UNIT III STUDY GUIDE Physical Properties of the Three States of Matter: Part 2 Course Learning Outcomes for Unit III Upon completion of this unit, students should be able to: 1. Explain the physical and chemical properties of fire. 1.1 Explain the three modes of heat transfer. 1.2 Define the process of combustion. 5. Define and use basic terms and concepts associated with the chemistry and dynamics of fire. 5.1 Illustrate the differences between thermally thin and thermally thick 5.2 Explain flammability in terms of both fire and properties and application. 6. Discuss various materials and their relationship to fires as fuel. 6.1 Compare the differences between an intensive property and an extensive property of a material. 6.2 Analyze the terms fire consequences, hazard and risk. Reading Assignment Chapter 5: Heat Transfer Chapter 6: Combustion, Fire, and Flammability Unit Lesson In 1991, one of the most spectacular fire sequences came to life as Ron Howard directed the film Backdraft. For many, this was their first experience with the phenomena of a backdraft. In the movie there were several backdrafts and the screenplay writer (Widen, 1991) describes one of the fire scenes as: Inside the smoke is like liquid lead. Going by feel, they hump the hose up one staircase after another, crawling on their hands and knees toward a dull red glow. Turning a corner, they enter. Totally ablaze. Brian looks up in wonder at the buffeting waves of flame in the ceiling, at the CREECHING timbers crumbling to the white-hot floor. At the walls HOWLING in bestial agony. It is the most horrifying, and wonderful thing he has ever seen. AXE : Wash it to the windows? It's gonna flash, Stevie. We gotta get behind it. STEVIE: Nah, listen to it. It'll just steam on us. It won't flash. Go high in the ceiling. Adcox and Grindle shrug and pull their helmets down tight, expecting the worst. Adcox opens up the nozzle, turning loose a high pressure BLAST OF WATER into the ceiling. The fire SCREAMS in manic anger and HEAVES a cloud of HOWLING steam that WHIRLS back and BAKES them like lobsters. Brian gasps for air as swirling ash batters his facemask. A window somewhere EXPLODES. Burning Factory A Vast Room Day. (Widen, 1991) Was this a backdraft? Were the waves of flame on the ceiling a flameover? Was the smoke, that looked like liquid lead, the first signs of a rollover? Was the fire, screaming in manic anger and heaving a cloud of howling steam that whirls back and bakes them like lobsters, a flashover? What are these phenomena, in which a fire has consumed all available oxygen? Is it a flameover, rollover, flashover, or even an explosion when more oxygen is made available? Although some of the descriptors are to exemplify the effects in movies, are they accurate? Do we truly understand the differences between each of these phenomena? Some may say, yes, they know. However, Gorbett and Pharr (2011) warn that fire changes drastically FIR 3301, Fire Behavior and Combustion 1
through the progression and that, suppression personnel may misread the conditions UNIT x STUDY unless they GUIDE fully comprehend anticipated fire development in enclosure fires. Failure to understand Title differences in enclosures based on size and contents leads to fatalities and injuries of responders (p. 228). Moreover, Gorbett and Hopkins (2007) write, A recent review on the subject of flashover, backdraft, and smoke layer ignitions (i.e. rollover/flameover) has revealed that there are few papers on any one of these subjects and almost none discussing all three phenomena (p. 1). The authors continue to warn that many of the publications are not even technically accurate or combine the phenomena into one definition. On the internet there are many videos of firefighters making entry into hostile environments with obvious signs of one of these phenomena. Why? Is it the lack of understanding? Is it situational awareness and the lack thereof? Is it tradition and the mindset of having to make entry? Do you understand these very important phenomena that occur in enclosed structures, compartments or even open structures that involve flame propagation or turbulent plumes? What is a backdraft? What is a flameover or a rollover? What is a flashover? Backdraft In the1991 movie Backdraft the screenplay writer describes the backdraft phenomena as: Hissss... Rimgale climbs to his feet as fire eats at the wall. A baby backdraft wagging its tail. He goes to a dazed Brian s side, lifting him by his armpits and helping him outside. Rimgale sees a bedroom door ajar on the far side of the house. Hissss [backdraft occurs]. (Int. Swayzak s House Night) The screenplay writer uses the descriptor hissss and then says that the backdraft wags its tail as a means to describe this phenomenon. Is this accurate or movie special effects? Gorbett and Pharr (2011) state, Backdraft is an example of fuels diffused in air and burning with rapid flame spread rates, which result in a pressure rise of explosive force (p. 38). IFSTA (1998) suggests backdraft is, When sufficient heat is confined in an area, the temperatures of combustible materials rise to their ignition points. These materials will not ignite, however, unless sufficient