Smoke Plume Mass Flow
Calculate the mass flow of a fire's smoke plume by the Heskestad correlation, ṁ = 0.071·Q̇_c^(1/3)·z^(5/3), from the convective part of the heat release rate Q̇_c (kW) and the height above the fire base z (m). The result, in kg/s, is the amount of hot gases and smoke rising and accumulating, governing the design of smoke control and exhaust systems (mechanical or natural) that keep a smoke-free layer for safe evacuation. The flow grows strongly with height. Enter the convective heat fraction and the height.
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Smoke plume mass flow (Heskestad)
In a fire, hot gases and smoke rise as a plume, dragging in (by entrainment) the surrounding cool air as they climb — which is why the plume grows wider and more massive the higher up it is measured. The Heskestad correlation for the plume mass flow in the zone above the flames is ṁ = 0.071·Q̇_c^(1/3)·z^(5/3), where Q̇_c is the convective fraction of the heat release rate (typically ~70% of the total HRR, since part of the heat leaves as radiation, in kW) and z is the height above the base of the fire (m). The result, in kg/s, is the amount of smoke and gases reaching that height and accumulating under the ceiling, forming the smoke layer that gradually descends. This is the key calculation in smoke control: to keep a clear layer above people's heads during evacuation (and so firefighters can see), the exhaust systems — mechanical (fans) or natural (openings at the top) — must extract smoke at the same rate the plume produces it at the design layer height. Since the flow grows strongly with height (5/3 exponent), tall atria and halls generate enormous plumes, demanding powerful exhaust systems. Sizing this correctly is what guarantees visibility and breathable air along the escape routes. Enter the convective heat fraction and the height.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.