The second line of defense for the workers and the well to prevent a blowout is the group of equipment called blowout preventers (BOPs). BOPs and associated valves are installed on top of the casing head before drilling ahead after rigging up. These high-pressure safety valves and associated equipment are designed to shut off the well hole and prevent the escape of the underground fluids and prevent a blowout from occurring.

After installation, the BOP and associated valves are pressure tested to insure integrity and proper operations.
The BOP and associated equipment consists of:
BOP Stack
Annular BOP
Ram-Type BOP
Choke Manifold
Accumulator