The Measurement Of Heat Release Rates By Oxygen Consumption Calorimetry In Fires Under Suppression

A series of open-space fire experiments was conducted at the National Fire Laboratory (NFL) to validate the capabilities of the NFL room-size oxygen-consumption calorimeter, and to assess the importance of accounting for actual water vapour content in the exhaust gases in calculating heat release rates (HRR). Water spray was used to partially suppress some of the fires, and to add significantly to the humidity of the exhaust gases. The equations normally used in the fire research community for oxygen calorimeter assume unsuppressed fires, and that water vapour in the exhaust gases is due solely to the humidity of the incoming air and to combustion reactions. This paper derives the basic equations for computing heat release rates based on the principle of nitrogen balance. The general equations take into account all sources of water vapour, including incoming air, combustion reactions, and evaporation due to suppression. The equations are then simplified to i) neglect all humidity, and, ii) consider