If a flammable mixture is compressed prior to ignition, the resulting explosion pressure will be considerably higher than if the same mixture was ignited at normal atmospheric pressure.
Pressure piling can occur as a result of sub-division of the interior of a flameproof enclosure, which prevents the natural development of an explosion.
An explosion at one side of an obstacle pre-compresses the flammable mixture at the other side, resulting in a secondary explosion that can reach an explosion pressure around three times that of the initial explosion.
To prevent pressure piling, manufacturers must ensure that in any cross-section within an enclosure, there is adequate free space around any potential obstruction, which may be a large component or a number of components (typically 20-25% of the total cross-section).
