When determining how best to prevent, mitigate, and suppress a fire, how a fire would behave in a particular space must be understood. As part of the fire protection services provided, ARS uses a variety of programs to determine the potential behavior of a fire and how each variable within a space would impact that behavior.
ARS uses fire models for the following purposes:
- To demonstrate code compliance
- To demonstrate the ability to meet performance-based criteria
- To analyze configurations not addressed by codes
- To support fire probabilistic risk analysis using NUREG/CR-6850
Types of Fire Models
When performing fire modeling, ARS uses a variety of programs that have been verified and validated to demonstrate code compliance. The fire modeling team at ARS employ three different types of fire modeling programs: algebraic, zone, and the fluid dynamic or computational fluid dynamic model.
FDS – Computational Fluid Dynamic Model
When determining compartment variables at a specific location, or when geometric features are expected to play a significant role in the results, ARS fire protection engineers and consultants use the FDS computational fluid dynamic model. Some prefer the FDS model because it can solve for a temperature profile, and the user receives a complete set of data containing the information needed for a comprehensive fire risk analysis.
CFAST – Zone Model
ARS fire protection engineers and consultants use this model when performing a two-zone model analysis. This model is a classic two-zone fire model that predicts the compartment conditions for the upper and lower gas layers. CFAST subdivides each compartment into two control volumes with a relatively hot upper layer (hot gas layer) and a relatively cool lower layer (fresh air). Each layer has its own energy and mass balances, and the model assumes that the temperature and gas concentrations are constant throughout the zone. The CFAST model accounts for the size and geometry of the room when simulating the effects of a fire and can model the flame and plume regions around a fuel source.
FDTs – Algebraic Model
This model is used by ARS fire protection engineers and consultants to solve for correlation based on experiments, and some algebraic models can be direct inputs for a zone model. In these applications, the user evaluates one data point with closed-form algebraic expressions. Algebraic models, when used properly, can provide an estimate of fire variables such as hot gas layer (HGL) temperature, heat flux from flames or the HGL, smoke production rate, depth of the HGL, and the actuation time for detectors. Algebraic models are helpful because they require a minimum of computational time. These models are useful primarily as screening tools.