A Web-based Introduction to Fire Modeling
Definitions
Boundary Surface:
Some models are run by breaking space into different zones, or Control Volumes. The surface of the control volume is called the boundary surface.
Cone Calorimeter:
The Cone Calorimeter is an apparatus used for bench scale testing. It is comprised of a radiant heater, specimen holder, ignition source, load cell and a collection hood. Within the collection hood are ports for temperature and gas sampling. By measuring the Species Yields of the gasses, the mass lost from the burning object, and temperature the burning characteristics of the sample can be modeled.
Control Volume:
Certain models are run by breaking space up into different zones. Usually within each zone or control volume, the properties are assumed constant. This way an engineer only needs to calculate what is happening on the control volumes Boundary Surface and not the control volume itself. It is important to note that the larger the control volume, the less work (i.e. computational time and cost) but the larger the Error.
Empirical:
When data is from experimental tests (like from the Cone Calorimeter) the data is called Empirical. Usually many tests will be run and a trend line (or average) will be computed for all the tests. This trend line is what is then used as empirical data.
Error:
Error is the difference between the measured value and the theoretically correct or Empirically tested value. Since Empirical data comes from testing, it is not difficult to see that the lowest error would be when modeling items close to what was tested.
Heat Release Rate:
Heat released (Q in mathematical language) is the power of the fire, Heat Release Rate () is the power/time, the power released rate. In metric units is Watts or Jules/second and in English units, it is in Btu/hour. To give an idea of how much heat is released a typical propane grill, when on high, will release 30, 000 Btu of heat. A typical bed will have an average HRR of 28, 433 Btu/min, if the bed burns for 5 minutes, then the bed produces 142, 165 Btu. Room fires are very hot and release a lot of energy.
Mass Loss Rate:
A specimen looses its mass at this rate. In the Cone Calorimeter the load cell records the loss of mass, the rate (mass/time) is used to determine the burning characteristics of the sample.
Navier-Stokes equations:
These large differential equations describe fluid flow. Almost always these equations are not used in full, many times assumptions will be made to reduce the computational time; some problems just cannot be solved.
Re-radiation:
When a fire develops in a room or enclosure a smoke layer develops. Although the fire itself is releasing energy in the form of radiation, the smoke layer is too. This combination is what makes enclosure fires so fast. Not only does the fire heat new items to burn; the smoke layer does as well. To a lesser extent all the walls and commodities within a room also re-radiate, but to a much lesser degree then the smoke layer.
Species Yield:
The concentration of gas, usually toxic, is known as the species yield. Most often species yield is given in parts per million.
References
1. Babrauskas, Vytenis “Fire modeling: An introduction for attorneys" www.doctorfire.com/mod_test.html
2. Phillips, William ?Computer Simulation for Fire Protection Engineering? pg5-1 to 5-10 SFPE Handbook, 2nd Edition 1995
3. Janssens, Marc ?Calorimetry? pg3-16 to 3-36 SFPE Handbook, 2nd Edition 1995
4. Babrauskas, Vytenis ?The Cone Calorimeter? pg3-37 to 3-52 SFPE Handbook, 2nd Edition 1995
5. ASTM D 2859, ?Standard Test Method for Flammability of Finished Textile Floor Covering Materials? American Society for Testing and Materials, Philadelphia
6 . NFPA 72 ?National Fire Alarm Code? National Fire Protection Association, 1999 Table B-2.3.2.3.1(d)
7 . NFPA 286 ?Standard Method of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth? National Fire Protection Association, 2000
8 . Stroup, David W. ?Using Field Modeling to Simulate Enclosure Fires? pg3-152 to 3-159 SFPE Handbook, 2nd Edition 1995
9 . Walton, William D. ?Zone Computer Fire Models for Enclosures? pg3-148 to 3-151 SFPE Handbook, 2nd Edition 1995
10 . Ramachandran, G ?Stochastic Models of Fire Growth? pg3-296 to 3-310 SFPE Handbook, 2nd Edition 1995
11 . Karlsson & Quintiere ?Enclosure Fire Dynamics? CRC Press 2000 pg 255 to 305
12 . Modarres & Hu ?Reliability? pg5-33 to 5-45 SFPE Handbook, 2nd Edition 1995
13 . Wright, James F. ?The use of Monte Carlo Simulation in Mechanical, Physical, Chemical, and Nuclear Systems? http://www.drjfwright.com/c/montecarlosimulation.html
14. Friedman, Raymond ?International Survey of Computer Models for Fire and Smoke? Combustion Science and Engineering, Inc.2002 www.firemodelsurvey.com/index.html
