Purging Procedures Flashcards

Before purging a gas installation that has been disconnected for more than 12 months, what additional step is required?

Answer: A full tightness test of the installation before introducing gas, to confirm no deterioration has occurred during the period of non-use

Pipework that has been inactive for extended periods may have developed leaks due to joint deterioration or corrosion. A full tightness test before introducing gas is essential to confirm integrity before purging.

What is the maximum permissible pressure drop during a domestic gas tightness test using a water gauge or electronic manometer?

Answer: No drop is acceptable for a new installation — any pressure drop indicates a leak requiring investigation

For a new gas installation, no pressure drop is acceptable. Any drop indicates a leak that must be traced and repaired. Temperature compensation must be applied for extended tests, but any residual drop indicates a fault.

What type of leak detection fluid must NOT be used on gas pipework?

Answer: Any liquid containing oil or grease — these can contaminate oxygen systems and must not be used on oxygen-enriched gas systems. Standard gas installations use approved leak detection fluids or electronic detectors

Standard leak detection fluids (including washing-up liquid) are acceptable on natural gas installations. However, oil or grease-containing fluids must never be used on oxygen-enriched or medical gas systems. Electronic gas detectors are the preferred method for gas installations.

What is the purpose of the 'stabilisation period' at the start of a gas tightness test?

Answer: To allow temperature and pressure to equalise after pressurising, preventing a false reading due to adiabatic heating of the compressed gas

When gas is compressed into pipework during pressurisation, adiabatic heating temporarily raises the pressure. The stabilisation period allows the temperature — and therefore the pressure — to equalise before the test reading is taken.

What is the risk if a decommissioning purge is not carried out before dismantling a gas connection?

Answer: Residual gas in the pipe will escape when the connection is broken, creating an explosive atmosphere that can be ignited by any nearby ignition source

Any residual gas in disconnected pipework will escape when the connection is broken. If sufficient gas accumulates and meets an ignition source (sparks, flames, static), it can ignite explosively. Decommissioning purge removes this risk.

After completing all gas work, what is the final check before handing the installation back to the customer?

Answer: Confirm all appliances operate correctly, check combustion quality with a flue gas analyser, confirm CO alarm is present and working, provide all documentation, and brief the customer

The handover must confirm correct appliance operation, satisfactory combustion analysis, CO alarm presence and function, completion of all required documentation (commissioning records, gas safety certificates where applicable), and a customer briefing on emergency procedures.