Pipeline Purging and Cleaning

Pipeline purging removes air, debris, or residual product from pipelines before commissioning or decommissioning.
Purging with compressed air or nitrogen displaces oxygen and can create asphyxiation hazards at discharge points.
Nitrogen is odourless and invisible — workers have died from entering areas where nitrogen has displaced oxygen.
Pipeline pigging involves launching a pig through the pipeline under pressure to clean or inspect the bore.
Pig launching and receiving traps are pressurised and must be depressurised before opening.
Flushing with water at high flow rates generates large volumes of discharge that must be managed.
Chemical cleaning uses acids, alkalis, or solvents that require COSHH assessment and waste disposal controls.
Purge and cleaning operations should be covered by a method statement and permit to work.
Vent points and discharge outlets must be positioned to prevent exposure to personnel.
Communication between the launch and receiving end of the pipeline must be continuous during pigging.

Asphyxiation	Nitrogen and other purge gases displace oxygen at discharge points — entering these areas causes rapid unconsciousness and death.
Pressure hazards	Pipeline pigs travel under pressure and pig traps must be fully depressurised before opening to prevent ejection.
Chemical exposure	Cleaning chemicals and contaminated flush water pose health and environmental risks requiring strict controls.

Do

Don't

Prepare a method statement and obtain a permit to work for all purging operations
Position vent and discharge points away from occupied areas and safe routes
Monitor oxygen levels at discharge locations when purging with nitrogen or inert gas
Depressurise pig traps completely and confirm zero pressure before opening doors
Maintain continuous communication between the launch and receiving ends during pigging
Complete a COSHH assessment for any chemical cleaning agents used in the pipeline
Manage flush water discharge through settlement or treatment before release
Brief all personnel on the purging schedule, hazard zones, and exclusion areas
Use warning signs and barriers around vent points and discharge outlets
Verify the pipeline is clear and clean using CCTV or flow testing after the operation

DON'T enter areas where nitrogen purging has displaced oxygen without monitoring
DON'T open pig trap doors until the trap is fully depressurised and vented
DON'T stand in front of pig trap doors during opening — residual pressure can eject debris
DON'T discharge flush water containing chemicals into watercourses without treatment
DON'T launch a pig without confirming the receiving end is ready and manned
DON'T carry out purging operations without a permit to work in place
DON'T ignore the smell of chemicals or gas at any point during cleaning operations
DON'T assume the pipeline is clean after one pass — verify with testing or inspection
DON'T use compressed air where nitrogen is specified for inerting flammable pipelines
DON'T leave vent points unguarded where personnel could be exposed to discharge

See also: Pipeline Safety Awareness | Hydrostatic Pressure Testing

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