yup. NG just kind of floats through the air but it certainly rises. Mercaptan is introduced to create the smell.Must be why the water heater code has it 18" off the garage floor
Years ago one of the kids around Ponca had a parent that worked at the ONG where they introduced the mercaptan to the NG. It takes just a few parts per million to create the smell to alert us. Those kids got a bottle of it and drove around the Conoco refinery and parts of town dumping it on the street. It was almost mass panic. The Refinery shut down all operations, emergency services was called out along with all LEO and fire.
Took a couple hours to figure out that it was not a NG leak.
Wasn't you was it?