NIST Special Publication 1041 

CFAST – Consolidated Model of 

Fire Growth and Smoke Transport

(Version 6)

User’s Guide

Richard D. Peacock 

Walter W. Jones 

Paul A. Reneke 

Glenn P. Forney 
NIST Special Publication 1041

CFAST – Consolidated Model of Fire 

Growth and Smoke Transport

(Version 6)

User’s Guide

Richard D. Peacock 

Walter W. Jones 

Paul A. Reneke 

Glenn P. Forney 

Fire Research Division 

Building and Fire Research Laboratory

August 2005

U.S. Department of Commerce 

Carlos M. Gutierrez, Secretary 

Technology Administration 

Phillip J. Bond, Under Secretary for Technology 

National Institute of Standards and Technology 

Hratch G. Semerjian, Acting Director 
Certain commercial entities, equipment, or materials may be identified in this 

document in order to describe an experimental procedure or concept adequately. Such 

identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Special Publication 1041 

Natl. Inst. Stand. Technol. Spec. Publ. 1041, 109 pages (August 2005) 

CODEN: NSPUE2 

U.S. GOVERNMENT PRINTING OFFICE 

WASHINGTON: 2005

_________________________________________ 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Internet: bookstore.gpo.gov — Phone: (202) 512-1800 — Fax: (202) 512-2250 

Mail: Stop SSOP, Washington, DC 20402-0001

User’s Guide Version 6 Contents • v 

Contents 

Chapter 1 Introduction 1

Background........................................................................................................1 

Chapter 2 Getting Started 3

Installation from the CFAST Web Site..............................................................3 

Computer Hardware Requirements....................................................................4 

Computer Operating System and Software Requirements ................................4 

Verifying Correct Installation and Operation ....................................................4 

Chapter 3 Running CFAST 6

Creating a CFAST Input Data File ....................................................................6 

File Naming and Location ...............................................................................10 

Starting a CFAST Calculation .........................................................................11 

Running CFAST from CEdit ...............................................................11 

Running CFAST from a Command Prompt ........................................12 

Chapter 4 Setting up the Input File for CFAST 14

Overview..........................................................................................................14 

Simulation Environment ..................................................................................16 

Naming the Calculation, the Title Input ..............................................16 

Setting Time Limits and Output Options.............................................17 

Ambient Conditions.............................................................................18 

Compartment Geometry...................................................................................20 

Defining Compartment Size and Position............................................22 

Modeling the Compartment as a Tall Shaft or Long Corridor.............23 

Thermal Properties of Boundaries .......................................................25 

Compartment Connections...............................................................................26 

Defining Horizontal Natural Flow Connections (Doors, Windows) ...27 

Defining Vertical Natural Flow Connections (Ceiling or Floor Holes, 

Hatches) ...............................................................................................30 

Defining Mechanical Ventilation Connections....................................32 

Prescribing Fires ..............................................................................................35 

Defining Fire Objects...........................................................................38 

Associating Fire Objects with One or More Instances of the Fire in the 

Compartments of the Simulation .........................................................41 

Special Features ...............................................................................................44 

Sprinklers and Detectors......................................................................44 
vi • Chapter 1 Introduction User’s Guide Version 6 

Defining Targets ..................................................................................45 

Defining Compartment Area................................................................47 

Inter-compartment Heat Transfer (Conduction) ..................................48 

The Ceiling Jet – An Additional Zone.................................................50 

Scenario and Software Limits..........................................................................51 

Chapter 5 Output 52

Overview..........................................................................................................52 

Detailed Outputs ..............................................................................................53 

Output for Initialization .......................................................................53 

Output for Main Output Variables.......................................................59 

Output for Wall Surface and Targets...................................................60 

Output for Gas Species ........................................................................61 

Output for Vent Flows .........................................................................62 

Spreadsheet Output ..........................................................................................63 

Primary Output Variables (project.n.csv) ............................................63 

Species Output (project.s.csv)..............................................................64 

Vent Flow (project.f.csv) .....................................................................64 

Temperatures and flux (project.w.csv) ................................................65 

Error Messages.................................................................................................65 

References 69
User’s Guide Version 6 Acknowledgement • vii 

Acknowledgement 

The CFAST model has been under development for more than 20 years. The primary developers are 

Walter Jones, Richard Peacock, Glenn Forney, Rebecca Portier, Paul Reneke, John Hoover, and 

John Klote. 

There have been contributions through research and published papers at Worcester Polytechnic 

Institute, University of California at Berkeley, VTT of Finland and CITCM of France. An important 

guide to development of the model has been from many people around the world who have provided 

ideas, suggestions, comments, detailed questions, opinions on what should happen in particular 

scenarios, what physics and chemistry are needed and what types of problems must be addressed by 

such a model in order to be useful for real world applications. 

In addition to support by NIST, at least two outside organizations have provided support for the 

development of the model, its documentation, and validation. At the U.S. Navy, Naval Research 

Laboratory, Jean Bailey, John Hoover, and Pat Tatem provided support for model development, 

including the vertical flow and corridor flow algorithms. The U.S. Nuclear Regulatory Commission 

(NRC) has supported experiments to validate CFAST as part of an international collaboration to 

study the application of fire models to nuclear power plants. NRC has also partially funded the 

development of the Windows version of CFAST, the documentation described in this document and 

the evaluation of the model per ASTM E1355. 

User’s Guide Version 6 Disclaimer • ix 

Disclaimer 

This software was developed at the National Institute of Standards and Technology by employees of 

the Federal Government in the course of their official duties. Pursuant to Title 17 Section 105 of the 

United States Code this software is not subject to copyright protection within the United States and 

is in the public domain. The software is an experimental system. NIST assumes no responsibility 

whatsoever for its use by any party. This software is provided "as is." You accept the software “as 

is” and acknowledge that NIST makes no warranty of any kind, express, implied or statutory, 

including, without limitation, the implied warranty of merchantability, fitness for a particular 

purpose, non-infringement and data accuracy. NIST does not represent or warrant that the operation 

of the software will be uninterrupted or error-free, or that any defects will be corrected. NIST does 

not warrant or make any representations regarding the use of the software or the results thereof, 

including but not limited to the correctness, accuracy, reliability, or usefulness of the software. You 

may freely use, copy or distribute this software. 

Users are warned that CFAST is intended for use only by those competent in the field of fire safety 

and is intended only to supplement the informed judgment of the qualified user. The software 

package is a computer model which may or may not have predictive value when applied to a specific 

set of factual circumstances. Lack of accurate predictions by the model could lead to erroneous 

conclusions with regard to fire safety. All results should be evaluated by an informed user. 

Intent and Use 

The algorithms, procedures, and computer programs described in this report constitute a 

methodology for predicting some of the consequences resulting from a prescribed fire. They have 

been compiled from the best knowledge and understanding currently available, but have important 

limitations that must be understood and considered by the user. The program is intended for use by 

persons competent in the field of fire safety and with some familiarity with personal computers. It is 

intended as an aid in the fire safety decision-making process. 

User’s Guide Version 6 Chapter 1 Introduction • 1 

Chapter 1 Introduction 

Background 

CFAST is a two-zone fire model used to calculate the evolving distribution of smoke, fire 

gases and temperature throughout compartments of a building during a fire. These can range 

from very small containment vessels, on the order of 1 m3 to large spaces on the order of 

1000 m3. This guide describes how to obtain the model, verify its correct installation, create 

input data in an appropriate form, and analyze of the output of a simulation. 

The modeling equations used in CFAST take the mathematical form of an initial value 

problem for a system of ordinary differential equations (ODEs). These equations are derived 

using the conservation of mass, the conservation of energy (equivalently the first law of 

thermodynamics), the ideal gas law and relations for density and internal energy. These 

equations predict as functions of time quantities such as pressure, layer height and 

temperatures given the accumulation of mass and enthalpy in the two layers. The CFAST 

model then consists of a set of ODEs to compute the environment in each compartment and a 

collection of algorithms to compute the mass and enthalpy source terms required by the 

ODEs. The formulation of the equations, their solution, and discussion of validation and 

verification of the code are presented in a companion document1

.. 

All of the data to run the model is contained in a primary data file, together with databases 

for objects, thermophysical properties of boundaries, and sample prescribed fire 

descriptions2

. These files contain information about the building geometry (compartment 

sizes, materials of construction, and material properties), connections between compartments 

(horizontal flow openings such as doors, windows, vertical flow openings in floors and 

ceilings, and mechanical ventilation connections), fire properties (fire size and species 

production rates as a function of time), and specifications for detectors, sprinklers, and 

targets (position, size, heat transfer characteristics, and flow characteristics for sprinklers). 

Materials are defined by their thermal conductivity, specific heat, density, thickness, and 

burning behavior. Throughout the discussion on the model inputs, notes are included to 

provide additional insight on the model’s operation. 

The outputs of CFAST are the sensible variables that are needed for assessing the 

environment in a building subjected to a fire. These include temperatures of the upper and 

lower gas layers within each compartment, the ceiling/wall/floor temperatures within each 
2 • Chapter 1 Introduction User’s Guide Version 6 

compartment, the visible smoke and gas species concentrations within each layer, target 

temperatures and sprinkler activation time. 

Many of the outputs from the CFAST model are relatively insensitive to uncertainty in the 

inputs for a broad range of scenarios. However, the more precisely the scenario is defined, 

the more accurate the results will be. Not surprisingly, the heat release rate is the most 

important variable, because it provides the driving force for fire-driven flows. Other variables 

related to compartment geometry such as compartment height or vent sizes, while important 

for the model results, are typically more easily defined for specific design scenarios than fire 

related inputs. 

The first public release of CFAST was version 1.0 in June of 1990. This version was 

restructured from FAST3 to incorporate the "lessons learned" from the zone model CCFM4, 

namely that modifications and additions to the model are easier and more robust if the 

components such as the physical routines are separated from the solver code used by the 

model. Version 2 was released as a component of Hazard 1.2 in 19945. The first of the 3.x 

series was released in 1995 and included a vertical flame spread algorithm, ceiling jets and 

non-uniform heat loss to the ceiling, spot targets, and heating and burning of multiple objects 

in addition to multiple prescribed fires. Ignition was assigned based on a critical heat flux, a 

critical temperature, or a critical time input by the user. As CFAST evolved over the next five 

years, version 3 included smoke and heat detectors, suppression through heat release 

reduction, better characterization of flow through doors and windows, vertical heat 

conduction through ceiling/floor boundaries, and non-rectangular compartments. In 2000, 

version 4 was released and included horizontal heat conduction through walls, and horizontal 

smoke flow in corridors. Version 5 improved the combustion chemistry. Version 6 includes 

a new user interface written for Windows and revisions to the input file and model. The 

current version is 6.0 
User’s Guide Version 6 Chapter 2 Getting Started • 3 

Chapter 2 Getting Started 

Installation from the CFAST Web Site 

CFAST is documented by two publications, this user’s guide and a technical reference 

guide1. The technical reference guide describes the underlying physical principles, provides a 

comparison with other models, includes an evaluation of the model following the guidelines 

of ASTM E13556. This user’s guide describes how to use the model and applies to version 6 

and later. All the documentation is available on the web site. 

All of the files associated with CFAST can be obtained at: 

http://fire.nist.gov/cfast 

Information about new versions, bug fixes, and documentation for the model and software 

are available on this web site. The CFAST distribution consists of a self-extracting set-up 

program for Windows-based 

PCs. 

After downloading the set-up 

program to a PC, doubleclicking on the file’s icon 

walks the user through a 

series of steps for installation 

of the program. The most 

important part of the 

installation is the creation of 

a directory (called 

c:\nist\cfast6 by default) in 

which the CFAST 

executable files, sample 

cases, and supplemental data 

files are installed. 
4 • Chapter 2 Getting Started User’s Guide Version 6 

Computer Hardware Requirements 

CFAST requires a relatively fast processor and a sufficient amount of random-access 

memory (RAM) for complex cases. The processor should be at least as fast as a 1 GHz 

Pentium III, with more than 256 MB of memory for complex cases. Typical calculation times 

for a 2 compartment scenario can range from a few seconds to multiple hours, depending on 

the details of the scenario. Plus, a large hard drive is needed to store the output of 

calculations. It is not uncommon for a single calculation to generate output files as large as 1 

GB. 

Computer Operating System and Software 

Requirements 

CFAST and the input editor CEdit run under Microsoft Windows. The latest version has been 

tested and runs on both Windows 2000 and Windows XP. 

Verifying Correct Installation and Operation 

Sample input files are provided with the program for new users who are encouraged to first 

run the sample calculations before attempting to create an input file. To run the model, 

browse to the location of the CFAST input files (default location is c:\nist\cfast6\data, and 

double click on the file named standard.in. This should open the file in the CFAST input 

editor, CEdit. The simple test case can be run from the program menu by selecting “Run!” 

and then “Model Simulation, CFAST” 

This runs a very simple test case and it should be completed quickly. Additional details on 

running CFAST are included in the next chapter. To verify that the installation has been done 

correctly, the output of the model should appear as follows. 
User’s Guide Version 6 Chapter 2 Getting Started • 5 

This case checks several attributes of the installation including the presence of the database 

files (see auxiliary files in the section on building input files). Additional explanation of the 

results of this run is described in Chapter 5. 
6 • Chapter 3 Running CFAST User’s Guide Version 6 

Chapter 3 Running CFAST 

Running CFAST is relatively simple. All of the parameters that describe a given fire scenario 

are entered into a text file that is referred to as the "data" or "input" file. In this document, the 

data file is designated as filename.in, where "filename" stands for any character string that 

helps to identify the simulation. All of the output files associated with the calculation would 

typically have this common prefix. In addition to the input file, there are often several 

external files containing input parameters for the simulation. These files are referred to as 

"database" files, which contain parameters describing common materials and fuels. 

The CFAST distribution includes a Windows-based input editor called CEdit that allows the 

user to enter details of a simulation in a standard Windows format, save the data file to disk, 

and run the simulation with CFAST from within the program. Typically, all simulations 

would be developed and run from within CEdit. For numerous, similar or lengthy 

simulations, the fire model CFAST can be run from a command prompt window. 

It is suggested that a new user start with an existing data file, run it as is, and then make the 

appropriate changes to the input file for the desired scenario. By running a sample case, the 

user becomes familiar with the procedure and ensures that his/her computer is up to the task 

before embarking on learning how to create new input files. 

Creating a CFAST Input Data File 

All of the data to run the model is contained in an input data file. Also needed are databases 

for objects, thermophysical properties of boundaries, and sample prescribed fire descriptions 

provided with the model. These files contain information about the building geometry 

(compartment sizes, materials of construction, and material properties), connections between 

compartments (horizontal flow openings such as doors, windows), vertical flow openings in 

floors and ceilings, and mechanical ventilation connections), fire properties (fire size and 

species production rates as a function of time), and specifications for detectors, sprinklers, 

and targets (position, size, heat transfer characteristics, and flow characteristics for 

sprinklers). Materials are defined by their thermal conductivity, specific heat, density, 

thickness, and burning behavior (heat release rate, ignition properties, and species yields). 

The input data file provides the program with parameters to describe the scenario under 

consideration. The parameters are organized into groups of related variables. Each line of the 
User’s Guide Version 6 Chapter 3 Running CFAST • 7 

input data file contains inputs related to a single group and begins with a keyword that 

identifies the input. For example, compartment geometry is described by a set of lines 

(keyword COMPA) that define the width, depth, and height of each compartment. A 

description of the input parameters can be found in Chapter 4. 

Typically, the input data file will be created with the input editor, CEdit, included with the 

CFAST distribution. A shortcut to the input editor is placed on the start menu during 

installation. To run, select Start, Program Files, and CFAST. Details of the program and its 

inputs are described in chapter 4. 

The program includes a number of menu items for 

ancillary functions. In addition to the normal file 

menu items to open and save input data files or to 

exit the program, a “Run!” menu is included to 

execute or view the current simulation. Menu items 

include the following: 

• Create Geometry File: used to create a geometry file for visualization with the 

program smokeview. The input data file is saved, if necessary, and CFAST is run 

with an option to only run through initialization. The resulting geometry can be 

viewed with the “Simulation Visualization, Smokeview” menu item, below. 
8 • Chapter 3 Running CFAST User’s Guide Version 6 

• Model Simulation, CFAST: runs the current input data file specification with the 

fire model CFAST. The input data file is saved, if necessary, and CFAST is run 

to completion. Additional details are described below in the section on starting a 

CFAST calculation. In order to visualize the results of the simulation with the 

program smokeview, the Smokeview Output Interval must be set to a non-zero 

value on the simulation Environment page. This is described in more detail in 

chapter 4. 

• Simulation Visualization, Smokeview: runs the program smokeview with the 

previously defined smokeview geometry file. This allows the user to see the 

compartment geometry and connections or view the results of the simulation 

visually. Additional details on the use of smokeview are included in the user’s 

guide for smokeview7

. 

Two additional menu items can be selected to control details of the model simulation using 

CFAST. 

• Show CFAST Window: If checked, this menu item allows the user to see the 

windows command prompt that is used to execute the CFAST model when the 

Model Simulation, CFAST menu item is used. By default, this is not checked. 

Normally, this can be left unchecked. For troubleshooting, this can be selected to 

see additional details of the calculation as it progresses. 
User’s Guide Version 6 Chapter 3 Running CFAST • 9 

• Detailed Output File: If checked, this menu item directs the CFAST model to 

produce a detailed text output file. Details of the output are included in chapter 5. 

 The “Tools” menu allows the user to view or change the 

database of material thermophysical properties used by 

the model and to select desired engineering units used in 

the input editor CEdit. Menu items include the following. 

• Edit Thermal Properties: Heat transfer through compartment surfaces, to 

secondary fire objects, or other targets that may be specified depends on userspecified thermal properties for the materials. These may be view or changed by 

the user as desired. It is important to note that these are global parameters that are 

not tied to any particular simulation. Thus, if values are changed, the changed 

values will affect all future simulations or repeated runs of earlier simulations. 

Materials properties include thermal conductivity, specific heat, density, 

thickness, and emissivity. Materials included in the database provided with the 

program are textbook values of common building and furnishing materials. 

In addition, a series of constants that define the absorption of HCl on 

compartment surfaces can be specified. Values for gypsum wallboard are 

included in the database supplied with the program. 

