Natural gas can be dangerous if it leaks, which is why companies add an ingredient to make detecting natural gas easier just by smelling the air. If you smell natural gas, get out of the building as fast as possible and call the authorities.
In one home, the owners smelled natural gas and assumed a leak. They called the authorities after evacuating the house, only for firefighters to discover that there was no leak after all. Apparently the cat had jumped on the stove and turned one of the burners on without the gas igniting. After verifying that no leak was responsible, the owners and their cat were able to go back inside safely.