I went to walmart and found these self heating drinks/soups. All you have to do is twist a knob and wait a couple minutes and its ready. After looking online i wasn't able to get a straight answer. Is there a difference between the warming chemicals in the soups vs. hand warmers. I'm looking for information on what they use in those drinks, as well as other chemical reactions to release heat to heat something small like a drink. Are there more potent combinations that are still safe for people to use in things like the self heating drinks?