During Process Hazard Analyses (PHAs) for processing facilities, a number of Independent Protection Layers (IPLs) may be identified as having the capability to reduce the risk of a given consequence occurring. One or more of these IPLs may be required to reduce risk to tolerable levels. Typically, these IPLs are identified during a Layers of Protection Analysis (LOPA), but other methods can be used.
Once IPLs have been identified, the process of managing them has just started. Designation of an IPL adds Operational and Maintenance requirements that often exceed typical practices. This presents an operating facility with the challenge of changing Operation and Maintenance practices to not only ensure that the credited IPLs are well understood, but that their protective functions remain available and meet the performance requirements that were defined for them.
The IEC 61511 and ISA 84.00.01-2004 Standards provide a framework for managing of Safety Instrumented Systems (SISs) and the Safety Instrumented Functions (SIFs) that were identified by the Hazard Analysis process. However, these standards are silent on managing of other non-SIF IPL types. This has led some operating organizations to conclude that there are no requirements relative to the non-SIF IPLs, resulting in a lack of proper management for these non-SIF IPLs.
This paper discusses the various types of IPLs and the requirements and methods for assuring their availability. The basic ownership requirements are described along with observations relative to the difficulty that real facilities have had in addressing these requirements, particularly with respect to the less visible IPL types such as those IPLs that are not associated with SIFs.
After discussing the ownership requirements and obstacles to meeting those requirements, the paper will discuss how use of a Safety Lifecycle database can overcome these obstacles. It will demonstrate how effective application of a Safety Lifecycle database can enable an operating organization to manage those requirements with maximum effectiveness and value, with minimum impact of existing organizational structures and accountabilities.