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Fire Safety and Protection

Fire Safety and Protection. PUBH 3310. November 8, 2010. Objectives. Know and understand: Principles of combustible and flammable liquids, including limits, and classification Basics of fire chemistry Fire classes How extinguishing agents work Be familiar with Types of fire extinguishers

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Fire Safety and Protection

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  1. Fire Safety and Protection PUBH 3310 November 8, 2010

  2. Objectives • Know and understand: • Principles of combustible and flammable liquids, including limits, and classification • Basics of fire chemistry • Fire classes • How extinguishing agents work • Be familiar with • Types of fire extinguishers • How to control flammable liquid hazards • Basic fire prevention and protection

  3. Fire Safety and Protection • Outline • Introduction • Fire Chemistry • Flammable and Combustible Liquids • Fire Types • Extinguishing Fires • Extinguishing agents • Fire extinguishers • Controlling Fire Hazards

  4. Introduction • Fire is a substantial risk • Annual $2.2 billion loss • Over 300 workplace deaths • Over 3% of workplace fatalities • Fire losses can be catastrophic • Unlike other hazards, the event may not be self- limiting • Fire hazards MUST be controlled to a very low level of probability because potential losses are so high

  5. Chemistry of Fire • Fire is Combustion • Rapid oxidation • Four Components of Combustion: • Oxygen • Atmosphere (21% O2) • Chemical oxidizers • Fuel • Solids • Surface-to-mass ratio affects burn rate • Liquids • Vapor burns, not the liquid • Gases

  6. Chemistry of Fire • Four Components of Combustion (cont.) 3. Heat • Heat of combustion • Other sources of heat: (can cause ignition) • Chemical reactions • Decay • Slow oxidation • “Spontaneous combustion” • Electricity • Arcing, resistance heating • Mechanical friction 4. Chemical Chain Reaction • Propagated by free radicals

  7. Chemistry of Fire • Combustion products can be very toxic • Soot, smoke • Carbon dioxide • Carbon monoxide • Caused by incomplete combustion • Hydrogen cyanide • Hydrogen sulfide • Phosgene • Acid Gases • Hydrogen Chloride • Sulfur dioxide • Nitrogen oxides • Ammonia • Acrolein • Metal Fumes

  8. Definitions • Ignition temperature • Temperature where ignition (production of flame) and burning will continue after the source of ignition or the source of heat is removed • “Fahrenheit 451” for books! • Flash point • Lowest temperature at which a liquid gives of sufficient vapor for sustained burning, also know as the “fire point”

  9. Definitions • Flammable liquid • Liquids with a flash point below 100 °F • Can burn at ambient temperature = more hazardous • Acetone, gasoline • Combustible liquid • Liquids with a flash point 100 °F or greater • Must be heated before they can burn = less hazardous • Diesel fuel

  10. Flammable and Combustible LiquidsOSHA and NFPA Classification NFPA “diamond”

  11. Flammability limits • Lower explosive limit, LEL [or LFL] • The lowest concentration of vapor in air that can be ignited, ignition cannot occur below this concentration • not enough fuel to burn • Upper explosive limit, UEL [or UFL] • The highest concentration of vapor in air that can be ignited, ignition cannot occur above this concentration • not enough oxygen to burn • Explosive range [or flammable range] • The spread between the LEL and UEL

  12. Explosive (Flammable) Range Explosive energy Concentration UEL LEL

  13. Flammable concentrations also may be extremely toxic! (O2 deficient) (Fuel deficient) TLV PEL IDLH LEL UEL 1-100 ppm 1000-5000 ppm 1-20 percent (typical) (typical)

  14. Fire Types • Flame fire • Gases or vapors • High burning rate • Surface fire • Solids • Burning rate may be slow • Explosion • An event leading to a rapid increase of pressure

  15. Fire Types • Explosions • Deflagration • Combustion wave propagates at subsonic velocity • Detonation • Combustion wave propagates at supersonic velocity • Gas or vapor explosion • Combustion of pre-mixed gas or vapor • Dust explosion • Finely divided solids, suspended in air

  16. Fire Types • Explosions (cont.) • Boiling Liquid Expanding Vapor Explosion, BLEVE • Flash evaporation after vessel rupture • Very dangerous • Fire • Oxygen deficiency • Physical damage • May not involve combustion • Steam, etc.

