(Everett Kennedy Brown/European Pressphoto Agency)

On July 5, an awful smell wafted into the town of Throop, N.Y. Throop is a small village tucked amid the Finger Lakes, a half-hour drive west of Syracuse. In the month leading up to the fumes, the U.S. temperatures had cranked up to record highs, data from the National Oceanic Atmospheric Administration show. Throop was not exempt from the summer swelter. Nor did the heat wave stop, continuing to sap the town dry in July.

Finger Lakes farmers bemoaned the lack of moisture. “We are just beginning July now, and what is August going to be like? This is nuts,” Jarret Winum, who runs a farm in nearby Stanley, N.Y., with his wife, told the Daily Messenger in early July. “We need rain.”

What came instead was the stench.

Concerned, residents of Throop called New York’s Department of Environmental Conservation. The department traced the stinking and smoking source, per the DEC’s Wednesday statement, to a “burning pile of horse manure” outside an unnamed Throop stable.

The poop had spontaneously combusted.

Broadly speaking, fire needs only three ingredients: heat, oxygen and fuel. If the conditions are right, a spark is optional. The process of spontaneous combustion hinges on what some scientists call auto- or runaway ignition. Once temperatures within a heap of organic matter — energy-rich fuel — hit about 300 to 400 degrees Fahrenheit, they can catch flame.

Microbes that break down organic matter and release heat can push up the temperatures within hay piles or compost heaps. But to get to runaway ignition temperatures, the heaps must no longer have a moisture buffer.

“An analogy is potatoes in a pot of boiling water that only start to burn after the water has boiled off,” as scientists wrote in the journal Compost Science & Utilization in 2002. Spontaneous combustion has engulfed hay, yard trimmings, coal seams, landfills and tire piles. (Human spontaneous combustion — which the BBC reported was ruled to be the cause of death of a 76-year-old man in 2010 — is a far more dubious prospect. Although our bodies can burn within incinerators and other superhot fires, humans are majority water by weight. At the time of the British combustion, pathologist Mike Green told the BBC the fire was probably started by a match or cigarette. Internal organs do not skyrocket to 300 degrees without a cause. “There is a source of ignition somewhere,” he said, “but because the body is so badly destroyed the source can’t be found.”)

In Throop, the piles of horse manure blazed. Horse manure, especially when sawdust or hay gets mixed in, is an energy-rich fuel, on par with wood chips for carbon and oxygen content. It’s “well suited for combustion,” as Swedish researchers put it while evaluating the stuff for a possible source of heating in a 2009 paper. (It would not be the first fecal fire fodder. Yak dung, as used in Tibet, has been criticized as a global warming pollutant.)

The owners of the stables told Don Damrath, an officer for the New York DEC, that the poop heaps “ignite frequently.” Usually, the wind blows the smoke and smell away from the area population.

It was different this month. “This time, the winds were carrying the smoke into neighbors’ windows, and the flames spread dangerously close to a valley full of dry vegetation and dead trees,” according to the DEC’s statement. For two hours, local firefighters from three different departments battled the flames before the fire was put out.

The DEC said it advised the stable owners to solve the combustion problem “immediately.”