Exploding Pig Farm Mystery

At first, the manure was just harmlessly foaming. Only later on did things get lethal. 
Hog farms in the Midwest are great big barns sitting on top of great big pits filled with a great deal of awful-smelling manure. The pigs walk about on a slatted floor that lets manure fall into the pit several feet below. Around 2007, farmers began noticing pig poop acting funny. The normally liquid mixture started producing foamy bubbles, rising up and up, past the slats, right to the pigs’ cloven hooves.
Then it got worse. Among the gases in the bubbling foam are two of special note: methane and hydrogen sulfide—both highly flammable. All it takes is a small spark and Kaboom! In September 2011, a barn explosion killed 1,500 pigs and seriously injured one worker. It was just the most serious in a string of barn explosions that have cost farmers millions of dollars in the past several years.
Scientists have scrambled to solve the mystery of the exploding hog-manure foam, but no straightforward answer as emerged so far.

 Source: Nautilus