When planting a large tree or a tree that is gonna grow into a large tree you should plant the tree 30 to 40 feet away from a natural gas line.
As the tree grows the roots will start to spread out and could work their way towards the gas line which can tear into the gas line and cause a gas leak.
For small shrubs and other small plants you can plant them 10 feet away from the gas line and be safe.
But for trees that grow larger eventually you should plant them at least 30 feet away from the gas line to be safe.
The further away from the gas line you plant the tree the better but between 25 feet to 30 feet is usually good enough.
You can ask your gas company as to their regulations and they will tell you the correct distance to plant the tree away from the gas line for safety.
My gas company wanted a tree planted 30 feet away from the gas line for safety.