The Fire Dynamics Simulator (FDS) User’s Guide is the primary reference for anyone performing computational fluid dynamics (CFD) simulations of fire-driven flows. It is comprehensive and authoritative, but its length and technical density can easily overwhelm new users. This article explains how to use the guide efficiently, which sections matter most at each stage, and how to integrate it with more practical learning resources.
Structure of the FDS User Guide
The User’s Guide is organized into three main parts, each targeting a different level of experience.
Part I – The Basics of FDS focuses on installation, running FDS on different operating systems, and general user support. This is where you learn how to actually launch simulations. If your goal is to quickly run an FDS case on Windows, this step-by-step practical guide is often more effective than reading the manual alone.
Part II – Writing an FDS Input File is the core of the document. It explains how to define geometry, fires, ventilation, materials, and output quantities. This section is essential if you want to build simulations from scratch. Beginners usually benefit from first following this guided tutorial that walks through the creation of a complete input file, and then using the User’s Guide as a reference.
Part III – Development Tools is intended for advanced users and developers. It covers source code management, compilation, and development workflows.
It is important to note that the User’s Guide explains how to use the software, not the underlying theory. For governing equations, numerical methods, and model assumptions, the FDS Technical Reference Guide must be consulted.
Fundamental Operational Chapters
Some chapters are fundamental regardless of the type of simulation you are building and should be considered mandatory reading.
Chapter 3, Running FDS, explains how to launch simulations on Windows, macOS, and Linux, including parallel execution using OpenMP and MPI. This chapter is essential to understand how FDS interacts with your hardware.
Chapter 5, Input File Structure, describes the syntax of FDS input files. FDS is based on namelist groups, each starting with an ampersand (&) and ending with a forward slash (/). Understanding this structure is critical before attempting any serious modeling.
Chapter 23, Alphabetical List of Input Parameters, is one of the most important sections of the entire manual. It provides compact tables listing every keyword, along with units and default values.
Chapter 24, Error Codes, is a key diagnostic resource. When FDS stops with an error, this chapter usually tells you why and where to look for a solution.
Core Modeling Chapters
Building an FDS simulation requires a solid understanding of geometry, boundary conditions, fire modeling, and output configuration.
Geometry and Thermal Properties (Chapters 7–8)
Geometry in FDS is defined using rectilinear volumes. Obstructions (OBST) are described in Chapter 7.2 and are created using coordinate bounds (XB). The manual also explains how to handle thin obstructions and overlapping surfaces.
Openings such as doors and windows are typically created using HOLE records, described in Chapter 7.2.8, which remove portions of existing obstructions.
Surface properties are defined using SURF namelists. Chapters 7.1 and 7.4 explain how every obstruction surface must be assigned a surface ID to define thermal behavior, burning characteristics, or heat transfer properties.
Chapter 8 introduces thermal boundary conditions and material definitions (MATL). This is required for simulations involving heat conduction through solid elements, either in one or three dimensions.
Fire, Combustion, and Ventilation (Chapters 9, 10, 13)
Fire modeling is primarily covered in Chapter 9. Chapter 9.1 describes pyrolysis and the use of Heat Release Rate Per Unit Area (HRRPUA), which is the most common method for defining a fire source without modeling detailed solid-phase chemistry.
Ventilation is addressed in Chapter 10. Simple supply and exhaust vents are covered first, while Chapter 10.2 introduces HVAC network modeling for cases where pressure-driven flows are important.
Combustion chemistry is discussed in Chapter 13, including both mixing-controlled combustion and finite-rate reaction models.
Sensors, Control Logic, and Automation (Chapter 18)
Chapter 18 covers measurement and control logic. Devices (DEVC), described in Chapter 18.1, are used to record point measurements such as temperature, smoke concentration, or velocity.
Control functions (CTRL), explained in Chapter 18.5, allow users to implement logical conditions and automation, such as activating fans or opening vents only when specific criteria are met.
Data Extraction and Visualization (Chapter 22)
Post-processing is a critical part of any FDS analysis, and Chapter 22 explains how to configure output data.
Slice files (SLCF) generate two-dimensional contours of gas-phase quantities such as temperature or velocity. Boundary files (BNDF) record data on solid surfaces, including wall temperature and heat flux. Isosurfaces (ISOF) allow the visualization of three-dimensional contours at specific values, such as the stoichiometric mixture fraction to identify flame regions.
Alphabetical Reference
Chapter 23 deserves special emphasis. Once you know which namelist group you are working with, this chapter becomes the fastest way to find available parameters, units, and default values. Table 5.1, the Namelist Group Reference Table, is particularly useful for jumping between detailed explanations and parameter summaries.
Troubleshooting and Error Handling
Errors are unavoidable in FDS modeling. Chapter 4.2 lists common user mistakes, including syntax errors and numerical instabilities. Chapter 24 explains error codes and often points directly to the section of the manual related to the problem. For output files, Table 27.1 provides a clear reference for file extensions such as .sf and .bf.
Learning Path
The FDS User’s Guide is not designed as a tutorial. It is a reference manual intended for users with a solid background in fluid dynamics, thermodynamics, and fire science. It supports professional judgment but does not replace it.
For beginners, a structured learning path, starting from a simple working simulation and progressing toward more complex models, is far more effective.
Our FDS Fundamentals course can help bridge the gap between theory, documentation, and practical application.