(52m) Safety Optimization of the Spatial Configuration of Buildings in Refineries Using QRA

The purpose of this study is the development of a methodology for dynamic optimization of the spatial configuration of the building infrastructure in oil refineries applying quantitative risk assessment (QRA) principles. The method developed focuses on fatal effects from possible accidents in production and storage units according to API 752. A In brief, QRA is used as a bridge to quantify the risk and apply API 752 standards as guide towards plant design optimization when retrofitting is at hand.

The assessment methodology includes the classification of the buildings of interest according to API 752, the identification of accident scenarios that may affect these buildings, the identification of the relevant equipment, the consequences and risk assessment of the selected scenarios, the individual and social risk assessment within the buildings, the selection of the appropriate assumptions for the risk assessment and the identification of security enhancement measures. This enhancement is one of the most important tasks due to its affection on measures budget.

We have applied this integrative approach to study the possibilities for safety optimization in a typical large-scale European refinery by re-designing the spatial configuration of the administrative and worker buildings on site. In our application, the buildings included were 64. The building cohort consists of:

• 5 buildings constructed by reinforced concrete
• 28 buildings constructed by reinforced concrete frame and brickwork masonry
• 17 are constructed by steel and metal frame
• 14 ISOBOX buildings

The examined scenarios considered catastrophic rupture of the unit or the escape of the vessel’s content in 10 minutes and applied in all columns, vessels, and containers with a capacity of more than 5 m3 in the refinery. For pressurized storage tanks, in addition to the above, examined scenarios for leakages and failures of the connected pipelines. Furthermore, liquid content pipelines were examined for pool fire accidents while NG-LPG-Propane pipes were simulated for catastrophic failures and a hole equal to 20% of pipes diameter, as the Bevi Risk Assessment Manual (RIVM, Netherlands) suggests.

Modeled accidents comprised BLEVE-fireballs, jet fire, pool fire, flash fire, and UVCEs. The selection of the mathematical models to describe each accident was based on assiduous check of model’ attributes and the related recommendations of industrial and health and safety standard organizations, such as TNO, UK Health and Safety Executive, and DNV GL. Weather conditions selection played a key role in the results as the appropriate parameter selection (e.g., the distance in which ignition surface will be found or the height of interest, etc.). We performed the simulations using Phast/Safeti v.8.22 (DNV-GL) and updated it with in-house models of key processes including specific measures designed to optimize the safety performance of the plant. Event tree identification, equipment failure frequencies, and ignition probabilities determination were based on the BEVI manual by the Dutch Ministry of the Environment, while data from the European Gas Pipeline Incident Data Group (EGIG) were used for the underground gas pipeline. The mortality criteria inside buildings were determined in the technical specifications of the study based on literature and computational research.

According to the results regarding location specific risk (LSR) there was a need to take measures in the buildings where the probability of loss of life is bigger than the fatality risk limit adopted as acceptable according to the technical specifications of the study (1E-05). Indicatively, one of the measures mentioned is the movement of some mobile buildings in new locations. In addition, Societal Risk calculation proved that the refinery was operating above the limits set by RIVM in the EU (RIVM guidelines were adopted in the technical specifications). In order to evaluate the possible measures and the normal operation of the refinery according to API 752 we carried out a horde of parametric studies.

Recommendations included the shielding of selected buildings against thermal radiation using external thermal insulation, the use of high-strength exterior windows against high temperatures, and the appropriate change of orientation of external openings of the buildings.

Overall, our dynamic optimization methodology for plant and process safety by design has been demonstrably attractive as a means to ensure inherent safety in plant retrofits or new designs by integrating traditional quantitative risk assessment at the process level with optimization algorithms fed with acceptable risk criteria and spatial optimization of buildings in complex plant configurations such as large-scale oil refineries.