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.

Review from Last Week (Chapter 3) Combustion/Fire Fire Triangle Fire Tetrahedron Pyrolysis Smoldering/Flaming

Combustion CO Fire Classifications

StagesIgnitionGrowthFully DevelopedDecay

Flashover Backdraft Compartmentation Heat Transfer

From

Un

it 4

A

ssig

nm

ent

Traditional Fire Behavior

Typical Fire Behavior?

Fire Dynamics

• The detailed study of how chemistry, fire science, and the engineering disciplines of fluid mechanics and heat transfer interact to influence fire behavior. NFPA 921 Guide for Fire and Explosion Investigations, 2008 Edition

What is B-SAHF?

Acronym used to help size up critical fire behavior indicators.

Consists of the following:Building FactorsSmokeAir TrackHeatFlame

Let’s discuss each critical factor! Building-

Can be pre-planned to determine fire loadsFuel packages*Inventory fire behavior indicators present

before a fire beginsConstruction and featuresWill 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.

Conshohocken,PAAugust 2008

Ventilation-Controlled Fire A fire in which the heat release rate or

growth is controlled by the amount of air available to the fire.

“Ventilation-Limited Fire”

Fuel-Controlled Fire

Fire in which the heat release rate and growth rate are controlled by the characteristics of the fuel, such as quantity and geometry, and in which adequate air for combustion is available.

“Fuel-Limited Fire”

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!

B-SAHF for each phase

Model can be used for each phase of fire.

Get your reading assignment from Fire Growth and Development http://cfbt-us.com/pdfs/FBIandFireDevelopment.pdf

Turn to page 4 and let’s review the phases and the application of B-SAHF.

House

Street

Alpha

Bravo

Charlie

Delta

Other parts of the puzzle

Ventilation controlled firesOperations 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.

A single burning item or object exposed to heat transfer resulting from a fire is referred to as a fuel package. Fuel packages can be comprised of a single fuel (e.g., wood, plastic) or they may be composites of a number of different materials (e.g., upholstered chair, sofa, or mattress).

Fuel Package

Approximate Peak Heat Release Rates

Burning cigarette 5 W  Burning match 80 W Burning coffeemaker 40 kW Small Trash Can, Trash Bag Fires 50 to 300

kW Burning Upholstered Chair 80 kW to 2.5 MW Burning Upholstered Sofa 3 MW to 5 MW Burning Christmas Tree 1.6 MW to 5.2 MW

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?

To Do…

Review Key Terms Read Fire Growth and Development Attend the Weekly Seminar Respond to the Discussion Board Complete and Submit the Unit 6 Project Take the Self-Check Quiz Check out Extra! Extra!