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FIR 2303, Fire Behavior and Combustion 1

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

1. Detail the physical properties of the three states of matter. 1.1 Explain why radiative, conductive, and convective heat transfer in fires is especially important. 1.2 Describe the difference between thermally thin and thermally thick materials related to heat

conduction and radiation. 1.3 Explain how the methods of heat transfer create issues in firefighting with the development and

movement of fire.

Course/Unit Learning Outcomes

Learning Activity

1.1

Unit Lesson Chapter 4 Chapter 5 Unit II Essay

1.2

Unit Lesson Chapter 4 Chapter 5 Unit II Essay

1.3

Unit Lesson Chapter 4 Chapter 5 Unit II Essay

Required Unit Resources Chapter 4: Flow of Fluids Chapter 5: Heat Transfer

Unit Lesson Review In the previous unit, we covered the concepts associated with the dynamics of fire and the outcome of combustible reactions being determined by thermodynamics. In addition, we understood the lack of preparedness was cited for firefighter injuries and fatalities. Several authors suggested it was the result of the attitudes and behavior of firefighters over simplifying fire behavior and combustion (Gann & Friedman, 2015). In the lesson, we covered the main constituents in fire growth, learning the rate at which fire will spread over adjacent combustible materials is affected by mass, energy, heat, and enthalpy. We learned an enthalpy flow is from one point to another because of a temperature difference. We understood that fire starts at the boundary where vaporization of a liquid turns into a volatile gas mixing with air (oxygen) reaching a continuous state resulting in combustion (Figure 1). The sauce pan will absorb some energy by the layer of

UNIT II STUDY GUIDE

Three States of Matter

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volatiles above the surface of the cooking oil. Then convective and conductive heat exchange occurs above including the volatile gas. We understood that combustion, as a negative enthalpy reaction, is an exothermic chemical reaction between a fuel and an oxidizer resulting in the generation of substantive heat and light (Gann & Friedman, 2015). We saw an explanation of enthalpy reaction where cooking oil, as a liquid, became vaporized and, as it burned, suspended solids in smoke resulting in flammable, volatile mass of solids and aerosols (Figure 2 and Figure 3).

Combustion, according to these authors, always involves oxidation at the molecular level. In this unit, we will cover the three states of matter. Three States of Matter Matter is found in three states: solid, liquid, and gas (Gann & Friedman, 2015). As firefighters, when we enter a structure fire, we see matter in the form of physical material all around us. Some of the physical material undergoes a chemical reaction producing intense heat and light through a process of enthalpy. If there are three states of matter, is fire a solid, a liquid, or a gas? Is there a physical and chemical change with matter? What are the phase changes related to fire?

Fire has a significant effect on matter or structure. As reviewed in Unit I’s Points to Ponder–Building on the Scenario, the structure fire resulted from a sauce pan with cooking oil (liquid matter) left unattended on the stove. The fire grew to one or two rooms (solid matter) being involved. One reason the fire grew rapidly is the characteristic of the matter in the compartment (rooms) enclosed the flames. We saw the heat generation and the nature of combustion products in Figure 2 as the fire transitioned during the growth of the fire to the fully developed phase in the one or two rooms of the apartment. The fire was spreading with turbulent smoke. How was the fire transmitted from the different states of matter? As firefighters, do we really care about the conductivity of materials regarding heat or even if heat remains at a uniform temperature as it is transmitted across the different materials (matter) and its thickness? When we advance handlines down the hallway, do we see the conductivity of solid materials and how fast the heat flows through it using radiant exposure equations (Figure 4)? Is it even important to a firefighter? Several years ago, experienced fire tacticians focused on the temperatures involved in structure fires due to the assigned rating of the personal protective equipment and not on the transfer of heat from one matter to another (International Fire Service Training Association [IFSTA], 2013). They based this on the color, volume, velocity, and density of smoke as an indicator of the estimated temperature. After all, are we only concerned with reading smoke?

Figure 1

Figure 3 Figure 2

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There have been a lot of articles and discussion on reading smoke to help predict fire behavior and temperatures within a structure. Dodson (2005) suggested that since 1970, many experienced fire tacticians felt that the ability to read smoke was intuitive and that their experience and understanding of fire behavior could not be taught through cognitive abilities but could be learned only through repeated exposure at actual fires. Could these same fire tacticians read smoke today? with the same accuracy? with a multitude of low- mass synthetic matter? This is not saying reading smoke is not important. It is one of those skills that we need to understand in addition to understanding the states of matter and how fire is conducted through the different materials. In the fire academy, we learned about convection, radiation, and conduction as the methods of heat transfer. Maybe in a simpler time, this was all we needed to know. However, there is more to fully understanding the transfer of heat in today’s world of dangerous synthetic materials (matter) that respond to heat like gasoline on a fire.

