Double Block and Bleed uses two sequential isolation elements and an intermediate vent or monitoring point. This configuration increases safety during maintenance.
Two independent barriers
If the first valve has an internal leak, the second provides additional isolation.
Bleed point
The intermediate space can be vented or monitored to determine if gas is leaking past either of the two valves.
Relationship with LOTO
This configuration does not replace the required lockout/tagout procedure. It is used in conjunction with it.
Important prerequisite
The bleed line must lead to a safe location and must be used only in accordance with the facility's approved procedure.
