UNIT VI STUDY GUIDE
Various Materials and Their
Relationship to Fire as Fuel
Course Learning Outcomes for Unit VI
Upon completion of this unit, students should be able to:
2. Categorize the components of fire.
2.1 Define the two main types of smoke aerosols and how soot forms.
2.2 Analyze the two principal methods for quantifying aerosol content of smoke.
4. Describe and apply the process of burning.
4.1 Describe the mass of burned fuel that can lead to loss of visibility due to smoke obscuration.
4.2 Demonstrate the principal combustion products formed in fires.
Reading Assignment
Chapter 10:
Combustion Products
Unit Lesson
In Episode 215 of Chicago Fire, the screenwriters, Brandt and Haas (2014) write:
A major high-rise fire sends [Station] 51 downtown and seems like the perfect opportunity for
Jones to redeem herself. With the elevators on the fritz, the whole squad hikes up 18 flights
of stairs carrying all their gear, only to find a raging fire within and a wealth of victims inside.
Jones struggles to keep her cool as she learns the differences between reality and training.
With Casey and Herrmann’s help, she manages to make it through, but the experience
serves as a humble reminder of her place on Squad. (p. 6)
In this episode, the Chicago firefighters make their way down the high-rise corridor with fire roaring and raging
over their heads as it licks at their helmets. The flames glowed orange-yellow as they leaped from the ceiling
and walls in a fiery dance and the air was clear from any soot or smoke. The images of the actors’ faces were
completely visible through the oversized SCBA face masks. Where was the smoke? Where was the soot or
any other by-products of the fire? After all, structure fires have smoke or fire effluent. Even though it is a
television show, are we teaching the wrong information regarding combustion products? According to Gann
and Friedman (2015):
Smoke, or fire effluent, consists of aerosols (soot particles and liquid droplets) and gases.
Each of the smoke components, as well as the smoke itself, is characterized by its yield—that
is, its mass per unit mass of fuel consumed. (p. 193)
As a result, all fires have some amount of smoke or soot particles. Gann and Friedman (2015) suggest soot is
made up mostly of carbon occurring from under ventilated burning. In addition, carbon is present in soot
particles as the result diffusion flames and fuel-rich premixed flames (Gann & Friedman, 2015). Gorbett and
Pharr (2011) supposed, “Soot may result when unburned carbon remains following incomplete combustion,
but the remaining fuel is not charred” (p. 69). Several other authors describe the particles of incomplete
combustion as soot aggregates (Farias, Carvalho, Köylü, & Faeth; 1995; Köylü, Ü. Ö. & Faeth, 1994). Gann
and Friedman (2015) support these findings stating, “In larger, more turbulent fires, many more soot particles
form. When they leave the flame, they encounter and stick to other particles, forming aggregates as much as
thousands of times larger, a process called coagulation” (p. 177). Santoro (1987) supports the formation of
soot particles in turbulent diffusion flames and adds that laminar flames also cause the formation of soot
particles. Santoro (1987) states, “Temperature, pressure and fuel structure have been shown to be
particularly important in determining the amount of soot formed” (p. 516). Each of these authors supposed
FIR 3301, Fire Behavior and Combustion
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that smoke aerosols are laden with droplets of condensation from fire gases and
soot
particles.
These larger
UNIT
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formations of particles, discussed by Gorbertt and Pharr (2015), make visibilityTitle
more difficult for firefighters
even though it is crucial for firefighters to see through these smoke particles. The authors suggested, “Seeing
through smoke from even a small fire can be challenging” (p. 187).
Points to Ponder
Units respond to a warehouse fire with light to moderate smoke visible from several blocks
away. As units reached the warehouse the smoke that appeared to be light to moderate in
color became darker and even turbulent. The first arriving unit pulled a 200’ pre-connect and
extended it off of a 200’ – 3” line in order to reach the rear of the warehouse. As they donned
their SCBA facemask they began to push towards the area of the fire. At first they were able
to cut through the smoke with just flash lights and the nearby exit sign was still visible. As
they pushed deeper into the warehouse the light was cutting the smoke less and less. Finally
the dark smoke was completely concealing everything inside the warehouse making it more
and more difficult to search with the flash lights only penetrating a few inches. The soot
particles in the air seemed to soak up every ounce of the light as the layers of smoke
developed quickly. The heavy soot made it nearly impossible to confirm the direction they
needed to continue and they would have become completely disoriented except for
maintaining contact with the hose line.
