or more) dissimilar (incompatible) gasses are mixed into the same container, their individual component pressures (partial pressures) do not average out, but instead add together to become the overall total pressure (as do the partial component pressures of nitrogen, oxygen and carbon dioxide in the atmosphere to total 14.7psi at sea level), thus creating the dangerous overpressure condition. In this case the safety relief valve will be inadequate at relieving this excess pressure.

3 tons