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CFD > Ch4 Fire Dynamics > Flashcards

Ch4 Fire Dynamics Flashcards

1
Q

Firefighters should have a scientific understanding of combustion, fire, heat, and temperature. Fire can take various forms, but all fires involve a heat producing chemical reaction between some type of fuel and an oxidizer, most commonly oxygen in the surrounding air.

A

Oxidizers are not combustible but will support or enhance combustion.

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2
Q

Fuels must be in a gaseous state to burn; therefore solids and liquids must become gaseous in order for ignition to occur… p120

A

Piloted ignition occurs with an external flame or heat source with sufficient heat or thermal energy to start the combustion reaction.

Autoignition occurs without any external flame or spark to ignite fuel gases or vapors. The fuel’s surface is heated to the point at which the combustion reaction occurs.

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3
Q

While the heat from a fire is dangerous to anyone exposed to it, exposure to toxic gases found in smoke and/or lack of oxygen causes most deaths.

A

True

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4
Q

Gases always move from areas of __________ to areas of __________.

A

High pressure to low pressure

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5
Q

Heat transfers from warmer objects to cooler objects because heated materials will naturally return to a state of thermal equilibrium in which all areas of an object are a uniform temperature.

A

True

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6
Q

Gases with a vapor density of less than 1 will rise, while those having a vapor density of greater than 1 will sink.

A

True

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7
Q

Liquids that are __________ than water are more difficult to extinguish using water as the sole extinguishing agent.

A

less dense (lighter)

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8
Q

__________ is the tendency of gases to form into layers according to temperature, gas density, and pressure.

A

Thermal layering

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9
Q

Wood shakes, even when treated with fire retardant, can significantly contribute to fire spread.

A

True

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10
Q

The oldest and simplest model, the fire triangle, shows three elements necessary for combustion to occur. They are?

A

Heat, fuel, and oxygen

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11
Q

Concentrations above the upper explosive limit are said to be too what to burn?

A

They are too “rich” to burn

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12
Q

Concentrations below the lower explosive limit are said to be too what to burn?

A

They are too “lean” to burn

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13
Q

Most residential fires that develop beyond the incipient stage become ___________.

A

ventilation limited

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14
Q

_______________ occurs when a structural member fails and introduces a new source of oxygen to the fire.

A

Unplanned ventilation

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15
Q

___________ of the fuels as well as their ___________ will also influence the rate and intensity of fire spread.

A

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

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16
Q

The thermal properties of the building that can contribute to rapid fire development are?

A

Insulation, heat reflectivity, and retention

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17
Q

___________ is a toxic and flammable substance produced in the combustion of materials containing nitrogen

A

Hydrogen cyanide

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18
Q

__________ is a toxic and flammable product of the incomplete combustion of organic materials.

A

Carbon monoxide

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19
Q

_____________ is a significant byproduct of the combustion or polyurethane foam used in many household furnishings.

A

Hydrogen cyanide

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20
Q

_____________ is a product of complete combustion or organic materials; creates an oxygen deficient atmosphere.

A

Carbon dioxide

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21
Q

____________ is the transfer of thermal energy by the circulation or movement of a fluid (air).

A

Convection

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22
Q

The transfer of heat through and between solids is ___________.

A

conduction

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23
Q

____________ is the transmission of energy as electromagnetic waves, such as light, radio, x-ray without and intervening medium.

A

Radiation

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24
Q

The stage when more of the fuel initial fuel package becomes involved and the production of heat and smoke increases is…

A

Growth stage

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25
Q

Consumes the available fuel or oxygen and the heat release rate begins to decline is what stage of fire development?

A

Decay stage

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26
Q

Starts with ignition when the three elements of the fire triangle come together and the combustion process begins is what?

A

Incipient stage

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27
Q

When all combustible materials in the compartment are burning at their peak heat release rate based on available oxygen is what stage?

A

Fully developed

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28
Q

The most common oxidizer of fires is found in the ___________.

A

oxygen in the air

29
Q

In terms of fire behaviour, the ______________ of a fuel converts into heat and light during combustion.

A

potential chemical energy

30
Q

Reactions that emit energy as they occur are known as…

A

Exothermic reactions (fire burning)

31
Q

Reactions that absorb energy as they occur are…

A

Endothermic reactions (converting water into steam)

32
Q

The type of combustion that occurs more slowly and at a lower temperature, producing a smouldering glow in the materials surface is…

A

Non-flaming combustion

33
Q

_________________ requires liquids or solids fuels to be converted to the gas phase through the addition of heat…

A

Flaming combustion

34
Q

Ignition without the addition of external heat is known as ____________.

A

spontaneous ignition

35
Q

The amount of energy delivered over a given period of time is the definition of _______.

A

power

36
Q

The energy release in fire is directly proportional to the amount of oxygen available for combustion.

A

True

37
Q

____________ occurs when an extinguishing agent interferes with this chemical reaction, forms a stable product and terminates the combustion reaction.

A

Chemical flame inhibition

38
Q

A fire that is said to be in the growth stage until the fire’s heat release rate has reached its peak, either because of a lack of fuel or a lack of oxygen.

A

In other words, when a fire cannot grow without the introduction of a new fuel source or a new oxygen source, it has left growth stage and become fully developed.

39
Q

There are two types of fully developed fires. What are they?

A

Fuel limited and vent limited

40
Q

When sufficient oxygen is available for flaming combustion, the fire is said to be…

A

Fuel limited

41
Q

________ is a significant indicator of flashover…

A

Roll over

42
Q

__________ is an indicator of a backdraft…

A

Pulsing smoke

43
Q

A __________ can occur when a mixture of unburned fuel gases and oxygen come in contact with an ignition source.

