Decrease of carbon dioxide concentration and entrainment of horizontally spreading ceiling jet

•Mass flow rate of ceiling jet was estimated from CO2 measurement within the ceiling jet.•Dependence of CO2 concentration on radial distance was examined.•Dependence of entrainment coefficient against radial distance was investigated.

Knowledge about the mass flow rate of a ceiling jet in a large space is important for predicting smoke behavior, determining suitable smoke control equipment, and designing the operating conditions in the early stages of a fire. Here, full-scale ceiling jet tests with a flat unconfined ceiling were conducted. The mass flow rate of a ceiling jet spreading in the radial direction was estimated based on measurement of carbon dioxide concentration. The relation between the entrainment properties of the ceiling jet and radial distance was experimentally investigated. Empirical formulae representing the dependence of the carbon dioxide concentration decrease with radial distance was developed. The entrainment coefficient characteristic by ceiling jet was also described.