Leak before burst describes a pressure vessel designed such that a crack in the vessel will grow through the wall, allowing the contained fluid to escape and reducing the pressure, prior to growing so large as to cause fracture at the operating pressure.
Many pressure vessel standards, including the ASME Boiler and Pressure Vessel Code and the AIAA metallic pressure vessel standard, either require pressure vessel designs to be leak before burst, or require pressure vessels to meet more stringent requirements for fatigue and fracture if they are not shown to be leak before burst.
I suspect these tanks are so small as to not be classified as pressure vessels and are more like simple containers. That would limit their size so hopefully any explosions will be small and distributed over a long duration of time.
Depending on where they are in the process, they may be pressure vessels.
Not quite sure. If they are just regular pressure vessels, that would be worse as they will pop, not split.
IIRC, existence of one or more pressure relief valves meets the spec. The valves allow a controlled release of stored material to stabilize containment pressure.
Once released, that material may ignite, but that is secondary to keeping the tank integrity.
The danger is when fire outside the containment vessel is up against the vessel wall. In such a case, the fire outside the tank will simultaneously heat both the tank wall and the material inside the tank. As long as the level inside the tank remains ABOVE the level of this heated zone the material itself will absorb the heat, and tend to keep the temperature of the vessel wall below a temperature at which it might fail. If the fire goes on long enough to boil off the contained material until the level gets down to where the heated zone is, the tank wall temperature will rise rapidly to a point where the strength of the steel falls below the set point of the pressure relief valve(s). Under those conditions the tank wall will burst, and the vaporized material inside the vessel will be forcibly expelled directly into the fire until internal tank pressure drops below external atmospheric pressure.
If that material is flammable, it will convert a burning fire into a massive blowtorch until the tank pressure falls below atmospheric. The rate of release will cause material to exit the ruptured tank so quickly that it will not just suddenly stop when internal pressure equals external pressure, but will overshoot, so there will be a moment of pressure reversal that will cause the tank to suck back and draw burning material back into the tank.
THAT is when the BIG KABOOOOM will happen.
What vaporized material remains inside the tank — IF its molecular structure includes oxygen enough to support self-combustion, as is the case with peroxides — will ignite instantly causing a pressure spike that will act upon the area of the existing tank rupture with such force as to completely tear the rest of the tank apart.
This is called a BLEVE (ble-vee) and is the most dangerous situation possible with flammable materials under compromised containment. Pieces of the shattered containment vessel can be hurled through the air to astounding distances.
This subject-specific video is instructive: