🔥6A-6D Combined Fire development and stages set

What factors does a compartment surrounding a fire affect?

Available ventilation, access to additional fuel, and heat losses or gains.

What are the two basic types of compartment fires?

Fuel-limited and ventilation-limited fires.

What is a fuel-limited fire?

A fire with sufficient oxygen available for flaming combustion where fuel characteristics control development.

What is a ventilation-limited fire?

A fire that has enough fuel but insufficient oxygen to continue burning or spreading to all available fuel.

How do all compartment fires begin?

They begin in the incipient stage as fuel-limited fires.

What can happen as a fire grows?

It can remain fuel-limited if enough oxygen is available or consume available oxygen and become ventilation-limited.

What are the four stages of fire development?

Incipient, growth, fully developed, and decay.

What three factors control fire development?

Fuel properties, available ventilation, and heat conservation.

What is the incipient stage?

The stage where ignition occurs and the fire is initially small and confined to a portion of the first fuel ignited.

What happens during the growth stage?

More of the initial fuel becomes involved, and heat and smoke production increase.

What can radiant heat do during the growth stage?

It can pyrolyze nearby fuels and spread fire to new fuel packages.

What is the fully developed stage?

The stage when combustible materials in the compartment are burning at their peak heat release rate based on available oxygen.

What is the decay stage?

The stage when the fire consumes available fuel or oxygen and heat release rate declines.

What can happen if oxygen is introduced to a ventilation-limited fire during decay?

The fire can reenter growth and rapidly become fully developed.

What is open burning or free burn?

A fuel-controlled condition with sufficient oxygen available to burn fuel until it can no longer sustain combustion.

What is the ceiling jet?

Hot gases that rise in the plume until they reach the ceiling and then spread horizontally.

What happens to temperature during the incipient stage?

It begins increasing but remains only slightly above ambient in areas directly affected by the fire and plume.

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

Flame height reaching approximately 2.5 feet (750 mm).

What happens when flame height reaches approximately 2.5 feet?

Radiated heat begins transferring more heat than convection and the fire enters the growth stage.

Can transition from incipient to growth occur quickly?

Yes, it can occur in seconds depending on the fuel type and configuration.

What happens during the growth stage?

The fire begins influencing more of the compartment, and ventilation and compartment configuration increasingly affect fire behavior.

What is air entrainment?

The drawing of air into the fire.

How does air entrainment affect an unconfined fire?

It cools the plume and reduces flame length and vertical extension.

How does the location of a fuel package affect air entrainment?

A fire in the middle of a room can entrain air from all sides, near a wall from three sides, and in a corner from two sides.

What is the combustion zone?

The area around a fire where sufficient air is available to feed combustion.

What is thermal layering?

The formation of layers of gases according to temperature, density, and pressure.

What happens to the hottest gases when thermal layering occurs?

They form the highest layer.

What happens to cooler gases?

They form lower layers.

What is a flow path?

The space between an air intake and an exhaust outlet through which air and fire gases move.

What happens when the hot gas layer gains mass and energy?

Pressure increases and the layer can spread downward and laterally.

What is the neutral plane?

The interface between the hot gas layer and cooler air where net pressure is approximately zero.

What happens above the neutral plane at an opening?

Hot gases at higher pressure exit the compartment.

What happens below the neutral plane?

Lower-pressure outside air is drawn into the compartment.

What is ventilation-limited decay?

A condition in which there is insufficient oxygen to maintain combustion, causing heat release rate to decrease while fuel-rich gases accumulate.

Why can a ventilation-limited fire remain dangerous even when heat release decreases?

High temperatures can remain and the compartment can contain large amounts of unburned flammable gases.

What happens when fresh air enters a ventilation-limited fire?

Heat release rate and fire growth can increase rapidly.

Why is opening a door or window dangerous in a ventilation-limited fire?

It can create a new flow path and introduce oxygen to fuel-rich gases.

What are the two major rapid-fire-development events?

Flashover and backdraft.

What is flashover?

A rapid transition from the growth stage to the fully developed stage in which combustible materials and fuel gases in a compartment ignite almost simultaneously.

What happens to the compartment environment during flashover?

It changes from a two-layer environment to a single, well-mixed hot gas layer extending from floor to ceiling.

What temperature can occur during flashover?

Gas temperatures can reach 1,100°F (593°C) or higher.

What is rollover?

The ignition of accumulated unburned fire gases in the upper layer, with flames propagating through the hot gas layer or across the ceiling.

Is rollover itself flashover?

No, rollover is an indicator of flashover and generally precedes flashover, but it does not necessarily result in flashover.

What four elements characterize flashover?

A rapid transition to fully developed fire, rapid occurrence, an enclosed compartment, and pyrolysis/ignition of exposed fuel surfaces.

What two major factors determine whether a compartment fire progresses to flashover?

Sufficient fuel/heat release rate and adequate ventilation.

What are smoke indicators of possible flashover?

Rapidly increasing smoke volume, turbulence, darkening color, increasing optical density, and a lowering hot gas layer or neutral plane.

What are heat indicators of possible flashover?

Rapidly increasing compartment temperature, pyrolysis of fuel packages away from the fire, and hot surfaces.

What are flame indicators of possible flashover?

Isolated flames or rollover in the hot gas layer or near the ceiling.

What is backdraft?

An explosively rapid combustion event caused when oxygen is introduced into a compartment containing hot, fuel-rich gases from incomplete combustion.

What conditions produce backdraft?

A high concentration of heated flammable gases with insufficient oxygen for flaming combustion followed by introduction of oxygen.

What can cause a backdraft?

Creating a horizontal or vertical opening such as opening a door or window.

What is the basic requirement for a backdraft?

Hot, fuel-rich smoke must mix with air and reach an ignition source or sufficient ignition conditions.

What are smoke indicators of backdraft?

Pulsing smoke around small openings and smoke-stained windows.

What is an airflow indicator of backdraft?

High-velocity air intake.

What are heat indicators of backdraft?

High heat and crackling or breaking sounds.

What is a flame indicator of backdraft?

Little or no visible flame.

What factors affect how violent a backdraft will be?

Smoke volume, confinement, temperature, pressure, and the speed at which fuel and air mix.

What is a fully developed fire?

A fire whose heat release rate has reached its peak because fuel or oxygen limits further growth.

What are the two types of fully developed fires?

Fuel-limited and ventilation-limited.

What limits a fuel-limited fully developed fire?

The amount of available fuel.

How can a fuel-limited fire's heat release rate be increased?

By adding more fuel.

What limits a ventilation-limited fully developed fire?

The available oxygen and ventilation openings.

How can additional ventilation affect a ventilation-limited fire?

It can provide more oxygen and increase the peak heat release rate.

Can ventilation alone convert a ventilation-limited fire to a fuel-limited fire?

No. Additional ventilation alone will not make that transition.

What is fuel-limited decay?

Decay that occurs as a fuel-limited fire consumes its available fuel and heat release rate decreases.

What is ventilation-limited decay?

Decay caused by insufficient oxygen, in which the fire can potentially return to growth when oxygen is reintroduced.

How can firefighters reduce the risk when dealing with ventilation-limited decay?

Cool hot fire gases before ventilation or immediately after forcible entry to reduce the likelihood of gases igniting when fresh oxygen is introduced.