Positive isolation methods are those which remain effective even if there is equipment failure or operator error. These techniques apply not only to vessels, piping and tanks but also to pneumatic and hydraulic equipment.
The sketch shows some of the various isolation techniques that can be used to protect workers in the process industries. The process containing toxic or flammable chemicals under pressure is on the left; the open system, where the workers are present, is on the right. The order is from the least to the most secure.
There are many ways of isolating equipment. Each offers different levels of security. They include:
Level 1 — Closed Valve
Level 2 — Closed Valve with Open Bleeder
Level 3 — Double Block and Bleed
Level 4 — Block and Bleed with Line Break
Level 5 — Block, Bleed and Spectacle Blind
Level 6 — Double Block and Bleed with Blind
Level 7 — Double Block and Bleed with Line Break
Pipe Blinds
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