• Select Engineering Units: The CFAST model uses input values and provides 

output in S.I. units. Within the input editor, CEdit, the user may select engineering 
10 • Chapter 3 Running CFAST User’s Guide Version 6 

units of choice for input and output. These values are saved in the windows 

registry and may be changed at any time. 

 The View menu allows the user to view and / or print the input data 

file, output file (if the simulation has been run and a text output file 

generated) and the log file of the simulation. 

 The Help menu accesses the online version of this user’s guide, the 

CFAST web site, or an about dialog box that displays the user license 

and version of the program. 

File Naming and Location 

By default, the CFAST installation places all program files in the directory c:\NIST\CFAST6 

and sample input data files in the directory c:\NIST\CFAST6\DATA. While these locations 

can be changed during installation, the documentation in this user’s guide assumes these 

locations. File naming conventions in CFAST limit the length of file names to the DOS 

standard of 8 characters plus a three character extension such as standard.in. By default, all 

input data files are assumed to be located in the data directory at c:\NIST\CFAST6\DATA 

and all output files are written to this directory as well. 

In addition, there are several files that CFAST uses to communicate with its environment. 

They include 1) an input data file, required for every simulation, 2) the thermal properties 

database, 3) additional secondary fire source objects, 4) a binary data file containing all 

calculated values from the simulation, and 6) a series of spreadsheet files of important output 

variables. Documentation of the input data file is included as chapter 4 of this user’s guide. 
User’s Guide Version 6 Chapter 3 Running CFAST • 11 

The format of the configuration file, thermal database, and object databases are detailed in 

the appendices. Specification of the history and restart file is included in chapter 4. 

In CFAST, simulations are arranged as projects with all the files associated with a single 

simulation sharing a common base file name. For a simulation with a base file name of 

“project”, the built-in naming conventions would identify the files of the simulation as 

follows: 

• input: project.in 

• text output file: project.out 

• spreadsheet output files: (Normal output) project.n.csv, (Species output) 

project.s.csv, (Flow output) project.f.csv, (Wall surface temperatures, targets and 

sprinklers) project.w.csv 

• smokeview geometry file: project.smv 

• smokeview plot file: project.plt 

• binary output file: project.hi 

Starting a CFAST Calculation 

Running CFAST from CEdit 

Typically, model simulations are run directly from the input editor, CEdit. To run the model, 

either open an existing input data file from the program menus with “File”, “Open,” or create 

a new input data file within CEdit. The model is run by selecting “Run!” and then “Model 

Simulation, CFAST.” 
12 • Chapter 3 Running CFAST User’s Guide Version 6 

This opens a window that shows the progress of the simulation, with information on the 

environment in each compartment of the simulation. Several buttons are also available as 

follows: 

 The close button is disabled while the model is running. Once the simulation is 

complete (stopped by the user with the stop button), the close button closes the window and 

returns to the main input editor. 

 The stop button halts execution of the simulation, but leaves the simulation 

window on the screen. The stop button is available only when the simulation is in progress. 

 Normally, model outputs are displayed and updated only at any of the time 

intervals specified on the environment page. For complex calculations, there may be a 

significant time period between display updates. The update button allows the user to see the 

current state of the calculation at any time. The update button is only available when the 

simulation is in progress. 

Running CFAST from a Command Prompt 

The model CFAST can also be run from a Windows command prompt. CFAST can now be 

run from any folder, and refer to a data file in any other folder. The fires and thermophysical 

properties have to be in either the data folder, or the executable folder. The data folder is 

checked first and then the executable folder. 

[drive1:\][folder1\]cfast [drive2:\][folder2\]project 
User’s Guide Version 6 Chapter 3 Running CFAST • 13 

The project name will have extensions appended as needed (see below). For example, to run 

a test case when the cfast executable is located in c:\nist\cfast6 and the input data file is 

located in c:\data, the following command could be used: 

c:\nist\cfast6\cfast c:\data\testfire0 <<< note there is no extension. 

If the command is entered as \bin\cfast \bin\data\testfire0.in, then CFAST will try to open 

testfire0.in.in 

The database files for thermal properties and fire objects may be located either in the folder 

with the input data file or in the folder with the cfast executable. The model checks first in 

the data file folder and then in the cfast executable folder. If the files do not exist in either 

location, the simulation is not run. By default, names for these files are thermal.csv for the 

thermal properties file and *.o for the fire object files. 

Command line options 

• k - no key board access 

• i - initialization only 

• h - output header 

• c - compact output 

• f - full output (c and f are exclusive). Note the interaction of the f and c option. 

The default for the console output is /c. The default for the file output is /f. This 

default action can be overwritten by explicitly including the /f or /c option. Output 

goes to the screen if the print interval (second entry on the TIMES line) is positive 

and to the output file if the interval is negative. 
14 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

Chapter 4 Setting up the Input 

File for CFAST 

Overview 

CFAST is a computer program that uses an input file and generates one or more output files. 

The first step in performing a calculation is to generate a text input file that provides the 

program with all of the necessary information to describe the scenario under consideration. 

The most important inputs determine the geometry of the compartments in the scenario and 

the connections between these compartments. Next, the fire, detection, and suppression 

characteristics of the scenario are defined. Finally, there are a number of parameters that 

customize the output from the model. Each line of the file contains a keyword label that 

identifies the input, followed by a number of numerical or text inputs corresponding to the 

particular input keyword. A simple input file is shown below. This example is used in the 

discussion of the output in Chapter 5. 

All of the inputs to the model are discussed in this chapter. Following the discussion that 

details each input, their engineering units and default values, notes are included that provided 

additional guidance or frequently addressed problems that may be encountered by the user. 

These notes take the form of a bulleted list such as: 

VERSN,6,Cable tray fire -- base case 

TIMES,1800,120,0,0,30 

EAMB,293.15,101300,0 

TAMB,293.15,101300,0,50 

LIMO2,10 

WIND,0,10,0.16 

COMPA,Compartment 1,9.1,5,4.6,0,0,0,GLASSFB3,CONCRETE,CONCRETE 

HVENT,1,2,1,1,2.4,0,1,0,0,1,1 

OBJECT,bunsen,1,4.55,2.5,0,1,1,0,0,0,1 

OBJECT,Wood_Wall,1,4.55,2.5,0,1,1,0,0,0,1 

TARGET,1,2.2,1.88,2.34,0,0,1,CONCRETE,IMPLICIT,PDE 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 15 

• The inputs may be integers (a simulation time of 1800 s), real numbers (a mass 

loss rate of 0.0082 kg/s), or text (a floor material of CONCRETE), as appropriate. 

The input file is a comma-separated ASCII text file and may be edited with a 

spreadsheet program or any text editor. It is possible to use a word processor but it 

is important to save the file in ASCII text format and not in a word processing 

format. It is worthy to note that some word processors will save punctuation and 

other characters incorrectly for the simple ASCII text file used by CFAST. It is 

recommended that the input files be created with the input editor, CEdit, provided 

as part of the CFAST distribution. In addition to checking the input data for 

errors, it includes recommended limits for input values to assist in appropriate use 

of the model. 

• Each line of input consists of a label followed by one or more alphanumeric 

parameters associated with that input label, separated by commas. The label must 

always begin in the first space of the line and be in capital letters. Following the 

label, the values may start in any column, and all values must be separated by a 

comma. Values may contain decimal points if needed or desired. They are not 

required. 

• Inputs are in standard SI units. The maximum line length is 1024 characters, so 

all data for each keyword must fit in this number of characters. 

The installation program creates a shortcut to the input editor on the Windows start menu 

labeled “CFAST” that points to the input editor. Once started, the user is presented with a 

series of tabbed-pages for the various inputs in a CFAST input data file. 

These tabbed-pages organize the inputs for CFAST simulations into several categories: 

• Simulation Environment includes simulation time, specification of model 

outputs, and ambient conditions. Also included on the page are a constantly 

updated list of errors, warnings, and messages about the input file specification or 

model simulation. 

• Compartment Geometry defines the size, construction characteristics, and 

position of the compartments in a simulation. 

• Horizontal Flow Vents, Vertical Flow Vents, and Mechanical Flow Vents

allows the user to connect compartments with doors and windows, ceiling and 

floor vents, or forced air ventilation systems. 

• Fires include user specification of the initial fire source and any additional 

burning objects in one or more of the compartments of the simulation. 

• Detection / Suppression defines any heat alarms and sprinklers in the 

compartments of the simulation. 
16 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

• Targets provide the ability calculate the temperature and net heat flux to objects 

placed and oriented arbitrarily in the structure. 

• Surface Connections allows for more detailed description of the connections 

between compartments in the simulation to better simulate the transfer of heat 

from compartment to compartment in the simulation. 

Each of these tabbed-pages is described in more detail below. In addition, a series of menus 

allow the user to open and save files; run the simulation, or access help and program 

information. 

Simulation Environment 

The Simulation Environment page defines the initial conditions and simulation time for the 

CFAST input file. 

Naming the Calculation, the Title Input 

The first thing to do when setting up an input file is to give the simulation a title. The first 

line in the CFAST input data file must be the CFAST version identification along with an 

optional short title for the simulation. This is a required input. The title command is the line 

that CFAST keys on to determine whether it has a correct data file. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 17 

Title: The title is optional and may consist of letters, numbers, and/or symbols and may be 

up to 50 characters. It permits the user to label each run. 

Setting Time Limits and Output Options 

A TIMES line specifies the length of time over which the simulation takes place and how 

often output will be generated. This is a required input. There are one to four entries in this 

line 

Simulation Time (default units: s, default value, 900 s): The length of time over which the 

simulation takes place. This is a required input which should be entered even if all 

other fields are not included. The maximum value for this input is 86400 s (1 day). 

Text Output Interval (default units: s, default value, 50 s): The print interval is the time 

interval between each printing of the output values. If omitted or less than or equal to 

zero, no output values will occur. 

Binary Output Interval (default units: s, default value: no output): CFAST can store all of 

the results of the model simulation in a binary-formatted file which can be saved for 

later analysis or output using utility programs that come with the CFAST software. 

This input defines the time interval between outputs of the model results in binary 

format. 

Spreadsheet Output Interval (default units: s, default value, 10 s): CFAST can output a 

subset of the results of the model simulation in a comma-delimited alphanumeric 

format which can be read by most spreadsheet software. This is designed to be 

imported into a spreadsheet for further analysis or graphing of the results of the 

simulation. This input defines the time interval between outputs of the model results 

in a spreadsheet-compatible format. A value greater than zero must be used if the 

spreadsheet file is to be used. 
18 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

Smokeview Output Interval (default units: s, default value: 10 s): CFAST can output a 

subset of the results in a format compatible with the visualization program 

smokeview. This input defines the time interval between outputs of the model results 

in a smokeview-compatible format. A value greater than zero must be used if the 

spreadsheet output is desired. 

In addition to the input data file created specifically for a CFAST simulation, there are a 

number files that CFAST uses to define default values and other input information, and to 

output the results of the simulation for later analysis. They include 1) a thermal properties 

file, 2) files of predefined fire objects, 3) a binary history file, and 4) a spreadsheetcompatible output file. 

The thermal properties file contains material properties for compartment surfaces, target 

objects that may be placed in compartments in the simulation to monitor surface temperature 

and heat flux to the objects, and fire objects, in addition to the main fire in the simulation that 

may ignite based on their surface temperature or incident flux onto the surface of the object. 

The predefined fire objects files contain definitions for a number of reference fires from the 

literature or developed by the user that may be included in a simulation. The thermal 

properties and fire objects files may be modified by the user. Details of the files are included 

in the appendices. There are default files included in the CFAST distribution. 

Thermal Properties File: The name specifies a file from which the program reads data for 

names specified in the compartment, target, and object fire specifications. The default 

name is thermal.csv which is included with the CFAST distribution. The format of 

this file is detailed in the appendix. 

Ambient Conditions 

Ambient conditions define the environment at which the scenario begins. This allows the 

user to specify the temperature, pressure, and station elevation of the ambient atmosphere, as 

well as the absolute wind pressure to which the structure is subjected. Pressure interior to a 

structure is calculated simply as a lapse rate (related to the height above sea level) based on 

the NOAA/NASA tables8

. This modification is applied to the vents which connect to the 

exterior ambient. The calculated pressure change is modified by the wind coefficient for 

each vent. This coefficient, which can vary from -1.0 to +1.0, nominally from -0.8 to +0.8, 

determines whether the vent is facing away from or into the wind. The pressure change is 

multiplied by the vent wind coefficient and added to the external ambient for each vent 

which is connected to the outside. There is an ambient for the interior and for the exterior of 

the structure. Three keywords define the ambient conditions: TAMB for the interior of the 

structure, EAMB for the exterior of the structure is EAMB, and WIND for the wind 

information. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 19 

Ambient Temperature (default units: K, default value: 293.15 K): Initial ambient 

temperature inside (for TAMB) or outside (For EAMB) the structure at the station 

elevation. 

Ambient Pressure (default units: Pa, default value: 101300 Pa): Initial values for ambient 

atmospheric pressure inside (for TAMB) and outside (for EAMB) the structure at the 

station elevation. Default value is standard atmospheric pressure at sea level (0 m 

elevation) of 101.3 kPa. Input units are in Pa. These values define standard conditions 

as defined in Standard Atmosphere as noted in the Handbook of Chemistry and 

Physics9

 . There is a set of numerical approximations in the CFAST code which 

duplicate the pressure/temperature/altitude relationships in the handbook. 

Elevation (defaults units: m, default value: 0 m): The height where the ambient pressure and 

temperature were specified. This is the reference datum for calculating the density of 

the atmosphere as well as the temperature and pressure inside and outside of the 

structure as a function of height. 

Relative humidity (default units % RH, default value: 50 %): The initial relative humidity in 

the system, only specified for the interior with the TAMB command. This is 

converted to kilograms of water per cubic meter. 

The wind speed, scale height, and power law are used to calculate the wind coefficient for 

each vent connected to the outside. The wind velocity is specified at some reference height. 

The power law then provides a lapse rate for the wind speed. An assumption is that the wind 

speed is zero at the surface. The formula used to calculate the wind speed at the height of 

any vent is show below. The wind is applied to each external opening as a change in 

pressure outside of the vent. 

Wind Speed (default units: m/s, default value 0 m/s): Wind speed at the reference elevation. 
20 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

Scale Height: (default units: m, default value: 0 m)): Reference height at which the reference 

wind speed is measured. 

Power Law Coefficient (default units: dimensionless, default value 0.16): The power law 

used to calculate the wind speed as a function of height. Default value is 0.16. Using 

the notation that VW, is the wind speed at the reference height HW, and PW is the 

power law, the exterior pressure is modified by 2 δP = CW ρV and ( )

PW V = VW Hi HW

where Hi is the position of the vent1. 

• In order to see the effect of wind, the corresponding parameter for the ventilation 

keyword must be specified. The default for the wind vector is 0, which turns off 

wind effects. Please see the HVENT command, below. 

• The choice for station elevation, temperature and pressure must be consistent. 

Outside of that limitation, the choice is arbitrary. It is often convenient to choose 

the base of a structure to be at zero height and then reference the height of the 

structure with respect to that height. The temperature and pressure must then be 

measured at that position. Another possible choice would be the pressure and 

temperature at sea level, with the structure elevations then given with respect to 

mean sea level. This is also acceptable, but somewhat more tedious in specifying 

the construction of a structure. Either of these choices works though, so long as 

they are consistent. Usually, the station elevation is set to zero and the pressure to 

ambient. The effect of changing these values is small for small changes. There 

will be an effect for places at altitude such as Denver, Colorado, but even there 

the effect is not pronounced. Note that the equations implemented in the model 

are not designed to handle negative elevations and altitudes. It is suggested that 

the defaults be used. 

• These three parameters are optional. If they are not included in the input file, 

default values are used. 

Compartment Geometry 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 21 

The Compartment Geometry page defines the size, position, materials of construction, and 

flow characteristics for the compartments in the simulation. Initially, only the simulation 

environment page and the “Add” button on the compartment geometry page is enabled; all 

other pages are not available to the user for detailed inputs until a compartment has been 

added to the simulation. 

Most of the tabbed pages in the program are of similar design, with a summary of the defined 

items in table form at the top of the page, a series of buttons to add, remove, or modify the 

item highlighted in the summary table, and a number of individual inputs below which 

details all of the inputs for the item selected in the summary table. The buttons included on 

the compartment geometry page are as follows: 

Use the Add button to create a new compartment with default values for all 

entries. 

Use the Duplicate button to create a copy of the compartment currently selected 

in the summary table at the top of the page. The new compartment is added to the end 

of the list with the named changed to indicate it is a copy of the selected item. 

Use the Move Up and Move Down buttons to change the order of the 

list of compartments in the summary table. This simply changes the automatically 

assigned compartment numbers for the compartments. Compartments can be ordered 

as desired. 
22 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

Use the Remove button to delete the selected compartment from the list of 

compartments in the summary table. Other compartments are renumbered once the 

compartment is deleted. 

Compartment Name: Compartments are identified by a unique alphanumeric name. This 

may be a simple as a single character or number, or a description of the compartment. 

Defining Compartment Size and Position 

In order to model a fire scenario, the size and elevation of each compartment in the structure 

must be specified. For a compartment, the width, depth, compartment height and height of 

the floor of the compartment provide this specification. The maximum number of 

compartments for version 6 is thirty. The usual assumption is that compartments are 

rectangular parallelepipeds. However, the CFAST model can accommodate odd shapes as 

equivalent floor area parallelepipeds or with a cross-sectional area that varies with height. 

At least one compartment must be specified in the input file. There are no defaults for 

compartment size. There are defaults for absolute positioning (0,0,0). The fully mixed (single 

zone) and corridor models are turned off by default. 

Compartments in CFAST are most 

typically defined by a width, depth, and 

height. If desired, the user can prescribe 

the cross-sectional area of the compartment 

as a function of height from floor to ceiling 

for other shapes. The absolute position of 

the compartment with respect to a single 

structure reference point can be defined to 

ease visualization or to allow exact 

placement of vents and surfaces relative to 

other compartments in a detailed 

calculation. This specification is important 

for utilizing the corridor flow algorithm 

with the HALL command and for positioning the compartments for visualization in 

SMOKEVIEW. 

The relevant CFAST keywords are COMPA to define the compartment size and materials, 

HALL or ONEZ to define flow characteristics in the compartment, and ROOMA / ROOMH 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 23 

to define a variable cross-sectional area for the compartment. The COMPA command is 

required for each compartment as a basic definition for the compartment, even if there are 

subsequent modifications by the HALL, ONEZ, ROOMA, or ROOMH keywords which 

follow. Details of the CFAST keywords are included in the appendix. 

