Frank-Kamenetskii Model
Definition
A mathematical model (1939) for predicting the critical geometry above which a self-heating material will undergo thermal runaway to ignition, based on the ratio of heat generation rate (exponentially temperature-dependent) to heat dissipation rate; applied in fire investigation to assess whether spontaneous combustion was physically plausible.
- Year
- 1939
- Predicts
- Critical geometry for thermal runaway ignition
- Based on
- Ratio of heat generation to heat dissipation rate
- Forensic use
- Assessing plausibility of spontaneous combustion
Common questions
Why does the size and shape of a stored material matter to whether it can self-heat to ignition?+
Heat generation from slow oxidation scales with volume while heat loss to the surroundings scales with surface area, so larger or more compact piles have a lower surface-to-volume ratio and retain heat more effectively, which is exactly the geometric relationship the model quantifies to predict a critical size threshold.
How is the Frank-Kamenetskii model used to challenge or support a spontaneous combustion claim in fire investigation?+
Investigators plug in the material's known self-heating properties, ambient temperature, and the actual dimensions of the storage pile or container found at the scene to calculate whether that specific configuration could plausibly have reached thermal runaway, ruling the explanation in or out on physical grounds rather than assumption.
Does the model account for materials with uneven heat generation, such as oily rags stacked unevenly?+
The classical model assumes relatively uniform geometry and material properties, so real-world irregular configurations are typically approximated to a representative simplified shape, and investigators treat the result as an estimate of plausibility rather than an exact prediction.
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