1. Enclosure Fire Dynamics
Chapter 1: Introduction
Chapter 2: Qualitative description of enclosure fires
Chapter 3: Energy release rates, Design fires
Chapter 4: Plumes and flames
Chapter 5: Pressure and vent flows
Chapter 6: Gas temperatures
(Chapter 7: Heat transfer)
Chapter 8: Smoke filling
(Chapter 9: Products of combustion)
Chapter 10: Computer modeling
Each course unit represents breaking down the problem into individual pieces

2. Goals and expectations
Account for MLR and HRR including time dependance.
Get a feel for the size of HRR
Account for different test metods, weaknesses, strenghts and results
Account for the t-squared fire and its limitations
Account for enclosure effects on the HRR
Be able to produce a HRR-time curve

3. Your challenge…
There are an infinite number of fire scenarios possible for a building
What are some for this room?
When evaluating fire safety, a limited (small) number of fire scenarios can actually be reviewed and tested
Fire safety requires the selection of the most severe fires
With natural fires, we do not know the fuel in advance => assumed design fire

4. Fuel packages

5. Fire scenarios
Evaluating fire development in a building requires that a number of fire scenarios be developed
These include a prediction of heat release, but also involve
Location, ventilation
Suppression, structural fire protection
For example: 5 MW fire in the base of the atrium with ventilation system turned off and sprinklers at the top of the space

6. Heat release rate-definitions
Heat (energy) release rate
Energy released from mass burned
J/s  W
kJ/s  kW
MJ/s  MW
A very good measure of the size of fire and potential for injury to people and buildings

7. Heat release rate (HRR)
Time dependence for most fuels
Both area and mass loss rate change with time
Are these a function of only the fuel?
Combustion efficiency
The growth rate of fire (area) and mass loss rate are functions of the conditions inside the enclosure

8. It is important to gain a feeling for the size of typical fires
Light bulb W
Wastebasket kW
Wood chair with foam seat 200–500 kW
Upholstered chair 500 – 1500 kW
Upholstered couch 1000 – 3000 kW
1 m2 pool of gasoline 2.5 MW
3m high stack of wood pallets 7 MW
2 m2 plastic commodity 4.9 m high MW

9. Fire testing Measure how much oxygen is used while material burns
For every kg O2 used kJ of energy are formed
Enormous amounts of data are available showing Heat Release Rate for very many materials
Databases

10. Cone calorimeter
Measure heat release and mass loss at different flux levels
Almost constant 13kJ/g O2 consumed

11. Example heat release rate as a function of external flux

12. Furniture calorimeter
Results represent burning in open
Cone calorimeter data can be used to predict performance

13. HRR for furniture

14. HRR for mattress

15. HRR for workstation

16. HRR for Christmas trees

17. Room Calorimeter

18. Mass loss rate (MLR) from pool fires
MLR = f(pool diameter & fuel)
Values for each fuel from tables,
Finally calculate HRR
Limiting regression rate is the value found for pool fires generally > 1m in diameter where the MLR no longer increases as pool size increases.
K=extinction absorption coefficient of the flame and is a function of the liquid
Beta = mean beam length correction
Do not need to know k and beta separately, thus only give the product in tables.

19. t2 Fire Growth Rates Q=t2

20. t2 Fire Growth Rates Q=t2

21. t2 Fire Growth Rates Heat release rate increases with time
n is usually taken equal to 2
to=600 =0.003 kW/s2 (slow)
to=300 =0.012 kW/s2 (medium)
to=150 =0.047 kW/s2 (fast)
to= =0.190 kW/s2 (ultra fast)
The times, to, are how long in seconds each fire growth rate takes to reach 1 MW

22. Use of t2 fires Simplification to a complicated problem
Appear to match some test results
Represents a constant flame spread velocity
Increase in area of a circle with radius

23. Examples given in the literature: Ultra fast fire growth
Upholstered furniture
Stacked furniture
Packing materials in rubbish pile
Non-fire retarded foam plastics
Boxes in vertical storage arrangement

24. Examples given in the literature: Fast fire growth
Displays and padded work stations
Bedding
Hotels
Schools, offices

25. Examples given in the literature: Medium fire growth
Shop counters
Office furniture
Dwellings

26. Examples given in the literature: Slow fire growth
Floor coverings
Fire retardant mattress

27. Storage fire growth measurements with 10 MW calorimeter

28. Rack storage fires grow faster than t2

29. Creating a design fire Decide growth rate using knowledge of
Type of building or occupancy (industry, discotek, school, office) => decide growth rate
Or use knowledge combustible material (stack of pallets, mattreses, etc)
Decide maximum Heat Relesase Rate (HRR)
Use data or calculations or both
Sprinkler? Then often use 5 MW

30. Complex HRR Curve

31. What design fire would you use in this space?

32. Any questions? Next unit: Plumes and flames