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Firefighter I > Chapter 4: Fire Dynamics > Flashcards

Chapter 4: Fire Dynamics Flashcards

1
Q

Fire dynamics

A

describes the meeting point between fire science, material science, fluid dynamics of gases and heat transfer

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2
Q

Oxidizers

A

are not combustible but will support or enhance combustion

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3
Q

Using science to remain safe

A

o Identify fire dynamics
o Anticipate the next stages of the fire
o Anticipate how operations may impact fire behaviour

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4
Q

Physical science

A

is the study of matter and energy

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5
Q

Matter

A

physical materials that occupy space and have mass

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6
Q

A physical change

A

occurs when a substance remains chemically the same but changes in size shape or appearance
o ex: water freezing liquid to solid and boiling liquid to gas

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7
Q

Chemical reaction

A

when a substance changes from one type of matter into another such as two or more substances combining to form compounds

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8
Q

Oxidization

A

a chemical reaction involving the combination of an oxidizer such as oxygen in the air with other materials
o Can be slow such as the combination of oxygen with iron to form rust, or rapid, as the combustion of methane (natural gas) or an explosion

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9
Q

Energy :

A

Is the capacity to perform work

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10
Q

Work and In the case of heat

A

occurs when a force is applied to an object over distance or when a substance undergoes a chemical, biological, or physical change

in case of heat work means increasing a substances temperature

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11
Q

Potential energy

A

represents the amount of energy that an object can release at some point in the future

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12
Q

heat of combustion:

A

The potential energy available for release in the combustion process
o The rate at which fuel releases energy overtime depends on many variables including, chemical composition, arrangement, density of fuel, availability of oxygen for combustion

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13
Q

Kinetic energy

A

is the energy that a moving object possesses (releasing energy)

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14
Q

how does kinetic energy work

A

o When heat is introduced the molecules within the field begin to vibrate
o As the Heat (thermal energy) increases, these molecules vibrate more and more rapidly

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15
Q

There are many types of energy including

A

chemical, thermal, mechanical, electrical, light, nuclear, sound

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16
Q

All energy can

A

change from one type to another

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17
Q

Energy is measured in

A

joules

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18
Q

joule

A

international system of units (SI)
o The quality of heat required to change the temperature of 1 g of water by 1°C is 4.2 joules

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19
Q

British thermal unit (BTU):

A

customary system of measurement
o Is the amount of heat required to raise the temperature of 1 pound of water by 1°F
o 1055J= 1 BTU

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20
Q

Exothermic reactions

A

reactions that emit energy as they occur
o Fire is an exothermic chemical reaction that releases energy in the form of heat and sometimes light

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21
Q

Endothermic reactions

A

reactions that absorb energy as they occur
o Ex converting water to steam

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22
Q

Fire triangle and fire tetrahedron are used to

A

to explain the elements of fire and how fires can be extinguished

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23
Q

The fire triangle shows

A

three elements necessary for combustion to occur: fuel, oxygen and heat
o Remove any one of these elements in the fire will be extinguished

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24
Q

the fire tetrahedron model includes

A

the chemical chain reaction to explain flaming or gas phase combustion

o reducing agent (fuel)
o chemical chain reaction
o heat
o oxidizing agent

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25
Q

Fuels must be in a state to burn

A

Fuels must be in a gaseous state to burn

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26
Q

off gassing

A

When heat is transferred to a liquid or solid the substance as temperature increases in the substance starts to convert to a gaseous state

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27
Q

Pyrolysis

A

off gassing of solids
o Process/Chemical change of breaking down of a solid to a gas
o (solid fuel converted to gaseous fuel-lighter to wood off gases )

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28
Q

Vaporization:

A

physical change in liquids -off gassing of liquids (liquid converted to vapor)

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29
Q

Piloted ignition

A

occurs when a mixture of fuel and oxygen encounter an external heat source with sufficient heat or thermal energy to start the combustion reaction
o Most common form of ignition

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30
Q

Auto ignition

A

occurs without any external flame or spark to ignite the fuel gases are vapours
o The fuels surface is heated to the point at which the combustion reaction occurs (pyrolysis)

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31
Q

Autoignition temperature (AIT)

A

is the minimum temperature at which a fuel in the air must be heated in order to start self-sustained combustion

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32
Q

The autoignition temperature of a substance is always

A

The autoignition temperature of a substance is always higher than its piloted ignition temperature

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33
Q

Combustion

A

is a chemical reaction

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34
Q

There are two modes of combustion

A

non-flaming and flaming

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35
Q

Nonflaming combustion

A

occurs more slowly and at lower temperature producing a smouldering glow
o The burning may be localized on or near the fuel surface where it is in contact with oxygen

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36
Q

Flaming combustion and occurs when

A

produces a visible flame above the material surface
o occurs when a gaseous fuel mixes with oxygen in the correct ratio and heats to ignition temperature

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37
Q

Flaming combustion Requires

A

liquid or solid fuel to be converted to the gas phase
o When heated both liquid and solid fuels will emit vapours (pyrolysis) that mix with oxygen, gases ignite, producing flames above the material surface

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38
Q

The fire tetrahedron accurately reflects the conditions required for

A

required for flammable combustion
 Each element of the tetrahedron must be in proper proportion and removing any element will interrupt the chemical chain reaction and stops flaming combustion

