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A Simplified Relation Between Hot Layer Height and Opening Mass Flow

Johansson N. and Van Hees, P., 2014. A Simplified Relation Between Hot Layer Height and Opening Mass Flow. Fire Safety Science 11: 432-443. 10.3801/IAFSS.FSS.11-432


The mass flow of air through an opening in a well-mixed compartment fire can be calculated with a simple expression. Similar simple models are lacking for the stratified pre-flashover case. Usually an advanced computer model is required to calculate the mass flow through an opening in a pre-flashover compartment fire. However, two equations for the opening mass flow through an opening are presented and validated in this paper. The presented equations are predominantly valid for temperatures above 200°C and predictions with the equations are shown to be within 10% of results from computer simulations and experimental measurements. The equations can also be combined with existing plume models in order to give an estimate of the hot layer height in a compartment fire with a predefined heat release rate.


hot layer height, zone model, mass flow, fire dynamics

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