Abstract: Gas generating apparatus comprises an electrochemical cell having gas generating (2) and counter electrodes (3) with an intervening body of electrolyte (9). Current passing between the electrodes causes the generation of gas at the gas generating electrode. A first membrane (24) permeable to gas but substantially impermeable to the electrolyte is positioned sufficiently close to the gas generating electrode (2) that gas generated by the gas generating electrode diffuses through the electrolyte and out through the membrane under the influence of a gas concentration gradient, substantially without forming bubbles in the electrolyte and irrespective of the orientation of the apparatus.

Abstract: An oxygen sensor (1) with an inlet (2) connects with a small chamber (3). An inlet provided with a diffusion barrier (4) permits flammable gas and oxygen to enter the chamber. The oxygen concentration within the chamber is low, and a catalytic element (5) within the chamber causes combustion of flammable gas, thus consuming oxygen within the chamber. The signal from the oxygen sensor is processed to calculate a concentration for the flammable gas.