  17. Extinguishing fires • The Fire “Triangle” or Tetrahedron • Four components • Oxygen • Heat • Fuel • Chain reaction • Removing any component stops the fire Fire tetrahedron Fire triangle (flames represent the fourth component)

  18. Extinguishing Fires • Removing component stops fire (cont) • Removing fuel • Shut off fuel supply • Pump liquid from burning tanks • Cooling (removes heat) • Applying water

  19. Extinguishing Fires • Removing any component stops fire (cont.) 3. Limiting oxygen • Mechanical smothering • Foam • Displace oxygen with inert gas • Potentially fatal O2 deficiency Foam blanket excludes oxygen

  20. Extinguishing Fires • Removing any component stops fire (cont.) 4. Interrupting chain reaction • Capture free radicals using a chemical agent • Dry chemical • Fire retardant • Halogenated hydrocarbon

  21. Portable Fire Extinguishers • Fire Extinguisher basics • Fire class • Extinguisher rating • Extinguisher types • Selection • Use and training

  22. Extinguishing Fires • Fire Classification • Extinguishing methods are based on fire class • Class A • Ordinary combustibles • Wood, paper, rubbish • Extinguishwith water, chemical agents • Class B • Flammable liquids • Water may aggravate a burning liquid fire • Extinguish with foam, chemical agents Class A Class B

  23. Extinguishing Fires • Fire Classification (cont.) • Class C • Fires in electrical equipment • Use non-conductive extinguishing agent • Class D • Combustible metal fires • Extinguish by smothering with dry powder • Water will cause burning metals to explode • Class K • Kitchen fires • Wet chemical smothers and cools Class C Class D Class K

  24. Fire Extinguisher Rating • Rated by fire type and extinguisher effectiveness • "A” unit • 5 quart water or equivalent • Example: 1-A = 1 ¼ gallons water or equivalent • “B” unit • Square feet of burning liquid • Example: 10-B means untrained operator can extinguish 10 ft2 flammable liquid fire • “C” • No units, electrically non-conductive, safe for class C fires • “D” and “K” • No units, suitable for Class D or Class K fires

  25. Fire Extinguisher Types • Most extinguishers are “stored pressure” type • Pressurized with air or nitrogen • Pressure gauge equipped

  26. Fire Extinguisher Types • Liquified gas extinguishers • CO2 • No pressure gauge

  27. Selecting Fire Extinguishers • Applicable fire class (A,B,C, etc.) • Size • Bigger is better • Special applications • CO2, clean agent or water mist to protect electronic equipment • Kitchens

  28. OSHA Requirements for Fire Extinguishers • Placement • Maximum 75 foot travel distance for "A" or "D“ • Maximum 50 foot travel distance for "B“ • Inspection • Monthly visual • Annual maintenance • Periodic hydrotest • Training and Education • For all workplaces with fire extinguishers • Unless properly trained, employees are prohibited from using extinguishers

  29. Using a Fire Extinguisher • P.A.S.S. • Pull Pin • Aim at base of fire • Squeeze handle • Sweep back and forth

  30. Using a Fire Extinguisher • Sound the alarm first! • Only for use on “incipient” fires • For outside use, attack from upwind • Two extinguishers are better than one • Attack from different directions • Don’t risk injury to protect property

  31. Controlling Fire Hazards • Flammable liquid safety • Limit quantities • "Safety" cans • “Fusible” closing devices Parts washer with fusible link holding lid open. Link melts and lid closes in case of fire.

  32. Controlling Fire Hazards • Liquid safety (cont.) • Store liquids in flammable liquid cabinets or rooms • Ventilation • Pressure relief valves • Etc. Flammable liquid storage cabinets have many fire safety features.

  33. Controlling Fire Hazards • Liquid safety (cont.) • Controlling ignition sources • Grounding and bonding • Non-sparking tools • Approved dispensing hoses • Classified "explosion proof" wiring • "Hot Work Permit“ • For welding, etc. • First, test for LEL • Observer stands by with extinguisher or fire hose

  34. Controlling Fire Hazards • Fire Suppression Systems • Automatic sprinklers • Wet pipe (buildings) • Dry pipe (industrial) • Deluge • Dry chemical • CO2, HALON

  35. Conclusions • Fire hazards MUST be controlled to a very low level of probability • Fire components are heat, oxygen, fuel, and chemical chain reaction • “Flammable” liquids more hazardous than “Combustible” • There are several fire and explosion types (BLEVE, etc.) • Fires are extinguished by removing a fire component (from the fire “tetrahedron”) • Fire extinguishers are selected by fire class and rating • Fire extinguisher use = P.A.S.S. • Flammable liquid hazard control includes quantity limits, static electricity control and safe storage

  36. Web Resources • OSHA • http://www.osha.gov/SLTC/firesafety/index.html • FEMA extinguisher training • http://www.youtube.com/watch?v=BLjoWjCrDqg

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