F80 Fire Behavior and Combustion Principles 2

Question 1

What is the lower explosive limit (LEL) of a fuel vapor?

Accepted Answer

The minimum concentration of fuel vapor in air required to sustain ignition

Answer

The lower explosive limit (LEL) is the minimum fuel vapor concentration in air below which the mixture is too lean to ignite.

Question 2

What is autoignition temperature?

Accepted Answer

The lowest temperature at which a material ignites spontaneously without an external ignition source

Answer

Autoignition temperature is the minimum temperature at which a material will self-ignite without any spark or open flame present.

Question 3

Which phase of fire development follows the incipient (early growth) stage?

Accepted Answer

Free-burning stage

Answer

After the incipient stage, the fire enters the free-burning (growth) stage where it grows rapidly and consumes available fuel.

Question 4

What does pyrolysis refer to in fire science?

Accepted Answer

Chemical decomposition of materials due to heat, producing combustible gases

Answer

Pyrolysis is the thermal decomposition of solid or liquid fuels by heat, generating flammable gases that feed and sustain combustion.

Question 5

How does fire primarily spread within a structure via convection?

Accepted Answer

Through rising hot gases and smoke carrying heat to upper levels and adjoining compartments

Answer

Convective heat transfer occurs as buoyant hot gases and smoke rise and travel horizontally, spreading fire to upper floors and adjacent spaces.

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