As we see fire and smoke, we need to understand there is more than just fire and smoke. It is gasification of solids and aerosols in the form of soot (hydrocarbons and fibers). The explanation of transfer learned in the fire academy for conduction is the transfer of heat from one body to another by direct contact. The illustration used in many textbooks is a firefighter advancing towards a fire (Figure 5) suggesting this is the simplest form of heat transfer (IFSTA, 2013). Radiation is explained as heat waves traveling in straight lines in all directions (IFSTA, 2013). The most common method of heat transfer is convection and defined as the transfer of heat through the circulation of matter that is heated (Avillo, 2008). Some authors have even stated different views on the modes of heat transfer. Gann and Friedman (2015) suggested the transfer occurs in two ways of conduction and radiation, stating that convection is an independent mode of heat transfer. Avillo (2008) suggests there are three modes of heat transfer and lists them as conduction, radiation, and convection, and that they contribute to fire extension on the fire ground. In fact, many fire instructors have stated there are three modes of heat transfer. What are your thoughts on the modes of transfer? We know that everything is made up of matter (molecules), and when heated, they absorb heat and energy. Some molecules in matter move faster than others, based on color, thickness, and texture of the surface. It is believed that convection is not an independent mode of heat transfer, and it contributes, along with radiation and conduction, to transfer heat, which is thermal energy.

Figure 4 Figure 5: Conduction

Figure 6: Radiation Figure 7: Convection

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Let’s look at a charcoal grill example. Place charcoal in a grill, and ignite it (Figure 8). You will feel heat from the flames in the form of radiation (radiant heat) when it is first lit. Then what happens when the flames died down and the charcoal turns to embers with no flame? If you place your hand over the charcoal about two feet away, you feel the radiant heat and convection. Then, slowly move toward the charcoal embers, and you feel the radiant heat. Then, back your hand away from the charcoal, and the heat is diminished. If you place food on the grill grates, you see conduction (Figure 9) at the surface by direct contact. While sitting close to the grill you will feel the convection (Figure 10) as the heat is being circulated around the grill and towards you. If you place the lid/cover over the grill, you no longer feel the heat from

convection if the lid is sealed properly. In addition, with the lid off, if you introduce a fan between you and the grill, you will no longer feel the heat as convection (Figure 11). However, if you were to relocate to the opposite side you would feel intense heat as the fan’s wind has increased the movement of the heated molecules in the air as convection. The fan would have an effect on conduction and radiation as the wind would increase the rate of release of heat from the glowing embers of the charcoal to the grill grate and produce more radiant heat. Nonetheless, convection is an independent mode of heat transfer. Some textbooks combine it with conduction because the air molecules are referred as fluid (Gann & Friedman, 2015). Using the grill example applied to a structure fire, wind would have the same effect and increase the rate of release of heat to create a hostile fire environment.

Building on the Scenario Firefighters in Apartment 2-B observed the propagation of flames from the kitchen through the open doorway into the living room. The radiant heat began to cause the fabric on the couch to give off smoke. Flames devoured the fabric on the back of the couch and then part of the floor. The smoke initially decreased at the ceiling level and then rapidly started to develop. As heat continued to build, the flames grew in magnitude then began to spread across the ceiling and other items. Radiant emission from the flames and the hot upper layer of smoke increased. The fire in the living room increased continuing to burn their heads where their Nomex hoods were not donned properly, and even firefighters who donned their hoods properly were being burned. Once again, the fire appeared to rapidly decrease, and the heat rate being produced decreased quickly until the sliding glass door broke allowing the wind to reignite the material inside the room. The firefighters finally had enough pressure in the handline and opened the nozzle. The nozzle did not appear to have an effect on the flames, and smoke continued to bank down. Command became concerned as thick black smoke in the thermal column was pushing into the atmosphere and then appeared to be drawn back towards the fire. The black smoke issuing out the windows and sliding glass door became turbulent as the volume increased. The smoke appeared to be thicker and thicker almost like black soot. Wind gusts began to drive the fire along the soffit/eaves of the third floor giving the appearance that the fire was doubling in size. At the same time Tower 2 was conducting search and rescue and checking for extension using the Thermal Image Camera (TIC) in Apartment 2-H (across from 2-B) and noticed a significantly high temperature reading at the ceiling. After opening the gypsum board and removing 16 inches of fiberglass installation, smoke and embers were seen around the steel I beam, and then within seconds, fire spread across the ceiling.

