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 = %

Concentration Explosive energy LEL UEL

Relationship between toxicity and flammability Toluene Example: TLV PEL IDLH LEL UEL ppm ppm 1-20 percent TLV=50 ppm, PEL = 200 ppm, IDLH = 500 ppm, LEL = 1.1%, UEL 7.1% O 2 deficient

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 NFPAOSHAFlashpointBoiling point Flammable Liquids 4IA<73F< 100F 3IB<73F>100F 3IC>73 - <100F Combustible liquids 2II>100 - <140F 2IIIA>140 - <200F 1IIIB>200F Non- combustible 0

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 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

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 –CO 2, 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 –CO 2, HALON