Pressure piling, explosion

Gleim, E. J. and Marcy, J. R, A Study to Determine Factors Causing Pressure Piling in Testing Explosion-Proof Enclosures, RI. 4904, U.S. Bureau of Mines. 

Explosion calculations, 499-504 Estimating destruction, 501 Overpressure, 502 Pressure piling, 501, 504 Relief sizing, 505 Scaled distance, 502, 503 Schock from velocity, 503 TNT equivalent, 499-504 Explosion characteristics of dusts, 515 Explosion suppression, 518 Explosion venting, gases/vapors, 504 Bleves, 504 Explosions, 482 Blast pressure. 496 Combustion, 482 Confined, 482 Damage, 498-501 Deflagration, 482 Detonation, 483... 

SINGH, J., Gas Explosions in Inter-Connected Vessels Pressure Piling, Trans. I. Chem. E. 72 (1994) Part B 220-228. 

Greater increases in pressure are encountered when two or more vessels are interconnected, owing to a phenomenon known as pressure piling. This phenomenon is characterised by the development of explosion pressure in the second and subsequent vessels, which is very much higher than when only one single volume is involved. 

The phenomenon of pressure piling is an important potential hazard in systems with interconnected spaces. The pressure developed by an explosion in Space A can cause pressure/temperature rise in connected Space B. This enhanced pressure is now the starting point for further increase in explosion pressure. This phenomenon has also been seen frequently in electrical equipment installed in areas using flammable materials. 

Restrictions such as orifices in pipelines may intensify a detonation by promoting pressure piling, which results when there are interconnected spaces such that the pressure rise in one space causes a pressure rise in a connected space. The enhanced pressure in the latter then becomes the starting pressure for a further explosion. 

The volumes of liquid hydrogen and the proportion of solid air were varied in a constant containment volume roughly equal to the free volume in a proposed in-pile vacuum vessel. Gaseous tests were also carried out in an attempt to compare the pressure vs. time curves of the liquid explosions with equivalent gaseous hydrogen/air explosions in the same containment volume. 

A sudden explosion having broken the inner wall of the loop would bring the pressure in the evacuated space to about one atm. A pressostat connected to this space would detect this and would immediately shut down the pile by lowering the safety rods. (This safety device has never been necessary as of this date.)... 

Detonating the munitions underwater significantly reduces the noise. It also leads to a more complete destruction of the explosive because the water pressure confines the initiating blast. It is noted below that the French would pile the mustard (gas) shells on a tidal flat with the explosives on top, wait for the tide to come in and then... 

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