CCN1 Purging Procedures

Question 1

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

Accepted 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)

Answer

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.

Question 2

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

Accepted 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

Answer

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.

Question 3

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

Accepted Answer

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

Answer

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.

Question 4

When must a decommissioning purge be carried out?

Accepted 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

Answer

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.

Question 5

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

Accepted Answer

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

Answer

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.

ACS CCN1 Practice Test

ACS CCN1 Practice Test

CCN1 Purging Procedures