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

The cleaning of gas pipework using high-pressure water

Answer

The removal of debris from a gas main before commissioning

Answer

The testing of a flue system for blockages

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 is harmless and purging is an optional precaution

Answer

Air in the pipework only causes the appliance to fail to light — no explosion risk

Answer

New pipework contains only clean air so purging is not necessary

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

Into the kitchen via the gas cooker burners

Answer

Into the boiler flue

Answer

Purging into a room is acceptable if windows are 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

Only before major renovation work

Answer

Only for commercial gas installations

Answer

Only when pipework is being permanently abandoned

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 pressure gauge at the meter

Answer

A manometer at the appliance

Answer

Purging is verified by smell alone

Question 6

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

Accepted Answer

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

Answer

Purge all at once from the meter with a very large gas volume

Answer

Leave the gas on for 15 minutes and allow natural purging to occur

Answer

Purge by lighting appliances in sequence from the furthest to the nearest