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39
Q

how does flaming combustion work

A

 Ignition is where the combustion process begins. a heat source pyrolizes a fuel, creating fuel gases. Those glasses mix with oxygen and ignite creating fire

o As the heat transfers to the gasoues combustion products they expand and begin to rise and move away from the fire due to buoyancy

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40
Q

Products of combustion

A

as fuel burns its chemical composition changes which produces new substances
o Heat and smoke

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41
Q

Smoke

A

is the product of incomplete combustion

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42
Q

Incomplete combustion

A

is combustion that is incomplete when any of the fuel is left after combustion has occurred
 Combustion is incomplete in a structure fire meaning that some of the fuel does not burn but instead gets entrained with hot gases and rises aloft

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43
Q

unburned fuel is smoke and has a potential to

A

burn

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44
Q

When the air supply is limited the level of incomplete combustion is

A

higher which produces more smoke

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45
Q

Most structure fires involve multiple types of fuel including

A

o Carbon-based fuels: wood, cotton
o Hydrocarbon fuels: plastics, synthetic fibers
- gases

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46
Q

Carbon monoxide

A

is a toxic product of the incomplete combustion of organic materials
 Colorless, odourless gas present at almost every fire
 CO combines with haemoglobin about 200 times more effectively than oxygen does

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47
Q

Hydrogen cyanide

A

toxic and formable substance produced in the combustion and materials containing nitrogen is also commonly found and smoke
 Natural fibre such as wool, cotton, silk
 Resin such as carbon fibre or fibreglass
 Synthetic polymer such as nylon or polyester
 Synthetic rubber such as neoprene silicone and latex
 HCN is 35 times more toxic than CO
 Prevents the body from using oxygen at the cellular level
 Can be inhaled ingested or absorbed into the body where it then targets the heart and brain
 Enters the bloodstream and prevents the blood cells from using oxygen properly killing the cells

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48
Q

Carbon dioxide

A

it’s a product of complete combustion of organic materials
 Not toxic in the same way as CO or HCN displaces existing O2 creating an oxygen deficient atmosphere

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49
Q

Formaldehyde

A
  • Colourless gas with a pungent irritating odour that is highly irritating to the nose
  • 50-100 ppm can cause severe irritation to respiratory tract a serious injury
  • Exposure to high concentrations can cause injury to the skin
  • Formaldehyde is a suspected carcinogens
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50
Q

Nitrogen dioxide

A
  • Reddish brown gas or yellowish brown liquid which is highly toxic and corrosive
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51
Q

Irritants in smoke

A

are substances that cause breathing discomfort and inflammation of the eyes, respiratory tract and skin
- Smoke contains significant amounts of unburned fuels in the form of solid and liquid particulates

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52
Q

Pressure

A

Is the force per unit of area applied perpendicular to a Surface

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53
Q

Standard temperature 68F 20c and atmospheric pressure gases…

A

remain calm and don’t move

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54
Q

Differences and pressure above or below standard atmosphere pressure,it creates

A

movement in gases

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55
Q

Gas always moved from areas of —-pressure to areas of —— pressure

A

Gas is always moved from areas of high-pressure to areas of low pressure

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55
Q

Heated gasses will

A

rise remain aloft and generally travel up and out

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56
Q

cooler fresh air will

A

generally travel inward toward the fire this exchange of air creates a convective flow

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57
Q

Heat release rate

A

total amount of heat released per unit time

The heat release rate is typically measured in kilowatts or megawatts

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58
Q

Heat

A

is the thermal kinetic energy needed to release the potential chemical energy in a fuel

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59
Q

how does heat work at the molecular level

A

o Heat vibrates fuel molecules
o Fuel changes from solid or liquid to gas
o The fuel emits flammable vapours which can ignite and release thermal energy
o Thermal energy heats uninvolved fuels

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60
Q

Temperature

A

is the measurement of heat
o Temperature is the measurement of average kinetic energy in the particles of a sample of matter
o Measured using several different scales

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61
Q

A dangerous misconception is that temperature…

A

is an accurate predictor for measurement of heat transfer

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62
Q

Heat flux

A

is a measure of heat energy transfer rate

o Measured in kilowatts per square meter

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63
Q

Heat transfer and PPE

A

temperature tells wether its safe to go in environment
o Heat transfer rate determines how long PPE will protect the firefighter in environment

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64
Q

Sources of thermal energy

A
  • Chemical, electrical, and mechanical energy are common sources of heat that resukt in the ignition of a fuel
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65
Q

Chemical energy

A

oxidation
- Chemical energy: the most common source of heat in combustion reactions

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66
Q

The potential for oxidization exists when

A

any combustible fuel is in contact with oxygen

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67
Q

Self heating

A

a form of oxidation, is a chemical reaction that increases the temperature of a material without the additional external heat

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68
Q

Spontaneous ignition

A

which is ignition without the addition of external heat

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69
Q

For self heating to progress to spontaneous ignition, following factors are required:

A

o The insulation properties of a material immediately surrounding the fuel must be such that heat cannot dissipate as fast as it is generated
o The rate of heat production must be great to raise the temperature of the material to its autoignition temperature
o The available air supply in and around

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70
Q

rags soaked in linseed oil have a potential for spontaneous ignition because

A

the natural oxidization of this vegetable oil and the cloth will generate heat if some method of heat transfer such as air movement around the rags does not dissipate heat
o also charcoal and hay/manure

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71
Q

The rate of most chemical reactions increases as

A

temperature of the reacting materials increases

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72
Q

Electrical energy can generate temperatures

A

high enough to ignite any combustible materials near the heated area

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73
Q

Resistance heating

A

electric current flowing through a conductor produces heat

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74
Q

Overcurrent or overload

A

is unattended resistance heating
o when the current flowing through a conductor exceeds its design limits

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75
Q

arcing

A

the arc is a high temperature luminous electric discharge across a gap or through a medium such as charred insulation

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76
Q

Arcs may be generated when there is

A

a gap in the conductor such as a cut or frayed wire or when there is a high voltage, static electricity or lightning

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77
Q

Sparking:

A

when an electrical arc occurs, luminous (glowing) particles can form and splatter away from the point of arcing

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78
Q

Mechanical energy

A

friction and compression.

