Chemistry of Combustion

Matter

Anything that has mass and occupies space

Atom

Smallest unit of matter with a nucleus of protons and neutrons

Molecule

Two or more atoms chemically bonded together

Element

A substance with only one type of atom that cannot be broken down further

Compound

A substance with more than one type of atom chemically bonded (e.g. H₂O)

Mixture

Two or more substances physically mixed but not chemically bonded

States of Matter

Solid, liquid, gas — change of state occurs when energy is added or removed

Energy

The ability to do work; forms include heat, light, electricity, atomic, potential, kinetic

Law of Conservation of Energy

Energy cannot be created or destroyed, only converted

Triangle of Fire

The three requirements for combustion: heat, fuel, oxygen

Class A Fires

Fires involving solid organic materials (wood, paper, textiles, plastics)

Class B Fires

Fires involving flammable liquids and solids (miscible or non-miscible with water)

Class C Fires

Fires involving flammable gases such as natural gas or LPG

Class D Fires

Fires involving metals (e.g. magnesium, titanium), water is dangerous

Class F Fires

Fires involving high-temperature cooking oils and fats

Electrical Fires

Not a separate class; use non-conducting extinguishing agents

Conduction

Heat transfer by direct contact between materials

Convection

Heat transfer by movement of heated fluids or gases

Radiation

Heat transfer by electromagnetic waves, without direct contact

Inverse Square Law

Heat radiation reduces with the square of distance; double the distance = quarter the radiation

Flashpoint

Lowest temperature a substance gives off vapour that ignites briefly with an ignition source

Firepoint

Lowest temperature at which vapours are produced fast enough to sustain burning

Spontaneous Ignition Temperature

Lowest temperature at which a substance ignites without external ignition

Spontaneous Combustion

Self-heating of organic materials (e.g. haystack) until ignition temperature is reached

Smouldering

Slow combustion of a solid in air without flame, producing much smoke

Range of Flammability

The gas-to-air percentage mix needed for combustion; too lean or too rich won’t burn

Methods of Extinguishment

Starvation (remove fuel), Smothering (remove oxygen), Cooling (remove heat), Chain reaction inhibition (square of fire)

Chain Reaction Inhibition

Stopping radical reactions in combustion; extends triangle of fire to square of fire