There have been a number of accidents like this. Manure pits are deadly, but they're the de facto way of handling waste in large-scale confinement animal feeding operations, because it's much easier to shoot a high-pressure hose at 25,000 pounds of shit per day than it is to shovel it.
Really, there isn't a safe, sustainable, and cost-effective way to deal with that much manure that close together. Yet another reason why large-scale CAFOs are a Bad Idea.
Here's an article by a Midwestern ag economist about large-scale feeding operations that I recommend taking a look at if you're unaware of the issues involved. It starts off dispassionately enough, but by the end he's talking revolution. It's pretty hard to stay impartial and let-the-free-market-decide after hearing enough stories like this one. I come from several generations of Iowa livestock farmers; believe me, I don't have any qualms about raising animals for food, or about eating animal products in and of itself. But stories like this are the reason I quit buying meat and dairy that aren't sustainably produced.