Thursday, November 12, 2015

Uploading text files for Issues on GitHub

I recently got notification from GitHub support that they now allow Write access for uploading text files to Issues posts.  This is welcome news.

Thanks to Dave McGill for testing this new feature.

This means that when you post an Issue you can attach your input file.  But remember you need to append ".txt" to the file name.  For example, if your input file is simple_test.fds, you need to change the name to simple_test.fds.txt or just simple_test.txt.

Tuesday, November 10, 2015

FDS 6.3.1 Maintenance Release

Today we posted a maintenance release, FDS 6.3.1, bundled with Smokeview 6.3.2.

The main motivation for pushing out this release is to correct a bug in the mixing step for multi-step and finite-rate chemistry calculations.  The default simple chemistry model is not affected.

An optional input parameter DT_HVAC has been added to help stabilize duct flow calculations.

Additionally, we have been working on testing FDS scaling on large compute clusters, like Titan at Oak Ridge National Laboratories.  The results for weak and strong scaling on our burn cluster at NIST are published in the new user's guide and we have added an option to suppress output diagnostics, which slow the code for large jobs.

FDS-SMV website

FDS-SMV download page

Installation Instructions

FDS Release Notes

Smokeview Release Notes

Thursday, November 5, 2015

CFAST 7 Released

Although this blog is intended primarily for news about FDS and Smokeview, we want to turn your attention for the moment to the zone model CFAST (Consolidated Fire And Smoke Transport). CFAST has been around since the late 1980s, and as the word "consolidated" implies, it was intended to unify into one code base various zone models that were developed at NIST and elsewhere in 1980s. It's been around for 25 years and has undergone 7 major revisions; the latest was released this week.

Many of you might be surprised to learn that CFAST is even still around. Why do we need CFAST when we have FDS? Doesn't FDS do everything that CFAST does, and more? Yes, it does, but FDS doesn't run in a second. Over the past decade, we've collaborated with the U.S. Department of Energy and the U.S. Nuclear Regulatory Commission, both of which still endorse the use of CFAST for its own inspectors and licensees in doing hazard analyses of high risk facilities. These analyses, or probabilistic risk assessments (PRAs), typically involve facilities with hundreds of compartments, many of which are simple and not heavily loaded with combustibles. CFAST is a great tool for doing "screening" analyses of these compartments. FDS is sometimes used in cases where the fire scenario does not conform to the basic assumptions of CFAST -- usually it is geometric complexity that demands CFD as opposed to a two-zone model.

Because we have a limited staff at NIST, we have tried to leverage all of the fire modeling expertise we have in maintaining CFAST. You will notice that the latest releases of FDS and CFAST are both installed in a folder called "firemodels" on a Windows PC. CFAST and FDS are in the same organization on GitHub,, they use the same experiments for validation, they use the same basic installation process under Windows, and most importantly, they both use Smokeview.

CFAST 7 is a significant overhaul of the model, but not because we added new features. In fact, we removed many features, streamlined the source code and documentation, and improved (hopefully) the graphical user interface. We did this because we realized that CFAST was too bloated with unvalidated, undocumented, untested, and unnecessary features that detracted from its real value of being a simple, robust compartment fire model. How did this happen? Easy -- and it should be seen as a cautionary tale to anyone who wants to develop a new fire model. If you take a look at a survey conducted by the engineering firm Combustion Science and Engineering,

you'll notice that there have been over 50 zone models developed in the past 3 decades, but only 3 (in the survey anyway) are still under some kind of maintenance. The rest -- who knows? We suspect, based on our own experience, is that developing a zone model is fairly easy, but maintaining it is hard. We spend more time doing routine maintenance work for FDS than we spend developing new features. CFAST is certainly not as complex as FDS, but it still requires good documentation, a usable interface, verification and validation, and compatibility with evolving computer operating systesm. The team that developed CFAST has dwindled down to a few people, principally Rick Peacock, and its long term prospects are uncertain. At the very least, the latest overhaul of CFAST has put it in a better place with respect to long term maintenance, but no matter how good our current practices are, no model can sustain itself on auto-pilot. Those 50 plus zone models have essentially rotted -- even if one is able to recompile and run them, they would not pass a thorough quality review that we expect of fire models these days. These old codes were basically academic exercises developed by individuals or organizations who had no particular long term plan for them.

In the next few months, we're hoping to do some kind of survey to assess who is using CFAST so that we can plan for the future. Your input will be critical. There is no point in expending scarce resources on a model that is not used. We hope, however, that if you take a look at the new CFAST you will find that it still has a role to play in fire protection engineering. Don't be shy with your feedback. If something doesn't work, or even if something seems more difficult than it should be, let us know. CFAST uses GoogleGroups for general discussion:!forum/cfast

and GitHub for specific Issue Tracking: