Purging Procedures Flashcards

What is 'purging' in the context of gas pipework?

Answer: The process of displacing air or inert gas from pipework with gas (commissioning purge) or displacing gas with air or inert gas (decommissioning purge)

Purging involves displacing one gas with another. Commissioning purge replaces air in new or repaired pipework with gas. Decommissioning purge replaces gas in pipework with air or inert gas before it is worked on or abandoned.

Why is it dangerous to simply turn on the gas supply without purging new pipework?

Answer: Air trapped in the pipework mixes with incoming gas, creating a potentially explosive air-gas mixture that could ignite when the appliance attempts to light

Air remaining in new or repaired pipework mixes with incoming gas to create an air-gas mixture within the explosive range. If an appliance attempts to ignite this mixture, an explosion can result. Purging eliminates this risk.

According to IGE/UP/1, how must a purge of domestic gas pipework be carried out safely?

Answer: Into the outside atmosphere via an appropriate vent point — never into a confined room or near ignition sources

IGE/UP/1 requires that purges of domestic gas pipework are discharged to the outside atmosphere via an appropriate vent point, away from ignition sources. Purging into a room creates an explosion risk even with windows open.

When must a decommissioning purge be carried out?

Answer: Before any gas pipework is cut, disconnected, or opened for work — to displace gas with air or inert gas and prevent ignition during work

A decommissioning purge must be carried out before cutting, disconnecting, or opening gas pipework for any purpose. Displacing gas with air or inert gas prevents ignition of residual gas during hot work or other activities.

What instrument is used to verify that gas has fully purged air from new pipework and reached the appliance?

Answer: A gas detector or combustible gas indicator at the appliance connection point

A combustible gas indicator (or gas detector) is used at the appliance connection to confirm that gas has displaced all air and reached the point of use. Smell alone is unreliable and insufficient.

What is the correct approach for purging a very long gas pipe run in a domestic installation?

Answer: Purge in sections, venting each section to the outside atmosphere, confirming gas presence at each stage before moving to the next

Long pipe runs should be purged in sections, venting each section to the outside and confirming gas presence before proceeding. This ensures complete purging throughout and minimises the volume of gas discharged at any one point.