Heat release rate (HRR) is the rate at which a burning item gives out energy, measured in kilowatts. Per unit area of specimen it is written kW/m². More than any other single quantity, HRR predicts fire growth: double the heat release and, roughly, you halve the time available to escape. This is why modern fire regulation is built on measuring it.
The quantities on a report
Peak HRR is the highest point of the curve - the worst moment of the fire. Total heat release (THR) is the area under the curve - the whole energy contribution. Time to ignition and the shape of the early curve show how quickly the peak is reached, which is what indices like FIGRA combine (peak divided by the time to reach it, in the SBI formulation) to classify growth speed. A fire-retarded product typically shows a delayed, flattened curve; an untreated one spikes early.
How it is measured: oxygen consumption
Almost every HRR instrument on this site uses one discovery: burning materials release a nearly constant amount of heat per kilogram of oxygen consumed (about 13.1 MJ per kg of O2), whatever the fuel. Measure how much oxygen disappears in the exhaust, and you have heat release - no need to catch the heat itself. The cone calorimeter applies this to a 100 mm specimen; the SBI applies it to a room corner; UL 9540A calorimetry applies it to a battery unit. Milligram-scale MCC reaches the same quantity by burning pyrolysis gases completely in a combustor.
Choosing measurement scale
Match the specimen to the question. Formulation screening: MCC. Product behaviour and classification inputs: cone calorimeter. Room-scale classification: SBI or the product's full-scale test. The instrument pages name the governing standard for each scale; start from the report your customer or regulator will read.