Chapter 2 Chemistry of Fire

Question 1

Flammable/Explosive Limit

Answer 1

% of a substance (vapor) in air that will burn once it is ignited

Most have upper (too rich) / lower (too lean) flammable limits

Question 2

Flash Point

Answer 2

Minimum temperature at which a liquid fuel gives off sufficient vapors to form an ignitable mixture w/air near the surface

At this temperature, the ignited vapors will flash but will not continue to burn

Question 3

Heat

Answer 3

The form of energy that raises temperature

Question 4

Ignition Temperature

Answer 4

The minimum temperature to which a fuel in air must be heated to start self-sustained combustion w/o a separate ignition source

Question 5

Fire is a byproduct of

Answer 5

combustion

Question 6

Combustion-

Answer 6

a self-sustaining process of rapid oxidation of a fuel which produces heat and light

Question 7

Conduction:

Answer 7

Direct contact of the two bodies or by an intervening heat conducting minimum; Aluminum copper and iron are good conductors while fibrous materials are not

Question 8

Convection:

Answer 8

Transfer of heat by the movement of air or liquid; Upward travel of hot gases within an open stairwell; Mushrooming effect is convection; Direct flame contact is a form of convection

Question 9

Radiation:

Answer 9

Heat can travel where matter doesn’t exist;

Example: Heat from the sun reaches the earth; Radiated heat will travel though a space until it reaches an opaque object; Major source of fire spread to an exposure

Question 10

Law of heat flow:

Answer 10

Heat tends to flow from a hot substance to a cold substance

Question 11

Fire Tetrahedron: 4 Components:

Answer 11

Oxygen (oxidizing agent), Fuel, Heat, Self-Sustaining chemical reaction

Question 12

Fuel: Can be found in 3 states of matter:

Answer 12

Solid, Liquid or Gas

• Only gases burn;
• Solid fuels are evolved to gases by pyrolysis;
• Liquids are evolved to gases by vaporization;
• Gaseous fires are the most dangerous b/c they are already in their natural state required for ignition

Question 13

Oxygen: Need approximately ___% for fire;

Answer 13

Need approximately 16%; Some fuels contain their own oxygen source

Question 14

Phases of Fire:

Answer 14

3 main progressive phases: Incipient, Steady state burning, and hot smoldering

All Phases in order:
Incipient Phase
Rollover
Steady State Burning Phase
Flashover
Hot Smoldering
Backdraft

Question 15

Incipient Phase:

Answer 15

Fire is limited to original materials of ignition. Temperature in room is only slightly increased

Question 16

Rollover:

Answer 16

Last warning before flashover. Unburned combustible gases released during the incipient or early steady state accumulate at the ceiling level. When the flammable range is reached they ignite and a fire develops at the ceiling level

Question 17

Steady state burning phase:

Answer 17

Sometimes referred to as free burning phase. Sufficient oxygen and fuel are available for fire growth and open burning to a point where total involvement is possible. Temperature at upper regions of the room exceed 1300 degrees. The fire will continue to grow until there is an insufficient amount of oxygen to react with the fuel, then enter the smoldering phase

Question 18

Flashover:

Answer 18

Occurs when flames flash over the entire surface of a room or area. Caused by the buildup of heat. Can be avoided by directing water at the ceiling level and room contents to cool materials below their ignition points. Today’s bunker gear lasts about 2 seconds in a flashover

Question 19

Hot smoldering phase:

Answer 19

Fire is reduced to glowing embers. Room completely filled with dense smoke and gases. Can force smoke through small cracks in building. Room temp in excess of 1000 degrees

Question 20

Backdraft:

Answer 20

Can occur in the late steady state burning phase or hot smoldering; Introducing oxygen into an oxygen deficient atmosphere

Question 21

Warning signs of a backdraft:

Answer 21

Dense black (carbon-filled) smoke
Pressurized smoke exiting small openings
Black smoke becoming dense gray yellow
Confinement and excessive heat
Little or no visible flame
Smoke leaving the building in puffs or at intervals
 Smoke stained windows
Muffled sounds
Sudden rapid movement of air inward as an opening is made

Question 22

Thermal Layering of gases:

Answer 22

Also known as heat stratification and thermal balance; Smoke is a heated mixture of air gases and particles as it rises

Question 23

Products of combustion:

Answer 23

When a fuel burns it undergoes a chemical change; 4 products of combustion: Light, Heat, Smoke, Fire Gases

Question 24

Flame:

Answer 24

is the visible luminous body of a burning gas; More complete combustion make the fire hotter and less luminous;

Question 25

Smoke:

Answer 25

consists of a mixture of oxygen, nitrogen, carbon dioxide, CO, carbon particles among others; CO is 210X more attractive to red blood cells than oxygen; The hotter the smoke is the faster it’s going to move; Most fire related death occur from CO

Question 26

Fire extinguishment theory:

Answer 26

Can be achieved by Temperature reduction, Fuel Removal, Oxygen Dilution, Chemical flame inhibition

Question 27

Classes of fire:

Answer 27

CLASS A: Wood, Paper, Rubber, Plastic
CLASS B: Liquids, Greases, Gases
CLASS C: Electrical (Equipment)
CLASS D: Combustible Metals