LOT/Specific/TBT-LOT-007

Process Isolation (Valves and Blinds)

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Process isolation uses valves and blind flanges to isolate sections of pipework containing fluids or gases.
It is essential before maintenance, modification, or inspection of pipework systems on process sites.
Valves alone may not provide positive isolation — they can leak, be incorrectly positioned, or pass through.
Spectacle blinds and spades provide positive mechanical isolation by physically blocking the pipe bore.
Double block and bleed arrangements use two valves with a vent between them for confirmed isolation.
The process fluid may be hazardous — chemicals, sewage, gas, or water under pressure.
A permit to work must be issued defining the isolation points and confirming zero energy before work starts.
Residual pressure and trapped fluid in isolated sections can cause injury when flanges are broken.
Only competent persons should carry out process isolation — incorrect valve operation can be fatal.
The isolation must be tested by venting or draining the isolated section to confirm zero pressure.

Prevent chemical exposure	Failed isolation releases hazardous process fluids onto workers.
Pressure danger	Residual pressure in isolated sections causes violent release when joints are broken.
Positive isolation	Valves alone can leak — blinds and spades provide absolute mechanical isolation.
Legal duty	PUWER and COSHH require confirmed isolation before maintenance on process systems.

Don't

Identify all isolation points from the piping and instrumentation diagrams (P&IDs).
Use spectacle blinds or spades for positive isolation on high-hazard systems.
Vent or drain the isolated section to confirm zero pressure before breaking joints.
Apply lock out tag out devices to all valves used for isolation.
Record all isolation points on the permit to work before starting maintenance.
Wear appropriate PPE for the process fluid — chemical suits, RPE, or face shields.
Check valve positions physically — do not rely on control room indications alone.
Use double block and bleed where single valve isolation is insufficient.
Brief all workers on the isolation arrangement and permit conditions.
Test the isolation integrity before anyone enters the isolated section.

DON'T rely on a single valve for isolation on hazardous process systems.
DON'T break flanges without first confirming the section is depressurised and drained.
DON'T remove blinds or spades until the permit is formally cancelled.
DON'T operate valves without confirming you have the correct one from the P&ID.
DON'T assume the system is empty because it has been shut down.
DON'T carry out process isolation without proper training and authorisation.
DON'T leave isolation valves unlocked or untagged during maintenance.
DON'T re-pressurise the system before confirming all workers and tools are clear.
DON'T skip the vent or drain test — it is the only way to confirm safe isolation.
DON'T ignore unusual smells or fluid weeps — they indicate isolation is not complete.

See also: Lock Out Tag Out Awareness | Permit to Work Awareness

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