Width: specifies the width of the compartment as measured on the X axis from the origin 

(0,0,0) of the compartment. 

Depth: specifies the depth of the compartment as measured on the Y axis from the origin 

(0,0,0) of the compartment. 

Height: specifies the height of the compartment as measured on the Z axis from the origin 

(0,0,0) of the compartment. 

Absolute Width Position: specifies the 

absolute x coordinate of the lower, 

left, front corner of the room. 

Absolute Depth Position: specifies the 

absolute y coordinate of the lower, 

left, front corner of the room. 

Absolute Floor Height: specifies the 

height of the floor of each 

compartment with respect to station 

elevation specified by the internal 

ambient conditions reference height 

parameter. The reference point 

must be the same for all elevations in the input data. For example, the two rooms in 

the example would be located at (0,0,0) and (0,2,2.3). 

Modeling the Compartment as a Tall Shaft or Long Corridor 

For tall compartments or those removed from the room of fire origin, the compartment may 

be modeled as a single, well-mixed zone rather than the default two-zone assumption. A 

single zone approximation is appropriate for smoke flow far from a fire source, where the 

two-zone layer stratification is less pronounced than in compartments near the fire. This is 

used in situations where the stratification does not occur. Examples are elevators, shafts, 

complex stairwells, and compartments far from the fire. 
24 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

For long hallways or corridors, there can be a significant delay time for the initial hot gas 

layer to travel along the ceiling to the far end of the compartment. By estimating the time 

required for a ceiling jet to travel in a corridor and the temperature distribution along the 

corridor, CFAST can delay flow into compartments connected to corridors until the ceiling 

jet has passed the connections to these compartments. 

50 % Decay Velocity: ceiling jet velocity at the distance from the reference point where the 

temperature falls off by 50 %. Default velocity and depth are calculated by the 

program based on the vent size, flow and layer thickness in the horizontal vent from 

which flow first enters the hallway, and on the width of the hallway1

. 

50 % Decay Depth: ceiling jet depth at the distance from the reference point where the 

temperature falls off by 50 %. 

50 % Decay Distance: distance from the reference point where the temperature falls off by 

50 %. 

• Since the algorithm depends on the flow into the hallway to determine default 

ceiling jet velocity and depth, the main fire compartment should not be specified 

as a hallway. In the main fire compartment, a stable layer will build before flow 

into the compartment through horizontal vents. 

• The zone model concept best applies for an enclosure in which the width and 

length are not too different. If the horizontal dimensions of the room differ too 

much (i.e., the room looks like a corridor), the flow pattern in the room may 

become asymmetrical. If the enclosure is too shallow, the temperature may have 

significant radial differences. The width of the plume may at some height become 

equal to the width of the room and the model assumptions may fail in a tall and 

narrow enclosure. Therefore, the user should recognize approximate limits on the 

ratio of the length (L), width (W), and height (H) of the compartment. 

• If the aspect ratio (length/width) is greater than about 10, the corridor flow 

algorithm should be used. This provides the appropriate filling time. Similarly, for 

tall shafts (elevators and stairways), a single zone approximation is more 

appropriate and the shaft option should be used. It was found experimentally that 

the mixing between a plume and lower layer due to the interaction with the walls 

of the shaft caused complete mixing. This is the flip side of the corridor problem 

and occurs at a ratio of the height to characteristic floor length of about 10. The 

following quantitative limits are recommended: 

Group Acceptable Special 

consideration 

required 

Corridor flow 

or shaft 

algorithm 

(L/W)max L/W<3 3<L/W<5 L/W>5 

(L/H)max L/H<3 3<L/H<6 L/H>6 

(W/H)min W/H>0.4 0.2<W/H<0.4 W/H<0.2 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 25 

Thermal Properties of Boundaries 

To calculate heat loss through the ceiling, walls, and floor of a compartment, the properties 

of the bounding surfaces must be known. This includes the thermophysical properties of the 

surfaces and the arrangement of adjacent compartments if calculation of intercompartment 

heat transfer is to be calculated. 

The thermophysical properties of the surfaces which define compartments are described by 

specifying the thermal conductivity, specific heat, emissivity, density, and thickness of the 

enclosing surfaces for each material and then assigning the material to the ceiling, walls, and 

floor of a compartment. Currently, thermal properties for materials are read from a thermal 

data file unique to CFAST. The thermophysical properties are specified at one condition of 

temperature, humidity, etc. There can be as many as three layers per boundary, but they are 

specified in the thermal database itself. (See the explanation in the section on auxiliary files 

for additional details.) 

The default name for the thermal properties database is thermal.csv. Another name can be 

used using the keyword THRMF in the input data file for the scenario of interest. This 

thermal data file is also used for targets and other objects 

The bounding surfaces are the ceilings, walls and floors that define a compartment. These are 

referred to as thermophysical boundaries, since each participates in conduction and radiation 

as well as defining the compartments, unless these phenomena are explicitly turned off. 

Ceiling Material (default value: Gypsum Board): material name from the thermal properties 

data file used for the ceiling surface of the compartment. 

Wall Material (default value: Gypsum Board): material name from the thermal properties 

data file used for the wall surfaces of the compartment. 

Floor Material (default value: Off): material name from the thermal properties data file used 

for the floor surface of the compartment. 

• If the thermophysical properties of the enclosing surfaces are not included, 

CFAST will treat them as adiabatic (no heat transfer). 

• If a name is used which is not in the database, the model should stop with an error 

message. The keyword in the data file simply gives a name (such as CONCRETE) 
26 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

which refers to the properties for that material in the thermal data file (see section 

4.2.3 and Appendix A for details on the thermophysical database). 

• Since most of the heat conduction is through the ceiling, and since the conduction 

calculation takes a significant fraction of the computation time, it is recommended 

that initial calculations be made using the ceiling only. Adding the walls 

generally has a small effect on the results, and the floor contribution is usually 

negligible. Clearly, there are cases where the above generalization does not hold, 

but it may prove to be a useful screening technique. A caveat in including floor 

properties is that the set of equations describing heat transfer becomes difficult to 

solve once the thermal wave from the compartments reaches the unexposed side 

of a floor. The back surfaces of compartments are assumed to be exposed to 

ambient conditions unless specifically specified (see the section on Intercompartment Heat Transfer (Conduction)) to specify heat transfer connections 

between compartments). 

Compartment Connections 

Flow through vents can be natural flow through doors, windows, or openings in ceilings and 

floors; or forced flow in a mechanical ventilation system. Natural flow comes in two 

varieties. The first is referred to as horizontal flow. It is the flow which is normally thought 

of in discussing fires. It encompasses flow through doors, windows and so on. The other is 

vertical flow and can occur if there is a hole in the ceiling or floor of a compartment. This 

latter phenomena is useful in some scenarios such as in a ship where openings in floors and 

ceilings through scuttles are common and in buildings with manual or automatic heat and 

smoke venting. 

Flow through normal vents is governed by the pressure difference across a vent. There are 

two situations which give rise to flow through vents. The first is flow of air or smoke driven 

from a compartment by buoyancy. The second type of flow is due to expansion which is 

particularly important when conditions in the fire environment are changing rapidly. Rather 

than depending entirely on density differences between the two gases, the flow is forced by 

volumetric expansion. 

In addition to natural flow, forced flow from mechanical ventilation can affect a fire as well. 

More important than affecting the fire, however, is the dispersal of the smoke and toxic gases 

from the fire to adjacent spaces, if ventilation continues to operate after a fire starts. 

Atmospheric pressure is about 100 000 Pa. Fires produce pressure changes from 1 Pa to 1000 

Pa and mechanical ventilation systems typically involve pressure differentials of about 1 Pa 

to 100 Pa. In order to address pressure-induced flow, pressure differences of about 0.1 Pa 

out of 100 000 Pa for the overall problem or 10-4 Pa for adjacent compartments must be 

tracked. 

The keywords which describe the various flow regimes are: 

• Windows and doors (horizontal flow through vertical vents): HVENT, specifies 

vent which connect compartments horizontally 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 27 

• Holes in a ceiling/floor (vertical flow through horizontal vents: VVENT, specifies 

a vent which connects compartments vertically 

• HVAC specification: MVENT specifies a vent which connects compartments 

with a forced flow 

For all three types of vents the size of the vent opening (expressed as a fraction of the 

original opening) may be changed: 

• EVENT change the opening fraction of the specified vent at a chosen time. 

Each of these commands is discussed in the sections that follow. 

Defining Horizontal Natural Flow Connections (Doors, Windows) 

Horizontal flow connections may include doors between compartments or to the outdoors as 

well as windows in the compartments. These specifications do not necessarily correspond to 

physically connecting the walls between specified compartments. Rather, lack of an opening 

simply prevents flow between the compartments. Horizontal flow connections may also be 

used to account for leakage between compartments or to the outdoors. 

Horizontal connections can only be created between compartments that physically overlap in 

elevation at some point. These may include doors between compartments or windows in the 

compartments (between compartments or to the outdoors). Openings to the outside are 

included as openings to a compartment with a number one greater than the number of 

compartments described in the geometry section. The relevant CFAST keyword is HVENT. 

Details of the CFAST keywords are included in the appendix. 
28 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

Most of the tabbed pages in the program are of similar design, with a summary of the defined 

items in table form at the top of the page, a series of buttons to add, remove, or modify the 

item highlighted in the summary table, and a number of individual inputs below which 

details all of the inputs for the item selected in the summary table. The buttons included on 

the horizontal flow vents page are as follows. 

Use the Add button to create a new horizontal flow vent with default values for 

all entries. 

Use the Duplicate button to create a copy of the horizontal flow vent currently 

selected in the summary table at the top of the page. The new vent is added to the end 

of the list with the named changed to indicate it is a copy of the selected item. 

Use the Move Up and Move Down buttons to change the order of the 

list of horizontal flow vents in the summary table. This simply changes the 

automatically assigned vent numbers for the vents. Vents can be ordered as desired. 

Use the Remove button to delete the selected horizontal flow vent from the list of 

horizontal flow vents in the summary table. Other vents are renumbered once the 

compartment is deleted.
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 29 

First Compartment: First of the two compartments to be connected by a horizontal flow 

vent. Compartments are numbered automatically by the input editor and by the 

model in the order they are read from the input data file and/or the order they appear 

in the summary table on the compartment geometry page. Compartment numbers 

begin with 1, so the first compartment is number 1, the second 2, and so forth. 

Second Compartment: Second of the two compartments to be connected by a horizontal 

flow vent. Compartments are numbered automatically by the input editor and by the 

model in the order they are read from the input data file and/or the order they appear 

in the summary table on the compartment geometry page. Compartment numbers 

begin with 1, so the first compartment is number 1, the second 2, and so forth. 

Vent Number: It is possible to define a total of 25 horizontal flow connections between any 

pair of compartments. A number from 1 to 25 uniquely identifies the connection. 

Normally, this number is automatically assigned by the input editor based on the 

order they appear in the summary table on the horizontal flow vents page. 

Sill (default units: m, default value: none): Sill height is the height of the bottom of the 

opening relative to the floor of the compartment selected as the first compartment. 

Soffit (default units: m, default value: none): Position of the top of the opening relative to the 

floor of the compartment selected as the first compartment. 

Width (default units: m, default value: none): The width of the opening. 

Horizontal flow vents may be opened or closed during the fire. The relevant CFAST 

keyword is EVENT. The initial format of EVENT is similar to HVENT specifying the 

connecting compartments and vent number. Each EVENT line in the input file details the 

open/close time dependent characteristics for one horizontal flow vent by specifying a 

fractional value and a time. The default is 1.0 which is a fully open vent. A value of 0.5 

would specify a vent which is halfway open. 

Initial Opening Fraction: Flow through horizontal vents is calculated based on the area of 

the vent. Normally, the vent is fully open. If desired, the user may specify a fraction 

between 0 and 1 that allows the vent to be partially or fully closed at the beginning of 

the simulation. In the model calculation, the vent width is multiplied by this fraction. 

The opening fraction may be changed at any time in the simulation through the use of 

the EVENT command. 

Change Opening Fraction At Time: Time during the simulation at which to change the 

opening fraction. 

Final Opening Fraction: for horizontal flow vents, the fraction specifies the fractional width 

opening of the vent. Fractional values must be between 0 and 1. 

Wind: The wind coefficient is the cosine of the angle between the wind vector and the vent 

opening. This applies only to vents which connect to the outside. The range of 

values is -1.0 to 1.0 with a default value of zero. In the input editor, this is specified 

as the angle between the face of the vent and the wind direction. 
30 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

There are also two parameters which are used to locate the compartments relative to each 

other. These are used to incorporate additional three dimensional information of the relative 

location of the vents with respect to each other. In the compartment view of CFAST, the 

orientation is that the rotation/translation point of the compartment is the back/bottom/left. In 

this view, both parameters would be with respect to the left hand side of the respective 

compartments. This allows the corridor filling model to incorporate a delay time for filling 

based on the separation between the vents. These parameters are needed only if the HALL 

command is used. 

First Compartment Offset: Horizontal distance between the centerline of this vent and the 

reference point in the first compartment. 

Second Compartment Offset: Horizontal distance between the centerline of this vent and 

the reference point in the second compartment. 

• The soffit and sill specifications are with respect to the first compartment 

specified and is not necessarily symmetric since the elevation of the second 

compartment may be different than the first. Reversing the order of the 

compartment designations does make a difference. 

Defining Vertical Natural Flow Connections (Ceiling or Floor Holes, 

Hatches) 

This section of the input data file describes these vertical flow openings. Examples of these 

openings are scuddles in a ship, or a hole in the roof of a residence. Combined buoyancy- and 

pressure-driven (i.e., forced) flow through a vertical flow vent is possible when the connected 

spaces adjacent to the vent are filled with gases of different density in an unstable 

configuration, with the density of the top space larger than that of the bottom space. With a 

moderate cross-vent pressure difference, the instability leads to a bi-directional flow between 

the two spaces. For relatively large cross-vent pressure difference the flow through the vent 

is unidirectional, from the high- to the low-pressure space. 

Connections can exist between compartments or between a compartment and the outdoors. 

Openings to the outside are included as openings to a compartment with a number one 

greater than the number of compartments defined in the scenario. These connections are 

described by the VVENT keyword. Each VVENT line in the input file describes one vertical 

vent. There are four parameters which include each of the connected compartments, the 

shape of the opening, and the effective area of the vent. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 31 

Most of the tabbed pages in the program are of similar design, with a summary of the defined 

items in table form at the top of the page, a series of buttons to add, remove, or modify the 

item highlighted in the summary table, and a number of individual inputs below which 

details all of the inputs for the item selected in the summary table. The buttons included on 

the vertical flow vents page are as follows. 

Use the Add button to create a new vertical flow vent with default values for all 

entries. 

Use the Duplicate button to create a copy of the vertical flow vent currently 

selected in the summary table at the top of the page. The new vent is added to the end 

of the list with the named changed to indicate it is a copy of the selected item. 

Use the Remove button to delete the selected vertical flow vent from the list of 

vertical flow vents in the summary table. Other vents are renumbered once the 

compartment is deleted.

Top Compartment: The top or first of the two compartments to be connected by a vertical 

flow vent. The vent is through the floor of this compartment. Compartments are 

numbered automatically by the input editor and by the model in the order that they 
32 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

are read from the input data file and/or the order they appear in the summary table on 

the compartment geometry page. Compartment numbers begin with 1, so the first 

compartment is number 1, the second 2, and so forth. 

Bottom Compartment: The bottom or second of the two compartments to be connected by a 

horizontal flow vent. The vent is through the ceiling of this compartment. 

Compartments are numbered automatically by the input editor and by the model in 

the order they are read from the input data file and/or the order they appear in the 

summary table on the compartment geometry page. Compartment numbers begin 

with 1, so the first compartment is number 1, the second 2, and so forth. 

Cross-sectional Area (default units: m2, default value: none): specifies the cross-sectional 

area of the vent connecting the two compartments. 

Shape: The shape factor is 1 for circular openings and 2 for square openings. 

Initial Opening Fraction: Flow through vertical vents is calculated based on the area of the 

vent. Normally, the vent is fully open. If desired, the user may specify a fraction 

between 0 and 1 that allows the vent to be partially or fully closed at the beginning of 

the simulation. In the model calculation, the vent area is multiplied by this fraction. 

The opening fraction may be changed at any time in the simulation through the use of 

the EVENT command. 

Change Opening Fraction At Time (default units: s, default value: none): Time during the 

simulation at which to change the opening fraction. 

Final Opening Fraction: for vertical flow vents, the fraction specifies the fractional crosssectional area of the vent. Fractional values must be between 0 and 1. 

• Although obvious, note that the top or first compartment must be the 

compartment on top of the bottom or second compartment. 

• Vertical connections can only be created between compartments that could be 

physically stacked based on specified floor and ceiling elevations for the 

compartments. Some overlap between the absolute floor height of one 

compartment and the absolute ceiling height of another compartment is allowed. 

However, whether the compartments are stacked or overlap somewhat, the 

ceiling/floor absolute elevations must be within 0.01 m of each other. The check 

is not done when the connection is to the outside. 

Defining Mechanical Ventilation Connections 

Fan-duct systems are commonly used in buildings for heating, ventilation, air conditioning, 

pressurization, and exhaust. Generally, systems that maintain comfortable conditions have 

either one or two fans. Residences often have a systems with a single fan. Further 

information about these systems is presented in Klote and Milke10 and the American Society 

of Heating, Refrigerating and Air Conditioning Engineers11. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 33 

The model for mechanical ventilation used in CFAST is based on the theory of networks and 

is based on the model developed by Klote12 This is a simplified form of Kirchoff's law 

which says that flow into a node must be balanced by flow out of the node. The equations 

used describe the relationship between the pressure drop across a duct, the resistance of a 

duct, and the mass flow. The pressure can be changed by conditions in a compartment, or a 

fan in line in the duct system. Resistance arises from the finite size of ducts, roughness on 

duct surfaces, bends and joints. In CFAST, default values are used for the duct properties, 

and thus mechanical ventilation connections are simply described by the connections to the 

two compartments and a fan whose throughput is a constant volumetric flow up to a userspecified pressure drop across the fan, dropping to zero at high backwards pressure on the 

fan. 

