Exploding Garbage Can

Required Training	Required PPE
UC Lab Safety Fundamentals Online Cryogen Safety at UC Davis	Lab coat, safety glasses/goggles, hearing protection, face shield, nitrile gloves, cryogen gloves
Performers Required: 2
Equipment	Chemicals
20 Gallon Trash Can	Liquid nitrogen (LN2)
Electric Kettle + Extension cord
200+ Plastic Balls (Pit or ping pong)
1 Liter or 600 mL thick walled bottle

Procedure:

1.) Place the garbage can away 10 feet from the audience, other performers, or anything fragile. Fill the garbage can with warm to boiling water until the bottom is covered (typically 2.5 L). To protect the can, a small bucket can be placed inside (this also helps bring up the water level).

2.) Fill the 1 L bottle ⅓ with liquid nitrogen. Ensure all volunteers are wearing hearing protection and that the audience has been warned to cover their ears before proceeding. The person who is handling the bottle should be wearing a face shield.

3.) Very quickly and tightly screw on the cap, then drop the bottle into the garbage can. Immediately after the bottle is dropped in, the other volunteer should quickly pour in the plastic balls. Give the can 10 feet of clearance and wait approx. 20-30 seconds for the explosion. The balls should be launched no greater than 20 feet in the air.

Clean-up: Find and pick up all plastic balls. If they are dirty, soak in water and lay out to dry. If they are damaged recycle them. Check the can for any cracks and recycle what remains of the 1 L bottle.

Hazards: The greater threat is the bottle exploding when the performer is trying to screw on the cap. Only experienced, confident volunteers should perform this duty. When the liquid nitrogen erupts from the bottle, it's possible that shards of soft plastic might be found. These should pose no threats as sharps, but precaution should be taken. The balls thrown into the air are lightweight and without force, but should still be avoided. In the event of a failed explosion allow the can to sit for 10 minutes then pour out the contents (away from any individual). Locate the bottle and puncture it with a long pole.

Principle: Liquid nitrogen rapidly turns from a liquid to a gas when exposed to room temperature conditions. When placed in a closed environment, like the capped bottle, gas pressure becomes very important because it is a consequence of molecules colliding with the walls of their container, thereby exerting a force on the container. The more pressure, the more force (P = F/A). The bottle erupts when the pressure in the vessel exceeds the maximum stress allowed. As the liquid nitrogen evaporates, more pressure builds up until the bottle explodes. The balls take that force and are launched into the air.

Notes: No more than a 1 L bottle should ever be used as the resulting explosion will launch the balls greater than 20 feet, hitting the ceiling (if inside of a lecture hall) and rupturing the garbage can. For the performer handling the bottle, initially screw on the cap only a little, still allowing positive pressure from the bottle. Position yourself, ensure your partner handling the balls is ready, then screw on the cap the rest of the way. This will help prevent incorrect placement of the cap.