Defining Grid Resolution for Trench Fire Modeling with FDS

Trench fires are often the design basis for fireproofing of piperacks and other critical components in a hydrocarbon processing facility. Prescriptive guidance based on API 2218 Fireproofing Practices in Petroleum and Petrochemical Processing Plants generally results in fireproofing being applied within 30-ft of a trench. Alternatively, fire modeling can be conducted as part of a performance-based approach to determine the extent of fireproofing necessary. Trench fires pose a unique challenge for modeling due to the smaller dimensions of the trench relative to other pool fire scenarios (e.g., sump fires). Current guidelines for fire models used at LNG facilities recommend at least 20 cells across the surface of a fire. However, this often leads to very high cell counts and simulations that require impractical computational resources and time.

This paper will detail a grid size sensitivity analysis for modeling trench fires with Fire Dynamics Simulator (FDS). By examining various trench fire scenarios (i.e., altering grid resolution for FDS validation cases) we aim to establish guidelines for more practical grid sizes. Balancing the need for accuracy and computational efficiency, our research contributes to the reliability of CFD models in the assessment of trench fire impacts on LNG facility design.