Pressure piling

Pressure piling is a term used to describe a phenomenon which can occur within an Ex ‘d’ certified enclosure.

If the inside of an enclosure is split into two distinct sections and a flammable gas ignites in the larger section the expanding gas would pressurise the unlit gas in the smaller section. This gas would ignite and, because it is at a pressure greater than normal so would the pressure of the explosion.

This phenomenon could occur if any unauthorised modifications had taken place in the interior of the enclosure. A flameproof enclosure is certified for use with the components it is supplied with so removing or adding different items into the enclosure would alter the internal volume and thus invalidate the certificate. Only items that are certified for use as replacements can be used. This is often referred to as replacing items “like-for-like”.

Where a threaded entry is different to that of a cable gland a flameproof threaded adaptor shall be fitted. Unused cable entries shall be fitted with a flameproof blanking element. To overcome pressure piling effects, each entry shall not have more than one thread adaptor when an adaptor is used. A blanking element shall not be used with an adaptor.

No unauthorised modifications are permitted.