|Dry Ice Ordnance|
Recycle plastic bottles. Make loud noises. Generate seismic anomolies.
WARNING: This is dangerous.
Do not try this.
This is an old trick.
The hot water causes the dry ice to turn into carbon dioxide gas. Gas pressure in the bottle increases as more and more gas is formed until the plastic meets its bursting pressure. Dry ice from industrial suppliers is almost 100% carbon dioxide and will give you a short fuse delay. Dry ice from catering or supplier can contain a a high percentage of water ice which can stretch the delay to a couple of hours in cold weather. Increasing the amount of dry ice used can shorten the delay a little bit but you get diminishing returns- twice as much ice will not cut the delay in half.
One interesting variation is the dry ice depth charge. Tie a rope around the neck of the bottle and attach it to a cinder block. Prepare the bottle as usual, and toss it into a body of water (like a pond) after tightening the cap. You will be able to feel the ground shake from the shock wave as the bottle bursts.