Damp in the word firedamp has nothing to do with moisture, as we ordinarily associate it, but rather with deadening, or choking, or stifling.
In fact the earliest meaning of damp when it mysteriously appeared in the language in 1480 was as a kind of noxious gas exhaled by a goat.
“After this dragon,” wrote Caxton in The Cronicals of Englond, “shal come a goot and ther shal come oute of his nostrel a domp that shal betoken honger and grete deth of peple.”
So firedamp, then, is in itself a choking gas, often encountered in coal mines, that may become violently explosive upon contact with a flame.
