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Flammability_ Combustion_ and Fire Protection

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									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
  – How to control flammable liquid hazards
  – Basic fire prevention and protection
                 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
       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%
LEL   Concentration   UEL
  Relationship between toxicity
         and flammability




 TLV   PEL    IDLH                 LEL      UEL   O2 deficient
 1 - 100 ppm 1000-5000 ppm         1-20 percent

Toluene Example:
   •TLV=50 ppm,              •LEL = 1.1%,
   •PEL = 200 ppm,           •UEL 7.1%
   •IDLH = 500 ppm,
                 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
              OSHA and NFPA
               Classification
               NFPA   OSHA   Flashpoint     Boiling point
Flammable       4      IA       <73F           < 100F
Liquids
                3      IB       <73F           >100F
                3      IC    >73 - <100F
Combustible     2      II    >100 - <140F
liquids
                2     IIIA   >140 - <200F
                1     IIIB      >200F
Non-            0
combustible
                 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
                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
               Explosions

• BLEVE
 – Boiling Liquid Expanding
   Vapor Explosion
 – Flash evaporation after
   vessel rupture
 – May not involve
   combustion
            Chemistry of Fire
• Combustion
  – Rapid oxidation
• Combustion components
  – Oxygen
     • Atmosphere (21%)
     • Chemical oxidizers
  – Fuel
     • Solids
         – Surface-to-mass ratio
     • Gaseous
     • Liquids (vapors)
     • BGases
           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
      Products of combustion
•   Heat              • Acid Gases
•   Soot, smoke         – Hydrogen Chloride
•   Carbon dioxide      – Sulfur dioxide
•   Carbon monoxide•   Nitrogen oxides
  – Incomplete     •   Ammonia
    combustion
• Hydrogen cyanide •   Acrolein
• Hydrogen sulfide •   Metal Fumes
• Phosgene
            The Fire Triangle

• Four
  components:
  –   Oxygen
  –   Heat
  –   Fuel
  –   Reaction
• Removing any
  component
  stops the fire
           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
          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
          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
          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
         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
        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
          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
         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
         Fire Extinguishers

• Liquified Gas
  – CO2, Class BC
  – HALON, Class
    ABC
• Dry powder
  – Class D (no
    rating)
  – Cartridge
    operated
 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
      Using a Fire Extinguisher

• P.A.S.S.
  –   Pull Pin
  –   Aim at base of fire
  –   Squeeze handle
  –   Sweep back and forth
    Controlling Fire Hazards

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

• Fire Suppression
  Systems
  – Automatic sprinklers
     • Wet pipe (buildings)
     • Dry pipe (industrial)
  – Deluge
  – Dry chemical
  – CO2, HALON

								
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