An experimental study was performed in which a combustible ceiling was simulated by injecting town gas in porous burners covering a portion of the ceiling of a long duct with a primary gas fire at one end. Temperature profiles of the ceiling flame and radiometer and radiation pyrometer readings were taken at different points. The primary gas rate and the position and rate of ceiling gas were varied. The data were used to calculate the emissivity and absorption coefficients of the ceiling flames by an approximate method which takes into account the variation of temperature across the flame. The name emissivity was about 0.5. This high value was attributed to the high concentration of soot in the flame. The adddition of fuel at ceiling level by the injection of gas was found to increase flame length and the radiation falling on the floor considerably, particularly at low primary gas flow rates.