A

smoke explosion

44
Q

When firefighters ventilate windows or make entry into a building, they establish new flow paths between the fire compartment and exterior vents of the building.

A

True

45
Q

Air pockets in empty wall cavities are a feature of older structures.

A

True

46
Q

What are four ways electrical heating can occur?

A

Resistance heating, over current/overload, arcing, sparking

47
Q

One candle burns at at the same temperature as ten candles. However, the heat release rate of ten candles is ten times greater than one candle at the same temperature.

A

The increased heat release rate results in an increased heat transfer rate to an object.

48
Q

The measure of the rate of heat transfer to or from a surface, typically expressed in kilowatts per square meter (kW/m2) is the definition of what?

A

Heat flux. Translated to an interior fire environment, the temperature in the structure may be within tolerances for PPE however, the heat flux to the PPE from the fire indicates the real measurement of how long the PPE will protect you.

49
Q

In a compartment fire, the location of the fuel package in relation to the compartment walls affects the amount of air that is entrained and thus the amount of cooling that takes place…

A

Fires in fuel packages in the middle of the room entrain air from all sides.
Fires in fuel packages near walls can only entrain air from three sides.
Fires in fuel packages in corners can only entrain air from two sides.

50
Q

Describe the four types of FLASHOVER indicators…

A

Building indicators: interior configuration, fuel load, thermal properties and ventilation.

Smoke indicators: rapidly increasing volume, turbulence, darkening color, optical density, lowering of the the hot gas layer or neutral plane.

Heat indicators: rapidly increasing temperature in the fire compartment, pyrolysis of contents or fuel away from fire.

Flame indicators: isolated flames or roll over in the hot gas layers or near ceilings.

51
Q

What four factors determine a flow path’s effectiveness to transport ambient air to the seat of the fire?

A

Size of the vent opening, length of the path traveled, number of obstructions, elevation differences between the base of the fire and the opening.

52
Q

What is the difference between a physical change and a chemical reaction?

A

A physical change is when something goes from one state of matter to another. Solid to liquid to gas.

A chemical reaction is when a substance changes from one form of matter into another such as two or more substance combining to form compounds.

53
Q

What is the difference between the fire triangle and the fire tetrahedron?

A

The fire triangle is the three components for fire. Fuel, oxygen, and heat.

The fire tetrahedron is the three key components but also has the chemical chain reaction needed for self sustaining fire.

54
Q

Describe how thermal energy impacts fire behaviour…

A

As the heat (thermal energy) increases these molecules vibrate and move more rapidly. The fuel’s kinetic energy is the result of these vibrations in the molecules.

55
Q

The minimum temperature at which a liquid gives off sufficient vapors to ignite, but not sustain combustion…

A

Flash point

56
Q

The temperature at which a piloted ignition of sufficient vapors will begin a sustained combustion reaction… p139

A

Fire point

57
Q

The proximity and orientation of a solid fuel relative to the source of heat also affects the way the fuel burns.

A

For example, if you ignite one corner of a sheet of plywood that is lying flat, the fire will consume the fuel at a relatively low rate. The same plywood positioned vertically will burn much more rapidly because the heated vapors rise over more surface area and transfer heat to the plywood.

58
Q

The orientation of the fuels as well as their surface to mass ratio will also influence the rate and intensity of fire spread. p168

A

True

59
Q

Any open space with no complete fire barrier dividing it is considered a compartment… p171

A

True

60
Q

The area surrounding a heat source in which there is sufficient air available to feed the fire is the ______ zone? p149

A

Combustion zone

61
Q

Construction, renovation, and demolition hazards… p175
Buildings under construction are subject to rapid fire spread when they are partially completed because many of the protective features such as gypsum wall board and automatic fire suppression systems are not yet in place.

A

Abandoned buildings or structures under going renovations or demolition are also subject to rapid fire spread.

62
Q

Vent limited, fully developed fires present a hazardous situation to firefighters. The potential for a window failure to provide fresh oxygen and increase the peak heat release rate can endanger both firefighters and potential victims. To reduce the risk of unpredictable window failure, firefighters must transition the fire from vent limited to fuel limited… p158

A

With the high heat of combustion found in modern furnishings, the only mechanism to transition the fire is to extinguish some of the burning fuel. It is not possible to make enough openings in a compartment to transition a fire from vent limited to fuel limited conditions.

63
Q

At normal ambient temperatures (68 f/20 c), materials can ignite and burn oxygen concentrations as low as 15%. When oxygen concentration is limited, the flaming combustion will diminish, causing combustion to continue in non-flaming mode.

A

Non-flaming or smouldering combustion can occur at extremely low oxygen concentrations even when surrounding environment’s temperature is relatively low.

64
Q

With the high heat of combustion found in modern furnishings, the only mechanism to transition the fire is to extinguish some of the burning fuel.

A

It is not possible to make enough openings in a compartment to transition a fire from vent limited to fuel limited conditions.

65
Q

Inorganic fuels do not contain carbon examples are…

A

Hydrogen or magnesium

66
Q

If the structural elements of the building become involved in the fire, not only does the structure itself provide a new source of fuel, but the fire may be burning in hidden cavities throughout the building.

A

These hidden spaces make finding and extinguishing the fire more difficult and increase the potential of building collapse.

67
Q

For flaming combustion to occur, fuels must be…

A

in a gaseous state. Thermal energy is required to change solids and liquids into the gaseous state. Vapor is common term used to describe the gaseous state of a fuel that would normally exist as a liquid or a solid at a standard temperature and pressure.

68
Q

What can lead to a back draft happening inside a compartment?

A

When potential backdraft conditions exist in a compartment, the introduction of a new source of oxygen will return the fire to a fully involved state rapidly.

CFD (37 decks)

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