Pneumatic Pressure Testing

Pneumatic pressure testing uses compressed air or nitrogen to verify the integrity of pipework and vessels.
Pneumatic tests store significantly more energy than hydrostatic tests at the same pressure due to gas compressibility.
A failure during pneumatic testing can cause a violent explosion with lethal blast and fragment hazards.
Exclusion zones during pneumatic testing must be much larger than for equivalent hydrostatic tests.
The test pressure, hold time, and acceptable leakage rate must be specified in the test procedure.
All personnel must be evacuated from the exclusion zone before the test pressure is applied.
Pressure must be raised in incremental stages with checks at each stage before proceeding.
The Pressure Systems Safety Regulations 2000 apply to pneumatic testing of pressure systems.
Soap solution or gas detection is used to find leaks once the system is pressurised.
The test medium must be suitable — oxygen must never be used for pneumatic testing.

Explosion risk	Compressed gas stores enormous energy — a pneumatic test failure produces an explosion far more violent than a hydraulic failure.
Lethal fragments	Pipe and fitting fragments from a pneumatic burst travel at high velocity, causing fatal impact injuries at distance.
Legal requirement	The Pressure Systems Safety Regulations 2000 require safe systems of work for all pressure testing activities.

Do

Don't

Follow a written test procedure specifying pressure, hold time, and acceptance criteria
Establish exclusion zones that account for the stored energy of the compressed gas
Evacuate all personnel from the exclusion zone before pressurising the system
Raise pressure in controlled incremental stages with visual and audible checks at each step
Use dry nitrogen or oil-free compressed air as the test medium — never oxygen
Ensure all connections, joints, and end caps are rated for the test pressure
Use calibrated pressure gauges to monitor the test and confirm the hold period
Check for leaks using soap solution or gas detection once the test pressure is achieved
Depressurise the system fully before approaching to investigate any anomalies
Record the test results including pressure, duration, temperature, and any leaks found

DON'T allow anyone inside the exclusion zone during pneumatic pressurisation
DON'T use oxygen for pneumatic testing under any circumstances — it creates fire risk
DON'T raise pressure rapidly — use controlled incremental stages with checks
DON'T approach the system to investigate leaks while it remains pressurised
DON'T use fittings, valves, or end caps not rated for the pneumatic test pressure
DON'T conduct a pneumatic test where a hydrostatic test is practicable and safer
DON'T leave a pressurised system unattended without continuous monitoring
DON'T apply the full test pressure without first holding at intermediate stages
DON'T ignore small leaks — depressurise, repair, and retest before acceptance
DON'T underestimate the stored energy — pneumatic failures are far more violent than hydraulic

See also: Hydrostatic Pressure Testing | Pressure Testing Safety

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