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Re: Computer modeling
Posted by:
J L Mazerat (IP Logged)
Date: September 28, 2020 10:33AM
Let’s see if I can answer this question. NIST did a comparison of CFD model, Zone Model, and the Hand Calculation Method. They compared the predicted HGL temperature rise to the measured HGL temperature rise of an experiment. From this comparison they were able to show the error rate at different time in the burn experiment for each of the models and the hand method. This showed that in the initial stage of the fire all the models and the hand method matched the temperature rise of the actual fire. As the fire progressed there was a deviation in each of the models and the hand method from the actual temperature rise in the actual burn experiment. From this data they were able to say that at a specific time the error rate for a specific model or the hand method. In this case, the data indicates that at 300ºC (572ºF) there was a potential average error rate of +/- 13%. If we extrapolate this to a temperature of 1100ºF (593ºC), which it the temperature the U.S. Fire Administration states is the approximate temperature when one can expect flashover to take place, one would expect this average error rate to increase proportionally. Would you agree this is what one can expect? The 572ºF is approximately 52% of the 1100ºF. Where I do not believe the error rate will increase 52%, it is reasonable to believe there would be some increase.
Based on your answer, is one to conclude that the CFD model, the Zone model, and the Hand Method use the same mathematical and phenomenological approaches? If this is a correct conclusion, then I can agree that the CFI calculator cannot be compared to these other models and to the hand method based on what you are saying. If they are not the same mathematical and phenomenological approaches, then I have a problem understanding why the same test that was done in the verification and validation of the accuracy of these models and methods cannot be done using the CFI calculator.
Jim Mazerat
Forensic Investigations Group