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Fire and Explosion Safety: Understanding, Prevention, and Reaction

Explore conditions leading to fires and explosions, determining flammability limits, utilizing inerting for prevention, and understanding types of reactions. Learn about flash points, fire points, and flammability diagrams for safe handling of combustible materials.

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Fire and Explosion Safety: Understanding, Prevention, and Reaction

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  1. Safety • Determine conditions where fires and /or explosions can occur. • Develop estimates for upper/lower flammability limits in mixtures • Utilize inerting to prevent fires/explosions.

  2. Combustion/Fire/Explosion

  3. Where Does Reaction Occur? • In gas phase where ignition source, oxygen and fuel coexist. • Can be autocatalytic under certain conditions. • May not need ignition source if temperature is high enough.

  4. Types of Reactions • Slow Oxidation • Energy can be absorbed by surroundings without increase in temperature. • Fire • Energy released can be dissipated by environment with an increase in temperature to a stable point. • Deflagration/Explosion • Energy released cannot be fully dissipated by environment and temperature continuously increases.

  5. Definitions • Flash Point Temperature • Enough fuel exists in air to create a flammable mixture. Will “burn out”. • Fire Point Temperature • Enough fuel exists in air to create a sustainable flammable mixture. • Flammability Limits • Volume percent ranges of fuel in air where burning occurs.

  6. LFL Lower Flammability Limit • Partial pressure of fuel is too low to keep reaction going • UFL Upper Flammability Limit • Partial pressure of oxygen is too low to keep reaction going

  7. Sources for LFL/UFL • MSDS sheets where data was obtained experimentally. • Mixtures of Fuels • Can be calculated with known LFL/UFL of all components

  8. Calculating LFL/UFL of Mixtures

  9. 20:80 Hexane/Heptane Liquid at 25 oC • Assume Liquid is in equilibrium with air in headspace • Calculate mole fraction of each component using Raoult’s Law or suitable model. • Calculate LFL/UFL of mixture

  10. Temperature Dependence of LFL/UFL

  11. T = 20 oC

  12. Pressure Effects

  13. Flammability Diagrams • Flammability Diagrams • Compression and Ignition

  14. 40% Nitrogen 40% Fuel 20% Oxygen

  15. Original Mixture 40% Nitrogen 40% Fuel 20% Oxygen Dilute with Air

  16. Original Mixture 40% Nitrogen 40% Fuel 20% Oxygen Dilute with Air Air Added Original Fuel

  17. Constructing Flammability Diagram Fuel + zO2 CO2 + H2O 1. Draw Air Line 2. Enter LFL & UFL • Determine z • LOC = zLFL(use data, if available) UFL LFL

  18. Constructing Flammability Diagram Fuel + zO2 CO2 + H2O • Add StoichiometricLine • Get Pure Oxygen LFLand UFL (if available) LOC UFL LFL

  19. Constructing Flammability Diagram Fuel + zO2 CO2 + H2O 7. Construct Curve LOC Flammable Region

  20. Compression of Gases

  21. Acrylic Acid ProcessCompressor Section

  22. Safety (MSDS) data for hexane Physical data Appearance: colourless liquid Melting point: -95 C Boiling point: 69 C Vapour density: 3 (air = 1) Vapour pressure: 132 mm Hg at 20 C Specific gravity: 0.659 Flash point: -10 F Explosion limits: 1.2% - 7.7% Autoignition temperature: 453 F

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