Beneath abandoned mines, coal smolders in silence—and the water meant to stop it may, under certain conditions, be feeding the fire. A new study published in Nature reveals that moisture does not suppress coal oxidation in a simple, linear way: at a precise threshold of 6.15%, water paradoxically maximizes the coal's chemical reactivity, lowering the energy barrier to combustion rather than raising it. Only when saturation exceeds 12.7% does moisture begin to reliably suppress the slow oxidation that precedes spontaneous ignition. The finding reframes a long-held assumption in mine safety, sug