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FIR 2303, Fire Behavior and Combustion 1

Course Learning Outcomes for Unit I Upon completion of this unit, students should be able to:

2. Categorize the components of fire. 2.1 Distinguish measurement in understanding fire behavior.

5. Define the concepts associated with the chemistry of fire.

5.1 Recognize the chemical elements that are related to fires.

6. Discuss various materials considered fuel for fires. 6.1 Describe the change among the states of matter and the changes in enthalpy associated with

each.

Course/Unit Learning Outcomes

Learning Activity

2.1 Unit Lesson Chapter 1 Unit I Essay

5.1 Unit Lesson Chapter 3 Unit I Essay

6.1 Unit Lesson Chapter 1 Unit I Essay

Required Unit Resources Chapter 1: Fire Measurement and the SI System of Units Chapter 3: Physical and Chemical Change, pp. 39–41

Unit Lesson Concepts Associated with the Dynamics of Fire What is fire behavior and combustion? Many of us believe we know the answer either from life experiences on the fire ground or from classes taken in the fire academy. However, do we really know? What are the characteristics of fire and its behavior or combustion? Is there an art to reading fire? Is fire behavior its own language? Senior fire officials may have taught us the fire triangle or even the tetrahedron. Do you really understand it? Is fire as simple as removing one of the elements and it goes out, or is there more? Is there a need to understand the differences between mass and weight that involves heat, energy, and smoke? Do you really need to know the importance of measurement in understanding fire behavior? Do we really need to understand enthalpy in relation to heat or smoke? Do we need to understand buoyant smoke and any incomplete combustion involving a fire? Why are these concepts important in understanding fire? Has the need to understand fire behavior gone unheeded? Are you prepared and equipped to undertake the principles of fire behavior and combustion? According to ancient Greek mythology, fire was stolen from the gods and given to humankind by Prometheus (Morris, 2017). In Greek mythology, since fire was introduced, it has been used for good and evil over the centuries. When controlled, fire provides heat, energy, and light. Out of control fire is devastating and has

UNIT I STUDY GUIDE

Concepts Associated with the Dynamics of Fire

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caused many injuries and deaths. Gorbett and Pharr (2011) have reviewed the devastation of fire throughout the centuries, describing fire is a serial killer that continues today. Fire-related injuries and even deaths have been contributed to the behavior and attitude of firefighters (National Fallen Firefighter Foundation, 2013). They further suggested one of the causes is the lack of preparedness. Gorbett and Pharr (2011) suggest these injuries and deaths many times are due to firefighters not understanding fire behavior. Are you prepared as a firefighter? Are injuries or even deaths the result of poor decisions on the fire ground due to not completely understanding fire behavior and combustion? We all know fire is the rapid oxidation of a combustible material releasing heat, light, and various reaction products in the exothermic process of combustion (Gorbett & Pharr, 2011). In addition, we understand the components of combustion, using oxygen, fuel, and heat to explain the ignition, growth, and then decay of the fire. Using the fire tetrahedron, we can describe how combustible material near the fire off-gasses and the area around the combustible material must be cooled to stop the fires progression and the superheated air-track. According to Gann and Friedman (2015), understanding fire behavior and combustion causes one to realize that measurement is another key component to understanding the fire phenomena. The authors note that firefighters need to know when the fire started, how rapidly it grew, how hot it became, and how severe the threat to the population. They continue by suggesting firefighters need to quantify this information to understand fire. In the fire service, we understand that the terms “fast moving” or “big” in relationship to smoke and fire have different meanings to each of us. Many times, our definitions are based on experience, and the definitions change throughout our career. What was once a big fire, may be moderate today. According to Gann and Friedman (2015), in order to quantify fire behavior, we need to understand measurement in terms of SI units from the French term, Système International d’ Unités). Gorbett and Pharr (2011) define SI units as a “system for quantifying measurement that uses meters, liters, grams, and calories” (p. 19). How can one compare measurement to fighting fire? Is it essential in firefighting? Are we really going to perform calculations on the fire ground to understand the phenomena of fire? Gann and Friedman (2015) suggest the basic measurements for fire phenomena to occur is time, length, area, volume, mass, density, force, pressure, enthalpy and energy, power, and temperature. How do you apply each of these? In the scenario below, how would you use measurement to help understand the fire phenomena? Points to Ponder In the scenario in the right sidebar, did the fire generate energy? Did the energy increase within the fire room? Was there transfer of heat from one object to another? Was there an increase in pressure within the volume of the room? Was there an increase of temperature noted? Was there an increase in the spread of fire outside the room of origin?

Building on the Scenario A caller reported a fire at a Garden Apartment. Engines 2 and 5, Tower 2, Rescue 2, and Battalion 1 were dispatched for a possible structure fire involving an apartment building. While reporting the morning traffic, the local news channel observed a column of smoke coming from the direction of the apartment and notified dispatch. Upon Engine 2’s arrival, he reported heavy smoke from Side “A.” Engine 5 was ordered to lay a supply line into Engine 2. Engine 2’s officer and one firefighter went to the front door, entering the foyer area, and advanced up the stairs and down the hallway. As they opened the door, they immediately observed thick black smoke pulsing and banking down to the floor under pressure. As they advanced the handline into the apartment, they noticed the kitchen cabinets were well involved, and they could make out the stove with a saucepan on it. Within seconds after reaching the kitchen, the temperature in the room increased, burning their faces where their Nomex hoods were not donned properly. When opening the nozzle, there was a loss of pressure in their handlines. As a result, the fire appeared to double in size within a few minutes. At the same time, Tower 2’s engineer described thick black smoke pushing into the atmosphere from the second-floor window. The apartment’s dimensions are 32’4” x 20’6” x 8’.