In this scenario, does the smoke aerosol present a risk to the firefighters? Why did the smoke conditions
change from being able to cut the particles and aerosols with light to being completely obscured? Was it the
fire-generated soot and aerosols that reduced the visibility? Does the heavy soot exceed the tenability limit of
the firefighters? The International Organization for Standardization (2013) cautions, “There are multiple
mechanisms by which fire-generated aerosols affect the fire threat to people and the environment” (ISO,
2013, p. 2). These threats can be through smoke obscuration and “the level at which people cannot orient
themselves and constructively identify a path to safety” (Gorbertt & Pharr, 2015, p. 193). In both of these
statements by the authors they are referencing the tenability concerning the length of time individuals are
exposed to soot and aerosols. However, firefighters are protected through the use of protective clothing
ensembles.
Click here to access an interactive media file.
As seen in Episode 215 of Chicago Fire, the fuel used has a substantial effect on the sooting tendency. Premixed fuels used in television series produce less soot but structure fires involving diffusion flames produce a
substantial amount of soot. These sooting tendencies typically produced in a diffusion flame is seen as
orange-yellow color and referred to as incandescent soot particles (Gorbett & Pharr, 2011). Diffusion flames
are seen as a less-localized flame and tend to burn slower, producing more soot as oxygen is diffused into
the flame. In premixed flames the oxidizer reaction is not as predominate as the fuel mixture where, “The
resulting combustion occurs where the fuel and air mixture are within the fuel’s flammable range” (Gorbett &
Pharr, 2011, p. 72).
In this unit you will analyze why smoke is sometimes black and sometimes white in appearance. You will see
the tendencies of different fuels with respect to the type of flames that produce soot, whether pre-mixed or
diffusion flames. You will be able to explain the reason for this difference by describing the two main types of
smoke aerosols and explain why they are important in fires. You will evaluate and understand why soot forms
and how the aerosol content of smoke changes. You will be able to describe the smoke-point height method
for estimating the relative sooting tendency of a gaseous fuel. You will be able to approximate the mass of
burned fuel that can lead to the loss of visibility due to smoke obscuration. Lastly, you will be able to explain
the principles of operation for ionization smoke alarms and photoelectric smoke alarms, and identify the
differences in what they detect by understanding that photoelectric smoke alarms measure the light scattered
by the soot and aerosols.
References
Brandt, M., & Haas, D. (Writers). (2014). Keep your mouth shut [Television series episode]. Chicago Fire.
New York, NY: National Broadcasting Company
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Corbett, G., & Pharr, J. (2011). Fire dynamics. Upper Saddle River, NJ: Pearson
Education.
UNIT
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Title
Farias, T., Carvalho, M., Köylü, Ü., & Faeth, G. (1995). Fractal and projected structure properties of soot
aggregates. Retrieved from http://fire.nist.gov/bfrlpubs/fire95/PDF/f95062.pdf
Gann, R., & Friedman, R. (2015). Principles of fire behavior and combustion (4th ed.). Burlington, MA: Jones
& Bartlett.
Gorbett, G., & Pharr, J. (2011). Fire dynamics. Upper Saddle River, NJ: Pearson.
International Organization for Standardization. (2013). Fire chemistry: Generation and measurement of
aerosols. Retrieved from https://www.iso.org/obp/ui/#iso:std:iso:29904:ed-1:v1:en
Köylü, Ü., & Faeth, G. (1994). Optical properties of soot in buoyant laminar diffusion flames. Journal of Heat
Transfer (116) 4, pp. 971-979.
Santoro, R. (1987). Soot particle formation in diffusion flames. The Pennsylvania State University. Retrieved
from https://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/32_3_NEW%20ORLEANS_0887_0513.pdf
Suggested Reading
As you view this video remember some of the techniques and examples do not follow FESHE curriculum
guidelines and outcomes for incident command, scene size-up, or fire attack. In addition this type of training is
not recommended for the demonstration of fire combustion.
This course is about fire behavior and combustion and the purpose of viewing this video is to watch the
combustion of soot when heat in the form of a fare is applied as the ignition source. The soot in the video
consists of mostly carbon resulting from under-ventilated burning of material in the metal container. You will
see aerosol droplets resulting from condensation of gases that are beginning to cool as they leave the vicinity
of the flames inside of the container. However, as seen in the video, the aerosol droplets will ignite when the
fare is placed in the right mixture as it is leaving the container. In the video you will see two main types of
smoke aerosols distinguished by the color of the smoke.
Smoke Combustion
https://www.youtube.com/watch?v=OxnxhewgFL8
Learning Activities (Non-Graded)
Review What You Have Learned
The Challenging Questions at the end of Chapter 10, on page 194, will help you evaluate smoke, or fire
effluent, consists of aerosols (soot particles and liquid droplets) and gases.
This is a non-graded activity, so you do not have to submit it. However, if you have difficulty or questions with
the concepts involved, contact your instructor for additional discussion and/or explanation.
FIR 3301, Fire Behavior and Combustion
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