Heat release rate is the power of a fire, measured in kilowatts or megawatts, and it is the quantity fire scientists reach for first when asked how big a fire is. It equals the mass of fuel being gasified per second multiplied by the effective heat of combustion, written \( \dot{Q} = \dot{m} \cdot H \). A wastepaper basket is roughly \( 100 \ \mathrm{kW} \), an upholstered armchair a few hundred, a fully involved room several megawatts. The rule that makes it central is that nearly every other quantity in compartment fire physics scales with it: plume temperature, smoke production, the depth of the hot layer, and the time available before conditions become untenable. The confusion it resolves is the use of temperature as a measure of fire size; a blowtorch is hotter than a burning sofa and vastly less dangerous, because temperature says how hot a small volume of gas is while heat release rate says how much energy is arriving every second. After this Concept you can size a fire in kilowatts rather than by how hot or how visible it looks.
In fireground thermal hazard analysis, temperature and heat release rate are distinct physical quantities: temperature is the average amount of energy contained within a substance, while heat release…