Computational Fluid Dynamics Study for Jet Fire Analysis
Read how ABS Group helped a petrochemical facility understand its fire, toxic and explosion risk using computational fluid dynamics (CFD).
Produce a 3D model of the building and jetfire
Conduct a shelter-in-place assessment using the thermal data from the model
Calculate thermal radiation along the ground plane and evacuation paths
A large petrochemical facility in the United States houses processes covered under the Occupational Safety and Health Administration’s (OSHA's) Process Safety Management (PSM) regulations. These regulations, contained in 29 CFR 1910.119, require a facility siting study to evaluate the potential hazards involving explosive, flammable and toxic materials in occupied buildings. After ABS Group performed an original facility sitting study, the results motivated our client to request a proposal for a Computational Fluid Dynamics (CFD) jet fire analysis to assess the feasibility of safe evacuation and using the building as a shelter-in-place.
- To understand the Jet Fire Risk
- To understand the feasibility of safe evacuation and/or use of the building as a shelter-in-place
CFD is a highly detailed modeling method that requires a 3D model for the area of interest. It allows for a more accurate flame growth model in and around process areas. Using CFD for jet fires can help our clients address impingement, flame lift-off and smoke obstruction more accurately. The study aimed to evaluate the hazardous environment (e.g., thermal loading, momentum loading) in and around the building using a CFD fire analysis. ABS Group used a 3D model generated from laser scans to support this work, then used the commercially available CFD software package FLACS for jet fire modeling and the NIST Fire Dynamics Simulator (FDS) software for heat transfer into building materials.
Initially, we used Process Hazard Analysis Tool (PHAST) software to model the jet fire. The resulting fire profile displayed the engulfing of much of the building in the jet fire. The PHAST jet fire profiles are approximated as a geometric cone that does not account for the downrange buoyancy lift of the fire as the jet momentum slows or directly impacts equipment or buildings. This study intended to investigate the jet fire in more detail utilizing CFD modeling to quantify how an impinged flame could thermally load the exterior surface and if exterior thermal loads around the building meet the thermal dose criteria for evacuation defined by the client’s guidance documents. Using prescriptive methods to determine the structural integrity of the building envelope, we compared the applied thermal loads from the jet fire with lookup tables and fire resistance charts for the in-situ building materials.
Using thermal results from CFD modeling, we modeled heat transfer into the building via FDS. We used a 3D model of the building with wall and roof thermal properties representative of the documented building construction. Once we applied the thermal radiation loads to the exterior surfaces based on the predicted values from the CFD detailed fire modeling, FDS calculated heat transfer through the wall as a function of time. Then, we tracked temperature profiles within the wall and roof and compared them with published thermal degradation temperatures of the components.
Our team also assessed the ability to evacuate the Control Room for jet fire hazards from the FSS. We calculated the thermal radiation from the fire along the ground plane and the integration of the thermal dose along the path, assuming a 10mph evacuation speed along an unobstructed path. Additionally, we evaluated the evacuation paths to the furthest exit of the building from each release.
Although we found the existing wall and roof components to support some level of fire resistance, it was not possible to determine a duration in which the building could be safely used as an emergency shelter. The results of the CFD modeling showed that evacuation from the North or South exits exceeds the evacuation vulnerability and thermal radiation criteria. As a result, we presented several solutions to the client to support them in achieving their desired outcomes.
We delivered value to our client by helping them improve and maximize the safety of their staff in the event of an evacuation during a fire. Without work like this, staff could be at risk of serious injury in the event of an accident. However, detailed analysis can be used to help visualize potential hazards and develop real-world solutions that reduce workplace risks.