Figure 9 Figure 8

Figure 10 Figure 11

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Points to Ponder What chemical changes occurred in the scenario fire shown in the column on the left of this page? Was the smoke coming off the solid fuel of the couch pyrolysis, creating gaseous fragments that are different from the structure of the couch (Figure 12)? Gorbett and Pharr (2011) referred to this as a stoichiometric mixture of the couch oxidizing during the combustion process where the proportion of reactants is such that there is no surplus of any reactant after the chemical reaction is completed. In other words, it is the ideal mixture where complete combustion occurs. What happened to the floor? The walls? The entire structure? The exposures? Was this an endothermic reaction as seen in Unit I? Was this direct molecular contact through convection, radiant heat, or conduction? Heat conductivity of a solid material is critical in how fast heat will travel; it is known as thermal conductivity. In thermal conductivity matter such as liquids or gases, are poor conductors compared to solids? The thickness of solid materials determines the speed in which heat travels and contributes to raising temperatures within the apartment. Some insulating materials, such as fiberglass, cannot stop the travel of heat but will reduce the rate of travel (Avillo, 2008). Gann and Friedman (2015) suggested that 16 inches of fiberglass is considered thermally thick, resulting in having good insulation qualities. The authors described thermally thick material (16-inch fiberglass insulation) as having no heat loss from the surfaces of the material (wood, gypsum board) adjoining the fiberglass as long as they maintain their ambient temperature. If the fiberglass insulation was 3 inches, then it would be considered thermally thin and insulation qualities would diminish (Gann & Friedman, 2015). This means the thinner layer of fiberglass would allow fire to penetrate into the area being insulated when exposed for long periods of time. For a thermally thin material, one or more of the other surface’s (wood, gypsum board) temperature is elevated, and heat is lost to one of the surrounding materials. In the scenario, the firefighters who donned their hoods properly were being burned due to the thermally thin material because of the exposure time to the heat allowing the garment to become too thermally thin allowing radiant heat and convective heat to burn them. Conclusion It is critical that firefighters understand physical and chemical changes in order to reduce injuries or even death. Some firefighters may believe that they just need to understand the simpler terms with the basic knowledge of fire behavior and combustion. However, as more and more synthetic polymer construction materials are being created, resulting in different reactions to fire, we need to understand the complex physical characteristics of fire behavior and combustion. Gann and Friedman (2015) suggest heat is transferred between bodies by conduction and radiation as modes of transfer. However, convection is not an independent mode of heat transfer. Thermal conductivity of the steel I beam in the scenario would decrease as temperature increases; whereas, the thermal conductivity of smoke increases with increasing temperatures.

References Avillo, A. (2008). Fireground strategies (2nd ed.). PennWell Corporation. Dodson, D. W. (2005, September 1). The art of reading smoke. Fire Engineering, 158(9).

https://www.fireengineering.com/articles/print/volume-158/issue-9/features/the-art-of-reading- smoke.html

Gann, R. G., & Friedman, R. (2015). Principles of fire behavior and combustion (4th ed.). Jones & Bartlett

Learning.

Figure 12

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Gorbett, G. E., & Pharr, J. L. (2011). Fire dynamics. Pearson. International Fire Service Training Association. (2013). Essentials of firefighting (6th ed.). Fire Protection

Publications.

Suggested Unit Resources In order to access the following resources, click the links below. Creative Commons has a time-lapse model that shows how fast heat travels through different materials. Click on the image below to see the model. Once the page populates, click on Preview, then the play button. The model includes metal, stone, fiberglass, and wood, which are like the materials noted in the garden apartment scenario for the case study; steel columns and steel I beams support the structure (metal), stone entrance, fiberglass panels in the stairwell, light weight wood (Type V lightweight wood-frame construction).

This report presents detailed and reduced-order finite element modeling of heat transfer in composite floor slabs with profiled steel decking. Jiang J., Main, J. A., Sadek, F., & Weigand, J. M. (2017). Numerical modeling and analysis of heat transfer in

composite slabs with profiled steel decking (NIST Technical Note No. 1958). National Institute of Standards and Technology. https://www.nist.gov/publications/numerical-modeling-and-analysis-heat- transfer-composite-slabs-profiled-steel-decking

Structural fire engineering (SFE) is a relatively new interdisciplinary subject that requires a comprehensive knowledge of heat transfer, fire dynamics, and structural analysis. Zhang, C., & Asif, U. (2015). Heat transfer principles in thermal calculation of structures in fire. Fire Safety

Journal, 78(November 2015), 85–95. https://www.nist.gov/publications/heat-transfer-principles- thermal-calculation-structures-fire

The fire industry relies on fire engineers and scientists to develop materials and technologies used to resist, detect, or suppress fire. Ezekoye, O. A., Hurley, M. J., Torero, J. L., & McGrattan, K. B. (2013, June 25). Applications of heat transfer

fundamentals to fire modeling. Journal of Thermal Science and Engineering Applications. https://www.nist.gov/publications/applications-heat-transfer-fundamentals-fire-modeling

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Radiation from buoyant diffusion flames, with and without impingement on a flat plate, is studied using a unique quantitative comparison of measured and simulated images. McDermott, R. J., Newale, A., Rankin, B., Lalit, H., & Gore, J. P. (2014, July 2). Quantitative infrared imaging

of impinging turbulent buoyant diffusion flames. Paper presented at the Thirty-Fifth International Symposium on Combustion, San Francisco, CA, United States. https://www.nist.gov/publications/quantitative-infrared-imaging-impinging-turbulent-buoyant-diffusion- flames

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.

When heated by a fire, building structural components (beams and columns) and partitions (walls, floors, and ceilings) can weaken. Use this image, along with the questions, to guide you in reflecting on the course material. Are the walls, floors, ceilings susceptible to a) ignition of combustibles of heat transfer from the steel I beam. b) smoke passing through cracks, or c) flames passing through more extensive openings?