The victim was found behind a kosher food market in North Lawrence by municipal workers who stopped to turn around their salting truck.
Nassau Police Lt. Kevin Smith says it appeared the man tried to light some cooking-fuel cans at about 2 a.m. Wednesday.
At the same time, he apparently tried to clean himself with some body wash liquid that contained alcohol. Police believe the flames from the cooking cans ignited the body wash, leaving the man to suffer fatal burns.
A volunteer ambulance crew attempted to assist, but police said he had already died.
The man's identity was not immediately known.