An operator of a petroleum bulk storage facility wanted to determine if the protection systems proposed for its soon-to-be refurbished site would conform to the latest good practice guidelines and be compliant with the Seveso Regulations.
As part of a comprehensive risk assessment process, Byrne Ó Cléirigh conducted a layers of protection analysis (LOPA) to determine the probability of a tank overfilling at the facility and to assess the risks associated with such an event. Our work included:
- A review of the operational arrangements at the tank farm.
- Development of a conceptual model of the tank farm system to identify and model the independent protective layers present.
- Identification of a series of initiating events that could potentially give rise to an overfilling scenario, determination of the probability of failure on demand (PFD) of independent protective layers for each event, and calculation of the overall probability of a tank overfilling at the site.
- An examination of the potential for common mode failures and an assessment of the reliability of the human element, i.e. the reliability of an operator to initiate a shut-down.
- Calculation of a reliability metric for the overfill protection system and comparison of this with established good practice guidance, including the recommendations from the Buncefield investigation.
- Consequence modelling of the impacts of a large pool fire - within the site and on the surrounding area.
Our analysis enabled the operator to better understand both the risk posed by a major accident arising from overfilling of a bulk storage tank and the overall effectiveness of the overfill protection system.
Importantly, our work also informed the development of a strong case to demonstrate that, with the planned upgrades to the overfill protection system in place, the risks associated with tank overfilling would satisfy the ALARP criteria, i.e. that the risks would be as low as reasonably practicable. Our findings were issued to the regulatory authority prior to commencement of the refurbishment works.