With the increased usage of natural gas and liquid propane, there have been more occurrences of fire and even explosion resulting from small leaks that can occur in the systems. Combustible gas detectors are constantly testing the air for the presence of these substances and go into alarm when the level of these gases reaches a level that may be hazardous. As propane is heavier than air, the detectors would be installed down closer to the floor as that is where the gas will begin to accumulate in the event of a leak. With natural gas being lighter than air, the detector would be installed higher on the wall as that is most likely where that particular gas would begin to gather. Right here in Maine in 2007, two mountain resort properties were destroyed by gas-induced explosions in homes that were infrequently visited by their owners. Thankfully, nobody was seriously hurt but both homes were totally destroyed. This small precaution may have saved both of those properties.