1. EVALUATION OF THERMAL RADIATION MODELS FOR FIRE SPREAD BETWEEN OBJECTS
Fire and Evacuation Modelling Technical Conference
Baltimore, Maryland August 2011
Rob Fleury Arup, Sydney, Australia
Michael Spearpoint University of Canterbury, New Zealand
Charles Fleischmann University of Canterbury, New Zealand

2. CONTEXT AND MOTIVATION
Zone model BRANZFIRE currently being upgraded to include risk-based modelling
Quantitative Risk Assessment tool
Monte Carlo sampling to address inherent uncertainty in design fires
Will include a radiation and ignition sub-model
Range of outputs – probabilistic outcomes
Project by Building Research Authority New Zealand (BRANZ) and the University of Canterbury, NZ. Funding from Foundation for Research Science and Technology

3. AIM Evaluate the performance of thermal radiation models
Will help determine if or when secondary objects ignite due to thermal radiation
Direct radiation from flames only
Work by others

4. APPROACH Experimental Comparison with theoretical models
Radiant heat flux measurements taken around gas burner
Comparison with theoretical models
Shokri & Beyler correlation
Point source model
Shokri & Beyler detailed method
Mudan method
Dayan and Tien method
Rectangular planar model
The main purpose of the experimental work was to provide a comprehensive set of radiative heat flux data to be used for comparison with the thermal radiation models

5. EXPERIMENTAL
Carried out at UC. For controllability and repeatability, a simple propane gas burner was used to model a burning object. This, however, represents a limitation in the experimental work. Burner aspect ratio. Burner angle. Location of heat flux gauges. And orientations. Range of heat release rates. In all, over 3000 independent measurements of radiant heat flux were taken, each one averaged over a 2min logging period.

6. FLAME HEIGHT Heskestad Thomas ImageStream Produced by ImageStream
Reference ImageStream (more info in paper). This work presents interesting opportunities in characterising the flame; however was chosen not to be investigated in great detail in this work, other than determining the mean flame height.
Produced by ImageStream

7. COMPARISON OF MODELS

8. COMPARISON OF MODELS 29% 221% 103% 58% 47% 41%
Re-explain different burner aspect ratios.
Point source model on average 29% percentage error from experimental results.
Point source equally accurate for square and rectangular fire sources.

9. COMPARISON OF MODELS
Average percentage error from experimental results for different target orientations
Vertical
Horizontal
Shokri and Beyler Correlation
99%
N/A
Point Source Model
18%
76%
Shokri and Beyler Detailed Method
50%
89%
Mudan Method
224%
205%
Dayan & Tien Method
35%
71%
Rectangular Planar Model
40%
None of the models were particularly strong at predicting the heat flux to horizontal targets.
For vert targets, point source most accurate by considerable margin.

10. COMPARISON OF MODELS
Average percentage error from experimental results for different radiant heat fluxes
<5 kW/m²
5-10 kW/m²
>10 kW/m²
Shokri and Beyler Correlation
126%
48%
29%
Point Source Model
17%
31%
Shokri and Beyler Detailed Method
46%
54%
49%
Mudan Method
205%
240%
238%
Dayan & Tien Method
36%
35%
Rectangular Planar Model
44%
40%
41%
The rather common advice of restricting the use of the point source model to applications where the radiant heat flux is 5 kW/m² or less was found to be irrelevant in this application

11. COMPARISON OF MODELS
Average percentage error from experimental results for different target positions
Central
Offset
Shokri and Beyler Correlation
101%
97%
Point Source Model
19%
17%
Shokri and Beyler Detailed Method
48%
52%
Mudan Method
215%
234%
Dayan & Tien Method
36%
33%
Rectangular Planar Model
45%
34%
Re-explain what the different target positions were, noting that the gauge orientation is still facing the fire.

12. LIMITATIONS TO RESULTS
Single object fires within compartments
Propane gas vs real objects (e.g. furniture)
Heat release rates 100 – 300 kW
Effective fire diameter: max 0.6 m
Input parameters
Most of the models more applicable to fires >1m in diameter.
Talk about input parameters and how there was limited opportunity to explore these. Therefore, largely fixed.
Overall, it cannot be said with certainty that the findings of this work extend to any application outside the conditions of the experimental programme. One can, however, make reasonable assumptions to extend the results to fires of a similar fuel and order of magnitude as those tested in this work

13. Ease of Implementation
SELECTING A MODEL
Two important factors for selecting model for BRANZFIRE:
Accuracy
Ease of Implementation
1. Point Source Model
2. Dayan and Tien Method
Point source most accurate based on the experimental results obtained. Also the most robust, able to deal with a range of conditions.
Ease of implementation. Also, fewer inputs required from user. For design purposes, many geometrical aspects may not be known, therefore the more complex models do not lend themselves well to computational models.

14. CONCLUSIONS
Generally, Point Source and Dayan & Tien models provide best match to experimental data
Point Source model (surprisingly) proved to be the most robust, in terms of dealing with different scenarios
Point source model relatively straight-forward to implement into two-zone model
Point Source model will form part of the radiation and ignition sub-model within BRANZFIRE

15. Thank you