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Reaction of Enthalpy

In the scenario, the cooking oil in the saucepan reached autoignition, creating a fire that continued until the room was totally involved. As the cooking oil was heated, a chemical reaction occurred (Figure 1 [Bonds “A-B” Molecule representing the cooking oil]) breaking bonds and vaporizing into a gas (Figure 2 [“A” “B” Molecular Fragments representing the volatile gas]). At this point, a change occurred, and heat is being released and absorbed by other solids, under a constant pressure, with a temperature rise around the reaction. As the vapors or gas ignites, combustion occurs (Figure 3). Energy is continually being released and absorbed under pressure (Figure 4) creating soot, a solid particle in the smoke, and collecting on the ceiling and walls. The process starts over as the soot is heated and thermal degradation (pyrolysis) occurs under pressure, creating a volatile gas (reacting with air) in the smoke that ignites (Figure 5) resulting in flashover, roll over, or backdraft. This continues creating a full-scale heat release (Figure 6). The absorption or the release of energy under pressure is known as enthalpy. During the enthalpy process the release of heat feeds back to the solids around the fire. This feedback is a loop that continues under pressure, either positive or negative. Figure 7 below shows the method of heat being released or absorbed though the enthalpy process.

Figure 1 Figure 2 Figure 3 Figure 4

Figure 5 Figure 6

Figure 7: Enthalpy

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Factors such as the nature of the material can influence the heat transfer in enthalpy. Depending on the nature of the exposed surface, the higher bond enthalpy requires more energy (heat) to break the bond. This also depends on the distance between the heat source and the exposed surfaces. Exothermic and Endothermic Reaction

If the reaction of enthalpy is positive, it is considered endothermic, and if it is negative, it is considered exothermic (Figure 8). The following is an example of this: a rag is used to coat an axe handle with linseed oil. You place the rag on the table and as the rag begins to dry, oxidation takes place, producing heat resulting in fire. The combustion of the rag is an exothermic reaction because you feel the heat from the fire. Exothermic reaction is the only phase in which you feel the heat when fighting fire. Figure 9 shows the rate of heat transfer of cooking oil as a liquid undergoing the combustion phase across the surface indicated. The flame above the saucepan is fed by the thermal degradation of the liquid cooking oil generated across the given surface of the saucepan. Diffusion flame is the rate of supply of vapors (as seen coming from the sauce pan) coupled to their rate of burning; at the same time, heat is being transferred from the flame to any surface around the fire (Drydale, 1985). This process is continually releasing energy necessary to produce the vapors to support combustion. As heat increases, the speed of the polymeric molecules increases as the cooking oil splits into smaller fragments, which can vaporize and escape from the surface of the sauce pan. This process is essential to maintain the flow of vapors and support the diffusion flame (Drydale, 1985).

Figure 8

Figure 9

Heat Loss

The Rate of

Transfer

Thermal Degradation

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Conclusion Lack of preparedness was cited in firefighter injuries and fatalities. Some of the reasons for the injuries and fatalities were the attitudes and behavior firefighters have about the chemistry and physics of fire. Understanding fire and how heat transfers, increasing flame spread from one object to another object, is the key to understanding fire behavior and fire processes. One of the main constituents in fire growth is learning the rate at which fire will spread over adjacent combustible materials is affected by mass, energy, heat, and enthalpy. It is hoped that understanding thermal degradation (pyrolysis) and gas phase of combustion will drive you to develop a more practical approach to understanding the principles of fire behavior and combustion.

References Drydale, D. (1985). An introduction to fire dynamics. Wiley. Gann, R. G., & Friedman, R. (2015). Principles of fire behavior and combustion (4th ed.). Jones & Bartlett

Learning. Gorbett, G. E., & Pharr, J. L. (2011). Fire dynamics. Pearson. Morris, L. (2017). Origins of fire according to the Greeks. National Geographic.

https://www.nationalgeographic.com.au/history/how-are-the-origins-of-fire-and-woman-linked.aspx National Fallen Firefighter Foundation. (2013). Everyone Goes Home—The 6 root causes of firefighter line-of-

duty-deaths. Everyone Goes Home. http://www.everyonegoeshome.com/wp- content/uploads/sites/2/2015/04/root-causes-lodds.doc

Suggested Unit Resources In order to access the following resources, click the links below. You are encouraged to watch at least the first 8 minutes of the 40-minute presentation by Steve Kerber and Dan Madrzykowski that gives a good overview of the related issues of science and firefighting. It was filmed at the International Association of Fire Fighters (IAFF) Redmond Symposium in August 2013. IAFF. (2013, August 23). Fire behavior and tactical considerations [Video]. YouTube.

http://www.youtube.com/watch?v=v2JcNonr4us Click here to access the transcript for this video.

Learning Activities (Nongraded) Nongraded Learning Activities are provided to aid students in their course of study. You do not have to submit them. If you have questions, contact your instructor for further guidance and information. For this activity, you are asked to prepare a reflection paper. Reflect on the concepts you have learned during your readings. What do you understand completely? What did not quite make sense? The purpose of this assignment is to provide you with the opportunity to reflect on the material you have read and to expand on it. If you are unclear about a concept, either review it in the textbook or ask your professor. Can you apply what you have learned to your career? How? This is not a summary. A reflection paper is an opportunity for you to express your thoughts about the material you are studying by writing about it. Reflection writing is a great way to study because it gives you a chance to process what you have learned and increases your ability to remember it.

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Use this image along with the questions to guide you in reflecting on the course material.

• What are your thoughts about the main topic of heat absorption and the release of heat under pressure?

• Why is fire behavior and combustion important to firefighting? • Explain the dynamics of a smoldering chair fire in a closed room that increases in size. How does the

heat absorption or release apply to the fire?