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NFPA 921 > Basic Fire Science > Flashcards

Basic Fire Science Flashcards

1
Q

What are the four components of the fire tetrahedron?

A

Fuel
Heat
Uninhibited chemical chain reactions
oxidizing agent

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2
Q

Fires can be prevented or suppressed by controlling or removing

A

one or more of the sides of the tetrahedron.

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3
Q

A fuel is

A

any substance that can undergo combustion.

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4
Q

The majority of fuels encountered are

A

organic. Which simply means that they are carbon based

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5
Q

Combustion of liquid fuels and most solid fuels takes place

A

above the fuel surface in a region of vaports created by heating the fuel surface.

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6
Q

Gaseous fuels do not require ______ or _____ before combustion can occur.

A

vaporization or pyrolysis

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7
Q

In most fire situations, the oxidizing agent is

A

the oxygen in the earth’s atmosphere.

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8
Q

Many chemical oxidizers contain readily released oxygen. List three examples:

A

Ammonium nitrate fertilizer

potassium nitrate

hydrogen peroxide

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9
Q

Every fuel-air mixture has an optimum ratio at which point the combustion will be most efficient. This ratio occurs at or near the4 mixture known by chemists as the

A

Stoichiometric ratio

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10
Q

Self sustained combustion occurs when

A

sufficient excess heat from the exothermic reaction radiates back to the fuel to produce vapors and cause ignition in the absence of the original ignition source.

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11
Q

Lower explosive (flammable) Limit

LEL

A

The minimum percentage of fuel in air in which combustion can occur is the lower explosive limit of the material.

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12
Q

Upper Explosive Limit

UEL

A

There is also a maximum percentage of fuel in air in which combustion can occur.

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13
Q

Complete combustion of hydrocarbon fuels containing only hydrogen and carbon will produce

A

carbon dioxide and water

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14
Q

When less air is available for combustion, as in ventilation controlled fires, the production of ______ increases as does the production of ______

A

Carbon monoxide increases as does the production of soot and unburned fuels.

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15
Q

Combustion products exist in all three states of matter:

A

solid, liquid and gas.

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16
Q

Solid material makes up the ash and soot products that represent the

A

visible “smoke”

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17
Q

Many of the other products of incomplete combustion exist as vapors or as extremely small tarry droplets or aerosols. These vapors and droplets often condense on surfaces that are cooler than the smoke, resulting in

A

smoke patterns that can be used to help determine the origin and spread of fire.

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18
Q

Soot and tarry products often accumulate more heavily on

A

ceramic-tiled surfaces than on other surrounding surfaces due to the heat conduction properties of ceramic tile. Those surfaces that remain the coolest the longest tend to collect the most condensate.

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19
Q

Smoke is generally considered to be

A

the collection of the solid, liquid, and gaseous products of incomplete combustion.

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20
Q

_______ flows occur because hot gases are less dense than cold gases. This causes the hot gases to rise, just as a hot air balloon rises.

A

Buoyant Flows

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21
Q

What causes a fire plume to increase in diameter as it rises?

A

As the hot gases rise, they mix with or entrain the surrounding air so that the flow of gases in the plume increases with height above the fire and at the same time the temperature of the plume is reduced by the entrainment of air. It is the entrainment of air into the plume that causes the plume to increase in diameter as it rises.

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22
Q

When a fire plume reaches the ceiling of a room, the gases turn to move laterally along the ceiling jet as a

A

ceiling jet.

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23
Q

The buoyancy of gases in a compartment fire causes flow into and out of a compartment through vents. In a compartment fire with a single vent opening, hot gases flow out through the upper portion of the opening, and fresh air enters in the lower portions of the opening.

A

Vent flows

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24
Q

The heat transfer rate per unit area

A

Heat flux

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25
Q

_____ is a measure that expresses the degree of molecular activity of a material compared to a reference point, such as the freezing point of water.

A

Temperature

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26
Q

____ is the energy that is needed to change the temperature of an object.

A

Heat

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27
Q

Heat transfer is measured in terms of energy flow per unit of time

A

kilowatts

The greater the temperature difference between the objects, the more energy transferred per unit of time and the higher the heat transfer rate.

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28
Q

_______ is classically defined as the transport of heat energy from one point to another caused by a temperature difference between those points.

