(49b) Top Ten Questions to Ask about Pressure Relief Systems in a Process Hazard Analysis

It is crucial for Process Hazard Analysis (PHA) teams to be aware that the mere presence of a pressure relief device does not necessarily constitute a valid safeguard against all overpressure scenarios for the protected system. This paper will present the following list of the ten most important questions for a PHA team to ask when considering pressure relief systems as safeguards.

1. Are set pressures appropriate for each protected system?
   • The paper will discuss appropriate relief device set pressures with respect to equipment Maximum Allowable Working Pressure (MAWP) and overall system pressure profiles.

2. Are pressure relief systems adequately sized for each applicable scenario?
   • The paper will discuss simple screening techniques to identify obviously undersized relief devices and conservative assumptions to employ when these techniques do not apply.

3. Are relief devices of appropriate type present for each applicable scenario?
   • The paper will discuss examples of appropriate and inappropriate device types for example overpressure scenarios.

4. Is the physical installation of pressure relief devices in compliance with applicable codes and standards?
   • The paper will discuss straightforward approaches to identifying non-compliant physical installations based on Process Safety Information (PSI).

5. Are pressure relief system discharge locations appropriate for each protected system?
   • The paper will present examples of appropriate and inappropriate discharge locations and methods for documenting relief to an unsafe location in a PHA.

6. Have pressure relief systems been properly considered as part of the facility Management of Change (MOC) program?
   • The paper will discuss examples of process changes that can have significant effects on the design of pressure relief systems.

7. Have any instances of pressure relief devices activating been properly identified and investigated as near misses?
   • The paper will emphasize the importance of tracking relief events as near misses.

8. Have the sitewide and offsite effects of global overpressure scenarios been properly considered?
   • The paper will provide examples of global overpressure scenarios.

9. Has the malfunction of pressure relief devices been properly considered?
   • The paper will provide examples of potential PHA consequences due to spurious activation of pressure relief systems.

10. Has the potential for vacuum relief, including potential air ingress through a vacuum relief device, been properly considered?
    • The paper will discuss examples of vacuum relief scenarios for pressure vessels and potential consequences of air ingress via vacuum relief devices.