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Flammability, Combustion, and Fire Protection

Flammability, Combustion, and Fire Protection. 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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Flammability, Combustion, and Fire Protection

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  1. Flammability, Combustion, and Fire Protection

  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 Hazards • 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 low level of probability, as losses are so high

  4. Flammability limits • Lower explosive limit, LEL (also LFL) • The minimum concentration of vapor in air below which a spread of flame does not occur when the vapor is in contact with a source of ignition • Acetone LEL = 2.5% • Upper explosive limit, UEL (also UFL) • The maximum concentration of vapor in air above which a spread of flame does not occur when the vapor is in contact with a source of ignition. • Acetone UEL = 12.8% • Explosive range (also flammable range) • The spread between the LEL and UEL • Acetone explosive range = 2.5 - 12.8%

  5. Explosive energy Concentration UEL LEL

  6. Relationship between toxicity and flammability Toluene Example: O2 deficient TLV PEL IDLH LEL UEL 1 - 100 ppm 1000-5000 ppm 1-20 percent • TLV=50 ppm, • PEL = 200 ppm, • IDLH = 500 ppm, • LEL = 1.1%, • UEL 7.1%

  7. Definitions • Ignition temperature • The temperature at which ignition (production of flame) and burning will be continued after the source of ignition or the source of heat is removed • Flash point • The lowest temperature at which enough vapor is given off near the surface of a liquid to produce a flammable mixture with air. • Flammable liquid • Liquids with a flash point below 100 F • Combustible liquid • Liquids with a flash point 100 F or greater

  8. OSHA and NFPA Classification

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

  10. 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

  11. Explosions • BLEVE • Boiling Liquid Expanding Vapor Explosion • Flash evaporation after vessel rupture • May not involve combustion

  12. Chemistry of Fire • Combustion • Rapid oxidation • Combustion components • Oxygen • Atmosphere (21%) • Chemical oxidizers • Fuel • Solids • Surface-to-mass ratio • Gaseous • Liquids (vapors) • BGases

  13. Chemistry of Fire • Combustion components (cont.) • Heat • Heat of combustion • Other sources of heat: (ignition) • Chemical reactions • Decay • Slow oxidation • Electricity • Arcing • Resistance • Mechanical friction • Chemical Chain Reaction • Propagated by free radicals

  14. Heat Soot, smoke Carbon dioxide Carbon monoxide Incomplete combustion Hydrogen cyanide Hydrogen sulfide Phosgene Acid Gases Hydrogen Chloride Sulfur dioxide Nitrogen oxides Ammonia Acrolein Metal Fumes Products of combustion

  15. The Fire Triangle • Four components: • Oxygen • Heat • Fuel • Reaction • Removing any component stops the fire

  16. Extinguishing a fire • Cooling • Applying water • Removing Fuel • Shut off supply to gas or liquid fires • Pump liquid from burning tanks • Limiting oxygen • Mechanical smothering • Foam • Displace oxygen with inert gas • Interrupt chain reaction • Capture free radicals using an extinguishing agent

  17. Fire Classification • Class A • Ordinary combustibles • Wood, paper, rubbish • Extinguish with water • Class B • Flammable liquids • Water may aggravate a burning liquid fire • Extinguish with foam, chemical agents

  18. Fire Classification • 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 • Special categories

  19. Extinguishing agents • Water • Removes heat from a fire • Streams, spray or fog • Best for Class A fires • Not for electrical or combustible metal fires • Water mist may be used on electrical fires. These are special fire extinguishers, filled with distilled water, that produce a fine mist (no solid stream of water) • Foam • Excludes oxygen from burning liquid fires • Aqueous Film Forming Foam (AFFF) • Fire can re-ignite if foam breaks down

  20. Extinguishing agents • Inert Gases • Displaces oxygen • Carbon dioxide, nitrogen • Halogenated Hydrocarbons • Inhibit chain reactions • HALON (bromo-fluoro-chloro-hyrdrocarbons) • Carbon tetrachloride (historically) • Ozone depleting • New, more ozone-friendly agents are available

  21. Extinguishing agents • Dry Chemical • Inhibit chain reactions • Sodium or potassium bicarbonate • For Class B or C fires • Multipurpose Dry Chemical • Monoammonium phosphate • For Class A, B, or C fires • Excludes oxygen by coating surfaces • Dry Powder • Excludes oxygen from burning metal • Sodium chloride, graphite

  22. Fire Extinguishers • Water • For Class A fires • Minimum 2 1/2 gallons or 2A • "A" unit rating = 5 quart water or equivalent • Usually stored pressure type • Inverting soda-acid extinguisher are obsolete and dangerous • Foam • For Class A or B • Stored pressure

  23. Fire Extinguishers • Dry Chemical • Class ABC or BC • "B" unit rating = 1 square foot flammable liquid fire • No rating for "C“ • Stored pressure or cartridge- operated

  24. Fire Extinguishers • Liquified Gas • CO2, Class BC • HALON, Class ABC • Dry powder • Class D (no rating) • Cartridge operated

  25. 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 • 5-year hydrotest • 12 yr. hydrotest for dry chemical or HALON (6 yr. recharge) • Training and Education • For all workplaces with fire extinguishers

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

  27. Controlling Fire Hazards • Flammable liquid safety • Limit quantities • Store liquids in flammable liquid cabinets or rooms • Use "Safety" cans • Ventilation • Pressure relief valves

  28. Controlling Fire Hazards • Flammable liquid safety • Controlling ignition sources • Grounding and bonding • Non-sparking tools • Approved dispensing hoses • Classified "explosion proof" wiring • "Hot Work Permit“ • For welding, etc. • Test for LEL • Observer stands by with extinguisher or fire hose

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

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