Course Firefighter I. Unit V Fire Behavior. Essential Question How does the physical state of matter affect the combustion process?

Transcription

1 Course Firefighter I Unit V Fire Behavior Essential Question How does the physical state of matter affect the combustion process? TEKS (c) (7)(B)(C) Prior Student Learning Chemistry and Physics of Fire Estimated Time 3 hours Physical States of Matter and the Combustion Process 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) = Propane = Carbon Monoxide = 0.96 II. Liquid Fuels and Specific Gravity A. Specific gravity is the weight of a substance compared to the weight of 1

2 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 2

3 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 2. 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 3. Carbon dioxide (CO 2 ) 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 4. 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 5. 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 3

4 Resources , Essentials of Firefighting (5 th 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 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

5 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 c. 1.0 d 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 5

6 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. CO 2 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. CO For practical purposes, firefighters should recognize all smoke as toxic and a hazard to human life. a. True b. False 6

7 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 7

8 Name Date Objectives 4 pts. Excellent Discussion Rubric 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: 8