Most of the tabbed pages in the program are of similar design, with a summary of the defined 

items in table form at the top of the page, a series of buttons to add, remove, or modify the 

item highlighted in the summary table, and a number of individual inputs below which 

details all of the inputs for the item selected in the summary table. The buttons included on 

the mechanical flow vents page are as follows. 

Use the Add button to create a new mechanical flow vent with default values for 

all entries. 
34 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

Use the Duplicate button to create a copy of the mechanical flow vent currently 

selected in the summary table at the top of the page. The new vent is added to the end 

of the list with the named changed to indicate it is a copy of the selected item. 

Use the Remove button to delete the selected mechanical flow vent from the list 

of mechanical flow vents in the summary table. Other vents are renumbered once the 

compartment is deleted.

From Compartment: The first compartment to which the mechanical ventilation system 

diffuser is connected. Fan flow is from this compartment. Compartments are 

numbered automatically by the input editor and by the model in the order they are 

read from the input data file and/or the order they appear in the summary table on the 

compartment geometry page. Compartment numbers begin with 1, so the first 

compartment is number 1, the second 2, and so forth. 

From Compartment Area (default units: m2

, default value: none): Cross-sectional area of 

the opening into the compartment. The area will be truncated if the midpoint (height) 

is set such that the height plus or minus the effective length is above the compartment 

ceiling or below the floor. 

From Compartment Height (default units: m, default value: none): Height of the duct 

opening above the floor of the compartment measured from the midpoint of the 

register. 

From Compartment Orientation: The orientation of the diffuser relative to the floor of the 

compartment. A horizontal diffuser implies vertical flow through the ceiling or floor 

of the compartment. A vertical diffuser implies horizontal flow through a wall of the 

compartment. 

To Compartment: The bottom or second of the two compartments to be connected by a 

horizontal flow vent. The vent is through the ceiling of this compartment. 

Compartments are numbered automatically by the input editor and by the model in 

the order they are read from the input data file and/or the order they appear in the 

summary table on the compartment geometry page. Compartment numbers begin 

with 1, so the first compartment is number 1, the second 2, and so forth. 

To Compartment Area (default units: m2

, default value: none): Cross-sectional area of the 

opening into the compartment. The area will be truncated if the midpoint (height) is 

set such that the height plus or minus the effective length is above the compartment 

ceiling or below the floor. 

To Compartment Height (default units: m, default value: none): Height of the duct opening 

above the floor of the compartment measured from the midpoint of the register. 

To Compartment Orientation: The orientation of the diffuser relative to the floor of the 

compartment. A horizontal diffuser implies vertical flow through the ceiling or floor 

of the compartment. A vertical diffuser implies horizontal flow through a wall of the 

compartment. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 35 

Flow Rate (default units: m3/s, default value: none): Constant flow rate of the forced-air flow 

from the first compartment to the second compartment. 

Begin Drop Off Pressure (default units: Pa, default value: 200 Pa): The description of the 

fan includes a drop off in flow beginning at a pressure specified by the user. Above 

this pressure drop, the flow gradually drops to zero flow. 

Zero Flow Pressure (default units: Pa, default value: 300 Pa): Specifies the pressure above 

which the flow through the mechanical ventilation connection is zero. 

Initial Opening Fraction: Flow through mechanical vents is calculated based on the area of 

the vent. Normally, the vent is fully open. If desired, the user may specify a fraction 

between 0 and 1 that allows the vent to be partially or fully closed at the beginning of 

the simulation. In the model calculation, the fan flow rate is multiplied by this 

fraction. The opening fraction may be changed at any time in the simulation through 

the use of the EVENT command. 

Change Opening Fraction At Time (default units: s, default value: none): Time during the 

simulation at which to change the opening fraction. 

Final Opening Fraction: for mechanical flow vents, the fraction specifies the fractional fan 

flow rate for the vent. Fractional values must be between 0 and 1. 

• CFAST does not include provisions for reverse flow through a fan. Calibrations 

for backward flow are not provided by fan manufacturers and the equations 

incorporated in CFAST do not allow for such flow. The problem is simply that in 

this flow regime, the fan has stalled, and will soon fail. 

Prescribing Fires 

A simulated fire in CFAST is implemented as a source of fuel mass which is released at a 

prescribed rate (the pyrolysis rate). Energy is released by the fuel and combustion products 

are created as it burns. The model incorporates two distinct types of fires: heat source and 

constrained. In the heat source specification, the fire simply energy at a rate prescribed by 

the user; no calculation or tracking of products of combustion is included. In the constrained 

fire, species production is calculated based on production yields prescribed by the user. In 

addition, for the constrained fire, the pyrolysis rate and resulting energy and species 

generation may be limited by the oxygen available for combustion. When sufficient oxygen 

is available for combustion, the heat release rate for the constrained fire is the same as for the 

unconstrained fire. 

The model can simulate multiple fires in one or more compartments of the building. These 

fires are treated as totally separate entities, with no interaction of the plumes. These fires are 

generally referred to as “objects” and can be ignited at a prescribed time, temperature or heat 

flux. 

CFAST does not include a pyrolysis model to predict fire growth. Rather, pyrolysis rates for 

each fire are prescribed by the user. While this approach does not directly account for 
36 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

increased pyrolysis due to radiative feedback from the flame or compartment, in theory these 

effects could be prescribed by the user as described in this section. In an actual fire, this is an 

important consideration, and the specification used should consider the experimental 

conditions as closely as possible. 

Unconstrained Fire

An unconstrained fire releases energy based on the pyrolysis rate of the fuel. This type of fire 

is applicable to fuels for which there is always sufficient oxygen in the fuel for combustion to 

take place and when the concentrations of products of combustion are not of interest. 

Constrained Fire 

A constrained fire releases energy based on the pyrolysis of fuel, but may be constrained by 

the oxygen available for combustion depending on the compartment conditions. Complete 

burning will take place only where there is sufficient oxygen. When insufficient oxygen is 

entrained into the fire plume, unburned fuel will be transported from zone to zone until there 

is sufficient oxygen and a high enough temperature to support combustion. In general, 

CFAST uses a simple definition of a combustion reaction that includes major products of 

combustion for hydrocarbon fuels: 

where the coefficients m1, m2, etc. represent appropriate molar ratios for a stoichiometric 

balance of the equation. For complete combustion of the simplest hydrocarbon fuel, methane 

reacts with oxygen to form carbon dioxide and water. The only input required is the pyrolysis 

rate and the heat of combustion. For fuels that contain oxygen, nitrogen, or chlorine, the 

reaction becomes more complex. In this case, production yields for the species are prescribed 

by the user. Stoichiometry is used to insure conservation of mass and elements in the 

reaction. The species which are calculated are oxygen, carbon dioxide, carbon monoxide, 

water, total unburned hydrocarbons (tuhc), and soot. Gaseous nitrogen is included, but only 

acts as a diluent. Production of hydrogen cyanide and hydrogen chloride are tracked solely 

based on user prescribed yields. 

The heat release rate for a constrained fire may be reduced below its prescribed value based 

upon the oxygen available for combustion. For the constrained fire, the burning rate may be 

less than the pyrolysis rate and cannot be simplified as in the case of the unconstrained fire. 

As fuel and oxygen are consumed, heat is released and various products of combustion are 

formed. 

Constraint on the Fire by Limiting Combustion by Available Oxygen (LOI) 

For a constrained fire, the heat release rate is limited by available oxygen. This limit is 

applied in three places: The first is burning in the portion of the plume which is in the lower 

layer of the room of fire origin; the second is the portion of the plume in the upper layer, also 

in the room of origin; the third is in the vent flow which entrains air from a lower layer into 

an upper layer in an adjacent compartment. The unburned hydrocarbons are tracked in this 

( )

m HCN m N soot total unburned hydrocarbo ns heat

C H O N Cl m O N m CO m CO m H O m HCl n o p q r

+ + + + +

+ + → + + +

3.76 ( )

3.76

6 1 2

1 2 2 2 2 3 4 2 5
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 37 

model. Combustion of CO to CO2 is not included in the model. Actual combustion chemistry 

is not considered in CFAST due to the complexities associated with detailed kinetics and 

transport. 

Visibility 

There are two calculations involving radiation in this model. One is for energy balance and is 

based on broadband radiation absorption. The amount of radiation absorbed in sensitive to 

the species present, specifically water vapor, soot and carbon dioxide. 

The other is for visibility of egress signs. This calculation is based solely on the soot 

concentration and is reported as optical depth (per meter). The conversion factor is based on 

the recent work by Mulholland and Croarkin13. The value for converting mass density in 

kg/m3 to optical depth is 3817 m2/kg. The value reported is intended specifically for 

assessing the visibility of egress signs, based on the work of Jin14. It is not applicable to the 

far blue or red regions of the spectrum and so should not be used for assessing optical 

detection of fires through smoke. 

Since chemical species are tracked only for a constrained fire, the optical depth for an 

unconstrained fire is fixed at 0.5 m-1 for the upper layer and 0.05 m-1 for the lower layer. 

Most of the tabbed pages in the program are of similar design, with a summary of the defined 

items in table form at the top of the page, a series of buttons to add, remove, or modify the 

item highlighted in the summary table, and a number of individual inputs below which 
38 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

details all of the inputs for the item selected in the summary table. The buttons included on 

the fires page are as follows. 

Use the Add button to create a new fire with default values for all entries. 

Use the Duplicate button to create a copy of the fire currently selected in the 

summary table at the top of the page. The new fire is added to the end of the list with 

the named changed to indicate it is a copy of the selected item. 

Use the Remove button to delete the selected fire from the list of mechanical 

flow vents in the summary table. Other vents are renumbered once the compartment 

is deleted.

Defining Fire Objects 

Fires in CFAST are defined as a series of individual fire objects which are then placed as 

desired in compartments in a simulation. 

Each fire object defines the time dependent variables of the fire are described by the mass 

loss rate, rate of heat release, fuel height, and fuel area inputs. Species production rates are 

specified in a manner similar to the fire, entering the rates as a series of points with respect to 

time. The species which are followed by CFAST are: carbon dioxide, carbon monoxide, 

hydrogen cyanide, hydrogen chloride, nitrogen, oxygen, soot, total unburned hydrocarbons 

and water. There is a separate calculation of the concentration-time product Ct. 

Each fire object is defined in a separate comma-separated spreadsheet file with an extension 

of “.o”. As many fire objects as desired may be defined by the user. One special fire object is 

named “mainfire.o” as is assumed to be a main fire source for the scenario, if included. The 

only difference between the main fire and other object fire is that the main fire is assumed to 

ignite at a user specified time. Other fire objects can ignite based on time, temperature or 

heat flux conditions. 

Use the New button to create a new fire object with default values for all entries. 

No time-dependent values are included in the new fire. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 39 

Use the Duplicate button to create a copy of the fire object currently selected in 

the summary table at the top of the page. The new fire object is added to the list with 

the named changed to indicate it is a copy of the selected item. 

Fire Object Name: The name from the collection of fire objects for the desired object. This 

corresponds to the name of the fire object file, without the extension. Specifying a 

name not found in the database causes CFAST to stop with an appropriate error 

message. 

Material (default value: none): material name from the thermal properties data file used for 

the object. The material properties are used to calculate heat transfer into the object 

from its surroundings. 

Length (default units: m, default value: none): specifies the length of the object. The choice 

of dimension to be designated as length, width, or thickness is arbitrary. Heat flux to 

the object surface is assumed to be incident to the surface defined by the length and 

width dimensions. 

Width (default units: m, default value: none): specifies the width of the object. 

Thickness (default units: m, default value: none): specifies the thickness of the object. 

Molar Mass (default units kg/mol, default value: 0.016 kg/mol) This is the conversion factor 

from mass density to molecular density for “Total Unburned Hydrocarbon,” the fuel 

vapor. It is used only for conversion to parts-per-million and has no effect on the 

model itself. 

Total Mass (default units: kg, default value: 10 000 kg): Total mass of the object. 

Heat of Combustion (default units: J/kg, default value: 50 000 000 J/kg): The energy 

released per kilogram of mass burned. 

Heat of Gasification (default units: J/kg, default value: none): The sum of the sensible and 

latent heat required to vaporize a unit mass of material. 

Volatilization Temperature (default units: K, default value: ambient): The temperature of 

the vapor as it is emitted from a fuel source. Typically, the initial fuel temperature is 

the same as the ambient temperature specified on the ambient conditions window. 

This may not be true if significant conductive or radiative heat transfer affects the 

fuel. This affects the enthalpy since temperatures below the lower layer ambient 

cause the plume to cool. The effect is not large, but it is noticeable. 

Ignition Temperature (default units: K, default value: volatilization temperature plus 

100 K): The lower temperature limit on the burning of fuel in a gas layer. Since 

CFAST does not support a combustion kinetics model, this is the algorithm used for 

fires out of vents. 

Radiative Fraction: The fraction of the energy produced in combustion that is radiated from 

the fire and plume. Within CFAST, the radiative fraction defaults to 0.3015; i.e., 30 % 

of the fire’s energy is released via radiation. For other fuels, the work of Tewarson16, 

McCaffrey17, or Koseki18 is available for reference. The typical range for the 

radiative fraction is from about 0.05 to 0.4. 
40 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

All of the time dependent variables depend on a predefined time line. The time input 

specifies a sequence of time points that define the timing of the fire. An entry indicates a 

point on the time-line when the mass loss rate, fuel height and other time dependent values 

are specified for the fire. This time is independent of the simulation time which is specified 

by the TIMES line. If the simulation time is longer than the total duration of the fire, the final 

values specified for the fire (mass loss rate, fuel height, fuel area, and species) are continued 

until the end of the simulation. 

The units for species (HCR, etc.) are kilograms per kilogram. However, the meaning is 

different for fuel properties and species production rates. The input for CT is the kilograms of 

"toxic" combustion products produced per kilogram of fuel pyrolyzed. Input for HCR is the 

mass ratio of hydrogen to carbon ratio in the fuel. Input for O2 is the mass ratio of oxygen to 

carbon as it becomes available from the fuel. Input the ratio of the mass of carbon to carbon 

dioxide produced by the oxidation of the fuel for OD. The input for CO is the ratio of the 

mass of carbon monoxide to carbon dioxide produced by the oxidation of the fuel. 

Time (default units: s, default values: none): specify a sequence of time points that define the 

timing of the main fire. An entry indicates a point on the time-line when the mass 

loss rate, fuel height and other time dependent values are specified for the fire. 

Pyrolysis Rate (Mdot) (default units: kg/s, default values: none): Pyrolysis rate of the fire as 

a series of time points consistent with the time specification. 

Heat Release Rate (QDot) (default units: W, default values: none): Heat release rate of the 

fire as a series of time points consistent with the time specification. 

Fire Height (default units: m, default values: none): Time-based values for height of the base 

of the fire. Actual height of the base of the fire is the sum of the value specified by 

MAINF for the main fire or OBJFL for object fires and this height specification for a 

particular time in the fire development. 

Area of the Base of the Fire (default units: m2

, default values: none): Cross-sectional area of 

the base of the fire. 

CO/CO2 (default units: kg/kg, default values: none): species yields ratios of carbon 

monoxide to carbon dioxide produced in the pyrolysis of the fuel. 

H/C (default units: kg/kg, default values: none): the hydrogen component of the pyrolyzed 

fuel. This is the ratio of hydrogen to carbon produced in the pyrolysis of the fuel. 

O/C (default units: kg/kg, default values: none): Oxygen component of the pyrolyzed fuel. 

O2 is the ratio of oxygen to carbon produced in the pyrolysis of the fuel. The O2 

input thus represents excess oxygen available from the fuel for combustion. For 

normal fuels, this input should be set to zero. 

HCN (default units: kg/kg, default values: none): Yield of hydrogen cyanide per mass of fuel 

produced in the pyrolysis of the fuel. 

HCl (default units: kg/kg, default values: none): Yield of hydrogen chloride per mass of fuel 

produced in the pyrolysis of the fuel. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 41 

Ct (default units: kg/kg, default values: none): Yield of a fictitious toxic species per mass of 

fuel produced in the pyrolysis of the fuel. For “normally toxic” materials, this takes a 

value of 1 and is typically changed by an order of magnitude for particularly toxic or 

non-toxic materials. It is not part of the mass balance for the fuel and system, but it 

just carried along as a transported species in flow through the structure. Ct is used as 

a measure of toxicity of a material. Typically the integrated Ct versus time product is 

calculated. For normal materials, a concentration-time product of 900 mg min/m3

 is 

an indication of incapacitation. 

• With the three parameters, heat of combustion (HOC), the pyrolysis and heat 

release rate are over specified. The model uses the last two of the three to obtain 

the HOC parameter. 

• By default, the fire is placed in the center of the compartment on the floor. If 

values for any of the three variables are invalid (i.e., less than zero or greater than 

the compartment dimension in the appropriate direction), the location for that 

direction defaults to the center of the appropriate direction. 

• In the input editor, time-dependent data are entered in a simple spreadsheet. 

Normal windows copy (Ctrl-C), cut (Ctrl-X), and paste (Ctrl-V) keyboard 

shortcuts are available for data editing. In addition, Alt-Ins will insert a complete 

row above the currently-selected row in the spreadsheet and Alt-Del will delete 

the current row in the spreadsheet. 

Associating Fire Objects with One or More Instances of the Fire in 

the Compartments of the Simulation 

Fire objects are placed in defined positions within a compartment of a simulation and 

oriented with a normal vector to the surface of the object. Ignition of an object may be at a 

specified time, a specified net incident heat flux on the surface of the object, or at a specified 

surface temperature of the object. The relevant CFAST keywords are MAINF for a simple 

point-source fire, OBJECT for a complex fire object, and HEATF for a heat source. 

The OBJECT keyword allows the specification of additional objects to be burned in the fire 

scenario. Positioning of the object within a compartment is specified in the same manner as 

for the main fire. 

Compartment of Fire Origin: specifies the compartment that contains the main fire for the 

simulation. Any compartment defined is valid. 
42 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

Type: constrained or heat source. For a constrained fire, species are tracked and heat release 

rate is limited by the oxygen available for combustion. For a heat source, the fire is a 

source of heat only, no mass is released, and species concentrations are not calculated 

by the model. 

Width (X) Position (default units: m, default value: compartment width / 2): Position of the 

center of the base of the fire measured in the x direction from the front lower left 

corner of the compartment origin (0,0,0) in the compartment of fire origin. 

