Physical States of Matter and the Combustion Process
Course
Firefighter I
Unit V
Fire Behavior
Essential
Question
How does the
physical state of
matter affect the
combustion
process?
TEKS
§130.299(c)
(7)(B)(C)
Prior Student
Learning
Chemistry and
Physics of Fire
Estimated Time
3 hours
Rationale
Understanding how fuel characteristics and their physical states affect the
combustion process, extinguishing methods, burning rates, and ignition is
important knowledge for firefighters. The more they understand the more
effective they will be in accomplishing their goals. Firefighting is inherently
dangerous, and the more a firefighter learns to prepare themselves for the
experience, the more effective and efficient they become.
Objectives
The student will be able to:
1. Explain specific gravity, vapor density, and the theory of surface-tomass ratio as related to the combustion process
2. Identify narcotic asphyxiate gases and irritants common in smoke
Engage
Engage students in a discussion relating fuel characteristics, their physical
states, and the combustion process. Explain how vapor density, specific
gravity, and surface-to-mass ratio can affect strategies and tactics used in
fighting fire and mitigating hazardous materials incidents. Use documented
experiences from fire service professional journals, or draw from the
instructor’s experience if possible. Use the Discussion Rubric for assessment.
Key Points
I. Gaseous Fuels and Vapor Density
A. Vapor density is the weight of a given volume of vapor or gas,
compared to an equal volume of dry air at an equal vapor pressure
B. All vapors or gases mix with air
C. The vapor density of air is 1
D. Vapors or gases that have a vapor density less than 1 are lighter than
air, and have a tendency to rise and dissipate unless kept in a
confined space
E. Vapors or gases that have a vapor density greater than 1 are heavier
than air, and have a tendency to seek low spaces and accumulate.
This characteristic can result in health and fire hazards
F. These vapor densities assume that the gas and the air are at the
same temperature (68 degrees F)
G. Vapor densities of some common flammable gases
1. Methane (natural gas) = 0.55
2. Propane = 1.52
3. Carbon Monoxide = 0.96
II. Liquid Fuels and Specific Gravity
A. Specific gravity is the weight of a substance compared to the weight of
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an equal volume of water at an equal temperature
B. Substances with a specific gravity less than 1 are lighter than water
C. Substances with a specific gravity greater than 1 are heavier than
water
D. Water and most flammable or combustible liquids don’t mix with each
other (immiscible)
1. This can be hazardous because the flammable or combustible
fuels will float on water where they could ignite or burn
2. This fact is important when considering firefighting tactics and
strategies, and the limits placed on extinguishment options
E. Water can be used to exclude oxygen from burning liquids with a
specific gravity less than 1
III. Surface-to-Mass Ratio
A. Surface-to-mass ratio is the surface area of a fuel in proportion to its
mass
B. Increasing the surface-to-mass ratio of a fuel increases its ignitability
1. The increased surface area exposes more fuel to the combustion
(pyrolysis) process, making it easier to ignite and sustain
combustion.
2. The simple orientation of a fuel can effectively increase the
surface-to-mass ratio
a. Plywood laid flat and subjected to a flame from underneath
exposes only one surface
b. Exposing the same piece of plywood to a flame on its edge
now exposes 3 surface areas (the top, the bottom, and the
edge)
C. The heat release rate (HRR) of the fuel is affected by surface-to-mass
ratio as well
1. HRR depends on fuel type, fuel quantity, and the orientation of the
fuel
2. HRR increases as more fuel becomes involved in the combustion
process
IV. Narcotic Asphyxiant Gases and Irritants Common in Smoke
A. While the heat from fire is dangerous, especially to anyone directly
exposed to it, most deaths associated with fire are caused by smoke
and its toxic byproducts
B. Smoke is made of gases, vapors, and soot (solid particulates) that are
inherently poisonous
1. For practical purposes, firefighters should recognize all smoke as
toxic, and a hazard to human life
2. The makeup of smoke is dependent on the type of fuel
C. Some common products of combustion are
1. Carbon monoxide (CO)
a. A byproduct of the incomplete combustion of organic
compounds (those fuels containing carbon)
b. The most common product of combustion found at structure
fires
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2.
3.
4.
5.
c. The leading cause of civilian fire deaths
d. A chemical asphyxiate that binds with the hemoglobin in the
blood, thereby inhibiting the transfer of oxygen to the body
and its organs
Hydrogen cyanide (HCN)
a. A byproduct of combustible fuels containing nitrogen
b. A chemical asphyxiate
c. Prevents the body from using oxygen at the cellular level
d. Most associated with the combustion of polyurethane foam,
which is commonly found or used in furniture and bedding
Carbon dioxide (CO2)
a. Is a byproduct of complete combustion, and although not
considered to be toxic, it produces its own hazard because it
can act as an asphyxiate by displacing oxygen
b. Also acts as a respiratory stimulant by increasing the
respiratory rate of its victims
Irritants
a. Byproducts of combustion that can make breathing difficult
and uncomfortable, and can inflame the eyes, respiratory
tract, and skin
b. Smoke can carry different and varied irritants, depending on
the fuel source
Particulates
a. Byproducts that can be inhaled and deposited in the mouth,
trachea, and lungs
b. May cause respiratory distress and irritation to the eyes
c. There may be additional health hazards specific to the fuels
being burned
Activities
Situational Awareness Exercise: Demonstrate and then discuss methods of
fire control/attack. Particularly direct attack, where the technique called
“painting” is used to cool down the surfaces in a compartment fire and slow the
process of pyrolysis. Water is gently applied and allowed to run down the
surface of the burning materials. Don’t apply the water long enough to upset
the thermal balance in the compartment. This happens when the steam
produced begins to condense, causing the smoke and hot gases to drop to
floor level. This makes the space untenable for firefighter and victims alike.
