Chapter 5 - Fire Dynamics

What is an example of an exothermic reaction?

Fire

What are the three elements of the fire triangle?

Fuel, oxygen, and heat

In solids, off-gassing is a chemical change known as pyrolysis; in liquids, it is a physical change called

. vaporization.

For piloted ignition to occur, the mixture of fuel and oxygen

must encounter an external heat source to start the combustion reaction.

The autoignition temperature (AIT) of a substance is

always higher than its piloted ignition temperature.

During flaming combustion, what is "pumped in" and mixed with fuel gases?

Fresh oxygen

The fire triangle illustrates the conditions required for ____ while the fire tetrahedron illustrates the conditions required for ____ .

nonflaming combustion; flaming combustion

During combustion, the potential chemical energy of a fuel converts into

heat and light.

In simple terms, products of combustion are

heat and smoke.

. Why do structure fires tend to have a lot of smoke?

Combustion is incomplete in a structure fire

Heated gases expand and become ____ ; when cooled they contract and become_____.

less dense; denser

The cause of most fire deaths is due to lack of oxygen and/or

exposure to toxic gases found in smoke.

Carbon monoxide is released when an organic material burns in an atmosphere with a _____ and exposure can result in hypoxia or death.

Which type of materials are likely to produce toxic levels of hydrogen cyanide when under burning conditions?

Upholstered furniture and carpets

Which product of complete combustion can displace oxygen, creating an oxygen-deficient atmosphere?

. Carbon dioxide

The movement of gases during a fire occurs because gases move

from areas of higher pressure to areas of lower pressure

When all available oxygen is consumed and not replenished, the heat release rate

decreases.

As heat begins to vibrate the molecules in a fuel, the fuel begins a physical change from a

solid or liquid to a gas.

Heat transfer rate is best measured by

heat flux.

Spontaneous ignition through self-heating is an oxidation process produced by

chemical energy.

Friction and compression generate

mechanical energy.

The rate of heat transfer depends on the _____ differences between the objects and the thermal conductivity of their materials.

temperature

Conduction occurs when a material is heated as a result of

direct contact with a heat source

In the fire environment, convection usually involves heat transfer through

the movement of hot smoke and fire gases

Which method of heat transfer can have a significant effect on the ignition of objects located some distance from a fire?

Radiation

During a fire, heat transfer methods tend to

occur together.

Most fuels are organic, meaning they contain _____ and other elements.

carbon

Why can gaseous fuels be the most dangerous fuel type?

They are already in the physical state required for ignition.

Most flammable liquids, such as gasoline, have a specific gravity less than 1, which means they are

lighter than water and will float.

. The main difference between flash point and fire point is that a

flash point temperature will not sustain combustion, while a fire point temperature can begin a sustained combustion reaction.

Liquids that are less dense than water are

more difficult to extinguish with water.

The primary consideration for how easily a solid fuel ignites is its

surface-to-mass ratio.

The energy released in fire is proportional to the

amount of oxygen available.

Oxygen concentrations above the upper explosive limit (UEL) are said to be too _____ to burn.

rich

The self-sustained chemical reaction process

increases the speed of the oxidation reaction.

What is the main difference between a fuel-limited fire and a ventilation-limited fire?

A fuel-limited fire has sufficient oxygen for combustion; a ventilation-limited fire does not have enough oxygen to continue to burn or spread.

Once ignition occurs and the combustion process begins, development in the ____ stage depends largely on the characteristics and configuration of the fuel involved.

incipient

What is a good visual indicator that a fire is leaving the incipient stage?

Flame height

Rapid fire development usually occurs during the ____ stage.

growth

When does a fire leave the growth stage?

When it cannot grow without the introduction of a new fuel or oxygen source

In thermal layering, the hottest gases typically form the

highest layer.

Thermal layering can be significantly altered by:

ventilation and flow paths.

The neutral plane can be found at openings where

hot gases exit and cooler air enters the compartment.

As the efficiency of combustion decreases in a hot gas layer, the heat release rate ____ and the amount of unburned fuel within the hot gas layer ____.

decreases; increases

A rapid transition from the growth stage to the fully developed stage is known as

flashover

What is an indicator of rollover?

Flames spread through the hot gas layer

. What is one indicator that a fire is approaching flashover?

Large volumes of darkening smoke

. What might a very low-level neutral plane indicate about a fire's behavior?

The fire is reaching backdraft conditions.

What causes backdraft in a ventilation-limited compartment fire?

An increase in ventilation

. What is one of the indicators of backdraft?

. Pulsing smoke movement around small openings in the building

How can firefighters help prevent backdraft from occurring?

By controlling or limiting ventilation openings

What factor determines the type of fully developed fire?

. Whether it is a lack of fuel or oxygen that is limiting the peak heat release rate

New sources of fuel introduced after a fire is fully developed will

allow fuel-limited fires to grow.

To reduce the risk of unpredictable window failure, firefighters must transition a fully developed fire from

ventilation-limited to fuel-limited.

A situation that might cause a fire to enter fuel-limited decay would be a compartment

that has failed and burned to the ground.

To ensure the decay stage of a ventilation-limited fire is its final stage, firefighters must

cool the hot fire gases before any further ventilation occurs

In the intake flow of a structure fire, the ambient air (higher pressure)

flows toward the seat of the fire and reacts with the fuel.

What determines the available flow path in a structure fire?

. The floor plan and openings in the structure

Firefighters can establish new flow paths for structure fires when they

. advance a hoseline or ventilate windows to make entry

Why should firefighters working in the exhaust portion of the flow path limit their time there?

Increased convective heat transfer can make conditions unsurvivable even in PPE.

Unplanned ventilation occurs when

a window or roof fails.

What is one way firefighters can influence fire dynamics at a structure fire?

Using doors to control the amount of air available to the fire

The two primary types of dangerous building conditions are those that contribute to the spread and intensity of the fire and those that

make the building susceptible to collapse.

Firefighters should have a knowledge of building construction and occupancy types when fighting structural fires in order to

determine the fuel load of a structure

How can a fire's location within a building influence fire development?

Fires in the upper level will generally extend downward much more slowly

When planning for potential fires in commercial, industrial, and storage facilities with large fuel loads, remember that

firefighters should perform and update preincident surveys to establish awareness of fuel load hazards.

When a fire becomes ventilation-limited in a compartment

. it can still reignite if more oxygen is introduced into the compartment

Assuming there is available oxygen, the higher the fuel load and the longer the fire burns, the

more fire spread accelerates.

To protect combustible roofs on structures adjacent to a fire building or wildland fire

perform exposure protection tactics on those structures' roofs.

How can firefighters use doors to their advantage during interior operations?

By closing them to control available oxygen sources

Open plan commercial structures, such as warehouse-style stores, have

. high fuel loads and no physical barriers to prevent the spread of fire and smoke.

How does a fire in a large compartment compare to a fire in a small compartment?

. A fire in a large compartment will normally develop more slowly than one in a small compartment.

. Unprotected engineered-steel and wooden trusses used in construction

can fail after five to ten minutes of exposure to fire.

When engineered roof joists fail quickly under fire conditions

there may not be any indicator to firefighters that the roof is failing.

Buildings under construction, renovation, or demolition

have increased fire risk.