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79
Q

The movement of two surfaces against each other creates

A

heat of friction that generates heat and or Sparks

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80
Q

Heat is generated when a gas is…
because…

A

compressed
o When a compressed gas expands, the gas absorbs the heat

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81
Q

Heat transfer:

A

transfer of heat from one point or object to another is a part of the study of thermodynamics

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82
Q

Heat transfer warmer objects to cooler objects because

A

heated materials will naturally return to a state of thermal equilibrium

The greater the temperature differences between the bodies the greater the transfer rate

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83
Q

Thermal equilibrium

A

in which all areas of an object are a uniform temperature
- Objects at the same temperature do not transfer heat

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84
Q

Heat transfers from one body to another by three mechanisms

A

conduction, convection, and radiation

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85
Q

Conduction:
and occurs when:

A

is the transfer of heat through and between solids
- Occurs when the material is heated as a result of direct contact with the heat source

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86
Q

conduction Results from

A

increased molecular motion and collisions between a substances molecules, resulting in the transfer of energy through the substance

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87
Q

The more closely packed the molecules of a substance are…

A

the more readily it will conduct heat

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88
Q

Heat transfer due to conduction is dependent upon three factors:

A

o Area being heated
o Temperature difference between the heat source and the material being heated
o Thermal conductivity of the heated material

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89
Q

Insulating material

Good insulators are materials that

The best insulators are those made of

A

slow the conduction of heat from one solid to another

Good insulators are materials that do not conduct heat well because their physical make up disrupts the point-to-point transfer of heat or thermal energy

The best insulators are those made of particles or fibers will void spaces between them filled with a gas such as air

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90
Q

Convection

A

the transfer of thermal energy by the circulation or movement of a fluid (liquid or gas)

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91
Q

convection In the Fire environment

A

In the Fire environment, convection usually involves transfer of heat through the movement of hot smoke and fire gases

The heat flows from the hot fire gases to the cooler structural surfaces, building contents and air

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92
Q

convection occurs in what direction?

A
  • Convection may occur in any direction
  • Vertical movement is due to the buoyancy of smoke and fire gases
  • Lateral movement is usually the result of pressure difference
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93
Q

Radiation

A

is the transmission of energy as electromagnetic waves,

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94
Q

Radiant heat

A

can become the dominant mode of heat transfer as the fire grows in size
- can have a significant effect on the ignition of objects located some distance from the fire
- Significant factor in the fire development and spread in compartments

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95
Q
  • Numerous factors influence radiant heat transfers including:
A

o Nature of the exposed surfaces: dark coloured materials in it and absorb heat more effectively than light coloured materials; smoother highly polished surfaces reflect more radiant heat the rough surfaces
o Distance between the heat source in the exposed surface: increasing distance reduces the effect of radiant heat
o Temperature of the heat source: unlike other methods of heat transfer that depends on the temperature of both the heat source and exposed surface, radiant heat transfer primarily depends on the temperature of the heat source

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96
Q

radiated heat energy travels

A

radiated heat energy travels in a straight line at the speed of light

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97
Q

Radiation is a common cause of

Radiated heat travels through

Materials that reflect, absorb, or scatter radiated energy will

A
  • Radiation is a common cause of exposure fires
  • Radiated heat travels through vacuums and air spaces that would normally disrupt conduction or convection
  • disrupt the heat transmission
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98
Q

Interaction among the methods of heat transfer

A
  • The fire radiates heat, causes convection heat through hot fuel gases, and conducts heat through burning materials or metals that are involved in the fire
  • Convected heat and radiated heat that reaches walls and ceilings heat still surfaces which begin to conduct heat to whatever extent possible based upon the materials thermal conductivity
  • But heat us surface well then begin to radiate heat which could lead to ignition, combustion, convection and so on
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98
Q

Fuel

A

the oxidized or burn material or substance in the combustion process
o gas, liquid or solid

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99
Q

reducing agent

A

the fuel in a combustion reaction
o fuels may be inorganic or organic

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100
Q

inorganic:

organic

A
  • inorganic: do not contain carbon
  • organic: contains carbon
    o most common fuels are organic
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101
Q

organic fuels can be divided into hydrocarbon based fuels such as:

A

o gasoline
o plastics
o fuel oil
o cellulose based materials (wood and paper)

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102
Q

the fuels heat of combustion is:

A

the total amount of thermal energy released when a specific amount of that fuel burns

103
Q

synthesized petroleum products

A

o have higher heats of combustion and may generate higher heat release rates than wood on a per mass basis

104
Q

power

and in terms of fire

A

is the rate at which energy transfers- the rate at which energy converts

in terms of fire behaviour, power is the heat release rate during combustion

105
Q

watt

A

the standard international (SI) unit for power
o 1 watt = 1 joule per second (j/s)

