Pressure piling describes phenomena related to
combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...
of
gases in a
tube or long vessel. When a flame front propagates along a tube, the unburned gases ahead of the front are compressed, and hence heated. The amount of compression varies depending on the
geometry
Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
and can range from twice to eight times the initial
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...
. Where multiple vessels are connected by piping, ignition of gases in one vessel and pressure piling may result in a
deflagration to detonation transition and very large
explosion
An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known ...
pressure.
In
electrical equipment in hazardous areas, if two
electrical enclosures are connected by a
conduit, an explosion of a gas in one of the compartments travels through the conduit into the next enclosure.
[Ernest C. Magison, ''Electrical Innstruments in Hazardous Locations 4th edition'', International Society of Automation, 1998 , page 153] The pressure of the 'primary' explosion together with the pressure from the 'secondary' explosion in the other compartment produces one huge explosion that the equipment cannot handle. Heat, arcs or sparks escape from the equipment and ignite any gas or
vapour that may be around.
Operators avoid this by not using conduits to join classified equipment together and by using barrier glands on cables going into the enclosure. This ensures that compartments remain separate at all times.
References
Combustion
Pressure
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