Assessing a Worst Credible Hazard Scenario and Impact to Portable Buildings Using API 753 Vs. DNV PHAST Vs. FLACS CFD Modeling

Operating entities are required to consider facility siting issues and the protection of personnel who have been assigned to duties that require the use of portable buildings. Owners and operators have the ability to apply recognized and generally accepted good engineering practice (RAGAGEP) consequence modeling tools to help in identifying safe locations for these buildings. The location of these buildings may have significant impacts on the cost of turnarounds, the response time for field personnel to abnormal events, and time to perform routine activities. This paper will present a comparison of several industry recognized modeling methodologies and their results on the determination of a safe location for portable buildings, i.e. API 753, DNV PHAST, and computational fluid dynamics (CFD).

The hazard scenario and consequence modeling case study in this paper was based on a large continuous reactor unit operation that was physically within a high length to width ratio congestion area. The potential for overpressure and resulting leak scenario was identified during the PHA/LOPA team meetings. The case study was based on this credible hazard scenario that involved a potential decomposition reaction with resulting high pressure and rupture of connecting reactor piping. The harmful event involved the rupture of a large flammable liquid feed line and vapor line from a recycle compressor.

With these results, the owner identified a need to relocate portable buildings to a safe location or require portable buildings designed for occupancy within the 0.6 or 0.9 psi overpressure radius to be of a design to protect the occupants. The authors will compare the portable building siting outcome of the three modeling methods, and substantiate the value of taking the escalating approach taken in the case study.