The operation of Major Accident Hazard (MAH) facilities requires a clear understanding of the potential causes of harm and the safeguards/barriers that are necessary in order to ensure that the potential for harm is eliminated, managed or reduced to a level which is as low as reasonably practicable (ALARP).
MAHs are low probability, high consequence events which if allowed to occur have the potential to cause multiple fatalities and/or catastrophic damage to the asset facilities and/or environment. A ‘Barrier Model’ is a visual means of representation of the lines of defence that serve to block MAHs from manifesting. The barriers that are present may be inherent as a result of the original design process, or physical such as instrumented protective systems, or interventional such as planned maintenance.
Barriers are also grouped by type in a Barrier Model: ‘Prevention Barriers’ or ‘Protection Barriers’ with the former aimed at preventing the unwanted hazardous event from occurring and the latter serving to prevent escalation of the unwanted hazardous event should it manifest itself. The Barrier Model is therefore constructed as a pictorial representation of each, with Prevention Barriers on the left, the unwanted hazardous event in the middle, and the Protection Barriers on the right. An illustration of such a Barrier Model is shown below in Figure 1 below.
Figure 1: Example of a Barrier Model
The performance criteria for each Barrier must also be formally established; this will facilitate the assimilation of barrier performance when it is tested periodically.
MAH Barriers typically comprise of a multitude of equipment items, certain of which would also be designated as Safety Critical Equipment (SCE). For example, Fire and Gas Detection is a MAH Barrier; it is an instrumented protective system which consists of multiple items of equipment (e.g. detectors, cabling, junction boxes, controls and the like) where most of those equipment items will also likely be SCE. The effectiveness of this system as a Barrier is clearly dependent on the functional operability and interaction of the individual items of SCE that are contained therein. The grouping together of SCE into their respective Barriers is therefore fundamental to the management of MAHs.
Barrier strength is a measure of the robustness of each barrier and a measure of how well MAHs are being managed in the context of the defined performance criteria. AIE achieves this by ensuring that the required SCE maintenance, inspection and/or function testing is performed appropriately in order to ensure the required level of performance is being achieved; the results from which are then robustly assessed in the context of Barrier strength.
Identification of MAH Barriers and Safety Critical Equipment
MAH Barriers and SCE must be maintained in a fit-for-purpose condition for safe production operations at MAH facilities. AIE advocates that it is the understanding of what is and what is not Safety Critical at component (i.e. equipment tag) level that is vitally important. This will thereafter serve to facilitate the assignment of appropriate maintenance, inspection and/or testing works to maximize equipment reliability and operability of said SCE.
AIE employs a robust but structured assessment methodology which serves to identify whether a given item of equipment is Safety Critical or not an ensure it is categorized into the correct MAH barrier.
Once identified, the barrier groups and SCE are then flagged within the Computerised Maintenance Management System (CMMS) with appropriately defined and scoped Planned Maintenance Routines (PMRs). This serves to provide the requisite level of assurance that SCE will meet their required functionalities for safe and reliable production operations.
MAH Barrier and SCE Condition Status
Once the periodic maintenance, inspection and/or testing has been completed, the condition of SCE should be formally assessed in the context of the required performance, and in particular, the effects of any deterioration or malfunctioning on the performance of the Barrier to which each belongs also needs to be formally verified.
The Barrier Model is particularly useful during instances where the removal of a given barrier or set of barriers for maintenance purposes, or where barriers may have malfunctioned or have degraded during operational service and are no longer fully functional. The effects, in terms of the possible weakening of the prevention and/or protective functions that each barrier is meant to provide then becomes readily evident.
Where degraded Barriers are encountered, this does not necessarily mean that production operations would be required to automatically cease. Continued operations could reasonably be supported provided that the risks associated therewith are properly understood and any supporting risk reduction measures are defined and implemented. In such circumstances therefore, an Operational Risk Assessment (ORA) would be required.
Performance Evaluation and Monitoring
AIE advocates the use of Key Performance Indicators (KPIs) to proactively detect weaknesses or failures of SCE and their associated Barriers. This enables remedial actions to be taken in advance of a MAH event, rather than in its wake. KPI monitoring, when specifically mapped in the context of SCE and Barrier group to the corresponding MAH, is a formal demonstration that MAHs are being managed to a high level of effectiveness.
To be meaningful and effective, KPIs should be robustly defined such that the purpose and performance characteristics can be readily understood. KPIs should therefore comprise of a range of specifically targeted leading and lagging metrics, with performance requirements clearly stated, and the performance trend subject to regular review.
Contact AIE today
AIE are actively working with a range of major energy providers in the provision of process safety services. We have a highly skilled workforce which possess the requisite knowledge and experience in this specialised area of operations. We are able to provide a complete service solution for our clients which ensures that process safety management is fully integrated and operationalised into our client’s business. Contact our team today for further information.