Two models for understanding combustion
The triangle brings together fuel, oxidant and activation energy. The tetrahedron adds the chain reaction sustaining flaming combustion. These are useful teaching models for identifying initiating conditions and forms of control. They are not a risk-calculation method and cannot, by themselves, establish how long a fire will last or how it will spread.
Related concept: Fire risk.
Fuel and oxidant
Fuel may be a solid, liquid, gas or dust. Its form, quantity and arrangement change its behaviour. The usual oxidant is oxygen in air, although other oxidisers exist. Separating incompatible materials, reducing exposed quantities and containing leaks are preventive decisions related to these factors. The absence of a visible flame does not remove ignition conditions.
Energy and chain reaction
A spark, hot surface or hot work may provide the initial energy. Combustion reactions and heat transfer can then sustain and spread the process. The energy needed depends on the substance and mixture. A seemingly small source can therefore matter in a sensitive atmosphere.
How the model guides prevention
The model helps ask which fuel might be released, which ignition source might coincide with it and how to prevent that combination. It also explains categories of extinguishing action: cooling, separating fuel, smothering or inhibiting the reaction. Practical selection must check compatibility with the material, electricity and people. Not every method of removing heat or air is safe.
Maintenance example
A hypothetical repair involves welding near a vessel containing solvent residues. Removing visible containers does not necessarily remove vapours. Preparation must examine residues, isolation, cleaning and relevant atmospheric checks. The triangle structures the questions, but authorising the work requires evidence of effective controls.
What the model leaves out
Smoke spread, building resistance, evacuation and human action require additional analysis. Nor do all combustion processes behave alike; embers or flameless processes may be present. The model is a training and preventive-discussion tool, not a justification for improvising firefighting actions.