Depth (Y) Position (default units: m, default value: compartment depth / 2): Position of the 

center of the base of the fire measured in the y direction from the front lower left 

corner of the compartment origin (0,0,0) in the compartment of fire origin. 

Height (Z) Position (default units: m, default value: 0 m): Position of the center of the base 

of the fire measured in the z direction from the front lower left corner of the 

compartment origin (0,0,0) in the compartment of fire origin. Actual height of the 

base of the fire is the sum of the value specified by FPOS and by FHIGH for a 

particular time in the fire development. 

Normal Vector X Component: specifies a vector of unit length perpendicular to the 

exposed surface of the object. (Depth) component is in the direction from the rear 

wall of the object compartment. Default value is a horizontal, upward facing object, 

unit vector = (0,0,1) 

Normal Vector Y Component: specifies a vector of unit length perpendicular to the 

exposed surface of the object. (Breadth) component is in the direction from the left 

wall of the object compartment. Default value is a horizontal, upward facing object, 

unit vector = (0,0,1) 

Normal Vector Z Component: specifies a vector of unit length perpendicular to the 

exposed surface of the object. (Breadth) component is in the direction from the floor 

of the object compartment. Default value is a horizontal, upward facing object, unit 

vector = (0,0,1) 

Plume Type: specifies the algorithm used to calculate entrainment of air into the plume. At 

present, only a plume based on the work of McCaffrey is allowed. 

Ignition Criterion Type: The type of ignition condition specified by the Ignition Criterion 

Value. Acceptable values are 1 for time, 2 for object surface temperature, and 3 for 

incident flux to object surface. 

Ignition Criterion Value: The numerical value at which ignition will occur. If it is less than 

or equal to zero, the default is taken. For constrained and heat source fires, the default 

is and ignition at time of zero. 

• Object fires are used to include additional burning objects in a simulation. For 

additional details, see the CFAST technical reference guide1,or Babrauskas and 

Grayson19. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 43 

Calculating Normal Vectors

The general equations for determining the normal vectors in the x, y, and z directions are: 

Normal vector in the x direction, x = x / (x2 + y2 + z2

)

.5

Normal vector in the y direction, y = y / (x2 + y2 + z2

)

.5

Normal vector in the z direction, z = z / (x2 + y2 + z2)

.5

The simplest way to calculate the unit vector is to draw an imaginary line at right angles (i.e., 

90o

 angle) from the exposed surface of the target and to extend this imaginary line until it hits 

the walls, floor or ceiling of the compartment in which it is located. This imaginary line is 

actually a vector that starts at the surface of the exposed target and terminates on a wall, 

floor, or ceiling. Once the start point and the end point of a vector are known, the unit vector 

for this imaginary line may be calculated as follows: 

x = (xend - xstart) / ((xend - xstart)

2

+(yend - ystart)

2

+(zend - zstart)

2

)

0.5

y = (yend - ystart) / ((xend - xstart)

2

+(yend - ystart)

2

+(zend - zstart)

2

)

0.5

z = (zend - zstart) / ((xend - xstart) 2+(yend - ystart)

2

+(zend - zstart)

2

)

0.5

As an example, assume the following scenario: 

• A square shaped target object is located in the middle of the floor of a 

compartment. 

• The target is constructed from no-combustible materials except the top. 

• The square shaped material is 1 m in depth, 1 m in breadth, and 1 m high. 

• The reference point (0,0,0) in the compartment is the lower left hand side of the 

rear wall. 

• The compartment is 3 meters in the x direction (i.e., the distance from the rear 

wall to the front wall of the compartment), 4 meters in the y direction (i.e., the 

distance from the left wall to the right wall of the compartment), and 5 meters in 

the z direction (i.e., the distance from the floor to the ceiling of the compartment). 

Since the only side of the target that is combustible is the top surface of the target object, an 

imaginary line is draw perpendicular (i.e., at a 90o

 angle) from the top surface of the target 

object and extended until it reaches the outer boundary of the compartment. In this case, 

since the top of the target object is facing the ceiling, the imaginary line would run straight 

up to the ceiling, running parallel to the four walls of the compartment, and terminating at the 

ceiling at the point (1.5 m, 2 m, 5 m). Since the vector starts at point (1.5-m, 2-m, 1-m) and 

terminates at (1.5-m, 2-m, 5-m), the unit vectors can be calculated as follows: 

x = (xend - xstart) / ((xend - xstart)

2

+(yend - ystart)

2

+(zend - zstart)

2

)

.5 

 = (1.5 – 1.5) / ((1.5 -1.5)2 + (2 – 2)2 + (5 - 1)2)

.5 = 0 

y = (yend - ystart) / ((xend - xstart)

2

+(yend - ystart)

2

+(zend - zstart)

2

)

.5

 = (2- 2)/ ((1.5 -1.5)2 + (2 – 2)2 + (5 - 1)2)

.5 = 0 

z = (zend - zstart) / ((xend - xstart) 2

+(yend - ystart) 2+(zend - zstart) 2)

.5
44 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

 = (5 - 1) / ((1.5 -1.5)2 + (2 – 2)2 + (5 - 1)2)

.5 = 1 

In this case, the unit vector is in the + Z direction. 

Special Features 

Sprinklers and Detectors 

Sprinklers and detectors are both considered detection devices by the CFAST model and are 

handled using the same input keywords. Detection is based upon heat transfer to the 

detector. Fire suppression by a user-specified water spray begins once the associated 

detection device is activated. A maximum of 20 sprinklers or detectors can be included for 

any input file and model run. These can be in one compartment or scattered throughout the 

structure. The DETEC keyword is used for both detectors and sprinklers. The first three 

parameters are required. The next three have defaults. The last three must be specified if this 

is a heat detector or sprinkler. 

Type: type of detector, use 1 for smoke detector and 2 for heat detector or sprinkler. 

Compartment the compartment in which the detector or sprinkler is located. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 45 

Activation Temperature: the temperature at or above which the detector link activates. 

Width (X) Position (default units: m, default value: none): position of the object as a 

distance from the left wall of the compartment (X direction). 

Depth (Y) Position (default units: m, default value: none): position of the detector or 

sprinkler as a distance from the front wall of the compartment (Y direction). 

Height (Z) Position (default units: m, default value: none): position of the object as a 

distance from the floor of the compartment (Z direction). 

RTI (default units: (m · s)1/2, default value: none): the Response Time Index (RTI) for the 

sprinkler or detection device. 

Spray Density (default units: m/s, default value: none): the amount of water dispersed by a 

water spray-sprinkler. The units for spray density are length/time. These units are 

derived by dividing the volumetric rate of water flow by the area protected by the 

water spray. The suppression calculation is based upon an experimental correlation by 

Evans20, and depends upon the RTI, activation temperature, and spray density to 

determine the behavior of the sprinkler. 

• Often, the activation of smoke alarms is simulated with a temperature-based 

criterion. Davis and Notarianni21 studied the activation of heat and smoke alarms 

in small and large compartments. They conclude that a temperature rise of 

approximately 5 ̊C corresponded to activation of ionization alarms for a range of 

fire sources and ceiling heights.. 

• Several cautions should be observed when using estimates of sprinkler 

suppression within the model: 1) the first sprinkler activated controls the effect of 

the sprinkler on the heat release rate of the fire. Subsequent sprinklers which may 

activate have no additional effect on the fire simulation. 2) The fire suppression 

algorithm assumes the effect of the sprinkler is solely to reduce the heat release 

rate of the fire. Any effects of the sprinkler spray on gas temperatures or mixing 

within the compartment are ignored. 3) The sprinkler always reduces the heat 

release rate of the fire. The ability of a fire to overwhelm an under-designed 

sprinkler is not modeled. 4) Since the dynamics of the sprinkler and direct effects 

of the spray on gas temperatures and velocities are not modeled, calculated times 

of activation of secondary sprinklers and / or detectors after the first sprinkler is 

activated should be not be modeled since the impact of the first sprinkler on the 

activation of additional sprinklers is not included in the CFAST model. 

Defining Targets 

CFAST can track and report calculations of the net heat flux striking arbitrarily positioned 

and oriented targets and the temperature of these targets. The relevant keyword used to 

specify targets is TARGE. 
46 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

In addition to any user-defined targets, there are always two targets that are automatically 

placed in any compartment containing a fire. Both are included for reporting purposes. The 

first is an “ambient target” and is intended to represent the net flux to a human body. This is 

used for the flux in the hazard calculation for tenability. The assumption is that the target will 

remain at ambient temperature, which is a surrogate for body temperature. The second 

determines the net flux to a horizontal target on the floor whose temperature is assumed to be 

the same as the floor surface. The calculation can be used to estimate the ignition of 

combustibles on the floor as a surrogate for estimating time to flashover, typically taken to be 

20 kW/m2

. Thus if one of the target keywords is used, it will be in addition to these two 

predefined targets. 

For all targets, heat flux is calculated to the surface specified by the user (with the normal 

vector). Conduction into the target is assumed to occur only from this surface. 

Compartment: The compartment in which the target is located. 

Width (X) Position: Position of the target as a distance from the left wall of the target 

compartment (X direction). 

Depth (Y) Position: Position of the target as a distance from the front wall of the target 

compartment (Y direction). 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 47 

Height (Z) Position: Height of the target above the floor (Z direction). 

Normal Vector X Component: specifies a vector of unit length perpendicular to the 

exposed surface of the target. (Width) component in the direction from the left wall of 

the target compartment. A value of 1 defines a vertical target facing into the 

compartment, unit vector = (1,0,0). 

Normal Vector Y Component: specifies a vector of unit length perpendicular to the 

exposed surface of the target. (Depth) component in the direction from the front wall 

of the target compartment. A value of 1 defines a vertical target facing to the right, 

unit vector = (0,1,0). 

Normal Vector Z Component: specifies a vector of unit length perpendicular to the 

exposed surface of the target. (Height) component in the direction from the floor of 

the target compartment. Default value is a horizontal, upward facing target, unit 

vector = (0,0,1). 

Material: Used to specify the wall material of the target. Any material from the thermal 

database used to represent wall materials may be used here. Since the transient heat 

conduction problem is not solved now for the target this parameter is not used. 

Solution Method: Optional parameter that indicates the solution method. STEADY for 

steady state solution, EXPLICIT for explicit solution, IMPLICIT for implicit 

solution. 

Material Solution Type: If METHOD is not STEADY, this parameter further indicates the 

equation type to be either ODE or PDE. For thermally thin materials, use ODE; for 

thermally thick materials, use PDE 

• The TARGE keyword performs a heat transfer calculation between the 

compartment and the target. The steady state option assumes that the target 

material reacts instantly to changing conditions and computes the target 

temperature that would result in a balance of incoming and outgoing heat (i.e., a 

steady state). If a transient target temperature is modeled, then one can either 

assume that there is a temperature variation within the target or assume that the 

target is “thin” and can be modeled using only one temperature. If the target is 

assumed to be thin then the ODE option should be used set since this is how the 

equations are solved. If the target is assumed to be thick then the PDE option 

should set. Finally, if one of the two transient options are set (ODE or PDE), the 

numerical solution can be solved using an explicit or an implicit method. 

Typically, the implicit method will work in all cases. The explicit method is 

recommended only when the implicit method fails to come to a solution. 

Defining Compartment Area 

The Compartment Geometry page includes two additional entries that may be used for 

defining compartment properties for spaces which are not rectangular in area. Values are 

entered in a spreadsheet. The CFAST keywords ROOMA and ROOMH keywords allow the 

user to define non-rectangular rooms by specifying cross-sectional area as a function of 
48 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

height. One set of values is included for each compartment that has a variable cross-sectional 

area. 

Height Value(s) (default units: m, default values: none): Values of height for the 

corresponding cross-sectional area values measured from the floor of the 

compartment. The values for the compartment correspond to cross-sectional area 

values included for the same compartment on the ROOMA command. 

Area Value(s) (default units m2

, default values: none): Values of cross-sectional area of the 

compartment as a function of height measured from the floor of the compartment. 

The values for the compartment correspond to height values included for the same 

compartment on the ROOMH command. 

Inter-compartment Heat Transfer (Conduction) 

The Surface Connections page allows the user to define heat transfer between compartments 

in a simulation. These may define vertical conduction through floors or ceilings or 

horizontal conduction through connecting wall surfaces. 

There are two keywords that define physical connections which affect heat conduction 

between compartments. They are: 

• VHEAT – ceiling/floor heat conduction (vertical heat flow) 

• HHEAT – heat transfer between connected compartment walls (horizontal heat 

flow) 

Energy can be transferred from compartment to compartment through solid boundaries 

(walls, ceilings and floors) by means of conduction. The heat transfer between connected 

compartments is modeled by merging the connected surfaces for the ceiling and floor 

compartments or for the connected horizontal compartments. The heat conduction problem 

is solved for the merged walls using a temperature boundary condition for both the near and 

far wall. As before, temperatures are determined by the solver so that the heat flux striking 

the wall surface (both interior and exterior) is consistent with the temperature gradient at that 

surface. This option is implemented with the VHEAT (for vertical heat transfer) and the 

HHEAT (for horizontal heat transfer) keywords. 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 49 

• Vertical Heat Transfer: Heat transfer between the ceiling and floor of specified 

compartments is included with the VHEAT keyword. Ceiling to floor heat 

transfer occurs between interior compartments of the structure or between an 

interior compartment and the outdoors. The model checks to make sure that the 

ceiling and floor are reasonably contiguous (within 0.01 m). The assumption is 

made that this is true for the entire ceiling and floor. 

• Horizontal Heat Transfer: Horizontal conduction between specified 

compartments is included with the HHEAT keyword. Conduction through 

vertical partitions (walls) occurs between interior compartments of the structure or 

between an interior compartment and the outdoors. 

First Compartment: First of the connected compartments. Order of the inputs is not 

important. 

Second Compartment: Second of the connected compartments. Order of the inputs is not 

important. 
50 • Chapter 4 Setting up the Input File for CFAST User’s Guide Version 6 

Fraction: Specifies the fraction of the vertical surface areas of the compartments which are 

connected can be specified. The fraction specifies the fraction of the vertical surface 

area connecting the first and second compartment pair. 

As an example, four cases were simulated by modeling all wall surfaces in a test case with 

gypsum and steel and by turning on and off the horizontal heat transfer option. The following 

table summarizes the results for these four cases. Each table entry gives the Upper room 1 

temperature, upper room 2 temperature, upper wall temperature in room 1 and upper wall 

temperature in room 2. 

HHEAT Off HHEAT Off 

Steel walls 1106/528.3/374.9/319 1118/535.3/399.6/340.2 

Gypsum walls 1147/545.4/462.9/338 1148/545.8/464.1/339.3 

The results are as one would expect. For each wall material turning HHEAT on leads to 

warmer calculated temperatures since the outside environment (where heat goes when 

HHEAT is off) is cooler than the adjoining room. The temperature differences are greater for 

steel than for gypsum since steel conducts heat more effectively. 

The Ceiling Jet – An Additional Zone 

Typically, zone models incorporate two zones in each compartment, one for the upper layer 

and one for the lower layer. A plume from a fire then pumps energy from the fire and lower 

layer into the upper layer. However, it has been observed that the heat loss from the upper 

layer to the ceiling and walls is higher than this paradigm would indicate. The cause is that a 

plume does not truly mix with the upper layer initially as indicated in the figure 

This leads to higher convective heat transfer than the mixed model would indicate. CFAST 

has incorporated a model of this additional heat loss based on the work of Cooper . Heat loss 

by this mechanism to the ceiling is well established, the loss to walls is somewhat more 

uncertain due to the uncertainty of how far the plume descends below the ceiling. 

To include ceiling jet effects in the calculation of the surface temperature of 

the ceiling, wall, or both surfaces, the CJET keyword is used. In the input editor, CEdit, this 

is included on the fires page. The ceiling jet calculation can be used for the ceiling, walls, or 

all surfaces. At present, this keyword effects only the calculation of the convective heating 

boundary condition for the conduction routines. If a particular surface is on, the ceiling jet 

algorithm is used to determine the convective heating of the surface. If the ceiling jet is off, 

the bulk temperature of the upper layer determines the convective heating. 

• Using this option affects all fires and it is suggested that this option be turned on 

and set to “CEILING.” 
User’s Guide Version 6 Chapter 4 Setting up the Input File for CFAST • 51 

Scenario and Software Limits 

CFAST is intended for use with a wide variety of fire scenarios. A number of limits to the 

inputs in the software implementation of the model are noted below. 

Maximum simulation time in seconds 86 400 

Maximum number of compartments 30 

Maximum number of fires which can be included in a single test case (including the main fire) 31 

Maximum number of fire definitions which can be included in a single fire database file 30 

Maximum number of data points for a single main or secondary object fire 21 

Maximum number of material thermal property definitions which can be included in a single thermal 

database file 

125 

Maximum number of slabs in a single surface material in the thermal database file 3 

Total number of ducts in all mechanical ventilation systems which can be included in a single test case 60 

Maximum total number of connections between compartments and mechanical ventilation systems which 

can be included in a single test case 

62 

Maximum number of independent mechanical ventilation systems which can be included in a single test 

case 

15 

Maximum number of targets which can be included in a single test case. In addition, the CFAST model 

includes a target on the floor of each compartment in the simulation and one for each object fire in 

simulation. 

90 

Maximum number of data points in a history or spreadsheet file 900 
52 • Chapter 5 Output User’s Guide Version 6 

Chapter 5 Output 

Overview 

The output of CFAST are the sensible variables that are needed for assessing the 

environment in a building subjected to a fire. These include temperatures of the upper and 

lower gas layers within each compartment, the ceiling/wall/floor temperatures within each 

compartment, the visible smoke and gas species concentrations within each layer, target 

temperatures and sprinkler activation time. The amount of information can be very large, 

especially for complex geometries and long simulations. 

The default output to the console is called the compact form, and shows the basic information 

about a scenario, including layer temperatures and the size of fires. Default text output 

provides a simple overview for the user to make sure the case runs as expected. 

The compact output for each compartment is listed across the screen and the compartments 

are listed down the screen starting with compartment one and ending with the outside. The 

example below shows the initial and final conditions for a calculation: 
User’s Guide Version 6 Chapter 5 Output • 53 

Time = 0.0 seconds. 

