Combustion Processes
(con’t from Unit 4)

 Discuss the B-SAHF model and what each letter stands for.
 Explain B-SAHF model for each phase of fire development and the use of the model for each phase.
 Discuss if the students think this is a useful tool for teaching fire dynamics to fire service professionals.

 Acronym used to help size up critical fire behavior indicators.
 Consists of the following:
 Building Factors
 Smoke
 Air Track
 Heat
 Flame

 Building-
 Can be pre-planned to determine fire loads
 Inventory fire behavior indicators present before a fire begins
 Construction and features
 Will help determine fire behavior and spread

 Smoke
 Along with air track the two most important indicators of fire behavior.
 Provides valuable cues as to the location of fire.
 Its burning regime (ventilation or fuel controlled).
 Stage of burning throughout the structure.

 Observe air movement from outside and continue while on the interior.
 Watch how smoke changes with fluctuations in the air track.
 Make air tracks work for you not against you!

 While heat cannot be observed directly, observe its effect on air track (i.e. velocity of smoke discharge), the building or exposures, and sensation of changes in temperature.
 Can be a significant fire behavior indicator
 It is important to remember that our personal protective equipment provides significant insulation and slows the transfer of heat and resulting sensation of changes in temperature.

 The most visible part of the B-SAHF model.
 Do not get so focused on visible flames that you miss important, but subtle building, smoke, air track, and heat indicators!
 Flame indicators such as location, volume, color, etc. provide help more complete picture but must be integrated with other factors to see the big picture!

 Ventilation controlled fires
 Operations conducted by firefighters can cause a ventilation controlled fire to enter back into the growth phase.
 Firefighters can be caught in vent induced extreme fire behavior.
 Watch the B-SAHF indicators to help recognize signs of impending extreme fire behavior.

 Rollover or flameover
 Flashover
 Backdraft

 Incipient or ignition stage:
 Occurs after ignition
 Flames are small and are contained within material first ignited.
 No oxygen reduction (21%)
 Convection brings in additional oxygen

 Growth stage:
 Fire grows in intensity and more fuel is involved releasing additional energy.
 Increased fuel consumption and heat generation.
 Heat carried up by convection and spreads horizontally until reaching the walls.

 Fully developed stage:
 After reaching walls, heated gases bank downwards into lower portions.
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Heat is radiated which brings materials in the room up to ignition temperature.
Oxygen is reduced to 9 – 12%.
 Upper portions 1000 degrees F.
 If flashover occurs it is between growth and fully developed stages.
 Hot temperatures but heat released slowed due to lack of oxygen.
 Backdraft conditions may be present.

 Backdraft
 Plenty of heat waiting on introduction of additional oxygen.
 Proper ventilation can prevent/reduce backdraft.

 Conduction
 Convection
 Radiation
 Direct flame

 How do you feel as a class after reading and reviewing the B-SAHF model?
 Is it a useful tool to train fire service professionals?