106
Q

Heat release rate

A

is the energy released per unit of time as a fuel burns and is usually expressed in kilowatts (kW) or megawatts (MW)

107
Q

Heat release rate depends on

A

the type, quantity and orientation of the fuel

108
Q

Heat release rate directly relates to

A

oxygen consumption because the combustion process requires a continuous supply of oxygen to continue

109
Q

The more oxygen available the ——- the heat release rate

A

the higher the heat release rate

110
Q

The heat release rate decreases if

A

all available oxygen is consumed and not replenished

110
Q

For flaming combustion to occur,

A

fuels must be in gaseous state

111
Q

Thermal energy is required to? in regards to gases

A

change solids and liquids to gaseous state

112
Q

Vapour:

A

the gaseous state of fuel that would normally exist as a liquid or a solid at standard temperature and pressure

113
Q

most dangerous of all gas fuels

A

Gaseous fuels such as methane (natural gas), hydrogen, and acetylen

114
Q

Vapour density

A

describes the density of gases in relation to air
o Air has a vapour density of 1
o Gases with a vapour density of less than 1 such as methane will rise
o Vapour density greater than 1 such as propane will sink

115
Q

Heated gases expand and become —- dense

When cooled they ———–

A

less

When cooled they contract and become more dense

116
Q

Liquids

A

have mass and volume but no definite shape except for a flat surface or the shape of their container

Unlike gasses, liquids will not expand to fill all of the container

117
Q

Liquid density is compared to

A

water

118
Q

Specific gravity

A

is the ratio of the mass of a given volume of a liquid compared to the mass of an equal volume of water at the same temperature
o Like vapour density but with liqid

119
Q

Liquids with a specific gravity less than 1 such as gasoline and most other flammable liquids are

A

lighter than water and will float on its surface

120
Q

Liquids with a specific gravity greater than 1, such as corn syrup are

A

heavier than wastere and will sink

121
Q

To burn, liquids must

A

vapourize

122
Q

Vaporization

A

is the transformation of a liquid to a vapour or a gaseous state

123
Q

For vaporization to occur the escaping vapours must

A

be a greater pressure than atmospheric pressure

124
Q

Vapour pressure

A

the pressure that vapours escaping from a liquid exert
o Indicate how easily a substance will evaporate into air
o Flammable liquids with a high vapour pressure present a special hazard to firefighters

125
Q

Rate of vaporization

A

determined by the vapour pressure of the substance and the amount of thermal energy applied

126
Q

Water converts to steam at 1701 degrees

A

Water converts to steam at 1701 degrees

127
Q

Flash point:

A

is the minimum temperature at which a liquid gives off sufficient vapours to ignite, but not sustain combustion, in the presence of a piloted ignition source (flash but go out immedietly because it cant produce enough heat to make vapours)

128
Q

Flash point is Commonly used to indicate

A

the flammability hazard of liquid fuels

129
Q

Liquid fuels that vaporize sufficiently at temperatures under ——-F present a significant flammability hazard

A

o Liquid fuels that vaporize sufficiently at temperatures under 100F (38c) present a significant flammability hazard

130
Q

Fire point

A

the temperature at which a piloted ignition of sufficient vapors will begin a sustained combustion reaction (flame is sustained because it can produce enough heat to make vapours)

131
Q

Solubility

A

describes the extent to which a substance will mix with water
o May be expressed in qualitive terms (slightly or completely) or as a percentage

132
Q

Miscible:

A

in water will mix in any proportion

Some liquids are lighter than water and wont mix

133
Q

Polar solvents

A

flammable liquids such as alcohols (methane,ethol) will mix readily with water
o Use alcohol resistant fire fighting foams specifically designed for polar solvents

134
Q

Hydrocarbon fuels: lighter and don’t mix with

A

water

135
Q

Liquids less dense than water are more

A

difficult to extinguish using water as the sole extinguishing agent- may disperse the buring liquid instead of extinguishing it
o Foam or chemical agent it extinguish liquid fuels that are not water soluble

136
Q

Water soluble liquids will mix with

A
  • Water soluble liquids will mix with some water based extinguishing agents such as many types of firefighting foam
    o Extinguishing agent will mix with water and become less effective
    o Use alcohol resistant fire fighting foams specifically designed for polar solvents
137
Q

Solids

A

have definite size and shape

138
Q

solids React differently when exposed to heat

A
  • Wax and metals will change their state and melt
    o Wood and plastics will not
139
Q

When solid fuels are heated

A

they begin to pyrolize (off gass) and release fuel gases and vapour
o The solid will begin to decompose and emit combustible vapours

140
Q

Solid fuels have a definite shape and size which significantly affects

A

how easly they ignite

141
Q

Surface to mass ratio:

A

the surface area of fuel in proportion to its mass
o Higher surface to mass ratio, less energy needed to ignite
o Low surface to mass ratio, more energy needed to ignite
- As this ratio increases the fuel particles become more finely divided, like shavings or sawdust

142
Q

The proximity and orientation of a sloid fuel relative to the source of heat also affects

A

the way fuel burns
o Ex if you ignite one corner of a sheet of plywood lying horizontally (flat) the fire will consume the fuel at a relatively slow rate. The same type of ply wood in a vertical position (standing up) burns more rapidly because the heated vapours rise over more surface area

143
Q

Normal air consist of about

A

Normal air consist of about 21% oxygen

144
Q

The energy released in fire is directly proportional t

A

the amount of oxygen available for combustion

145
Q

At normal ambient temperatures materials can ignite and burn at oxygen concentrations as low as

