Flame Height (Heskestad)
Estimate the mean height of a diffusion flame by the Heskestad correlation, L = 0.235·Q̇^(2/5) − 1.02·D, from the heat release rate Q̇ (kW) and the fire base diameter D (m). The result, in metres, is the visible flame height above the base — essential to assess the risk of fire spread by radiation, the thermal reach over structures and the activation of detectors and sprinklers. Height grows with the fire power to the 2/5 power and decreases with the base diameter. It is one of the classic fire dynamics correlations. Enter the heat release rate and the base diameter.
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Flame height (Heskestad correlation)
The flame height of a fire is not a cosmetic detail — it determines how far the fire reaches by radiation and direct contact, whether it will strike the ceiling and start spreading horizontally, and when detectors and sprinklers are triggered. The correlation most often used to estimate it is Heskestad's: L = 0.235·Q̇^(2/5) − 1.02·D, where Q̇ is the heat release rate (the power of the fire, in kW) and D is the diameter (or characteristic dimension) of the fire base (m). The result is the mean visible flame height above the base, in metres. The physics behind it is elegant: height grows with power raised to 2/5 (a fire 32× more powerful has a flame only 4× taller), and the −1.02·D term reflects that, for the same power, a fire spread over a wide base produces shorter flames than a concentrated one, because the combustion is distributed. Real flames flicker, so 'mean height' means the height at which flame is present about 50% of the time. This correlation is one of the cornerstones of fire dynamics and feeds calculations of fire spread, of heat flux onto structures and neighbouring walls, and of detection and suppression system activation. Enter the heat release rate and the base diameter.
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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.