Purging gas after meter or pipework work

Opening or replacing a meter can introduce air. Before recommissioning, establish what the relevant test section contains and whether purging is required under the applicable procedure. A meter display or odour observation alone is not a complete purge plan.

Tightness comes before purging into service

For commissioning, the published UP/1B scope requires tightness testing immediately before purging. Do not postpone soundness verification until after the purge. Taking components permanently out of service is a separately identified exception; use the appropriate decommissioning method.

Calculate the quantity

Under UP/1B Edition 4, calculate installation volume whenever purging is undertaken and determine PV = 1.5 × IV. This still applies if an earlier eligible appliance-loss comparison did not require IV because its loss was below the smallest permissible limit for the fuel.

Worked example: an established IV of 0.018 m³ gives a PV of 0.027 m³, or 27 litres. Include the components required by the procedure's actual boundary. A maximum meter flow rating is not an internal-volume measurement, and a familiar meter model does not justify a fixed purge time for every installation.

Select the discharge arrangement

Use the method permitted for the fuel, volume and setting. Establish the destination, ventilation and ignition controls before starting; gas or mixture must not accumulate in unsafe spaces. Opening a window alone does not validate every indoor purge arrangement.

Deliver the required volume and complete the specified checks. Noticing some gas early does not prove completion. Never use a naked flame as a detection method.

Close out the work

Complete the required restoration and appliance checks under the manufacturer instructions, record the work and leave the installation in a verified condition. This note teaches the decisions and calculation; it does not supply the full live purging procedure.