10% formalin is classified as "Aviation regulated liquid, n.o.s.," UN 3334. See the US Department of Transportation (DOT) letter of clarification for more information. DOT's definition of this classification is:
"This includes any material which is not covered by any of the other classes but which has an anesthetic, narcotic, noxious or other similar properties such that, in the event of spillage or leakage on an aircraft, extreme annoyance or discomfort could be caused to crew members so as to prevent the correct performance of assigned duties." (172.102©(2)(A35))
Only shipments "in commerce" require Department of Transportation (DOT) training. See the DOT interpretive letter to define in-commerce transportation.