why are the glass tube and rods always fire-polished after cutting?

Answer 1

I had a chemistry teacher who was a fanatic on that subject. First he explained that the edges were sharp (just as in the answer above). Then he did his "red circle oath." He promised that if he saw anyone making glass tubing apparatus without fire polishing the ends to make them safe he would prove the danger by twirling the edge of the glass in a circle on their palm. He convinced us all that fire polishing was mandatory and never had to do his "famous red circle" demonstration.

Answer 2

They are sharp and may contain some jagged edges. Fire-polishing helps melt out those hazards.