Compartment Upper Lower Inter. Pyrol Fire 

 Temp. Temp. Height Rate Size 

 (K) (K) (m) (kg/s) (W) 

----------------------------------------------------------------- 

 1 300.0 300.0 2.3 1.400E-03 2.530E+04 

 2 300.0 300.0 2.3 0.000 0.000 

 Outside 0.000 

Time = 200.0 seconds. 

Compartment Upper Lower Inter. Pyrol Fire 

 Temp. Temp. Height Rate Size 

 (K) (K) (m) (kg/s) (W) 

----------------------------------------------------------------- 

 1 1252. 475.1 0.63 0.278 4.831+06 

 2 828.7 325.4 1.0 0.000 0.000 

 Outside 1.609E+03 

The first column contains the compartment number. On each row with its compartment 

number from left to right is the upper layer temperature, lower layer temperature, the height 

of the interface between the two layers, the total pyrolysis rate, and finally the total fire size. 

The only value given for the outside is the total heat release rate of fires venting to the 

outside. 

Detailed Outputs 

The following sections describe each of the outputs from the model. Each section refers to a 

specific part of the print out and appears in the order the output appears. A description of 

each option follows. 

Output for Initialization 

This option prints the initial conditions to the output before the actual run starts. This merely 

mimics the inputs specified by the user in the input data file The initial conditions brake 

down into seven sections. Each is described below with the section name. The following 

explanation uses the output from the case STANDARD.DAT which is captured using the 

program report. STANDARD.DAT is included in the distribution. Please note, there are not 

mechanical ventilation or horizontal vents in STANDARD.DAT, so below the section saying 

there are no mechanical ventilation connections, there is an annotated section from additional 

data files, TESTVVENT.DAT, TESTHVAC.DAT and TESTSPEC.DAT. 

Overview: The overview gives a general description of the case. The output is fairly self 

explanatory. Doors, ..." is the total number of horizontal natural flow vent connections in all 

compartments of the simulation. "Ceil. Vents, ..." gives the total number of vertical natural 

flow vent connections in all compartments of the simulation. The last header on the line 

"MV Connections" has the total number mechanical flow connections to all compartments in 

the simulation. Times in these outputs come from the TIMES input. All times are in s. 

OVERVIEW 
54 • Chapter 5 Output User’s Guide Version 6 

Compartments Doors, ... Ceil. Vents, ... MV Connects 

 1 1 0 0 

Simulation Print History Restart 

 Time Interval Interval Interval 

 (s) (s) (s) (s) 

 1800 10 10 0 

Ceiling jet is on for all 

History file is STANDARD.HI 

Ambient Conditions: This section, like the overview section, needs little elaboration. It gives 

the starting atmospheric conditions for the simulation both for outside and inside the 

structure. Data for these outputs come from the TAMB and EAMB inputs. Temperatures are 

in K, pressure in Pa, elevations in m, and wind speed in m/s. Wind Power is the 

dimensionless power law coefficient from the WIND input. 

AMBIENT CONDITIONS 

Interior Interior Exterior Exterior Station Wind Wind Wind 

Temperature Pressure Temperature Pressure Elevation Speed Ref. Height Power 

(K) (Pa) (K) (Pa) (m) (m/s) (m) 

 300. 101300. 300. 101300. 0.00 0.0 10.0 0.16 

Compartments: The compartments section gives a summary of the geometry for the 

simulation. A simple table summarizes the geometry with compartments running down the 

page in numerical order. The various dimensions for each compartment are on the row with 

its compartment number. Two columns need explanation. The second to last column 

"Ceiling Height" gives the height of the ceiling relative to the station height in the Ambient 

Conditions section. Similarly the "Floor Height" refers to the height of the floor above the 

station height. 

COMPARTMENTS 

Compartment Width Depth Height Area Volume Ceiling Floor 

 Height Height 

 (m) (m) (m) (m^2) (m^3) (m) (m) 

--------------------------------------------------------------------------------- 

 1 9.10 5.00 4.60 45.50 209.30 4.60 0.00 

• Values for width, depth, height, and floor height come directly from the WIDTH, 

DEPTH, HEIGH, and HI/F specifications in the input data file. 

• Area is calculated as width x depth in m2. 

• Volume is calculated as width x depth x height in m3. 

• Floor height is the absolute elevation of the ceiling of the compartment and is just 

station elevation (from the ambient conditions section) + compartment height in 

m. 
User’s Guide Version 6 Chapter 5 Output • 55 

Vent Connections: Vent connections further divides into three distinct parts. Each part has 

its own sub heading. A description of each follows. 

Horizontal Natural Ventilation is the first table in the vent connections sections. Each row in 

the table characterizes one vent. The first two columns contain the two compartments 

connected by the vent. Each vent is ordered first by the lower number of the two 

compartments and then the numeric order of the second compartment. The third column 

gives the vent number. Column four is the width of the vent. The next two columns report 

the sill and soffit height for the vent relative to the floor of the first compartment. The 

seventh and eighth columns have a second listing of the sill and soffit height, this time 

relative to the station height. Area of the vent is in the last column. 

VENT CONNECTIONS 

Horizontal Natural Flow Connections (Doors, Windows, ...) 

From To Vent Width Sill Soffit Abs. Abs. Area 

Compartment Compartment Number Height Height Sill Soffit 

 (m) (m) (m) (m) (m) (m^2) 

--------------------------------------------------------------------------------------------------- 

 1 Outside 1 2.40 0.00 1.00 0.00 1.00 2.40 

• From compartment, to compartment, vent number, width, sill height, and soffit 

height all come directly from the HVENT specifications in the input data file. 

• Absolute sill height and absolute soffit height is the station elevation + 

compartment floor height + sill height. Absolute soffit height and absolute soffit 

height is the station elevation + compartment floor height + soffit height 

Vertical Natural Ventilation prints out in a similarly simple table. Again each vent is one 

row of the table. The first column is the upper compartment. The upper compartment is the 

compartment where the vent opens into the floor. The second column is the lower 

compartment where the vent is in the ceiling. The third column describes the shape of the 

vent, which can be either round or square. The fourth column gives the area of the vent. The 

last two columns are the height of the vent, relative to the floor of the lower room and 

relative to the station height respectively. 

This is the output from STANDARD.DAT 

There are no vertical natural flow connections 

There are no mechanical flow connections 

This is an alternate example that includes a vertical flow connection from 

TESTVVENT.DAT 
56 • Chapter 5 Output User’s Guide Version 6 

Vertical Natural Flow Connections (Ceiling, ...) 

Top Bottom Shape Area Relative Absolute 

Compartment Compartment Height Height 

 (m^2) (m) (m) 

---------------------------------------------------------------------- 

 2 1 Round 0.10 2.30 2.30 

which shows a circular hole in the ceiling of area 0.1 m2. 

• Top compartment, bottom compartment, shape, and area come from the VVENT 

specifications in the input data file. 

• Relative height is the height of the vent above the floor of the bottom 

compartment and absolute height is the height of the vent above the station 

elevation. 

Mechanical Flow Connections uses two tables. The first table lists all the connections to 

compartments and ducts. Each row is either a connection or duct. The first column tells to 

which system the duct or connection belongs. A system is a set of continuously linked 

connections, ducts and fans. The example contains only one system. If a second system had 

been part of the file, a line would have been skipped before starting into the second system. 

The second and fourth columns give both ends of either the connection or duct. The words 

"comp" or "node" proceeds the numbers in these two columns. "Comp" means a 

compartment number. Rows with a compartment number in either the "from" or "to" 

columns are connections to compartments, which are basically vents. The rest of the rows 

define ducts. The third and fifth columns give the elevations of the proceeding columns. 

The sixth column is the length which only applies to ducts. Connections do not have a length 

so the column is left blank. Next comes the cross sectional area. The last column tells the 

absolute roughness. This value is the resistance the duct provides to the flow of air. Like the 

length, this value only has meaning for a duct so it is blank for a connection. Air flows both 

ways though connections and ducts. The headers "from" and "to" say nothing about the 

direction of air flow. The headers only provide a convenient way of listing both ends of a 

duct or connection. 

Mechanical Flow Connections (Fans, Ducts, ...) 

Connections and Ducts 

System From From To To Length Area Rough 

 Elev. Elev. 

 (m) (m) (m) (m^2) (mm) 

-------------------------------------------------------------------------------------- 

 1 Comp 1 2.10 Node 1 2.10 0.12 

 Node 1 2.10 Node 2 0.00 2.30 0.08 0.00 

The second table lists the fans. The first five columns in the fan table appear almost the same 

as the connections and ducts table. The table lists, in order, the number of the system the fan 

is a part, the "from" node and its height, the "to" node and its height. A fan actually draws air 

from the first or "from" node and pushes it to the second or "to" node. In the second table, 

the headers give the direction of the flow of air. The sixth column is the fan number as 

defined in CEdit. The next two columns are the minimum and maximum pressures at which 
User’s Guide Version 6 Chapter 5 Output • 57 

the fan curve is defined. The rest of the row is made up of the two to five fan curve 

coefficients in the input file. 

Fans 

System From From To To Fan Minimum Maximum Fan Curve 

 Elev. Elev. Number 

 (m) (m) (Pa) (Pa) 

---------------------------------------------------------------------------------------------------- 

 1 Node 2 0.00 Node 3 2.10 1 0.00 300.00 0.14 -

4.33E-04 

 Node 3 2.10 Outside 2.10 0.12 

Thermal Properties The thermal properties section brakes into two parts. The first part is a 

table that lists the material for each surface of each compartment. The compartments appear 

as rows down the page in numerical order. From left to right next to the compartment 

number comes the material for the ceiling, wall and floor. The second part lists the entries in 

the thermal data base. The first line gives the database file used. Next comes a listing of 

each material used. In addition to materials for compartment surfaces, any materials specified 

for targets are also listed. For each listing of a material, the name is followed by the 

conductivity, specific heat, density, thickness and emissivity. Additionally, the HCl 

constants used to calculate the HCl deposition for the surface are displayed. 

THERMAL PROPERTIES 

Compartment Ceiling Wall Floor 

---------------------------------------------------------------------- 

 1 GLASSFB3 CONCRETE CONCRETE 

Thermal data base used: THERMAL.CSV 

Name Conductivity Specific heat Density Thickness Emissivity HCL B's (1->5) 

GLASSFB3 3.600E-02 795. 105. 1.300E-02 0.900 0.00E+00 0.00E+00 0.00E+00... 

CONCRETE 1.75 1.000E+03 2.200E+03 0.150 0.940 0.00E+00 0.00E+00 0.00E+00... 

PLYWOOD 0.120 1.215E+03 545. 1.300E-02 0.900 0.00E+00 0.00E+00 0.00E+00... 

• Material choices of the ceiling, walls, and floors come from the CEILI, WALLS, 

and FLOOR specifications in the input data file. 

• Materials properties for the chosen materials come from the specified thermal 

properties file. 

• Units for thermal properties are standard S.I. units. For thermal conductivity, 

W/m K; for specific heat, J/kg K; for density, kg/m3

; for thickness, m; emissivity 

is dimensionless. 

Targets: The entry for targets shows the orientation of additional targets specified in the data 

file. Note that the first two are always present. The third one is the target specified in the data 

file. Each target is numbered based on the order of the target specifications in the input data 

file. The compartment number, position of the target within the compartment, direction of 

the front face of the target object expressed as a normal unit vector to the surface, and object 

material. 
58 • Chapter 5 Output User’s Guide Version 6 

TARGETS 

Target Compartment Position (x, y, z) Direction (x, y, z) Material 

---------------------------------------------------------------------------------- 

 1 1 2.20 1.88 2.34 0.00 0.00 1.00 CONCRETE 

 2 1 2.15 1.65 0.00 -1.00 0.00 0.00 PLYWOOD 

 3 1 2.50 4.55 0.00 0.00 0.00 1.00 CONCRETE Floor, 

compartment 1 

• All of the inputs for targets come from the TARGE command in the input data 

file. Direction is specified as a unit vector as described in the section on target 

input. 

• Units for position and direction are all in m. 

Fires: The fire section lists all the information about the main fire and any object fires that 

might exist. All the information for each fire is listed separately. If there is a main fire, it 

comes first. Each fire listing has the same form. First is the name of the fire followed by a 

list of general information. Listed left to right is the compartment the fire is in, the type of 

fire, the x, y, z position, the relative humidity, the lower oxygen limit, and finally the 

pyrolysis temperature. A table of time history curves for the fire follows. The table contains 

all the time history curves for the fire. Each row on the table is a specific time given in the 

left most column. The rest of the columns give the values at that particular time. The 

column headers are keywords used in the datafile. The keyword meanings are: fmass is 

pyrolysis rate; hcomb is heat of combustion; fqdot is heat release rate; fhigh is height of fire; 

C/CO2 is carbon to carbon dioxide ratio; CO/CO2 is the carbon monoxide to carbon dioxide 

ratio; H/C is the hydrogen to carbon ratio; O/C is the oxygen to carbon ratio; HCN is the 

hydrogen cyanide production rate; and HCl is the hydrogen chloride production rate. 

FIRES 

Name: Main Fire 

Compartment Fire Type Position (x,y,z) Relative Lower O2 Pyrolysis 

 Humidity Limit Temperature 

 1 Constrained 3.00 5.70 0.00 50.0 12.00 300. 

 Time Fmass Hcomb Fqdot Fhigh C/CO2 CO/CO2 H/C O/C HCN HCL 

 (s) (kg/s) (J/kg) (W) (m) (kg/kg) (kg/kg) (kg/kg) (kg/kg) (kg/kg) (kg/kg) 

-------------------------------------------------------------------------------------------------------------- 

 0. 0.0 2.41E+07 0.0 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 60. 8.30E-03 2.41E+07 2.00E+05 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 120. 1.45E-02 2.41E+07 3.50E+05 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 180. 1.41E-02 2.41E+07 3.40E+05 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 240. 8.30E-03 2.41E+07 2.00E+05 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 300. 6.22E-03 2.41E+07 1.50E+05 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 360. 4.15E-03 2.41E+07 1.00E+05 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 420. 4.15E-03 2.41E+07 1.00E+05 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 480. 3.32E-03 2.41E+07 8.00E+04 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 540. 3.11E-03 2.41E+07 7.50E+04 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

 1800. 4.15E-03 2.41E+07 1.00E+05 0.0 0.0 0.0 0.16 0.0 0.0 0.0 

Name: WARDROBE Referenced as object # 1 

Compartment Fire Type Position (x,y,z) Relative Lower O2 Pyrolysis 

 Humidity Limit Temperature 

 1 Constrained 2.15 1.65 0.00 50.0 12.00 300. 
User’s Guide Version 6 Chapter 5 Output • 59 

 Time Fmass Hcomb Fqdot Fhigh C/CO2 CO/CO2 H/C O/C HCN HCL 

 (s) (kg/s) (J/kg) (W) (m) (kg/kg) (kg/kg) (kg/kg) (kg/kg) (kg/kg) (kg/kg) 

-------------------------------------------------------------------------------------------------------------- 

 0. 0.0 1.59E+06 0.0 0.0 0.0 0.0 0.33 0.0 0.0 0.0 

 70. 3.14E-02 1.59E+06 5.00E+04 0.0 1.60E-02 0.23 0.33 0.0 0.0 0.0 

 100. 8.17E-02 1.59E+06 1.30E+05 0.0 1.90E-02 0.13 0.33 0.0 0.0 0.0 

 140. 0.33 1.59E+06 5.30E+05 0.0 4.00E-03 9.00E-03 0.33 0.0 0.0 0.0 

 190. 1.57E-02 1.59E+06 2.50E+04 0.0 0.0 1.60E-02 0.33 0.0 0.0 0.0 

 200. 3.77E-02 1.59E+06 6.00E+04 0.0 0.0 3.10E-02 0.33 0.0 0.0 0.0 

 340. 1.57E-02 1.59E+06 2.50E+04 0.0 0.0 6.30E-02 0.33 0.0 0.0 0.0 

 1170. 3.10E-03 1.61E+06 5.00E+03 0.0 0.0 0.0 0.33 0.0 0.0 0.0 

• All of the inputs for the main fire come from the fire specifications in the input 

data file. Data for the object fire comes from the object data file included with the 

CFAST software. 

• Units for most values are included in the output. Fire position is in m, relative 

humidity is in %, lower oxygen limit is in volume percent, and pyrolysis 

temperature is in K. 

Output for Main Output Variables 

An expanded version of the compact default output called the normal print out can be 

obtained using the /f option. When requested, the normal print out is the first information 

printed at each interval. The first part of the print out looks similar to the default print out. It 

is laid out along the same lines, with the calculated values for each compartment listed left to 

right and compartments listed down. The left most column has the compartment. The next 

three columns also give the same values as the default output. They are upper layer temperature, lower layer temperature and interface height. The output changes at this point. The fifth 

column gives the upper layer volume. In the sixth, in parenthesis, is the percent of the total 

compartment volume the upper layer takes up. The pressure difference from ambient follows 

in the seventh column. The rest of the columns are the temperature of the bounding surfaces 

in K. 

Time = 1800.0 seconds. 

Compartment Upper Lower Inter. Upper Upper Lower Pressure Ambient Floor 

 Temp. Temp. Height Vol. Absorb Absorb Target Target 

 (K) (K) (m) (m^3) (m^-1) (m^-1) (Pa) (W/m^2) (W/m^2) 

---------------------------------------------------------------------------------------------------------------- 

 1 377.0 303.8 0.7236 1.76E+02( 84%) 1.000E-02 1.000E-02 -9.483E-02 437. 335. 

The second table of the normal print out has information about the fires. In essence it is two 

tables joined. The first part lists information by fire. It starts with the main fire, if there is 

one, and then the object fires down the page. The fires are listed in the second column 

followed by the plume flow rate, the pyrolysis rate and the fire size. The next three columns 

are then skipped. The next column with information is the amount of heat given off by each 

fire convectively, followed by the amount of heat given off radiantly. The second part starts 

after all the fires have been individually listed. It gives the totals for all fires in each 
60 • Chapter 5 Output User’s Guide Version 6 

compartment. The first column has the compartment number. The compartments start at one 

and are listed down the page in order. The third to fifth columns are the same as the first part 

except the values are totals for the compartment and not just for one fire. The sixth column 

has the total heat release rate that occurs in the upper layer. The next column has the same 

total in the lower layer. The eighth column has the total size of vent fires in the 

compartment. The last two columns of the table gives the convective and radiative parts of 

the fire heat release. 

Fires 

Compartment Fire Plume Pyrol Fire Flame Fire in Fire in Vent Convec. Radiat. 

