The village of Nanjiawan, in south-west China is known as the Invisible Fire Village. The air over there is so thick with methane gas that a single spark can ignite a huge fire. Villagers have learned to live with and even make use of the methane, but they are also very cautious when working, so not to start fires accidentally.
The methane in the village air actually comes from the ground – it seeps out of the soil, causing the air to randomly burst into balls of fire. The concentration of the gas is so high that no one in the village can ever strike a match, light a cigarette or use any electrical equipment. They need to be careful while working in the fields as well, because their metal tools could create sparks if struck against a rock.