Food Preservation: What causes jars to break in a canner?

What causes jars to break in a canner?

Breakage can occur for several reasons:

Using commercial food jars rather than jars manufactured for home canning
Using jars that have hairline cracks
Putting jars directly on bottom of canner instead of on a rack
Putting hot food in cold jars
Putting jars of raw or unheated food directly into boiling water in the canner rather than into hot water (sudden change in temperature; too wide a margin between temperature of filled jars and water in canner before processing)