Abstract: A flue gas analyser for determining the efficiency of a burner burning a supply gas and producing a flue gas by: calculating an efficiency of the burner based on a detected amount of a first target gas in the flue gas and an expected amount of the first target gas in the flue gas; predicting an amount of a second target gas in the flue gas based on the efficiency of the burner; estimating a composition of the supply gas based on a detected amount of the second target gas in the flue gas and the predicted amount of the second target gas in the flue gas; and correcting the calculated efficiency of the burner based on the estimated composition of the supply gas.

Abstract: A dangerous level of gas safety monitor for indicating a level of a target gas in an atmosphere comprising: a sol-gel layer comprising a first phosphorescent material, exposed to the atmosphere; a light source enabled to stimulate the phosphorescent material; a detector enabled to detect light emitted by the phosphorescent material; a pressure sensor to determine the pressure of the atmosphere; a processor enabled to determine relative phase shift or time delay between the detected light emitted by the phosphorescent material and the emitted light of the light source, wherein the monitor is configured to provide an output indicative of a dangerous level of the target gas in the atmosphere, the output based on the determined pressure and relative phase shift or time delay.