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. Combusti ...

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

es in a

tube Tube or tubes may refer to: * ''Tube'' (2003 film), a 2003 Korean film * ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom * "Tubes" (Peter Dale), performer on the Soccer AM television show * Tube (band), a ...

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 and e ...

. Where multiple vessels are connected by piping, ignition of gases in one vessel and pressure piling may result in a

deflagration to detonation transition Deflagration to detonation transition (DDT) refers to a phenomenon in ignitable mixtures of a flammable gas and air (or oxygen) when a sudden transition takes place from a deflagration type of combustion to a detonation type of explosion. Descri ...

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 enclosure An electrical enclosure is a cabinet for electrical or electronic equipment to mount switches, knobs and displays and to prevent electrical shock to equipment users and protect the contents from the environment. The enclosure is the only part ...

s are connected by a

conduit Conduit may refer to: Engineering systems * Conduit (fluid conveyance), a pipe suitable for carrying either open-channel or pressurized liquids * Electrical conduit, a protective cover, tube or piping system for electric cables * Conduit curre ...

, 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 In physics, a vapor (American English) or vapour (British English and Canadian English; see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R. H. Petrucci, W. S. Harwood, and F. G. Herr ...

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 {{engineering-stub