PT Notes
Validating Safeguards for PHA
PT Notes is a series of topical technical notes provided periodically by Primatech for your benefit. Please feel free to provide feedback.
Validation of safeguards to demonstrate that installed safeguards meet specified requirements is critical for process safety. Indeed, any aspect of a PSM program that impacts PHA is a candidate for validation. However, a PHA team should not need to confirm that safeguards are correctly installed, functional, have a specified integrity level, etc., nor should they need to validate other aspects of process safety upon which PHA is based. Those are important tasks that are better performed by others before a PHA commences.
The inclusion of such validations within PHA would cause a serious distraction from identifying hazard scenarios, which is the key objective of PHA. Scenarios are identified in a brainstorming process that is critical for the identification of scenarios and anything that interferes with it, and is not necessary as part of PHA, must be avoided as it will most likely detract from scenario identification. Validation of safeguards falls into this category. The validation of information used in PHA is vital for a meaningful PHA but it does not belong as part of the PHA.
Furthermore, validation needs to be performed by qualified personnel with a different skill set than PHA team members using validation methods that are much different than PHA. Consequently, validation of safeguards, and other aspects of process safety that support PHA, should be performed before commencing PHA.
In contrast, considering whether safeguards are appropriate for a specific hazard scenario must be part of PHA and safeguards should be qualified before being entered into the worksheet using appropriate criteria. Assessing the performance of safeguards for a scenario must also address their ability to withstand adverse impacts from the scenario, e.g. fire water monitors that become inoperable owing to being engulfed by flame, and common cause failures with other scenario elements, e.g. operator action to isolate a tank when operator failure was a cause of the scenario requiring isolation of the tank.
It is desirable to prepare a Safety Requirements Specification (SRS) for each safeguard that can be used for validation. A SRS documents the functional and integrity requirements for a safeguard. The functional requirements describe what the safeguard does to prevent a hazardous state of the process and the integrity requirements specify how well the safeguard should perform and what is needed to support that performance level.
For more information, you can contact Primatech or consult the article:
On the Validation of Safeguards for Process Hazards Analysis by Paul Baybutt, Process Safety Progress, Volume 32, Issue 2, Pages 165–169, June 2013.
http://onlinelibrary.wiley.com/doi/10.1002/prs.11560/abstract