A

Heat transfer

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29
Q

Energy is transferred from the heated area to the unheated area at a rate dependent on

(conduction)

A

the difference in temperature and the thermal conductivity of the material.

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30
Q

High-density materials conduct heat faster than

A

low density

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31
Q

Phase changes most relevant in fire are

A

melting and vaporization.

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32
Q

In _____, the material changes from a solid to a liquid with no change in the chemical structure of the material.

A

Melting

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33
Q

In _____ , the material changes from a liquid to a vapor with no change in chemical structure of the material.

A

Vaporization

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34
Q

______ involves irreversible changes in the chemical structure of a material due to the effects of heat (pyrolysis)

A

Thermal decomposition

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35
Q

_________occurs when fuel vapors mix with air in the absence of an ignition source and the fuel-air mixture is subsequently ignited.

A

Premixed burning

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36
Q

Premixed flame spread can proceed as a _____ or as a _____.

A

deflagration (subsonic combustion) or as a detonation (supersonic combustion)

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37
Q

Deflagration velocities normally range from _____to ____/sec

A

cm/sec to m/sec

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38
Q

Detonation velocities are normally in the ____ of m/sec.

A

thousands of c/sec

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39
Q

In order from flammable gases and vapors of ignitable liquids to ignite, they must be mixed with a sufficient amount of _______ to allow the combustion reaction to occur.

A

Oxidizer (typically atmospheric oxygen)

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40
Q

The percentage of the mixture of gaseous fuel to air by volume must be within a specific range for combustion to occur. This is known as the ______ range of the fuel.

A

flammable or explosive range of the fuel.

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41
Q

The flammable or explosive range of a fuel is expressed as

A

a percentage of ignitable gas or vapor in air by volume.

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42
Q

The minimum percentage of fuel in air (by volume) in which combustion can occur is the

A

lower explosive limit (LEL)

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43
Q

In a mixture that is below its LEL no combustion will occur. This is because below the LEL there are insufficient fuel molecules in the mixture. The mixture can be said to be

A

“to lean”

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44
Q

There is also a maximum percentage of fuel in air (by volume) in which combustion can occur. This is called the

A

upper explosion limit (UEL)

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45
Q

In a mixture that is above the UEL, no combustion will occur because there are insufficient oxygen molecules in the mixture. These mixtures can be said to be

A

“too rich”

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46
Q

The difference between the lower and upper limits is called the

A

flammable or explosive range.

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47
Q

Fuel vapors and oxidizers are separate and combustion occurs in the region where they come together.

A

diffusion flame burning

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48
Q

The _____ of a material is a measure of the amount of heat that will flow across a unit area with a temperature gradient of 1 degree per unit of length.

A

Thermal conductivity

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49
Q

____ have high thermal conductivities.

A

metals

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50
Q

The ____ of a material is a measure of the amount of heat necessary to raise the temperature of a unit mass 1 degree, under specified conditions.

A

Heat capacity

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51
Q

____ and ____ have low thermal conductivities.

A

Plastics and glass

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52
Q

The _____ of a material is a measure of how easily the surface temperature of the material will increase when heat flows into the material.

A

Thermal inertia

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53
Q

In the ____ scale, water freezes at 32 and boils at 100 degrees.

A

Fahrenheit

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54
Q

What are the most familiar empirical temperature scales?

A

Fahrenheit and Celsius (Centigrade)

55
Q

The ______ scales are based on the lowest possible temperature of absolute zero, and therefore are called the absolute temperature scales.

A

Thermodynamic (absolute) Temperature scales

56
Q

The simplest definition of ______ is a theoretical lowest feasible temperature characterized by the absence of heat and molecular motion.

A

Absolute zero

57
Q

Thermodynamic temperature scales differ from empirical scales in that they are based on

A

the fundamental laws of thermodynamics or statistical mechanics instead of the scaling of properties of water.

58
Q

Thermodynamic temperature is measured in

A

Kelvins

Many engineering fields in the US hoever, measure thermodynamic temperature using the Rankine scale (symbol: R)

59
Q

The term _____ is used to describe the amount of fuel present, usually within a compartment.

A

Fuel load

60
Q

As the oxygen contained within a structure is reduced, the ____ of the fire decreases and as a result, the gas temperatures within compartments in the structure decrease.

