Dry ice is frozen carbon dioxide. When the carbon dioxide ice thaws, it expands dramatically into its gaseous state. When the force of the gases exceeds the plastic water bottle’s ability to contain it, the bottle “explodes” with a big bang, which is not too terribly dangerous.
Now if they were wrapped with nails it might work at very close range.
Thanks. That was a very good explanation.
MRE “bombs” were a lot of fun and not terribly dangerous, too. We’d stuff a MRE heater into a plastic water bottle, seal it up, and then move back until the bottle exploded from the pressure buildup. They were amazing loud but not very destructive.
At least one group of guys tried a much larger MRE “bomb” using a 5 gallon water jug and a substantial quantity of heaters. That one was a real bruiser—a real base wake up call. Soon after, a general order banned the practice.
The MRE heater “bombs” were great fun on those long, boring deployments to the desert—a decade or more of US military “blood and treasure” wasted on Saddam, interrupted briefly only when President Clinton wanted to wag the dog.