Week 1 Seminar

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Combustion Processes
(con’t from Unit 4)
Objectives
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.

What is B-SAHF?
Acronym used to help size up critical fire
behavior indicators.
 Consists of the following:

 Building Factors
 Smoke
 Air Track
 Heat
 Flame
Let’s discuss each critical factor!

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, the second critical factor

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.
Air Track and its impact
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!

Heat
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.

Flame, the visible part!
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!

Other parts of the puzzle

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.
Fire events

Rollover or flameover

Flashover

Backdraft
Fire stages

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
Fire stages

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.
Fire stages

Fully developed stage:
 After reaching walls, heated gases bank downwards into
lower portions.
 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.
Fire stages

Backdraft
 Plenty of heat waiting on introduction of additional
oxygen.
 Proper ventilation can prevent/reduce backdraft.
Transfer of heat

Conduction

Convection

Radiation

Direct flame
Is it useful?
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?

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