A

HRR (heat release rate)

61
Q

The _____ of flame is not necessarily an accurate indicator of what is burning, or of the temperature of the flame.

A

color

62
Q

The following flame height definitions define the three regions of a fire:

A

Continuously flaming region
(lower portion of visible flame)

Intermittently flaming region
(upper portion of the visible flame)

Plume region
(above the visible flame)

63
Q

If a fuel package is placed against a wall or in a corner, air entrainment into the plume can be restricted, creating an imbalance in the airflow. As a result of the imbalance in airflow, the flame and thermal plumes will?

A

bend toward the restricting surface

64
Q

_____ is known as solid phase combustion, also known as smoldering.

A

Solid phase combustion

flameless form of combustion whose principal heat source is char oxidation.

65
Q

_____ produces more toxic compounds than flaming combustion per unit mass burned, and it provides a chance for flaming combustion from a heat source too weak to produce flame directly.

A

Smoldering

66
Q

Some liquids are capable of being oxidized in the liquid phase. Most often tis only leads to ignition when the liquid is supported on a _____ substrate.

A

Porous substrate

linseed oil on rags.

67
Q

_____ is a solid phase burning process, which normally includes a thermal decomposition step to create a char, followed by solid phase burning of the char produced.

A

Smoldering

68
Q

Generally, self-heating and spontaneous combustion (self-ignition) are commonly encountered in

A

organic materials, such as animal and vegetable fats and oils.

Because these materials contain polyunsaturated fatty acids. Such fatty acids react with oxygen to generate heat. Unsaturated molecules contain carbon to carbon double bonds which are reactive.

69
Q

Self heating and spontaneous combustion of oils containing mostly saturated hydrocarbons, such as motor oil or lubricating oil, occur only

A

under elevated temperature conditions (e.g., an oil soaked rag wrapped around a steam pipe)

70
Q

Self heating to ignition requires a

A

a porous, permeable, and oxidizable material _ the material must have all three properties.

71
Q

The most commonly encountered forms of elf-heating and self-ignition by fire investigators are the following:

A

Polymerization of fatty acids (animal fats, cooking oils, and drying oils) in cellulose materials (wood, cloth, and paper)

Oxidation of carbonaceous materials (coal and charcoal)

Biologically induced oxidation (hay bales and compost)

Heat-induced oxidation of lingocellulose materials (usually wood fiber and cloth)

Polymerization reactions (plastics, rubbers, adhesives, and paint overspray particles)

72
Q

An _____agent is a chemical substance that , while not necessarily combustible by itself, can rapidly increase the rate of burning of other substances, or result in spontaneous combustion when combined with other substances.

A

Oxidizing agent

73
Q

Materials that undergo spontaneous combustion upon exposure to air are known as

A

pyrophoric

74
Q

Certain elements, particularly white phosphorus, sodium, potassium, and some finely divided metals, such as zirconium, spontaneously ignite when exposed to

A

air

75
Q

The range of ignition temperatures for solids ranges from about

A

270 degrees C to 450 degrees C

76
Q

Broadly speaking flame spread can be classified as

A

concurrent flame spread or counterflow flame spread

These terms relate the direction of flame spread compared to the direction of gas flow.

77
Q

Flames may spread differently on different portions of the same fuel package, for example, a flame may spread slowly across the horizontal surface of a chair cushion with spread increasing rapidly as the back of the chair becomes involved. If a material melts, it is likely to

A

drip and pool on horizontal surfaces. The dripping of liquefied polyurethane foam from furniture can form a pool fire under that furniture.

78
Q

The dominant method of spreading fire from one remote location to another remote location is through

A

radiation.

79
Q

Fire spread can also occur as a result of ______. This occurs when a flaming material drops down and ignites combustibles that it falls on or near.

A

“drop down”

80
Q

While glass cracks when the glass reaches 60-100 C, glass does not generally fall out until

A

flashover,

except when flames directly imping on the glass.

81
Q

The post flashover condition is called

A

full room involvement

82
Q

The onset of flashover occurs when

A

the hot gas laver imposes radiant energy levels (flux) on unignited fuels sufficient to ignite them.

83
Q

Poorly ventilated compartments or very large compartments may be fully consumed without

A

ever involving all the fuel packages at the same time.

