Dry ice bomb

From Wikipedia, the free encyclopedia

This article or section does not cite its references or sources.
Please help improve this article by introducing appropriate citations. (help, get involved!) This article has been tagged since September 2006.

A Dry ice bomb is a simple bomb typically made from a plastic bottle, water and dry ice. They are normally used recreationally rather than as weapons.

1 Construction
2 Energy calculations
3 Common Uses
4 Dangers
5 Guidelines for Safety
6 Popular culture references
7 See also
8 External links

[edit] Construction

Generally either a 20oz or 2 litre soda bottle is used. A couple of dry ice cubes are added, then a variable amount of water is added to speed up the sublimation process, the cap screwed on tightly, and the area cleared. As the dry ice warms it sublimates to gas, causing the pressure inside the bottle to increase and eventually explode the bottle, typically after several minutes. Often, the bottle will grow noticeably larger due to the extreme internal pressure before bursting.

[edit] Energy calculations

The burst pressure of PET bottles vary, large bottles tend to have slightly lower burst pressures. A 2 litre bottle may burst anywhere from 140 - 180 psi. While in theory the amount of dry ice it takes to reach 180 psi in a two litre bottle is about 50g, or about 32cm^3, generally more would be used for safety, as it's dangerous for the bomb not to go off. The amount of energy released varies with altitude, size, burst pressure, volume of water used, and elasticity of the bottle. A two litre bottle will release between 9.2 and 15.2 kJ of energy at sea level, and slightly less at higher altitudes due to lower atmospheric pressure. This energy is sometime harnessed in simple homemade Dry Ice Cannons.

[edit] Common Uses

Given the modern availability of dry ice at super markets and grocery stores many different ways of harnessing the potential energy of dry ice have emerged. Burying 2 liters and 3 liters under a few feet of soil significantly reduces the noise produced by dry ice bombs, but results in a very visually spectacular explosion similar to those used by directors to produce the effects of mortars or mines in war movies. Luckily the generally benign nature of Dry Ice means that these effects are practically harmless. Also, sinking dry ice bombs in pools produces a similar effect with water.

[edit] Dangers

Dry ice bombs are safer than conventional explosives, but do have some serious risks:

Early detonation. If too much water is poured in, or the water is too warm, burst pressure can occur within seconds, injuring the handler.
The shock wave can be extremely loud. Permanent hearing damage can occur even at substantial distances.
Shrapnel poses a danger to anyone within 20 yards. The cap is particularly dangerous.
In some areas dry ice bombs are illegal but even elsewhere the noise generated may violate local laws.
Leaving an unexploded dry ice bomb can be construed as public endangerment.

Bombs which do not detonate are a major safety issue. They can't be left, yet can't be safely approached. The normal advice is to detonate them from a safe distance with a pellet or BB gun.

[edit] Guidelines for Safety

Although dry ice bombs can be dangerous, there are a number of preliminaries and precautions that one can make to be substantially safer while producing and detonating.

The location should be away from people and outside of a neighborhood where the noise may alarm the residents. A large empty parking lot or field at least a quarter mile away from residential areas is ideal.
Ear protection should be worn at all times by all people within a close proximity (50 yards) of the bomb unless the bomb is under at least three feet of water.
Using plastic bottles are much safer than glass. Though both plastic and glass bottles produce shrapnel, plastic bottles produce between 2-4 pieces that are much less dangerous due to their size and density.
It greatly helps to have a pellet or BB gun handy when making bombs, in the case that it doesn't go off on its own. A pellet or BB gun is one of the safest methods of neutralizing it.
One should always be aware of the direction the cap is pointing when the bomb is set as occasionally the cap may shoot straight out from the bottle at considerable speed, and can harm anyone directly within its path.
One should always wear gloves when preparing dry ice. This will greatly reduce the risk of burns from dry ice handling.

[edit] Popular culture references

A dry ice bomb featured on Mythbusters - episode 57 "Mentos and Soda", which was first aired on August 9th, 2006.
The book "One Day in the Life of a Fool" by Jeremy M Gates includes a story about a dry ice bomb which failed to explode as planned, and later exploded after someone took it indoors.