Fireline intensity is the rate of heat release per unit time and per unit length of a fire front. With rate of spread, it is one of the most relevant quantities used in forest fire science. It allows to evaluate the effects of fuel treatment on fire behavior, to establish limits for prescribed burning or to support fire suppression activities. Although it is widely used, conversely its measurement is often coarse and has received very little attention. Furthermore, literature only refers to

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... dy state when dealing with this quantity. In the present paper, we measure directly the fireline intensity at laboratory scale by using the oxygen consumption calorimetry principle. This methodology allows us to provide this quantity not only for steady fires but also for unsteady spreading fires for the first time. We show that the current approach used to assess fireline intensity can lead to overestimation from about 20%. As the experiments were conducted under wellventilated conditions, the heat release rate calculated by calorimetry was compared to mass loss rate and heat of combustion taking into account the combustion efficiency.