A

15%

146
Q

When oxygen concentration is limited the flaming combustion will

A

diminish causing non flaming combustion and can continue at extremely low oxygen

146
Q

High ambient temperature, flaming combustion may

A

continue at considerably lower oxygen concentrations

147
Q

Many materials that do not burn at normal oxygen levels will burn in

A

oxygen enriched atmospheres

148
Q

Flammable (explosive) range

A

the range of concentrations of the fuel vapour and air
o The fuels flammable range is reported using the percent by volume of gas or vapour in air for the lower explosive (flammable) limit and for the upper explosive (flammable) limit
o There is an ideal concentration at which there is exactly the correct amount of fuel and oxygen required for combustion

149
Q

lower explosive (flammable) limit (LEL)

A

the minimum concentration of fuel vapour and air that supports combustion
o concentrations below the LEL are said to be too lean to burn

150
Q

upper explosive (flammable) limit (UEL):

A

the maximum concentration of fuel vapour and air that supports combustion
o concentrations below the UEL are said to be too rich to burn

151
Q

free radicals

A

formed by molecules of a fuel gas and oxygen that break apart during flaming combustion
o combine with oxygen or with the elemnts released from the fuel gas to form new substances (molecules) and even more free radicals
o the process increases the speed of the oxidation reaction

152
Q

chemical flame inhibition:

A

occurs when an extinguishing agent such as dry chemical or Halon-replacement agent interferes with this chemical reaction forms a stable product and terminates the combustion reaction

153
Q

compart fire development depends on

A

whether the fire is fuel limited or ventilation limited

154
Q

fuel limited

A

when sufficient oxygen is available for flaming combustion
o as long as the fire can reach more ignitable fuel it will continue to burn
o usually progresses through the stages of fire development in order

155
Q

ventilation limited

A

have access to all of the fuel needed to maintain combustion but the fire does not have access to enough o2 to continue to burn or spread to all the available fuels
o tend to enter an early stage of decay at the end of the growth stage because there is no longer enough o2 for the fire to become fully developed

156
Q

all compartment fires begin in the —– stage
once it reaches the —- stage
the fire will either remain —– ——
or the fire will consume all the oxygen and become —– ——

A

all compartment fires begin in the incipient stage, once it reaches the growth stage the fire will either remain fuel limited or the fire will consume all the oxygen and become ventilation limited

157
Q

stages of fire development
- 4 stages

A

incipient,growth,fully developed and decay

158
Q

3 key factors that control how the fire develops:

A

o The fuel properties
o The ventilation available
o Heat conservation

159
Q

Incipient stage:

A

starts with ignition when the three elements of the fire triangle come together and the combustion process begins
o At this point the fire is small and confied to a small portion of the fuel first ignited

160
Q

Growth stage

A

as the fire transitions from incipient to growth stage more of the initial fuel package becomes involved and the production of heat and smoke increases
o The fire may continue to grow to become full developed or may enter an early state of decay depending upon available o2

161
Q

Fully developed stage

A

when all the combustible materials in the compartment are burning at their peak heat release based on the available oxygen
o The fire is consuming the maximum amount of oxygen that it can

162
Q

Decay stage

A

: as the fire consumes the available fuel or oxygen and the heat release rate begins to decline, the fire enters the decay stage

o Fuel limited fires may self extinguish in this phase or reduce to smoldering
o Ventilation limited fires may also self extinguish however if oxygen becomes available before complete extinguishment these fires are likely to re-enter the growth stage and rapidly become fully developed

163
Q

Open buring or free burn

A

condition provides the most basic fire growth curve
o Representative of a fuel limited fire such as a campfire, or a sofa in a large empty warehouse

164
Q

o Fuel controlled

A

a single item burning either outside or in a large well ventilated space means ther is sufficient oxygen available to burn the fuel until it can no longer sustain combustion

165
Q
  • Development in the incipient stage depends largely upo
A

the characteritics and configuration of the fuel involved

166
Q

The following describe what occurs when a compartment fire enters the incipient stage:

A

o Radiant heat warms the adjacent fuel and co tinues the process of pyrolysis. A thin plume of hot gases and flame rises from the fire and mixes with cooler air in the compartment
o Ceiling jet: the hot gases in the plume rise until they encounter the ceiling and then begin to spread horizontally
o Hot gases in contact with the surface of the compartment and its contents transfer heat to other material

167
Q

incipient stage temperature

A
  • The temperature is only slightly above ambient
  • Occupants can safely escape and an extinguisher can extinguish
168
Q

A visual indicator that a fire is leaving the incipient stage is

A

flame height
o When flames reach 2.5F high, radiated heat begins to transfer more heat than convection and will then enter growth stage

169
Q

Growth stage
- A variety of fire behaviours can occur

A
  • The fire may consume all the oxygen and enter ventilation limited state of decay
    or
  • Ventilation may provide enough oxygen for rapid development and or growth to full development
170
Q

Rapid fire development usually occurs during

A

the growth stage

171
Q

Entrainment

A

drawing in air

172
Q

Unconfined fires draw air from

A

all sides

173
Q

the entrainment of air reduces what

A

cools the plume of hot gases reducing flame length and extension

174
Q

The following describes entrainment based on the positioning of fuel packages:

