Mysterious hog farm explosions stump scientists
A strange new growth has emerged from the manure pits of midwestern hog farms. The results are literally explosive.
Since 2009, six farms have blown up after methane trapped in an unidentified, pit-topping foam caught a spark. In the afflicted region, the foam is found in roughly 1 in 4 hog farms.
http://www.wired.com/wiredscience/2012/03/hog-manure-foam/