Answer:
The intent of the dye pack is to permanently stain the money taken in a bank robbery. This readily draws attention to it and identifies it as suspect. Hopefully the thief would drop the money, because of the stain, facilitating recovery by the bank. When a dye pack explodes, it is burning at 400 degrees so it is difficult to handle. The dye pack can stain the skin and clothing of the thief, but that isn't the primary intent. How long the stain remains on the skin would differ based on exposure.
First published on BankersOnline.com 9/17/07