Chapter 5

Question 1

Firefighting personnel should have an understanding of combustion and fire dynamic principles and be able to use them for fire scene size up and assessment of fire conditions both upon initial arrival and continuously over the course of the incident.

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Question 2

The combustion reaction can be characterized by four components: the fuel, the oxidizing agent, the heat, and the uninhibited chemical chain reaction.

Question 3

The difference between the fire tetrahedron model and the fire triangle model of combustion is the inclusion of the chemical chain reaction.

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Question 4

The chemical chain reaction provides the ability to sustain flames.

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Question 5

The fire triangle will only support a flash or flame or combustion in the condensed phase, such as glowing embers or hot charcoal.

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Question 6

A fuel is any substance that sustains combustion under specified environmental conditions.

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Question 7

The majority of fuels encountered are organic, which means that they are carbon-based and may contain other elements such as hydrogen, oxygen, and nitrogen in varying ratios.

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Question 8

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

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Question 9

Increased synthetic fuel loads and new construction materials with higher heat of combustion lead to higher heat release rate.

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Question 10

Pyrolysis is a process in which the solid fuel is decomposed, or broken down, into simpler molecular compounds by the effects of heat alone.

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Question 11

Pyrolysis precedes combustion and continues to support the combustion after ignition occurs.

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Question 12

the application of heat causes vapors or pyrolysis products to be released where they can burn when in proper mixture with air and a sufficient ignition source is present, or if the fuel’s autoignition temperature is reached.

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Question 13

If the thermal exposure to the fuel is increased, the rate of pyrolysis may increase.

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Question 14

Heats of combustion typically range from 10 Mj/kg to 4Mj/kg with hydrocarbon-based products having two to three times higher values than natural products.

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Question 15

Air in the earth’s atmosphere is made up of approximately 21 percent oxygen and 78 percent nitrogen.

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Question 16

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

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Question 17

When the amount of air is in balance with the amount of fuel, the burning is referred to as stoichiometric.

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Question 18

The heat release rate of a fire is variable over time and is dependent on the fuel load characteristics, oxygen available, and enclosure characteristics.

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Question 19

Heat flux is the measure of the rate of heat transfer to a surface, expressed in kilowatts per meter squared.

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Question 20

The higher the heat flux from a fire to surface, the faster the temperature of the surface will increase.

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Question 21

Self-sustained combustion occurs when 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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Question 22

Phase changes most relevant in fire a melting and vaporization.

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Question 23

thermal decomposition involves irreversible changes in the chemical structure of a material due to the effects of heat.

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Question 24

Thermal decomposition of a solid or liquid most often results in the production of gases.

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Question 25

At more moderate heating conditions, flexible polyurethane decomposes to a char and flammable gases or vapors.

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Question 26

Structure fires would be an example of diffusion burning.

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Question 27

Deflagration velocities normally range from cm/sec to m/sec, though velocities into the hundreds of m/sec are possible.

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Question 28

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

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Question 29

Premixed flame propagation in confined volume is normally considered a smoke explosion.

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Question 30

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

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Question 31

Diffusion flame burning is the ordinary sustained burning mode in most fires.

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Question 32

The lowest oxygen concentration in nitrogen is termed the limiting oxygen index.

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Question 33

For most fuel vapors, the LOI is in the range of 10 percent to 14 percent by volume at ordinary temperatures.

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Question 34

On average, 13.1Mj of heat is produced for every kg of oxygen consumed.

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Question 35

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

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Question 36

When less air is available for combustion, as in ventilation-limited fires, the production of carbon monoxide increases as does the production of soot and unburned fuels and pyrolyzates.

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Question 37

The application of water can produce large volumes of condensing vapor that will appear white or gray when mixed with black smoke from the fire.

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Question 38

White smoke from a fire compartment may be unburned pyrolyzate.

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Question 39

The higher velocity of the fire plume causes a local reduction in pressure.

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Question 40

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

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Question 41

The energy that causes a change in the temperature of an object is referred to as sensible heat, while the transfer of energy that results in phase change is called latent heat.

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Question 42

Conduction is heat transfer within solids or between contacting solids.

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Question 43

Firefighters often experience conductive heat transfer when wearing ppe during firefighting operations.

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Question 44

As the ppe absorbs heat energy from the fire environment, it is transferred conductively through the various layers of material and to the firefighter’s body.

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Question 45

Convection is the transfer of heat energy by the movement of heated liquids or gases from the source of heat to a cooler part of the environment.

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Question 46

During a fire, heat is transferred by convection to a solid when hot gases pass over cooler surfaces or when hot smoke mixes with atmospheric air.

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Question 47

The higher the velocity and turbulence of the gas, the greater the rate of convective heat transfer.

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Question 48

Radiation is a line-of-sight transfer of heat energy from a hot surface or gas to a cooler material by electromagnetic waves.

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Question 49

Although flame is often the greatest source of radiant heat transfer during a compartment fire, the smoke and hot gases that collect at ceiling level is also a source of radiant heat and often contributes to the ignition of materials.

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Question 50

Even though considered a light hazard, a residential room could easily have 5 MW to 15 MW of potential peak, HRR, provided sufficient oxygen/ventilation is available.

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Question 51

Fuel load can be used in conjunction with the size of vent openings to estimate the duration of fully developed burning in a compartment.

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