March 13, Wired – (Midwest) Mysterious hog farm explosions stump scientists.
A strange new growth has emerged from the manure pits of midwestern hog farms, and the results are literally explosive, Wired reported March 13. 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. There is nothing farmers can do except be very careful. Researchers are not even sure what the foam is. “This has all started in the last 4 or 5 years. We don’t have any idea where it came from or how it got started,” said an agricultural engineer of the University of Minnesota. The pits are emptied each fall, after which waste builds up again. Methane is a natural byproduct, and is typically dispersed by fans before it reaches explosive levels. However, inside the foam’s bubbles, methane reaches levels of 60 to 70 percent, or more than 4 times what is considered dangerous. The foam can reach depths of more than 4 feet. Disturb the bubbles and enormous quantities of methane are released in a very short time. Add a spark — from, say, a bit of routine metal repair, as happened in a September 2011 accident that killed 1,500 hogs and injured a worker — and the barn will blow. The foam can appear in one barn but not another on a farm where every barn is operated identically. Once the foam is established, it keeps coming back, regardless of cleaning and decontamination efforts. However, though it is now common in southern Minnesota and northern Iowa, and in adjacent parts of northwestern Illinois and southwestern Wisconsin, the foam does not seem to be spreading outside that area.
Source: http://www.wired.com/wiredscience/2012/03/hog-manure-foam/