A: The GMT combustibles monitor will respond to virtually all combustible gases. This includes methane, butane, propane, gasoline, naphtha, hydrogen, and a host of others. However, as with any sensor of this type, it must be calibrated so that its 4-20 mA output and alarm relay trip point are meaningful. If you specify propane when ordering, the GMT will be calibrated so that the analog output span is 0 to 100 percent of the lower explosive limit for propane (2.1 percent by volume). The alarm relay will be calibrated to trip at 25 percent of the lower explosive limit (0.54 percent by volume). It will still respond to all other combustibles, but the analog output and alarm relay trip points will not correspond to known values. If no gas is specified when the order is placed, the GMT will be calibrated for methane, which is the main component of natural gas and the industry standard for "general combustibles" monitoring.