My town had a gas leak explosion in the 1990s. The gas leaked into the basement from a crack in an old line under the sidewalk. No one noticed the smell. When the furnace kicked on, a large 2 story story building was leveled and killed the occupants. It blew some of the windows out of my house. I was 9 houses away from the one that exploded.
Where I live to damage 39 house many square miles would have to be covered.
When natural gas migrates underground, the soil can strip the odorant out of it so there is no smell.