Page 13 - Temporary Isolation of Relief Devices - CCPS Safe Work Practice

Strategies and Effective Practices

to Manage and Mitigate Hazards

Issue Safety System Override or PRD Isolation Permit with PTW to perform PRD isolation
g The Safety System Override or PRD Isolation Permit should specifically document:
• Steps required to mitigate risks associated with the PRD being isolated, such as positive isolation verification,
depressurization, draining, and purging.
• A summary of each overpressure cause and its mitigation means as identified during the Preparation phase.
• P&IDs with PRD tag number, valve isolation list required for safe handover, Area Operator and Panel Operator
accountable for safe handover and monitoring, respectively.
• P&IDs with tag numbers indicating other devices involved with the PRD being isolated.
• P&IDs indicating temporary minimum equivalent pressure relief (as applicable).
• Reference calculations demonstrating temporary minimum equivalent pressure relief is adequate for overpressure
protection (as applicable).
• Reference of the alternate overpressure protection risk reduction assessment (as applicable).
g Follow the site Safety System Override or PRD Isolation Permit procedure to perform PRD isolation and associated
work on the process.
g Enter the active Permit into the site’s register.

Follow site procedures if special activities are required during PRD isolation
g Examples include Hot Work Permit, Lifting Safety, Personnel Fall Protection, and related Safe Work Practices.
g Identify the location of the nearest safety shower, eye wash and emergency escape route to be used if needed.

Temporary PRD isolation and operating process monitoring
g At a minimum, physical keyed locks should be used to manage PRD isolation valve closure.
• Car seals, which are usually a metal or plastic loop seal arrangement that must be cut or broken to enable
valve closure, are discouraged for use on PRD isolation valves due to their lesser integrity in protecting against
inadvertent isolation valves closure.
• It is best practice to use captive key (also called a trapped key) interlock systems for PRD isolation valves, which
prevent their valve closing until certain pre-determined conditions exist, such as proper valve sequencing.

SAFE WORK PRACTICE, TEMPORARY ISOLATION OF RELIEF DEVICES 10