84
Q

Flashover times of ___to ___ minutes are not unusual in residential room fires tests and even shorter times to flashover have been observed in nonaccelerated room fires.

A

3 to 5 minutes

85
Q

Development of a ceiling layer of sufficient temperature to cause radiant ignition of exposed combustible fuels is necessary for

A

flashover.

86
Q

When a burning fuel package is away from a wall, air is free to flow into the plume from all directions and mix with the fuel gases. This brings air for combustion into the flame zone and ____ the upper part of the plume by entrainment.

A

cools

87
Q

If the fuel package or the fire plume is against a wall, a given fire size will lead to a ___ percent greater hot layer absolute temperature than the same fire size away from the wall.

A

30%

88
Q

When the same fuel package is placed in a corner, a given fire size will lead to a ___% greater hot later absolute temperature than the same fire size away from walls or corners.

A

70%

89
Q

_____ is the visible or measurable physical changes or identifiable shapes formed by a fire effect or group of fire effects.

A

Fire pattern

90
Q

______are the observable or measurable changes in or on a material as a result of exposure to the fire.

A

Fire effects

91
Q

______ and gasoline burn at essentially the same flame temperature.

A

Wood

92
Q

Identifiable temperatures achieved in structural fires rarely remain above _____C for long periods of time.

A

1040

93
Q

The binder in paint will ______ and _____ the color of the painted surface.

A

Char and darken

94
Q

The presence of large shiny blisters (alligator char) is not evidence that a liquid accelerant was present during the fire, or

A

that a fire spread rapidly or burned with greater intensity.

95
Q

The rate of charring of wood varies widely depending upon variable, including the following:

A 
Rate and duration of heating
Ventilation effects
Surface area to mass ratio
Direction, orientation, and size of wood rain
Species of wood
Wood density
Moisture content
nature of surface coating
Oxygen concentration of the hot gases
Velocity of the impinging gases
96
Q

The rate of charring and burning of wood in general has no relation to

A

its age once the wood has been dried.

Thus, old, dry wood is no more combustible than new kiln-dried wood if they have both been exposed to the same atmospheric conditions.

97
Q

Analysis of the depth of charring is more reliable for evaluating ______, rather than for the establishment of specific burn times or intensity of heat from adjacent burning materials.

A

fire spread

98
Q

The ___________ from point to point is the key to appropriate use of charring, locating the places where the damage was most severe due to exposure, ventilation, or fuel placement.

A

relative depth of char

(The investigator may then deduce the direction of fire spread, with decreasing char depths being farther away from the heat source.)

99
Q

_____ is characterized by the loss of surface material resulting in cracking, breaking, and chipping or in the formation of craters on concrete, masonry, rock, or brick.

A

Spalling

100
Q

___________ is the expansion or contraction of the surface while the rest of the mass expands or contracts at a different rate; one example is the rapid cooling of a heated material by water.

A

A mechanism of spalling

101
Q

________ is the basic chemical process associated with combustion.

A

Oxidation

102
Q

________ of some non combustible materials can produce lines of demarcation and fire patterns of use to fire investigators.

A

Oxidation

103
Q

The higher the temperature and the longer the time of exposure, the ____ pronounced the effects of oxidation will be.

A

more

104
Q

When uncoated iron or steel is oxidized in a fire, the surface first acquires a _______dullness.

A

blue-gray

105
Q

At elevated temperatures, iron may also combine with oxygen to form

A

Black oxides

106
Q

Copper forms a dark ____ or black oxide when exposed to heat.

A

red

The color is not significant. What is significant is that oxidation can form a line of demarcation. The thickness of the oxide depends upon the duration and intensity of the heat exposure. The more it is heated, the greater the oxidation.

107
Q

Rocks and soil, when heated to very high temperatures, will often change colors that may range from

A

yellowish to red

108
Q

Nearly all materials ____ when heated.

A

expand

109
Q

Bending and buckling of steel beams and columns occurs when the steel temperature exceeds approximately ____ degrees

A

500 C

110
Q

Carbon based fuels produce particles that are predominantly

A

carbon (soot)

111
Q

Enhanced soot deposition (acoustic soot agglomeration) is a phenomenon whereby the

(in many cases, the nature of soot deposition on certain surfaces of typical single or multiple station smoke alarms can show that the smoke alarm sounded or did not sound during a fire.