oxygen is available to support combustion (p. 348). As you review literature from the early 1900s until more recently, backdrafts were defined as smoke explosions. In fact as recently as 2007, some articles still referenced smoke explosion as a large buildup of super-heated smoke that ignites as an explosion. Some articles explain this phenomenon as a white smoke explosion. Sutherland (1999) suggested that during a slow developing fire experiment on smoke explosions the fire changes from a flaming to a smoldering fire. This transition period is seen externally as the smoke changes from a light grey smoke to a thick white smoke (p. 47). Whether, one defines the phenomena as a smoke explosion or a backdraft they have one thing in common, fire without adequate oxygen. Gorbett and Hopkins (2007) offer the most current definition for a backdraft, which was adapted from Quintiere and the Pagnie/Feischmann study as: Limited ventilation during an enclosure fire can lead to the production of large amounts of unburnt pyrolysis products. When an opening is suddenly introduced, the inflowing air forms a gravity current and begins to mix with the unburned pyrolysis products, creating a combustible mixture of gases in some part of the enclosure. Any ignition sources, such as a glowing ember, can ignite this combustible mixture. Resulting in an extremely rapid burning of gases/pyrolysis products forced out through the opening and causes a fireball outside the enclosure. (p. 13) Another important point to remember is that sometime during the flame propagation of the fire in an enclosed structure, the fire consumes the available oxygen and begins to transition into the decay phase with high heat still present until the introduction of ventilation. Flameover or Rollover Dunn (1999) suggests flameover is the rapid spread of flame over the surface of walls and ceiling walls, and ceilings painted or covered with a combustible finish can exhibit flameover (p.234). Whereas, NFPA (2004) defined flameover as the the condition where unburned fuel (pyrolysate) from the originating fire has accumulated in the ceiling layer to a sufficient concentration (i.e., at or above the lower flammable limit) that it ignites and burns; can occur without ignition and prior to the ignition of other fuels separate from the origin FIR 3301, Fire Behavior and Combustion 2
(p.7). Although Dunn (1999) suggests the flames spread over the surface of walls UNIT and x STUDY ceilings GUIDE and NFPA (2004) states it is unburned fuel from pyrolysate in layers at the ceiling, both are Title potential dangers to firefighters. Gorbett and Pharr (2011) refined their definition from NFPA and stated flameover can be defined as the condition where unburned fuel (pyrolyzate) from the originating fire has accumulated in the ceiling layer to a sufficient concentration (i.e., at or above the lower flammable limit) that it ignites and burns (p. 247). Flashover In the Backdraft movie there was a scene that appeared to be a flashover and then latter turned into a backdraft. Widen (1991) writes in the screen play: Brian can see Adcox testing the ceiling with a pike pole as Brian steps forward, under the power of a flame that beckons him as Dennis suddenly THROWS his body against Adcox, knocking him clear just as a flame EXPLODES DOWNWARD from the ceiling. (Ext. Building - Day - 20 Years Earlier) Although flashovers do not explode downward, a flashover is when a room becomes completely involved without any direct contact of flames. While the initial heat transfer mechanism in the early fire stages of a compartment fire is largely by convection, the heat transfer mechanism at and beyond flashover is primarily by radiation (Gorbett & Pharr, 2011, p. 239). NFPA 921 (2004) defines flashover as, A transitional phase in the development of a compartment fire in which surfaces exposed to thermal radiation reach ignition temperature more or less simultaneously and fire spreads rapidly throughout the space resulting in full room involvement or total involvement of the compartment or enclosed area (p.11). On the other hand Dunn (1992) suggested, Flashover is the explosion of a smoke-filled room into flame; it takes place after rollover (p. 57). Nonetheless, the newest definition from Gorbett and Pharr (2011) states that the result of the flashover is that every combustible surface within the room, compartment, or enclosure becomes ignited; the entire volume is involved in fire; and this fire can no longer be contained within the room of origin. Points to Ponder Units respond to an old three-story wood frame home (made from hard, rough-cut pine) that has been converted into a rooming house with multiple compartments. Heavy fire and smoke is showing on Side A on the second floor as turbulent black and brownish smoke was issuing from the windows, eaves and gable ends of the structure. Units make an aggressive knockdown of the fire and continue deep into the structure where fire was still visible using the TIC (thermal imaging camera). The smoke was in layers across the ceiling which appeared as residual smoke mixed with smoke from the fire. Pushing down the hallway the smoke appears to be lazier and maybe lighter in color. Heat