Pressure piling is a phenomenon 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. Combustion ...

gas Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...

es in a

tube Tube or tubes may refer to: * ''Tube'' (2003 film), a 2003 Korean film * "Tubes" (Peter Dale), performer on the Soccer AM television show * Tube (band), a Japanese rock band * Tube & Berger, the alias of dance/electronica producers Arndt Rör ...

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 a branch of mathematics concerned with properties of space such as the distance, shape, size, and relative position of figures. Geometry is, along with arithmetic, one of the oldest branches of mathematics. A mathematician w ...

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 eve ...

. 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 of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated ...

pressure. In

electrical equipment in hazardous areas In electrical engineering, electrical and safety engineering, safety engineering, hazardous locations (HazLoc, pronounced ''haz·lōk'') are places where fire or explosion hazards may exist. Sources of such hazards include gases, vapors, dust e ...

, 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 ...

s 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 Instruments 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 (Commonwealth 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. Herring, ''General ...

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 {{combustion-stub