Not so curious, really. Some history: pig manure smells so bad and neighbors (often recent arrivals after a developer builds houses not far down the road from a pig farm) complained so loudly that it became necessary to find something to reduce the odor. One solution that has gained traction since the 1980s was use of commercial preparations containing extract of Yucca schidigera. The inner juice of this desert plant (a cactus-like item that actually belongs to the lilly family) contains a group of compounds called saponins. Saponins produce such stable foams they are used in root beer for this very effect. An entirely unrelated property of (specifically) sarsaponin is its ability to inhibit the enzyme urease, which is secreted by microorganisms such as those in the digestive tract of pigs.

Urease normally converts urea (a nitrogen-containing component of manure and urine from the incomplete digestion of proteins) into ammonia, and ammonia is one of the most prevalent and offensive of all malodors among gases emanating from rotting manure. No urease activity, no ammonia, less obnoxious smell. A second reason these products control manure pit odors is that the foam they produce entraps some of the gases that would otherwise be released into the atmosphere, thus reducing the olfactory offense to pigfarm neighbors.

There are two US manufacturers - which for general reasons will not be named here, but a quick search of terms on the internet will easily identify them - of products that use Yucca schidigera extract to control livestock waste odors. And they have made a lot of money over the years selling their products to Midwestern pigfarmers. But now we have these exploding pigpens...

The relationship between exploding pig manure and the products used to reduce its odor, is that the foams referred to in the article actually result from the buidup of sarsaponin in the manure pits over time. There was no problem for years when the products were first used because the residual foaming compound was low. But now there is enough saponin buidup in these pits to form a VERY persistent foam. So persistent that much of the methane (and secondarily hydrogen sulfide) from the rotting pig manure is trapped in the foam, forming an explosive atmosphere beneath the pits.

All it takes to ignite the explosion is a spark, say from a lightswitch being thrown inside the barn, and the result is...well, if you got this far you probably read the article above as well, and now you know the rest. While this information is not widely known, that's how it really is, folks.