A

o Fires in fuel packages in the middle of the room can entrain air from all sides
o Fires in fuel packages near walls can only entrain air from 3 sides
o Fires in fuel packages in corners can only entrain air from 2 sides

175
Q

Combustion zone

A

area where sufficient air is available to feed the fire

176
Q

When the fuel package is not in the middle of the room the combustion zone…

A

expands vertically and a higher plume results

177
Q

A higher plume increases

A

the temperature in the developing hot gas layer at the ceiling level and increase the speed of development

178
Q

A fire is in the growth stage unitl

A

the fire’s heat release rate has reached its peak either because of lack of fuel or lack of oxygen

179
Q

2 common routes to full development are as follows:

A

o Fires that consume all available oxygen and transition to a ventilation limited decay
o Fire that have enough oxygen and move through the growth phase and possibly into rapid fire development

180
Q

Thermal layering

A

is the tendency of gases to form into layers according to temperature, gas density and pressure
o The hottest gases will form the highest layer while cooler gases will form lower layers

181
Q

——— from the hot gas layer acts to heat the interior surfaces of the compartment and its content

A

radiation

182
Q

Changes in ventilation and flow path can

A

significantly alter thermal layering

183
Q
  • As the mass and energy of the hot gas layer increases so does
A

the pressure

184
Q

Higher pressure causes the hot gas layer to spread

A

downward within the compartment and laterally through any openings such as doors and windows
- If there are ni openings for lateral movement, the higher pressure gases have no lateral path to follow to an area of lower pressure

185
Q

Isolated or intermittent flames

A

move through the hot gas layer up by roof
o Combustion of these hot gases indicates that portions of the hot gas layer are within their flammable range, and that there is sufficient heat to cause ignition
o The appearance of isolated flames is sometimes an immediate indicator of flashover

186
Q

Neutral plane

A

the interface between the hot gas layers and cooler layer of air
o The net pressure is zero, or neutral where the layers meet
o Neutral plane exists at openings where hot gases exit and cooler air enters the compartment

187
Q

o Hot gases at higher than ambient pressure exit through…..
o Lower pressure air from outside the compartment…..

A

o Hot gases at higher than ambient pressure exit through the top of the opening above the neutral plane
o Lower pressure air from outside the compartment entrains in the opening below the neutral plane

188
Q

Most residential fires that develop beyond the incipient stage become

A

ventilation limited

189
Q
  • As the interface height of the hot gas layer descends toward the floor, the greater volume of smoke begins to interrupt the entrainment of fresh air and oxygen to the seat of the fire and into the plume
    o This interruption causes the fire
A

o This interruption causes the fire within the compartment to burn less efficiently
o As the efficiency of combustion decreases (incomplete combustion) the heat release rate decreases and the amount of unburned fuel within the hot gas layer increases

190
Q

o As the efficiency of combustion decreases (incomplete combustion) the heat release rate decreases and the amount of unburned fuel within the hot gas layer increases
- The fire is now in a state of ventilation limited decay because:

A

o There is not enough oxygen to maintain combustion
o The heat release rate has decreased to the point that fuel gases will not ignite

191
Q
  • Although the heat release rate decreases in ventilation limited, the temperature
A
  • Although the heat release rate decreases in ventilation limited, the temperature in the room may remain high
    o Even if temperatures decrease, pyrolysis can continue
192
Q
  • If there are no other source of oxygen exists the compartment will
A

fill with black smoke and slowly cooling fuel gases
o If there is oxygen introduced it creates a rapid increase in the heat release rate and growth of the fire

193
Q

Rapid fire development

A

refers to the rapid transition from the growth stage or early decay stage to a ventilation limited, fully developed stage
o Among these events are flashover and backdraft

194
Q

To protect yourself and your crew, you must be able to:

A

o Recognize the indicators of rapid fire development
o Know the conditions created by each of these situations
o Determine the best action to take before they occur

195
Q

Flashover:

A

rapid transition from the growth stage to the fully developed stage is known as flashover
o When flashover occurs the combustible materials and fuel gases in the compartment ignite almost simultaneously; resulting in full room fire involvement

196
Q

flash over Typically occurs during

A

o Typically occurs during fires growth stage but may occur during fully developed stage as a result of ventilation

197
Q

o During a flshover the environment of the room changes from

A

o During a flshover the environment of the room changes a two layer (hot on top, cool on bottom) to a single well mixed hot gas condition from floor to ceiling
o The environment is untenable

198
Q

o As flashover occurs the gas temperatures in the room reach

A

1100 F (593c) or higher

199
Q

radiations part in flashover

A

o Radiation from the upper layer heats the compartments contents until they reach their ignition temperature simuletaneously
o When the upper layer ignites the amount of radiation increases to levels which rapidly ignite contents in the room

200
Q

o During flashover the volume of burning gases can increase from

A

approximately ¼ to ½ of the rooms upper volume to fill the rooms entire volume and extend out of any openings

201
Q

o A significant indicator of flashover is

A

rollover

202
Q

rollover

A

a condition where the unburned fire gases that have accumulated at the top of the compartment ignite and flames propagate through the hot gas layer or across the ceiling

203
Q

o Rollover may occur during the

A

the growth stage as the hot gas layer forms at the ceiling of the compartment
o Flames may appear in the layer when the combustible gases reach their ignition temperature

204
Q

Rollover will generally precede

A

flashover but it may not always result in flashover

205
Q

Rollover contributes to flashover conditions because

A

the buring gas athe the upper levels of the room generate tremendous amounts of radiant heat which transfers to other fuels in the room