During the discussion have the students explain specific gravity, vapor density,
and the theory of surface-to-mass ratio as related to the combustion process.
Use the Discussion Rubric for assessment.
Assessments
Physical States of Matter and the Combustion Process Quiz and Key
Discussion Rubric
Materials
Physical States of Matter and the Combustion Process computer-based
presentation
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Resources
0135151112, Essentials of Firefighting (5th Edition), International Fire Service
Training Association (IFSTA)
Accommodations for Learning Differences
For reinforcement, students will participate in peer teaching (mentoring), team
learning, guided research, and note taking (web based), and/or keep journals
with key words and definitions.
For enrichment, students will participate in extinguisher demonstration and
school inspection programs.
State Educational Standards
Texas Essential Knowledge and Skills for Career and Technical Education
§130.299 Firefighter I (One to Two Credits).
(7) The student analyzes the physical state of matter in which fuels are
commonly found. The student is expected to:
(B) Explain specific gravity, vapor density, and the theory of surface-tomass ratio as related to the combustion process; and
(C) Identify narcotic asphyxiant gases and irritants common in smoke.
College and Career Readiness Standards
III. Speaking
B. Develop effective speaking styles for both group and one-on-one
situations.
1. Participate actively and effectively in one-on-one
communication situations.
2. Participate actively and effectively in group discussions.
4
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Name:_____________________
____
Date:_________________
___
Physical States of Matter and the Combustion Process Quiz
1. _____ The vapor density of air is which of the following?
a. 0.1
b. 0.001
c. 1.0
d. 0.01
2. _____ Vapor densities presume that the gas and the air are at the same temperature.
That temperature is specified to be what?
a. 68 degrees Fahrenheit
b. 100 degrees Fahrenheit
c. 68 degrees Celsius
d. 100 degrees Celsius
3. _____ A) All vapors/gases mix with air, but those with a vapor density greater than (>) 1
have a tendency to rise and dissipate unless in a confined space.
B) Those vapors/gases that have a vapor density less than (<) 1 have a tendency
to seek low spaces and accumulate. This characteristic can result in health and
fire hazards.
a. Only statement A is correct.
b. Only statement B is correct.
c. Both statements are correct.
d. Neither statement is correct.
4. _____ A) Water and most flammable and combustible liquids mix with each other
(immiscible).
B) This can be hazardous because flammable or combustible fuels will sink below
the water where they could ignite or burn.
a. Only statement A is correct.
b. Only Statement B is correct.
c. Both statements are correct.
d. Neither statement is correct.
5. _____ Increasing the surface-to-mass ratio of a fuel increases its what?
a. Flammability
b. Ignitability
c. Specific gravity
d. All of the above
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6. _____ Increasing the surface area of a solid fuel makes it more susceptible to which of
the following?
a. Vaporization
b. Sublimation
c. Pyrolysis
d. Oxidation
7. _____ A) The orientation of a fuel can increase or decrease its surface-to-mass ratio.
B) Heat Release Rate (HRR) depends on fuel type, fuel quantity, and the
orientation of the fuel.
a. Only statement A is correct.
b. Only statement B is correct.
c. Both statements are correct.
d. Neither statement is correct.
8. _____ The most common product of combustion is which of the following?
a. HCN – hydrogen cyanide
b. CO – carbon monoxide
c. Solid particulates
d. CO2 – carbon dioxide
9. _____ This by-product of combustion acts as a respiratory stimulant by increasing the
respiratory rate of its victim.
a. HCN
b. CO
c. Smoke
d. CO2
10. _____ For practical purposes, firefighters should recognize all smoke as toxic and a
hazard to human life.
a. True
b. False
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Physical States of Matter and the Combustion Process Quiz Key
1. C
2. A
3. D
4. D
5. B
6. C
7. C
8. B
9. D
10. A
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Name_______________________________________
Date_______________________________
Discussion Rubric
Objectives
4 pts.
Excellent
3 pts.
Good
2 pts. Needs Some
Improvement
1 pt. Needs Much
Improvement
N/A
Pts.
Participates in group discussion
Encourages others to join the
conversation
Keeps the discussion progressing
to achieve goals
Shares thoughts actively while
offering helpful recommendations to
others
Gives credit to others for their ideas
Respects the opinions of others
Involves others by asking questions
or requesting input
Expresses thoughts and ideas
clearly and effectively
Total Points (32 pts.)
Comments:
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