In pure oxygen, things which are normally not flammable, such as iron or steel, can become very flammable.
In the following demonstration, a piece of steel wool is heated in a Bunsen burner flame, and then thrust into a jar containing pure oxygen. The iron glows with a bright yellow-orange color as it becomes hot enough to melt slightly, and throws off a shower of sparks. The slight "tick" sound heard during the demo is the sound of the glass jar breaking from the intense heat of the reaction. (The procedure is shown at three different levels of magnification.)
Video Clip: REAL, 4.81 MB
!!! Hazards !!!
The steel wool does throw off sparks when it is heated; make sure there is nothing flammable nearby.
Use tongs to place the steel wool in the oxygen jar.
John Emsley, The Elements, 3rd ed. Oxford, Clarendon Press, 1998, p. 148-149.
David L. Heiserman, Exploring Chemical Elements and their Compounds. New York: TAB Books, 1992, p. 32-36.