 Flow Rate Size Height Upper Lower Fire 

 (kg/s) (kg/s) (W) (m) (W) (W) (W) (W) (W) 

------------------------------------------------------------------------------------------------------------------ 

 Main 0.291 4.149E-03 9.998E+04 1.11 6.999E+04 3.000E+04 

 WARDROBE 5.026E-02 3.100E-03 4.988E+03 0.120 3.492E+03 1.496E+03 

 1 0.341 7.249E-03 1.050E+05 0.00 1.050E+05 0.00 

• Flame height is calculated from the work of Heskestad22 Valid for a wide range of 

hydrocarbon and gaseous fuels, the correlation is given by 

2 / 5 1.02 0.23 H = − + Qf

where H is the average flame height and Qf is the fire size. The mean flame height is defined 

as the distance from the fuel source to the top of the visible flame where the intermittency is 

0.5. A flame intermittency of 0.5 means that the visible flame is above the mean 50 % of the 

time and below the mean 50 % of the time. 

Output for Wall Surface and Targets 

The /f option provides two tables displaying information about wall surface or target 

temperatures and fluxes, and heat detectors or sprinklers. The left most column specifies the 

compartment number; followed by four columns providing the temperatures of the bounding 

surfaces of the compartment in contact with the ceiling, upper wall surface (in contact with 

the upper layer gases), lower wall surface (in contact with the lower layer gases), and floor, 

in that order. Next comes information about targets in the compartment, with each target 

listed on a separate line. Information in the columns includes the surface temperature of the 

target, net heat flux to the target, and the percentage of that net flux that is due to radiation 

from the fire, radiation from compartment surfaces, radiation from the gas layers, and 

convection from the gas surrounding the target. CFAST includes one target in the center of 

the floor for all compartments. Information on additional targets specified by the user in the 

input data file are also included, in the order specified in the input file. 
User’s Guide Version 6 Chapter 5 Output • 61 

Surfaces and Targets 

Compartment Ceiling Up wall Low wall Floor Target Target Flux To Fire Surface Gas 

 Temp. Temp. Temp. Temp. Temp. Target Rad. Rad. Rad. Convect. 

 (K) (K) (K) (K) (K) (W/m^2) (%) (%) (%) (%) 

--------------------------------------------------------------------------------------------------------------------------- 

 1 339.2 312.3 306.3 310.8 Floor 311. 863.4 0.0 27.9 74.7 -2.6 

 1 320. 1318. 0.0 7.7 71.7 20.6 

 2 367. 647.8 0.0 25.9 120.5 -46.4 

The second table provides information about heat detectors and sprinklers included in the 

input data file. For each output time, the output includes the sensor temperature, whether the 

sensor temperature has exceeded its specified activation temperature, and the temperature 

and velocity of the gas adjacent to the sensor. For sensors placed near the ceiling of a 

compartment with a fire, the temperature and velocity are those of the ceiling jet; for other 

compartments, it is the upper layer temperature and a default velocity of 0.1 m/s. 

Sensors 

 Sensor Smoke 

Number Compartment Type Temp (K) Activated Temp (K) Vel (M/S) 

---------------------------------------------------------------------------- 

 1 1 HEAT 3.149E+02 YES 3.136E+02 4.152E-01 

• Temperatures are all in K, fluxes in w/m2, and velocities in m/s. 

• In all cases, the flux to/from a target is net radiation or net convection. That is, it 

is the incoming minus the outgoing. So while a target or object is heating, the flux 

will be positive, and once it starts to cool, the flux will be negative. 

• Values for radiation from fires (fire rad.), radiation from surfaces (surface rad.), 

radiation from the gas layers (gas rad.), and convection from surfaces (convect) 

are expressed as a percentage of the net flux to target (flux to target). Positive 

values indicate heat gains by the target and negative values indicate heat losses. 

Output for Gas Species 

The /f option has two tables displaying information about the amounts of species in each 

layer. The species information follows the normal print out. The first table gives species 

concentrations for the upper layers of all the compartments and the second reports the same 

for the lower layers of all the compartments. Again the compartments are listed down the 

page and the information across the page. The species are each given in one of several 

different terms. Below each header is the units for the given value. Most of the headers are 

simply the chemical formula for the species being tracked. However, a couple are not 

obvious. "TUHC" is the total unburned hydrocarbons or the pyrolyzed fuel that hasn't 

burned yet. "OD" is the obscuration density, which is a measure of the amount of smoke. 

The last four columns, "HCl c", "HCl f", "HCl uw" and "HCl lw", are the amount of HCl 

deposition on the ceiling, floor, upper wall and lower wall respectively. 
62 • Chapter 5 Output User’s Guide Version 6 

Time = 1800.0 seconds. 

Upper Layer Species 

Compartment N2 O2 CO2 CO HCN HCL TUHC H2O OD CT 

 (%) (%) (ppm) (ppm) (ppm) (%) (%) (%) (1/m) (g-min/m3) 

------------------------------------------------------------------------------------------------------------------- 

 1 77.5 18.1 1.24 777. 568. 415. 0.00 2.55 7.26 353. 

Lower Layer Species 

Compartment N2 O2 CO2 CO HCN HCL TUHC H2O OD CT 

 (%) (%) (%) (ppm) (ppm) (ppm) (%) (%) (1/m) (g-min/m3) 

------------------------------------------------------------------------------------------------------------------- 

 1 79.3 20.7 7.209E-08 4.531E-05 3.312E-05 2.417E-05 0.00 7.677E-07 4.830E-07 0.860 

• The report by species for nitrogen, oxygen, hydrogen chloride and the total 

unburned hydrocarbons (fuel vapor in the layer) are percent by volume. Carbon 

dioxide, carbon monoxide and hydrogen cyanide are in parts per million, which is 

also a volume fraction. Optical depth per meter is a measure of the visibility in 

the smoke. This is covered in detail in the comment on visibility in the section on 

fires and species specification. The concentration-time (CT) calculation is an 

integration of the species input for type CT (See section for the input of CT) and 

is intended to represent a relative dose of toxic gas species23

Output for Vent Flows 

Information about hallway and vent flow is obtained by using this option. It includes two 

sections, one with information about hallway flow specified with the HALL command, and a 

larger section detailing mass flow through horizontal, vertical, and mechanical vents. For 

hallway flow, the output begins with the compartment specified as a hallway in the input data 

file, followed by the time at which gas began to flow into the hallway through the vent that 

connects the hallway to the main fire compartment. Following the start time are the average 

gas velocity, the layer depth of the initial flow down the corridor, and the distance from the 

end of the corridor that the hot layer is estimated to have reached. 

Hall Flow 

Compartment Start Time Velocity Depth Distance 

 (s) (m/s) (m) (m) 

---------------------------------------------------------------- 

 3 2.59 1.69 0.573 32.3 

The section for vent flow is titled "Flow Through Vents (kg/s)." Because flow is always 

given in positive values, each vent is listed twice. Once for flow going from compartment A 

to compartment B and a second time for flow from B to A. As the example below shows, the 

first column lists the compartment. The second column specifies the vent, including the type 

of vent (an “H” in this column stands for horizontal flow, such as through a doorway or 

window; a “V” here would mean vertical flow, such as through an opening in the ceiling, and 

an “M” stands for a mechanical ventilation connection) and the compartment from which the 

flow comes. Up to six additional columns detail the flow at this vent. Flow into and out of the 

compartment through the vent in the upper and lower layers are included, along with mixing 

between layers at the vent into the upper layer and into the lower layer. 
User’s Guide Version 6 Chapter 5 Output • 63 

Flow Through Vents (kg/s) 

To Through Upper Layer Lower Layer Mixing Mixing 

Compartment Vent Inflow Outflow Inflow Outflow To Upper To Lower 

-------------------------------------------------------------------------------------------------------- 

 1 H Outside #1 0.344 0.401 6.416E-02 

Outside H Comp 1 #1 0.344 6.416E-02 0.401 

• The mass balance is the sum of the flow in minus the flow out. (Note that this is 

an extended run to achieve results close to steady state.) For any compartment, 

this is just (“Upper Layer Inflow” + “Lower Layer Inflow” + “Pyrol Rate”) – 

((Upper Layer Outflow + Lower Layer Outflow) with the inflow and outflow 

summed for each vent. Note that the mixing flows are ignored since they are just 

exchanged between layers in the same compartment. For the above example, the 

mass balance is: 

(0.0 + 0.401 + 7.2x10-3 ) kg/s – (0.344 + 6.4x10-2) kg/s = -0.002 kg/s 

where the pyrolysis rate (from the”normal” output) is 7.2x10-3 kg/s. The result is about 

the right magnitude (about 0.5% of the mass flow into or out of the vent) for net mass 

loss. The mass loss should still be slightly negative since the compartment continues to 

heat. 

Spreadsheet Output 

A very important note for interpreting the spreadsheet output. These files capture a snap shot 

of the modeling data at an instant of time. This instance is determined by the fourth entry on 

the TIMES line of the data file. HOWEVER, there are events which can occur in between 

these reporting periods. Examples are the ignition of objects and the activation of detectors or 

sprinklers. These are NOT reported in these output files. 

Primary Output Variables (project.n.csv) 

There are two sets of information. The first is the compartment information such as layer 

temperature. This is output by compartment and there are seven entries for each 

compartment: 

'Upper Layer Temp', 'Lower Layer Temp', 'Layer Height', 'Volume', 'Pressure', 'Ambient 

Target', 'Floor Target'/ 

The second section is for fires. There are five entries per fire. This information is displayed 

for each fire (0 to numobjl) 

'Plume flow', 'Pyrolysis rate', 'Fire Size', 'Flame Height', 'Convective flow' 
64 • Chapter 5 Output User’s Guide Version 6 

The units of flow are kg/s, fire size in Watts, temperatures in Kelvin, pressure in Pascals and 

flux in W/m2

. 

Species Output (project.s.csv) 

At present, the eight species, oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), 

hydrogen cyanide (HCN), hydrogen chloride (HCL), water vapor (H2O), optical depth (OD), 

and concentration-time dose (CT) are listed. This set of eight is enumerated for each 

compartment, and are done sequentially by compartment. 

There will be N-1 (number of interior compartments) instances of 

Time C1 C1 ... 

 Upper Lower ... 

 O2 O2 ... for each species in order (see above) 

The units are O2 in %, CO2 in %, CO in ppm, HCN in ppm, HCL in ppm, H2O in %, OD in 

1/m, CT in g-min/m3. 

Vent Flow (project.f.csv) 

First is the horizontal flow through vertical vents such as windows and doors. There are two 

types of output, first to and from the outside, and second for interior compartments. The flow 

is broken down to flow in and out of the compartments. For flow to and from the outside 

(compartment N) there are two entries. For interior compartments, there are additional entries 

for entrainment into the upper and lower layers. Please see the technical reference guide for a 

detailed description of these flow fields. 

Second is the vertical flow through horizontal vents. There are two entries for each 

compartment, showing the total flow into or out of the compartment. 

Third is the mechanical ventilation. Once again, there will be an entry for each 

node/compartment pair, showing the total flow into or out of the compartment through this 

node. 

An example of horizontal flow for two compartments is 

‘Time’, ‘Inflow from 2 to 1', ‘Outflow to 2 from 1', ‘Mixing to Upper 1 ( 2 )’, ‘Mixing to Lower 1 ( 2 )’ 

and for vertical flow 

V Outflow from 1 to Out,V Inflow from 1 to Out 
User’s Guide Version 6 Chapter 5 Output • 65 

and for mechanical ventilation 

‘MV Inflow to 1', ‘MV Outflow from 1' 

Temperatures and flux (project.w.csv) 

This spreadsheet provides information on surface and target temperatures and flux, and 

reports on the current state of detectors and sprinklers (as a sub-set of detectors). Flux is 

reported in Watts/m2, and temperature in Kelvin. Activation of a detector is binary (yes or 

no). Velocity is in m/s. 

The first line in the spreadsheet is the compartment name or detector number, followed by 

the second line which is the measure being reported. 

‘Time’ ‘burn_room’ ‘burn_room’ ‘burn_room’ ‘burn_room’ ‘burn_room’ ... 

 ‘ceiling’ ‘upper wall’ ‘lower wall’ ‘floor’ ‘flux to target’ ‘total fire rad.’ ‘surface rad.’ ‘gas rad.’ and ‘conv. flux’ 

Following the compartment and target information is the detector output. The decoding for 

the type is 1 for a smoke detector, 2 for heat detector and 3 for other. In the activation 

column, 1 is yes and 2 is no. There will be a set of 10 columns for each compartment 

following this format. 

Error Messages 

In some (hopefully rare) cases, a simulation will fail to complete. In those cases, an error 

message provides guidance to the user on possible reasons for the failure. The message will 

contain an error number which provides a reference to additional information from the table 

below. Most often, these errors result from improper information in the input data files. 

During initialization of the program for a simulation, CFAST may stop with an error message 

if the simulation cannot be initialized due to a missing or incorrect file specification. The 

error codes are as follows: 

• 100 program called with no arguments (no input file) 

• 101 code for a free burning fire should not be reachable 

• 102 project file does not exist 

• 103 total file name length including path is more than 256 characters 

• 104 one of the output files is not accessible (for example, if a cfast case with this 

name is already running) 
66 • Chapter 5 Output User’s Guide Version 6 

• 105 error writing to an output file (openoutputfiles) 

• 106 a system fault has occurred. Applies to all open/close pairs once the model is 

running 

• 107 incompatible options 

• 108 not used 

• 109 cannot find/open a file 

• 110 error in handling the status input/output 

Error codes from 1 to 99 are from the routine which parses the input and will be reported in 

the .log file. The first set indicates a command with the wrong number of arguments. These 

errors indicate an error in a particular input command as follows: 

• Code 1, TIMES command 

• Code 2, TAMB command 

• Code 3, EAMB command 

• Code 4, LIMO2 command 

• Code 5, THERMAL or OBJECT commands 

• Code 7, MAINF command 

• Code 8, COMPA command 

• 10, HVENT command 

• 11, EVENT command 

• 12, MVENT command 

• 23, VVENT command 

• 24, WIND command 

• 25, INTER command 

• 26, MVOPN command 

• 28, MVDCT command 

• 29, MVFAN command 

• 32, OBJECT command 

• 34, CJET and DETEC command 

• 35, STPMAX command 

• 37, VHEAT command 

• 39, ONEZ command 

• 41, TARGE command 
User’s Guide Version 6 Chapter 5 Output • 67 

• 46, HALL command 

• 47, ROOMA command 

• 51, ROOMH command 

• 55, DTCHE command 

• 56, SETP command 

• 58, HHEAT command 

• 65, HEATF command 

 

The second set of errors related to parsing the input indicate specific errors with a command 

as follows: 

Error 

Code 

CFAST 

Command 

Error 

9 compa Compartment out of range 

26 inter Not a defined compartment 

27 mvopn Specified node number too large for this system 

30 mvfan Fan curve has incorrect specification 

31 Exceeded allowed number of fans 

33 object Object must be assigned to an existing compartment 

35 detect Invalid DETECTOR specification 

36 A referenced compartment is not yet defined 

38 vheat VHEAT has specified a non-existent compartment 

42 target Too many targets are being defined 

43 The compartment specified by TARGET does not exist 

44 Invalid TARGET METHOD 

45 Invalid equation type specified in TARGET 

49 rooma Compartment specified by ROOMA does not exist 

52 roomh Compartment specified by ROOMH is not defined 

53 ROOMH error on data line 

54 Data on the ROOMA (or H) line must be positive 

57 setp Trying to reset the SETP parameters 

61 hheat HHEAT specification error in compartment pairs 

62 Error in fraction for HHEAT 

63 Fire type out of range 

64 mainf The fire must be assigned to an existing compartment 

66 heatf The heat source must be assigned to an existing compartment 

67 mvent Compartment has not been defined 

68 Exceed one of the array bounds, ierror=68 (external), 69 (internal) and 70 (fan) 

71 event Undefined vent type 
68 • Chapter 5 Output User’s Guide Version 6 

Error 

Code 

CFAST 

Command 

Error 

72 inter Specification for interface height is outside of allowable range 

73 inter Compartments must be defined in pairs 

74 setp The requested “SETP” command does not exists 

75 Incorrect file reference 

76 Cannot read the parameter file 

77 Unsupported parameter 

Errors from 200 to 299 are errors which occur during data initialization as follows: 

Error 

Code 

CFAST 

Command 

Error 

200 inputmainfire cannot find the mainfire.o file in either the data or executable directory 

201 inputobject (read the object databases), too many targets being defined 

202 inputtpp (read the thermophysical database) cannot find the thermophysical properties 

file 

203 exceeded size of thermophysical properties data structure 

204 data format in the thermophysical data file is not correct 

205 initwall name is not defined in the thermophysical database 

206 readinputfile Incorrect CFAST version specified in input data file 

207 readcsvfile exceed array bounds for input (nrow) 

208 inputobject exceed array bounds for object fire (nv) 

209 inputmainfire exceed array bounds for object fire (nv) 

210 inputobject object name requested does not match the name in the object file 

211 spreadsheetnor

mal 

exceed number of entries in normal output (maxhead) 

212 hvinit fan not properly defined (mvent command) 

213 inittarg target points to a non-existent compartment 

214 target center out of range (outside compartment) 

215 inputobject cannot find the object file in either the data or executable directory 

216 normal vector cannot be zero 

Errors 400 and above are failures while the model is running. In particular, 610 through 685 

are failures when IDID<0 from DASSL/RESID. 
User’s Guide Version 6 References • 69 

References 

1

 Jones, W.W., Peacock, R.D., Forney, G.P., and Reneke, P.A., “CFAST – Consolidated Model of 

Fire Growth and Smoke Transport (Version 5), Technical Reference Guide,” National Institute of 

Standards and Technology, Spec. Pub. 1030 (2004). 

2

 Gross, D., “Data Sources for Parameters Used for Predictive Modeling of Fire Growth and Smoke 

Spread,” National Institute of Standards and Technology, NISTIR 85-3223 (1985). 

3

 Jones, W.W. and Peacock, R.D., “Technical Reference Guide for FAST Version 18,” National 

Institute of Standards and Technology, TN 1262 (1989). 

4

 Cooper L.Y. and Forney, G. P., “The Consolidated Compartment Fire Model (CCFM) computer 

application CCFM-VENTS – part I: Physical reference guide,” National Institute of Standards and 

Technology, NISTIR 4342 (1990). 