206
Q
  • There are 4 common element of flashover:
A

o Transition in fire development: represents transition from growth to fully developed
o Rapidity: happens rapidly often in a matter of seconds
o Compartment: there must be an enclosed space such as a single room or enclosure
o Pyrolysis of all exposed fuel surfaces: fire gases from all the combustible surfaces ignite

207
Q

Two interrelated factors determine whether a fire within a compartment will progress to flashover

A
  1. there must be sufficient fuel and the heat release rate must be sufficient for flashover conditions
  2. ventilation. A developing fire must have sufficient oxygen to reach flashover
208
Q

SCBA face pieces fail after 5 minutes of exposure to a heat flux

A

15kW/m2

209
Q

You must be aware of the following flashover indicators to protect yourself:

A

o Building indictors: interior configuration, fuel load, thermal properties and ventilation
o Smoke indicators: rapidly increasing volume, turbulence, darkening color, optical density and lowering of the hot gas layer and or neutral plane
o Heat indicators: rapidly increasing temperature in the compartment, pyrolysis of contents or fuel packages located some distance away from the fire or hot surfaces
o Flame indicators: isolated flames or rollover in the hot gas layers or near the ceiling

210
Q
  • Level of neutral plane observed from the exterior of the structure are also good indicators of fire behaviour within the structure as follows:
A

o High neutral plane: fire in early stages of development
 Note high ceilings can hide a fires stage
 A high neutral plane can also indicate fire above your level
o Mid level neutral plane: could indicate compartment has not yet ventilated or that flashover is approaching
o Very low neutral plane: may indicate that fire is reaching backdraft conditions
 Could also mean fire is below you

211
Q
  • When fire is in ventilation limited decay, the introduction of new oxygen can trigger
A

flashover quickly

212
Q
  • Flashover may not occur in every compartment fire, such as
A

large compartments

  • The fire may not progress to flashover but instead become ventilation limited and enter decay stage while continuing pyrolysis and increasing fuel conent of the smoke
213
Q

Backdraft

A

an expolosivley rapid combustion of the flammable gases

214
Q

what kind of fire can produce backdraft

A

o a ventilation limited compartment fire that can produce a large volume of flammable smoke and other gaes due to incomplete combustion. Fuel sources are unburned

215
Q

back drafts occur in spaces containing

A

containing high concentration of heated flammable gaes that lack sufficient oxygen for flaming combustion

216
Q

backdraft indictors include:

A

o Building indicators - Interior configuration, fuel load, thermal properties, amount of trapped fuel gases, and ventilation
o Smoke indicators - Pulsing smoke movement around small openings in the building; smoke-stained windows
o Air flow indicators - High velocity air intake
o Heat indicators - High heat, crackling or breaking sounds
o Flame indicators - Little or no visible flame

217
Q

The effects of a backdraft can vary considerably depending on a number of factors, including:

A

o Volume of smoke
o Degree of confinement
o Temperature of the environment
o Pressure
o Speed with which fuel and air mix

218
Q

2 main types of fully developed fires

A

ventilation limited and fuel limited

219
Q

“Fully developed” means

A
  • Means fire has grown as much as it can but can continure to grow if fuel/oxygen is reintroduced
220
Q
  • Fuel limited conditions
A

: the available fuel limits the peak heat release in a fuwl limited fully developed fire

221
Q

Ventilation limited conditions

A

lacks the oxygen available to grow because the number and size of openings in the compartment limit the entainment of air

222
Q

Ventilation liited fully developed fires present a hazardous situation for firefighter because

A

the potential for a window failure to provide fresh oxygen and increase peak heat release rate can endanger firefighters and civilians
o Firefighters must transition the fire from ventilation limited to fuel limited

223
Q

Fuel limited decay

A

after a fuel limited fire reaches the fully developed the stage the fire will decay as the fuel is consumed
o heat release rate begins to decrease but temperature of objects stay high
o compartment fires rarely enter state of fuel limited decay unless compartment burns all the way to the ground

224
Q

ventilation limited decay

A

not necessarily the last stage of the fires development
o to ensure that the decay stage of a ventilation limited fire is the fires final stage, a controlled transition from ventilation limited to fuel limited must take place
o firefighters must ensure no ventilation until heat release is complete

225
Q

structures:

A

composed of individual compartments connected by hallways, stairways or openings such as doorways

226
Q

flow path

A
  • the method by which the fire receives the needed oxygen to sustain the combustion reaction occurs through one or many flow paths
227
Q

the flow path is composed of 2 regions:

A

o the ambient air flow in
o hot exhaust flow out

228
Q

flow path direction

A
  • unidirectional due to pressure differences where ambient air flows toward the seat of the fire and reacts with the fuel
229
Q
  • the products of combustion flow
A

away from the fire toward the low pressure outlet
- in a structure fire the floor plan and openings within the structure determine available flow path

230
Q
  • a flow paths effectiveness to transport ambient air to the seat of the fire is based on the following:
A

o size of the ventilation opening
o length of the path traveled
o number of obstructions
o elec=vation differences between the base of the fire and the opening

231
Q

fireifghters working in the exhaust portion of the flow path will feel

A

the increase of temperature as the velocity and/or turbulence increases

232
Q

unplanned ventilation

A

occurs when a structural member fails usually because exposure to heat and intorduces a new source of oxygen to the fire
o could result from a failure of a: window, roof, doorway, wall
o can also originate from inside the building if the floors collapse

