HAZOP Facilitation and Functional Safety Support – Design of Spirit Blending Tanks

A  site which matures, blends and bottles whisky and operates as a lower-tier COMAH establishment required support in developing a compliant design for spirit blending tanks.  This forms part of their duties under COMAH to demonstrate risk has been reduced as low as reasonably practicable (ALARP). 

Arthian supported the project by providing external HAZOP facilitation and functional safety support.

Arthian engaged with the designers who developed the design for an improved level control system and automation of the bulk spirit transfer routes, to define the scope of the hazard studies and agreed to facilitate a HAZOP study for the proposed design modifications.

Arthian worked with the client and designer to review the design documentation and propose HAZOP study nodes which were mutually agreed to form  the HAZOP approach.

The HAZOP was then facilitated on site across a two day period, supported by an Arthian HAZOP leader with training accredited by the Institute of Chemical Engineers (IChemE) and an experienced HAZOP scribe.  Arthian led a multidisciplinary team to systematically assess the modifications to the design, considering multiple potential modes of operation and interfaces with existing systems.  The HAZOP team applied severity and likelihood rule sets to score scenario risk, to aid prioritisation of identified improvement measures which were recorded as HAZOP actions.  

The workshop identified a need for greater development of some elements of the process design, as well as a site focus on development of procedures to minimise the potential for human error leading to dangerous loss of containment.

Upon completion of the HAZOP study Arthian reviewed  the study records to identify a representative list of accident (i.e. event-consequence) scenarios which could result in major losses (safety, environment or economical). 

Arthian then allocated independent protection layers (IPLs) to these event-consequence scenarios to review the need for Safety Instrumented Functions (SIFs). Scenarios included  those identified in the HAZOP as being safety-critical, with the potential to cause a major accident, under COMAH. Arthian then evaluated these SIFs using the layer of protection analysis (LOPA) method.

LOPA is a methodical approach which examines the possible initiating events leading to a hazardous scenario, the protection layers present, and the event frequency compared to a maximum tolerable event frequency based on the risk matrix being used. 

The LOPA was facilitated by a TUV certified Functional Safety Engineer and supported by an experienced scribe.  The LOPA facilitator led a multi disciplinary team who systematically assessed the LOPA scenarios.  The team determined that none of the overfill scenarios required a SIL rated SIF.  

The assessment was then subject to further scrutiny by the application of sensitivity analysis, cost benefit analysis and discussion of how the proposed design met the requirement to reduce risk ALARP.  Recommendations for further risk reduction were proposed to the design team for consideration.

The HAZOP and LOPA reports and accompanying action close out will form part of the sites COMAH documentation and evidence that risk is appropriately managed on site.