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Justin M Edenbaum edited this page Sep 23, 2022 · 15 revisions

Register for the in-person OpenSES meeting on Friday, 30 September 2022, at 16:00 BST after BHR’s ISAVFT. This is your chance to influence updates to the program and documentation.

Welcome to OpenSES!

OpenSES is an open-source fork of version 4.1 of the Subway Environment Simulation (SES) computer program.

Subway Environment Simulation


The Subway Environment Simulation (SES) computer program is an engineering solver used to analyse tunnels and underground environments. SES was initially developed during the early 1970s as part of a United States Department of Transport funded initiative. The solver consists of analytical and predictive models for aerodynamic and thermodynamic phenomena based on one-dimensional computational theory. The original program was designed for mainframe computers and used punched cards for data input. Version 1 of the computer program was released in 1975. Following continued testing, improvements, and validation, Version 2 was released in 1976.

With SES Version 3 came the inclusion of models to aid the assessment of fire phenomena and designing emergency ventilation systems to control smoke movement. The one-dimensional computational theory was retained, as the SES Fire Model was designed with the ability to simulate the overall effects of a tunnel fire on the ventilation system. Version 3 was released in 1982. In March 1992, Version 3.01 was released as the first version developed for personal computers. The conversion to PCs brought improvements that allowed for larger and more detailed tunnel systems to be analysed. Data input for the computer program took the form of plain text files. The computer program and source code was publicly available.

In October 1996, development on SES Version 4 began. This work generally provided improvements related to the transition from mainframe to PC, validation of the Fire Model (using the Memorial Tunnel Fire Ventilation Test Program), and general bug fixes. Version 4.0 was issued in September 1997. In 2001, SES Version 4.1 was released. This version contained minor updates to the main program related to user input and providing better code compatibility with compilers available at the time.

SES Version 4.1 was the last publicly available version of the program before distribution was restricted. Other one-dimensional proprietary solvers have been developed from the models and source code included in Version 4.1. However, SES remains one of the pre-eminent tools used and specified in the analyses and design of tunnel ventilation systems.

Removing Restrictions on SES

After the tragic events of September 11, 2001, the United States Government became more sensitive to how bad actors could use software and data for nefarious purposes. Sometime in 2003, the United States Government halted the distribution of SES. While no official documentation can be found, there was a perception that the program was classified under the U.S. Sensitive Security Information (SSI) Program for perceived security issues. A campaign, spearheaded by NeverGray, began in September 2018 to petition the U.S. Government to remove any restriction for distribution of the program, source code, and documentation. Due to the committed efforts of this campaign, the SSI classification of SES Version 4.1 was removed in March 2021.

A copy of SES Version 4.1, as distributed prior to the SSI restriction, can be obtained from NeverGray.

Further Development

Presently, there is uncertainty regarding any further improvement to SES Version 4.1 by the U.S. Government. Also, other one-dimensional solvers developed from SES are proprietary and closed-source. A group of tunnel ventilation engineers have therefore decided to undertake an open-source fork of SES Version 4.1. Success has been demonstrated through the open-source development of tunnel ventilation industry tools such as Fire Dynamics Simulator and OpenFOAM. The OpenSES initiative aims to create a community that encourages the development of SES, allowing the program to progress along with the evolution of the tunnel ventilation and fire life-safety industry.


Keep track of the evolution of OpenSES over on our Release Notes page.

Third-party Tools

A list is provided of third-party tools suggested by members of the OpenSES community. These tools may help with user input and post-processing.