233
Q

unplanned ventilation is often a result of:

A

o occupant action
o fire effects on the building
o actions other than planned, systematic and coordinated tactical ventilation

234
Q

wind conditions

A

the wind can increase pressure inside and drive smoke and flames to unburned portions and onto firefighters
o must be aware of wind direction and velocity

235
Q

wind speeds as low as –kmph can create wind driven fire conditions

A

10

236
Q

smoke explosion:

A

occurs when a mixture of unburned fuel gases and oxygen comes in contact with an ignition source
o the result will be explosive, rapid combustion
o violent because they involve premixed fuel and oxygen

237
Q

firefighters can influence fire dynamics in a number of ways:

A

o temperature reduction: usimng water or foam agent
o fuel removal: eliminating sources of fuel in the path of fire
o oxygen exclusion/flow path control: using door control tactical ventilation techniques
o chemical flame inhibition: using extinguishing agents to inhibit or interrupt combustion reaction

238
Q

2 primary types of dangerous building conditions are:

A

o Conditons that contribute to the spread and intensity of the fire
o Conditons that make the building susceptible to collapse

239
Q

There may be many unkown factors that are not relected in fire resistance estimates such as:

A

o The duration of the fire up to the time of arrival
o The buildings contents
o Ways the building contents affect the heat release rate
o The heat release rate and intensity of the fire
o Renovations to the interior that may have compromised fire resistance

240
Q

Fuel load/fire load

A

the total quanity of combustible contents of a building, space or fire area
- At scene youwil onlybe able to estimate fuel load base dupon ypur knowledge and experience

241
Q

The orientation of the fuels as well as their surface to mass ratio will influence rate and intensity

A
  • Fires originating on upper levels generally extend downward much more slowly following the fuel path or as a result of collapse
242
Q

Assuming that there is available oxygen, the higher the fuel load, the more likely the fire will behave in the following ways:

A

o If structural members are part of the fuel load, structural integrity of the building will deteriorate faster.
o The longer the fire burns, the more fire spread accelerates.
o the fire may have a higher heat release rate.
o The structure may self-ventilate, introducing even more oxygen to the fuel-limited fire and accelerating fire development and involvement of combustible structural members.

243
Q
  • If fires are ventilation-limited, higher fuel loads indicate
A

a greater amount of unburned fuel that could reignite with the introduction of a new oxygen source.
- There may also be a greater amount of unburned fuel gases in the air because fuel packages pyrolized but did not begin combustion before the building became oxygen-limited.
- Such buildings are subject to backdrafts and flashovers if firefighters do not coordinate ventilation.

244
Q

Building compartmentation

A

is the layout of the various open spaces in a structure and includes
o Stories above or below
o Floor plan
o Openings between floors
o Continuous voids or concealed spaces
o Barriers to fire spread

  • Each of these elements may contribute to fire spread or containment
245
Q

Any space with no complete fire barrier dividing it is considered a

A

compartment
- Two rooms that a door way connects are considered two compartments only if the door is closed between them

246
Q

Legacy construction/older structures prior to approximately 1990 had the following features:

A

o Smaller compartments
o More compartments within the same square footage as modern homes
o Windows that could be opened for ventilation
o Air pockets in empty wall cavities; this construction technique used the air as insulation

247
Q

Modern single family structures may feature:

A

o Open floor plans
o High ceilings
o Atriums
o Lightweight manufactured structural components
o Sealed windows
o Wall cavities
o Synthetic insulation

248
Q

Building characteristics to consider when ventilating include:

A

o Occupancy classification
o Construction type
o Square footage and compartmentation
o Ceiling height
o Number of stories above and below ground level
o Number and size of exterior windows, doors, and other wall openings
o Number and location of staircases, elevator shafts, dumbwaiters, ducts, and roof openings
o External exposures
o Extent to which a building connects to adjoining structures
o Type and design of roof construction
o Type and location of fire protection systems
o Contents
o Heating, ventilation, and air conditioning (HVAC) system

249
Q

a fire in a large compartment will normally develop

A

slower due to greater volume of air and increased distance radiant heat must travel

250
Q

tall ceilings can make determining the extent of the fire development more difficult as

A

smoke can accumulate in the ceiling while conditions at floor level remain unchanged

251
Q
  • thermal properties of a building include:
A

o insulation: contains heat within the building which causes localized increase in the temperature and fire growth
o heat reflectivity: increases fire spread through the transfer of radiant heat
o retention: maintains temperature by slowly absorbing and releasing large amounts of heat

252
Q

failure of lightweight trusses and joists

A
  • unprotected engeneered steel and wooden trusses can fail after 5-10mins of exposure to fire
  • traditional wood joist roof tend to loose their strength when exposed to fire and beome soft and spongy before collapse
  • until they fall there may be noindicatio of danger
253
Q
  • construction, renovation and demolition hazards:
A

o additional fuel loads and ignition sources
o inoperative standpipes and sprinkler systems
o subject to rapid fire spread when they are partially completed
 breached walls, open stairwells, missing doors
o occupants may still be inside
o accumulation of debris can block exits
o contractors and owners/occupants don’t always follow local building codes

254
Q

What is the measurement of the average kinetic energy in the particles of a sample of matter?

A

Temperature

255
Q

Only mechanism to transition ventilation limited to fuel limited is to

A

Extinguish some of the burning fuel
-it is not possible to make enough openings

Firefighter I (14 decks)

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