I have no idea about other gas lines. I’ve got a 1000 gal propane tank behind my house for my use, and was a volunteer firefighter for 4 years or so in my rural area. Certainly aware of the dangers of propane :-)
They started putting odorants such as mercaptan compounds into natural gas (and propane) after the New London School explosion in Texas in 1937. The school was heated with natural gas from local oil wells and a leak under the school let a lot of gas build up before it exploded one afternoon, killing around 300 children and teachers.