Safety Checks, Tightness Testing and Purging
What the exam tests
Safety checks, tightness testing and purging. This domain tests the sequence: isolate, test, purge, prove and record. It also tests purging safety and the checks made before and after work.
Core rules
- Before work, identify the ECV, meter and appliance isolation points; check for existing leaks, corrosion and unsafe situations.
- Tightness testing follows I.S. 813: isolate the installation, stabilise, apply test pressure, observe for the specified duration and compare the drop with the permitted value for the volume.
- Purging displaces air from new pipework with gas, or gas with air for decommissioning. Purge to a safe, ventilated location, never into a room, drain or confined space.
- Prove gas at each appliance before attempting ignition; use a gas detector or approved method, not a flame.
- Record test pressures, durations, purge volumes and results.
Worked example
New pipework to a hob is completed. The installer isolates the meter, pressure-tests the pipework with air, then connects and purges the new section to outside. He proves gas at the hob test point, checks operating pressure and gas rate, and records the results. He does not purge into the kitchen or test for gas with a lighter. The reasoning: each stage proves a different property-strength, tightness, gas presence and appliance performance.
Marks-losing traps
Purging into a confined space; using oxygen or compressed air from an oil-lubricated compressor; skipping stabilisation; treating a small drop as acceptable without calculation; failing to prove gas at the appliance before lighting.