A

soot particulate in smoke forms identifiable patterns on such surfaces of the smoke alarm as the internal and external surfaces of the smoke alarm cover near the edges of the “horn” outlet, the edges of and “horn” sound outlets of the interior “horn” enclosures if present, and surfaces of the “horn” disks themselves

112
Q

Smoke alarms should be taken into evidence when smoke alarm performance may be an issue.

A

The alarm should be collected as evidence after being photographed in place.

Should not be altered by applying power, removing or inserting batteries or pushing the test button.

113
Q

Alarms still on the wall or ceiling should be secured intact with mounting hardware, electrical boxes, and wired connections. Removing ____ with the alarm may be needed to preserve the condition of the alarm and all electrical power connections.

A

a section of wall material

114
Q

A _____ is a distinct and visible fire effect generally apparent on non-combustible surfaces after combustible layers (such as soot, paint, and paper) have been burned away.

A

Clean Burn.

115
Q

Clean burn patterns produced by burning away of soot can be produced by

A

direct flame contact or intense radiated heat.

116
Q

_____ is used by fire investigators to describe numerous chemical and physical changes that occur in gypsum wall board surfaces during a fire.

A

Calcination

117
Q

Calcination involves a chemical change of the gypsum to another mineral,

A

anhydrite

118
Q

The deeper the calcination into the wallboard the

A

greater the total amount of heat exposure (heat flux and duration)

119
Q

Fire rated gypsum wall board contains ______ or ______ particles embedded in the gypsum to preserve the strength of the wall board during fire exposure.

A

Mineral fibers or vermiculite particles

The fibers add strength to the wall board even after it has been thoroughly calcined

120
Q

Glass that has received an impact will exhibit a characteristic ______ pattern.

A

Cobweb

The cracks will be in straight lines and numerous. The glass may have been broken before during or after the fire.

121
Q

_______ is a term used to describe a complicated pattern of short cracks in glass. These cracks may be straight or crescent-shaped. and may or may not extend through the thickness of the glass.

A

Crazing

A result of rapid cooling.

122
Q

______ glass fragments are more uniformly shaped than the complicated pattern of short cracks of crazing.

A

Tempered

123
Q

Incandescent lightbulbs can sometimes show the direction of heat impingement. As the side of the bulb facing the source of heating is heated and softened, the gases inside the bulb can begin to expand and bubble out the softened glass.

A

1

The bulged or pulled portion of the bulb will be n the direction of the source of the heating.

124
Q

In evaluating a distorted light bulb, the investigator should

A

be careful to ascertain that the bulb has not been turned in its socket or that the socket itself has not turned as a result of coming loose during or after the fire.

125
Q

Oily substances, which do not mix with water, float and create interference patterns on the surface of water. This results in a _____ appearance.

A

“rainbow” or “sheen”

Although ignitable liquids will create a rainbow effect, the observation of a rainbow effect should not be interpreted as an indication of the presence of ignitable liquids unless confirmed by a lab analysis.

126
Q

Body fat can melt and burn as a

A

liquid fuel.

127
Q

Muscle can change shape, char and burn. Heat causes dehydration and shortening of tendons and muscles. Bulkier flexor muscles, such as the biceps in the arms and quadriceps in the legs, shorten and contract, causing a body position known as the

A

pugilistic posture.

128
Q

Shorter muscles of the torso cause

A

arching of the neck and back.

129
Q

The _____ posture is a common post mortem response of muscle to heat and is not indicative of a behavioral response to events prior to or during the fire.

A

Pugilistic

Other responses by the body to heat could be criminal attempts to restrain the body.

130
Q

The skull can exhibit a _______ appearance regardless of the presence or absence of pre existing traumatic injury.

A

Fragmented or fractured

131
Q

A ______ is the visible or measurable physical changes or identifiable shapes formed by a fire effect or group of tire effects.

A

Fire pattern

132
Q

______ are the underlying data that are used by the investigator to identify fire patterns.

A

Fire effects

133
Q

_______ are the borders defining the differences in certain heat and smoke effects of the fire on various materials. They appear between the affected area and adjacent, less affected areas.

A

Lines or areas of demarcation

NFPA 921 (6 decks)

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