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%

Concentration

Exp

losi

ve e

nerg

y

LEL UEL

Relationship between toxicity and flammability

Toluene Example:

TLV PEL IDLH LEL UEL1 - 100 ppm 1000-5000 ppm 1-20 percent

•TLV=50 ppm, •PEL = 200 ppm, •IDLH = 500 ppm,

•LEL = 1.1%, •UEL 7.1%

O2 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 ClassificationNFPA OSHA Flashpoint Boiling point

Flammable Liquids

4 IA <73F < 100F

3 IB <73F >100F

3 IC >73 - <100F

Combustible liquids

2 II >100 - <140F

2 IIIA >140 - <200F

1 IIIB >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– 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