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Fire Behavior

Fire Behavior. Module 2. TS 2 –5. DEFINITION OF POWER. Amount of energy delivered over a given period of time Units of power English or Customary System — Horsepower International System of Units (SI) — Watts. TS 2 –6a. HEAT & TEMPERATURE TERMS.

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Fire Behavior

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  1. Fire Behavior Module 2

  2. TS 2–5 DEFINITION OF POWER • Amount of energy delivered over a given period of time • Units of power • English or Customary System — Horsepower • International System of Units (SI) — Watts

  3. TS 2–6a HEAT & TEMPERATURE TERMS • Heat — Energy transferred from one body to another when the temperatures of the bodies are different • Temperature — Measure of warmth or coldness of an object based on some standard (usually freezing and boiling points) • Degrees Celsius — SI unit of temperature measurement • 0C = freezing point of water • 100C = boiling point of water

  4. TS 2–6b HEAT & TEMPERATURE TERMS (cont.) • Degrees Fahrenheit — Customary unit of temperature measurement • 32F = freezing point of water • 212F = boiling point of water • Joule — Approved SI unit of all forms of energy, including heat • Calorie — Amount of heat required to raise the temperature of 1 gram of water 1 degree Celsius

  5. TS 2–6c HEAT & TEMPERATURE TERMS (cont.) • British thermal unit — Amount of heat required to raise the temperature of 1 pound of water 1 degree Fahrenheit • Mechanical equivalent of heat • 1 calorie = 4.187 joules • 1 Btu = 1,055 joules

  6. Thermal Balance • A fire seeks some sort of equilibrium between products flowing towards and away from the fire itself. • The energy coming into a fire must equal the energy being released. • The degree of thermal balance existing in a closed room during a fire’s development is dependent upon fuel supply and air availability as well as other factors. • The hot area over the fire (often termed the fire plume or thermal column) causes the circulation that feeds to the fire.

  7. Thermal Balance cont. • However, when the ceiling and upper parts of the wall linings become super-heated, circulation slows down until the entire room develops a kind of thermal balance with temperatures distributed uniformly horizontally throughout the compartment.

  8. Thermal Imbalance • Occurs through turbulent circulation of steam and smoke in the fire area and this leads to decreased visibility and uncomfortable conditions.

  9. Chemical Byproducts of Combusiton • Gases • Most gases produced by fire are toxic • Common gases include: • Carbon monoxide • Hydrogen cyanide • Phosgene

  10. IDLH Table

  11. Carbon Monoxide • Because carbon monoxide causes more fire related deaths than any other toxic gas, a greater explanation is needed. • This colorless, odorless gas is present with every fire. The poorer the ventilation and the more inefficient the burning, the greater the quantity of carbon monoxide is formed. • A rule of thumb, though subject to much variation, is that the darker the smoke, the higher the carbon monoxide levels. Black smoke is high in particulate carbon and carbon monoxide because of incomplete burning.

  12. CO (Continued) • Carbon monoxide concentrations in air above five-hundredths of one percent (0.05 percent) or 500 parts per million (ppm) can be dangerous. • When the level is more than 1 percent, unconsciousness and death can occur without symptoms. • Therefore, firefighters should not use signs, and symptoms as safety factors. Dizziness, headaches, nausea, vomiting, and cherry-red skin can occur at many concentrations, depending on the firefighter’s dose and exposure.

  13. CO (Continued) • The higher the carbon monoxide concentrations the quicker carboxyhemoglobin occurs • A firefighter’s general physical condition, age, degree of physical activity, and length of exposure all affect the actual carboxyhemoglobin level in the blood. • Firefighters frequently exposed to carbon monoxide develop a tolerance to it, and they can function without symptoms with residual levels of serum carboxyhemoglobin that would produce significant symptoms in an average adult.

  14. More CO • A 1-percent concentration of carbon monoxide will cause a 50-percent level of carboxyhemoglobin in the blood in 2½ to 7 minutes. • A 5-percent concentration will cause a 50-percent level of carboxyhemoglobin in the blood in 30 to 90 seconds • A firefighter previously exposed to high levels of carbon monoxide may react later in a safer atmosphere because the newly formed carboxyhemoglobin may be traveling through his body. • These firefighters should not be allowed to resume firefighting activities until the danger of toxic reaction has passed. Even with protection, a toxic condition could be endangering consciousness.

  15. Diffusion Flame • Consists of (3) basic elements: • Fuel • Oxygen • Heat

  16. Impact of Changing Conditions • Structure fires can be dynamic • Factors influencing fire development can change as fire extends from one compartment to another • Changes in ventilation likely most significant factors in changing behavior

  17. Temperature Reduction • One of the most common methods of fire control/extinguishment • Depends on reducing temperature of fuel to point of insufficient vapor to burn • Solid fuels, liquid fuels with high flash points can be extinguished by cooling

  18. Temperature Reduction • Use of water is most effective method for extinguishment of smoldering fires. • Enough water must be applied to absorb heat generated by combustion. • Cooling with water cannot reduce vapor production enough to extinguish fires in low flash point flammable liquids/gases.

  19. Temperature Reduction • Water can be used to control burning gases/reduce temperature of products of combustion above neutral plane. • Water absorbs significant heat as temperature raised, but has greatest effect when vaporized into steam.

  20. Fuel Removal • Effectively extinguishes any fire • Simplest method is to allow a fire to burn until all fuel consumed.

  21. TS 2–26 FUEL REMOVAL • Is used on solid, liquid, or gas fuels • Stops flow of liquid or gaseous fuel • Moves solid fuel out of fire path • Allows fire to consume all fuel

  22. Oxygen Exclusion • Reduces fire’s growth and may totally extinguish over time • Limiting fire’s air supply can be highly effective fire control action.

  23. TS 2–27 OXYGEN EXCLUSION OR DILUTION • Is used on solid, liquid, or gas fuels • Prevents air from reaching fuel (smothering) • Dilutes or displacing oxygen with an inert gas

  24. Chemical Flame Inhibition • Extinguishing agents interrupt combustion reaction, stop flame production • Effective on gas, liquid fuels because they must flame to burn • Does not easily extinguish surface mode fires

  25. TS 2–28 INHIBITION OF CHAIN REACTION • Is used on gas and liquid fuels • Uses dry chemicals and halogenated hydrocarbons • Interrupts chemical chain reaction (stops flaming)

  26. Velocity & Pressure • The speed at which smoke leaves a building is referred to as velocity. • Only two things can cause smoke to pressurize within a structure: • Heat • Volume

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