I'll bet Grey beard or Craig Miller will know what it is.
I know exactly what it is and one did the same thing on one of the rigs I worked on, but not for the reason most people think. It does happen, but it is rather rare that a tank fails due to failed safety valves or rusted out tank.
Ours was even more rare.
The most common reason they explode like ours is a buildup of heat inside the tank.
Here's how ours happened, and was confirmed by the compressor manufacturer GardnerDenver:
The rig had drilled surface hole, and was nippling up BOPs in the cellar and the drilling program called for dumping the low vis mud from the tanks and build up new higher vis higher weight mud before drilling out. They were almost finished building new mud, water usage was minimal. The electric motor powered compressor was piped to a water well and the valve barely cracked open, just enough for the well to flow a little. It just so happened, that the air usage meant the compressor ran almost constantly, cut on and off rarely and the exchange of hot compressed air in the tank for new outside air was minimum. The pressure never exceeded the set point for the safety valve.
Combustion needs 3 things.
1. Oxygen--readily provided from the air in the tank.
2. An ignition source.
The fuel came from the air/oil mix in the compressor tank. All piston type compressors like we were using allow a bit of compressor oil by the piston rings and it has to be bled out of the drain at the bottom of the tank occasionally.
The explosion occurred when the temperature inside the tank reached the ignition point of the compressor oil in the air/oil mixture.
In other words, it became an air oil..thermobaric bomb. The explosion destroyed the tank, the compressor itself, the 350KW generator and it's Cat engine sitting beside the compressor, peeled the 3/16 steel roof off the generator house, demolished the electrical switchboard for both generators, and a small diesel engine operated compressor used to build up air when the rig first moves in so the can start the generators. (had air starters on everything)
Threw shrapnel all over the location but fortunately, almost everone was busy nippling up BOBs.
Write up of a similar compressor explosion:http://metroforensics.blogspot.com/2016 ... s-and.html