was still high as it was radiating from the bead board walls from the knockdown. You could hear crackling in the walls as they were starting to cool down at the floor level. The TIC is indicating high heat in the last compartment on the right. Your hose line is in place and you opened the door to see oxygen starved flames come to life almost simultaneously with ignition. In the scenario, what happened? Was this a backdraft, a flameover, or a rollover? Gorbett and Pharr (2011) warn, Failure to understand differences in enclosures based on size and contents leads to fatalities and injuries of responders. Three distinct and commonly misunderstood phenomena flameover, backdraft, and flashover are the most dangerous because of the dramatic changes that occur rapidly throughout the compartment (p. 277). From the textbook we will evaluate intensive properties of materials that are independent of their mass or volume and extensive properties that are dependent on the expanse of the material. Also, we will analyze the temperature of a colder object can be heated by conduction or thermal radiation from a warmer body. Convection is a special case of conduction in which a fluid acts as an intermediary between the heat source and the cool object. We will also cover combustion as an exothermic chemical reaction between a fuel and an oxidizer resulting in the generation of substantive heat (and often light). We will evaluate the states of fire as it proceeds through both non-flaming and flaming stages. The non-flaming stages consist of smoldering and pyrolysis (with or without the participation of oxygen); the flaming stages include well-ventilated, underventilated, and post-flashover fire. Also, the reactions that initiate a fire proceed very slowly unless the fuel is heated to hundreds of degrees Celsius. We will understand that, for a fire to spread, some of the enthalpy FIR 3301, Fire Behavior and Combustion 3
from the ignition region must heat unburned material to a temperature at which UNIT it can x STUDY burn. Finally, GUIDE a fire can be extinguished by cooling, reducing the oxygen supply, separating the fuel and Title the oxidizer, and decreasing the concentration of the flame-propagating free radicals. References Corbett, G., & Pharr, J. (2011). Fire dynamics. Upper Saddle River, NJ: Pearson Education. Corbett, G., & Hopkins, R. (2007). The current knowledge & training regarding backdraft, flashover, and other rapid fire progression phenomena. TRACE. Retrieved from http://tracefireandsafety.com/fireinvestigationresearch/flashover%20backdraft%20paper- NFPA%20Boston.pdf Dunn, V. (1992). Safety and survival on the fireground. Tulsa, OK: PennWell. Dunn, V. (1999). Command and control of fires and emergencies. Saddle Brook, NJ: Fire Engineering Books & Videos. Gann, R., & Friedman, R. (2015). Principles of fire behavior and combustion (4th ed.). Burlington, MA: Jones & Bartlett. International Fire Service Training Association. (1998). Essentials of fire fighting (4th ed.). Stillwater, OK: Oklahoma State University Fire Protection. National Fire Protection Association. (2004). NFPA 921: Guide for fire and explosion investigation. Quincy, MA: Author. Sutherland, B.J. (1999, March). Smoke explosions. Fire Tactics. Retrieved from http://www.firetactics.com/smoke,%20sutherland.pdf Widen, G. (Writer). (1991). Backdraft [Script]. Retrieved from http://www.imsdb.com/scripts/backdraft.html Suggested Reading As you view these videos remember firefighters work in uncontrolled environments during emergency situations. Some of the tactics do not follow FESHE curriculum guidelines and outcomes for incident command, scene size-up, or fire attack. This course is about fire behavior and combustion. The purpose of viewing these videos is to watch combustion as an exothermic chemical reaction between a fuel and an oxidizer resulting in the generation of substantive heat (and often light). In addition, understand that for a fire to spread, some of the enthalpy from the ignition region must heat unburned material to a temperature at which it can burn, whether it leads to backdraft, flameover, or flashover, or not. East Houston, Texas Backdraft The Bravest Online https://www.youtube.com/watch?v=tb733alc9gw Flashover Or Backdraft Occurs While Crews Are In A Working House Fire https://www.youtube.com/watch?v=hfmzxewuuui Forward the video to 5.30 6:30 to observe the backdraft. Backdraft & Flashover https://www.youtube.com/watch?v=inrs4fdndr4 What Happens in a Backdraft? Animation of a backdraft with a description. https://www.youtube.com/watch?v=v6cft74ktbw FIR 3301, Fire Behavior and Combustion 4
Learning Activities (Non-Graded) Review What You Have Learned UNIT x STUDY GUIDE Title The Challenging Questions at the end of Chapter 5, on page 75, will help you evaluate materials that are intensive and which are extensive. 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. Review What You Have Learned The Challenging Questions at the end of Chapter 6, on page 94, will help you evaluate when is oxidation not combustion. In addition, six ways in which fire can originate and the four fundamental ways of extinguishing a fire. 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 5