Issue 17: Version 5 of Fire Dynamics Simulator and Smokeview Released
By Kevin McGrattan, Glenn Forney, Bryan Klein, Jason Floyd, Simo Hostikka and Timo Korhonen
In October 2007, the latest version of Fire Dynamics Simulator (FDS) and the visualization program, Smokeview, were released. FDS is a computational fluid dynamics (CFD) model of fire, and Smokeview is a graphics program that conveys the results of FDS in various forms of 3-D animation.
The first official version of FDS/Smokeview, released in 2000, was aimed at large scale simulations of smoke movement from prescribed, well-ventilated fires. This first version was ideal for design work where the fire's heat release rate is not predicted by the model, but rather specified by the model user. However, during the NIST Investigations of the World Trade Center collapse and the Station Nightclub fire, it became evident that FDS needed improved sub-models to make it an effective forensic tool. That is, there was now a need to simulate actual fires, rather than just hypothetical ones.
What's new in FDS/Smokeview?
Combustion: Previous versions of FDS generally assumed that fuel and oxygen readily burned on contact, a very good assumption for well-ventilated fires. However, most fire scenarios involve some degree of under-ventilation, in which case the production rate of carbon monoxide and soot, along with other toxic by-products, can dramatically increase. The combustion model in FDS has been improved so that it can now model extinction and the user now has the option to model rather than specify CO production.
Pyrolysis: The FDS solid phase algorithms have been overhauled to provide a better description of heat transfer and pyrolysis. First, there is an increased functionality that allows multiple layers of materials. This was an obvious improvement to make, given the experience with insulated steel in the WTC, and polyurethane foam covering plywood walls in the Station Nightclub. Next, the pyrolysis algorithm has been generalized to allow for multiple materials undergoing multiple reactions. The intent here is to retain the simplicity of past versions, but open up the possibility of increased complexity in describing how real materials burn.
Material Property Input: Versions 1 through 4 of FDS included a "database" of properties for common building materials, furnishings and other potential "fuels." These properties were a collection of bench-scale measurements, handbook values and "best estimates" that were often misunderstood and misapplied by the model users. Originally, the database was to serve as a set of examples, but given the scarcity of data for real materials, it became a de facto standard. As a result, starting with FDS version 5, the database has gone away. It is hoped that this will spur a renewed effort by the fire research community to develop new, or re-interpret existing, robust, practical methods of obtaining material properties, with an emphasis on fire-specific phenomena like pyrolysis and char formation.
Evacuation: FDS 5 contains an evacuation model developed at VTT, Finland, that allows the simulation of the fire and evacuation processes simultaneously. The obvious benefits of implementing an evacuation model directly into FDS are the straightforward computation of how the fire affects people, possibility for two-way coupling (people open doors and change the ventilation) and the time savings when the simulation geometry is defined for only one piece of software. In addition to the actual movement of people, the model tries to account for some of the evacuee decision making processes as well. The evacuation model is still in its early stages but has already found applications in practical fire safety engineering. More information can be found at www.vtt.fi/fdsevac.
Visualization: Smokeview remains the key to understanding the fairly complex FDS calculations that can consume days or weeks of computing time on an entire network of computers. Just processing the tremendous amount of data is a challenge in itself, and the rendering of clear, easy to understand animations means keeping up with the monthly advances in graphics hardware and software. Also, Smokeview has been designed to render the output of the NIST zone model CFAST.
Verification and Validation: In the past several years, organizations such as SFPE1 and the US Nuclear Regulatory Commission2 have conducted Verification and Validation (V&V) studies of different fire models. In short, V&V is a process to assess the accuracy of the mathematical solvers and the underlying physical assumptions of the models. For FDS, this was done informally, via journal articles, conference proceedings, and student theses, both at NIST and elsewhere. However, there was no systematic approach to the process. Now, there are "suites" of case studies and experimental datasets against which FDS will be checked periodically to ensure that the model retains the accuracy of previously reported studies. While this can be a somewhat tedious task, it is essential for maintaining quality control.
Support: FDS and Smokeview originated as "research" codes, and to this day can be a bit daunting to anyone new to fire modeling. However, there is a new emphasis on user support. By exploiting several free on-line services provided by Google, FDS/Smokeview now has an easy to use Discussion Group where users can post questions and comments, a simple bug-reporting service where cases can be assigned to one of the developers for rapid resolution, and a simple point and click download facility. In addition to improved support for users, FDS is now being developed and maintained using fairly common software development tools. The source code and manuals are stored in an external repository and can be accessed by all members of the team and anyone else who is interested in working with the actual source code. This idea of "version control" is not unusual to a commercial software development team, but it is relatively new for researchers whose primary education is not in computer science or information technology.
Finally, the most notable change in FDS/Smokeview 5 is the realization that the development and maintenance of sophisticated fire modeling software will require a collective effort by the fire research community. Although NIST remains the primary caretaker, professional societies, testing laboratories, universities, and consulting companies are playing an increasing role. Many of the changes made to the software and to its development infrastructure have been designed to facilitate its long-term maintenance by the various stakeholders. No single person or organization can do it alone.
For more information on FDS and Smokeview, see www.fire.nist.gov/fds/.
Kevin McGrattan, Glenn Forney and Bryan Klein are with the National Institute of Standards and Technology. Jason Floyd is with Hughes Associates, and Simo Hostikka and Timo Korhonen are with VTT, Finland.
- Evaluation of the Computer Fire Model DETACT-QS, Society of Fire Protection Engineers, Bethesda, MD, 2002.
- NUREG-1824 and EPRI 1011999, "Verification and Validation of Selected Fire Models for Nuclear Power Plant Applications," Vols. 1-7, U.S. Nuclear Regulatory Commission, Washington, DC and Electric Power Research Institute, Palo Alto, CA, 2007.
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