5

 Peacock, R. D., Jones, W. W., Forney, G. P., Portier, R. W., Reneke, P. A., Bukowski, R. W., and 

Klote, J. H., “Update Guide for HAZARD I Version 1.2,” National Institute of Standards and 

Technology, NISTIR 5410 (1994). 

6

 ASTM Standard Guide for Evaluating the Predictive Capability of Deterministic Fire Models, 

ASTM E1355-04, West Conshohocken, PA (2004). 

7

 Forney, G.P. and McGrattan, K.B., “User's Guide for Smokeview Version 4: A Tool for 

Visualizing Fire Dynamics Simulation Data.” Natl. Inst. Stand. Technol., Spec. Pub. 1017 (2004). 

8

 U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976. 

9

 The CRC Handbook of Chemistry and Physics, David Lide, Editor, CRC Press, Boca Raton 

(1994). 

10 Klote, J.K. and Milke, J.A., Design of Smoke Management Systems, American Society of 

Heating, Refrigerating and Air-conditioning Engineers, Atlanta, GA (1992). 

11 ASHRAE Handbook HVAC Systems and Equipment, American Society of Heating, Refrigerating 

and Air-Conditioning Engineers, Atlanta, GA (1992). 

12 Klote, J. H., A Computer Model of Smoke Movement by Air Conditioning Systems, NBSIR 87-

3657 (1987). 
70 • References User’s Guide Version 6 

13 G. W. Mulholland and C. Croarkin, Specific Extinction Coefficient of Flame Generated Smoke, 

Fire and Materials 24, 227 (2000). 

14 Jin, T. , “Evaluation of Fire Exit Signs in Smoke,” Systems Approach to Fire Safety in Buildings. 

Volume 2. Session 3. Active Systems Performance and Criteria: Smoke Control, Detection, 

Sprinklers. Session 4. Passive Systems Performance and Criteria: Combustibles, Fire Resistance. 

August 29-30, 1979, Tsukuba, Japan, III/73-78 pp, 1979. 

15 Drysdale, D., “An Introduction to Fire Dynamics,” John Wiley and Sons, New York, (1985). 

16 Tewarson, A., “Combustion of Methanol in a Horizontal Pool Configuration,” Factory Mutual 

Research Corp., Norwood, MA, Report No. RC78-TP-55 (1978). 

17 McCaffrey, B.J., “Entrainment and Heat Flux of Buoyant Diffusion Flames,” National Bureau of 

Standards (U. S.), NBS IR 82-2473 (1982). 

18 Koseki, H., “Combustion Properties of Large Liquid Pool Fires,” Fire Technology 25, 241 (1989). 

19 Babrauskas, V. and Grayson, S. J., “Heat Release in Fires” Elsevier Applied Science, London 

(1992). 

20 Evans, D. D., “Sprinkler Fire Suppression Algorithm for HAZARD,” Natl. Inst. Stand. Technol., 

NISTIR 5254 (1993). 

21 Davis, W. D. And Notarianni, K. A., “NASA Fire Detector Study,” Natl. Inst. Stand. Technol., 

NISTIR 5798 (1996). 

22 Heskestad, G., "Fire Plumes, Flame Height, and Air Entrainment" in The SFPE Handbook of Fire 

Protection Engineering, 3rd Ed., National Fire Protection Association (2002). 

23 Peacock, R. D., Jones, W. W., Bukowski, R. W., and Forney, C. L., “Technical Reference Guide 

for the HAZARD I Fire Hazard Assessment Method, Version 1.1,” Natl. Inst. Stand. Technol., 

Handbook 146 (1991). 
User’s Guide Version 6 Appendix A CFAST Keywords • A-1 

Appendix A CFAST Keywords 

All key words are case sensitive and all parameters are required. There are no defaults. If a 

parameter is missing, the model will terminate with an appropriate stop code. 

CJET 

CJET Ceiling_Jet_Flag 

This directive tells the model to calculate the effects of a ceiling jet in all compartments 

containing a fire. The possible flags are OFF, CEILING, WALL, or ALL. 

 OFF - not calculate ceiling jets effect 

 CEILING - include calculations for ceiling surfaces only 

 WALL - to include calculations for wall surfaces only (not recommended) 

 ALL - to include calculations for both ceiling and wall surfaces 

Example: 

CJET,CEILING 

COMPA 

COMPA Name Width Depth Internal_height Absolute_x_position Absolute_y_position 

Floor_Height Ceiling_Material Floor_Material_Name Wall_Material_Name 

The compartments are numbered internally as they are read in. The other key words which 
A-2 • Appendix A CFAST Keywords User’s Guide Version 6 

refer to compartment numbers then refer to these ordinals. Compartments must be defined 

before they are referenced by other commands. 

Example: 

COMPA,hallway,9.1,5.0,4.6,0.,0.,0.,CONCRETE,CONCRETE,CONCRETE 

DETEC 

DETEC Type Compartment Activation_Temperature Depth Width Height RTI Suppression 

Spray_Density 

The DETEC keyword is used for both detectors and sprinklers. Sprinklers and detectors are 

both considered detection devices and are handled using the same input keywords. Detection 

is based upon heat transfer to the detector. Fire suppression by a user-specified water spray 

begins once the associated detection device is activated. 

For the type of detector, use 1 for smoke detector and 2 for heat detector or sprinklers. If 

suppression is set to a value of 1, a sprinkler will quench the fire with the specified spray 

density of water. If turned off (a value of 0), the device is handled as a heat or smoke detector 

only – values entered for activation temperature, RTI, and spray density are ignored. 

The spray density is the amount of water dispersed by a water sprinkler. The units for spray 

density are length/time. These units are derived by dividing the volumetric rate of water flow 

by the area protected by the water spray. The suppression calculation is based upon an 

experimental correlation by Evans, and depends upon the RTI, activation temperature, and 

spray density to determine the behavior of the sprinkler. 

Example: 

DETECT,2,1,344.2,1.5,1.5,2.29,98,1,7.00E-05 

DTCHE 

DTCHE Minimum_Time Count 
User’s Guide Version 6 Appendix A CFAST Keywords • A-3 

The purpose of DTCHE is to prevent excessive computation with a very small time step. This 

often appears to users as a stalling condition, when it is simply the set of equations has 

reached a point that requires a very small increment in time for the solver to converge. A 

negative entry on DTCHECK turns off the time step checking algorithm. 

Example: 

DTCHECK,1.E-9,100 

EAMB and TAMB 

EAMB and TAMB Ambient_Temperature Ambient_Pressure Station_Elevation 

Relative_Hunidity. 

This key word is to set the ambient condition, TAMB for the internal and EAMB for outside 

the building. For the internal ambient, relative humidity sets the initial water concentration in 

the ambient air. For the external ambient, it sets the water content for air flowing into 

compartments through vents connecting to the exterior. Temperatures are in Kelvin, pressure 

in Pascals, and relative humidity in percent. 

Example: 

EAMB,300,101300,0, 

TAMB,300,101300,0,5 

EVENT 

EVENT TYPE First_Compartment Second_Compartment Vent_Number Time 

Final_Fraction. The “H” indicates a horizontal flow event that changes the vent opening. 

Final_Fraction is the percent of the full opening width expressed as a fraction. 

Used to open or close a vent. This replaces CVENT and applies to all vents for vertical flow 

(V), horizontal flow (H) and mechanical flow (M). The intent is to allow these events to be 

triggered by time, temperature or flux as is done with detectors. However, at the moment, 

time is the only option. 
A-4 • Appendix A CFAST Keywords User’s Guide Version 6 

The form for EVENT is 

EVENT H First_Compartment Second_Compartment Vent_Number Time Final_Fraction Decay_time 

EVENT V First_Compartment Second_Compartment V_ID Time Final_Fraction Decay_time 

EVENT M First_Compartment Second_compartment MVENT_ID Time Final_Fraction Decay_time 

Decay time is the time the event takes to happen and the units are seconds. 

Example: 

EVENT,H,1,2,1,10.,0.3,1 

HALL 

HALL Compartment Velocity Depth Decay_Distance

This command invokes the corridor flow algorithm. For long hallways or corridors, there can 

be a significant delay time for the initial hot gas layer to travel along the ceiling to the far end 

of the compartment. By estimating the time required for a ceiling jet to travel in a corridor 

and the temperature distribution along the corridor, CFAST can delay flow into 

compartments connected to corridors until the ceiling jet has passed the connections to these 

compartments.

If the aspect ratio of a compartment (length/width) is greater than about 10, this algorithm 

should be used. 

Example: 

HALL 3 0.15 0.1 16.7 

For each of the Velocity, Depth and Decay, using a value of (-1) will bypass this setting. This 

is so that, for example, the decay distance can be set while using default values for velocity 

and depth. 

HEATF 

HEATF ROOM POS(3) PLUME HRR
User’s Guide Version 6 Appendix A CFAST Keywords • A-5 

HHEAT First_Compartment Number_of_Parts N pairs of {Second_Compartment, Fraction} 

Used to allow heat conduction between pairs of compartments which have a contiguous 

vertical partition between them. There are two forms of this command. The first uses only a 

compartment number. In this case, the conduction connection 

The first form is to use only a compartment number. In this case, CFAST will calculate the 

conductive heat transfer to all compartments connected to this compartment by horizontal 

convective flow. The second form specifies the compartments to be connected and what 

fraction of the compartment is connected to an adjacent compartment. This latter is 

particularly useful for rooms which are connected to adjacent rooms as well as hallways. The 

user of the model is responsible for the consistency of these pairings. The model does not 

check to insure that the specified compartment pairs are located next to one another. 

Example: 

HHEAT,1,1,2,0.5

specifies that compartment one has one connection to compartment two and the fraction of 

wall surface through which heat is transferred is 1⁄2 of the wall surface of compartment one. 

HVENT 

HVENT First_Compartment Second_Compartment Vent_Number Width Soffit Sill 

Wind_Coefficient First_Compartment_Offset Second_Compartment_Offset FACE 

Initial_Opening_Fraction. 

Vent which allows horizontal flow of gases, through vents such as doors and windows. 

Compartment offsets are triplets from the compartment origin. FACE is an integer from 1 to 

4 counterclockwise from the origin defining which wall face to place the vent on when 

visualizing with Smokeview. It doesn't affect the dynamics of the calculation, just the way it 

looks. The size of the opening can be modified by EVENT. This changes the 

Opening_Fraction from the initial value (set above) to some other value. Typical use is to 

start with the door open (Initial_Opening_Fraction = 1) and use EVENT to close the door 

(Final_Fraction = 0). 

Example: 

HVENT,1,2,1,2.4,1.0,0.,0.,0.,0.,1,0.9 
A-6 • Appendix A CFAST Keywords User’s Guide Version 6 

INTER 

INTER Initial_Interface_Height_1 Initial_Interface_Height_2 ... Initial_Interface_Height_N 

This is used to set the initial interface height below the top of the compartment. A great deal 

of care is needed to use this, as the model has only rudimentary checks for the limits imposed 

(for example, the initial value must specify a height not greater than the compartment height. 

This does change the nature of a zone in the context of a zone model. 

Example: 

INTER 2 1.2 3 2.0 

LIMO2 

LIMO2 Lower_Oxygen_Limit 

This is the limiting oxygen index for gaseous combustion. In version 5 and earlier, it was on 

the CHEMIE line. It is global and applies to gaseous combustion in all plumes. Please read 

the technical reference manual for the meaning and implication of setting this parameter. 

Example: 

LIMO2,6 

would set the lowest limit for gaseous combustion to 6% 

MAINF 

MAINF ROOM POS(3) PLUME 

A simple fire. The key word refers to the mainfire.o file. POS is the three dimensional 
User’s Guide Version 6 Appendix A CFAST Keywords • A-7 

position vector, relative to the front, lower, left corner of the compartment. 

Example: 

MAINF,2,.1,.1,.1,1 

MVENT 

MVENT From_Compartment To_Compartment ID_Number From_Opening_Orientation 

From_Center_Height From_Opening_Area To_OpeningOrientation To_Center_Height 

To_Opening_Area Flow Begin_Dropoff_Pressure Zero_Flow_Pressure initial_fraction 

This replaces the more complex mechanical ventilation commands with a constant flow fan 

connection. The original commands MVOPN MVFAN MVDCT and INELV are not 

supported in this version. The command specifies a pair of openings connected by a constant 

volume flow fan. The fan flow can be modified with the EVENT key word. 

Example: 

MVENT,5,7,1,V,0.50,1.00,H,2.40,1.10,2.00,200.,300.,1.0 

OBJECT 

OBJECT NAME ROOM POS (3) PLUME IGNITION_TYPE IGNITION_CRITERION 

NORMAL (3)

This key word places a fire (designated objects for version 6) into a compartment. The 

NAME on the object line should match the name in the file. While the main fire (MAINF) 

places a very simple fire in a compartment, mimicking a sand burner, OBJECTs are intended 

to simulate real burning items and must have attributes such as an orientation. The format for 

the fire objects is shown in “V6 Fire Format.xls.” A position vector of (-1,-1,-1) puts the 

object in the center of the compartment on the floor. A pointing vector of (0,0,1) is facing 

upward. 

Example: 
A-8 • Appendix A CFAST Keywords User’s Guide Version 6 

OBJECT,WARDROBE,1,-1,-1,0.,1,0,0.00,-1,-1,-1 

ONEZ 

ONEZ Compartment 

For tall compartments or those removed from the room of fire origin, the compartment may 

be modeled as a single, well-mixed zone rather than the default two-zone assumption. A 

single zone approximation is appropriate for smoke flow far from a fire source where the 

two-zone layer stratification is less pronounced than in compartments near the fire. This is 

used in situations where the stratification does not occur. Examples are elevators, shafts, 

complex stairwells, and compartments far from the fire. 

Example: 

ONEZ,2 

ROOMA and ROOMH 

ROOMA and ROOMH Compartment Number_of_values Area(or Height) 

These key words allow the user to define non-rectangular rooms by specifying crosssectional area as a function of height. One set of values is included for each compartment that 

has a variable cross-sectional area. The format in both cases is the key followed by an index 

of the number of values. These key words must be used in pairs. 

Example: 

ROOMA 1 3 10.0 5.0 3.0 

ROOMH 1 3 0.0 1.0 2.0

specifies that compartment 1 has a cross-sectional area of 10 m2, 5 m2 and 3 m2 at elevations 

0.0 m, 1.0 m and 2.0 m respectively.
User’s Guide Version 6 Appendix A CFAST Keywords • A-9 

THRMF 

THRMF Thermophysical_Properties_File 

By default, thermophysical properties are obtained from the thermal.csv which is located in 

the directory where the model executables reside. This allows for another file to be used. 

Example: 

THRMF,NEWTHERMALFILE 

STPMAX 

STPMAX Maximum_Time_Step 

This specifies the largest time step that the model will take. The default value is one second. 

In most cases, the numerical routines adjust the time step appropriately; however, for long 

simulation times and slowly varying conditions, a larger value is appropriate. In cases where 

the fire height and vent soffits interact, the time step may need to be smaller. 

Example: 

STPMAX,0.2 

TARGE 

TARGE Compartment Depth Breadth Height Normal_Depth Normal_Breadth 

Normal_Height) Material Method Equation_Type 

CFAST can track and report calculations of the net heat flux striking arbitrarily positioned 

and oriented targets and the temperature of these targets. A non-zero normal vector must be 

specified as must a material from the thermophysical database. Method can be one of 

STEADY for steady state solution, XPLICIT for explicit solution, and MPLICIT for an 

implicit solution. 
A-10 • Appendix A CFAST Keywords User’s Guide Version 6 

Example: 

TARGE,1,2.20,1.88,2.34,0.00,0.00,1.00,CONCRETE,IMPLICIT,PDE 

TIMES 

TIMES Simulation_Time Print_Interval History_Interval Nornal_Output_Interval 

WallandTarget_Output_Interval Vent_Flow_Output_Interval Species_Output_Interval. 

Example: 

TIMES,360,-120,130,140,150, 

Printed output will be on the screen or in a file named project.out. The binary history output 

(for use with the DLL package) will be in project.hi. The four spreadsheet listings are in 

project.{n.csv, w.csv, f.csv and s.csv}. Please see Appendix ??? for a discussion of the 

format of each of these files. 

VERSN 

VERSN,version number, Title 

The header is $$CF$$ and is case sensitive. The major version number from the file must 

match the major version number kept internally (6 at the moment). 

Example 

VERSN,6,"Simple test of the object file input" 

VHEAT 

VHEAT First_Compartment Second_Compartment 
User’s Guide Version 6 Appendix A CFAST Keywords • A-11 

Heat transfer between the ceiling and floor of specified compartments can be incorporated 

with the VHEAT key word. Ceiling to floor heat transfer occurs between interior 

compartments of the structure or between an interior compartment and the outdoors. The 

model checks to make sure that the ceiling and floor are reasonably contiguous (within 0.01 

m), and the assumption is made that this is true for the entire ceiling and floor. 

Example: 

VHEAT,1,2 

The floor properties of the top compartment (1 in this case) and the ceiling properties of the 

bottom compartment (2 in this case) must be defined by COMPA and included in the 

thermophysical file. 

VVENT 

VVENT from_compartment to_compartment area shape initial_fraction 

Combined buoyancy and pressure driven (i.e., forced) flow through a horizontal vent 

(vertical flow) is possible when the connected spaces are filled with gases of different density 

in an unstable configuration, with the density of the top space larger than that of the bottom 

space. This type of flow is inherently different from horizontal flow (vertical vent) in that 

there is not layer to layer mixing from inverted plumes. This key word describes those 

horizontal openings between the compartments through which this type of flow occurs. Each 

VVENT line in the input file describes one horizontal vent. There are four parameters, the 

connected compartments, the shape of the opening, and the effective area of the vent. 

Example: 

VVENT,1,2,4.0,2,0.9 

WIND 

WIND Wind_Speed Scale_Height Power_Law_Coefficient 
A-12 • Appendix A CFAST Keywords User’s Guide Version 6 

The wind speed, scale height, and power law are used to calculate the wind coefficient for 

each vent connected to the outside. The wind velocity is specified at some reference height. 

The power law then provides a lapse rate for the wind speed. An assumption is that the wind 

speed is zero at the surface. This is the same format as in version 5. Please see the technical 

reference guide on the formula used in this calculation. 

Example: 

WIND,3.,10.,0.16