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7c. Dry Ice Bombs (Pyrotechnics)


This article is from the Pyrotechnics FAQ, by Hans Josef Wagemueller zoz@cs.adelaide.edu.au with numerous contributions by others.

7c. Dry Ice Bombs (Pyrotechnics)

Dry ice bombs are devices that use pressure to burst a container,
producing a loud report and limited shock effects. No chemical reaction
is involved - the container, usually a plastic 2-litre soft drink bottle,
is burst by the physical reaction of solid carbon dioxide, CO2, subliming
into gas. As the CO2 sublimes, the pressure builds up and eventually the
container ruptures.

The method is very simple - some dry ice is added to the container, some
water is added (about 1/3-1/4 full) and the cap is screwed on tight.
Within a short time the container will burst, usually extremely loudly.
The water can be omitted if a longer delay time is required. It is
reported that these devices can be manufactured using liquid nitrogen
instead of dry ice, and no water. This is not recommended as the delay
time will be substantially shorter.

Safety aspects:

Device: NEVER use glass or metal containers! I cannot stress this enough.
Dry ice bombs are extremely unpredictable as to when they will go
off, and a glass or metal container is very very dangerous to
both the constructor and anyone else in the vicinity. Plastic
bottles are much safer because the fragments slow down quicker,
and thus have a smaller danger radius around the device. Plastic
fragments are still very nasty though - don't treat the device
with any less caution just because it is made of plastic.

There is no way to tell how long you have until the dry ice bomb
explodes - it can be anywhere from a few seconds to half an hour.
Never add the water or screw the cap on the container until you
are at the site you want to use it and you are ready to get away.

Never go near a dry ice bomb after it has been capped. If a dry
ice bomb fails to go off, puncture it from long range with a
slingshot, BB gun, by throwing stones at it or similar. Some
indication of timing can be achieved by semi-crushing the
container before capping - once the container has expanded back
to its original shape it is no longer safe to be anywhere near.

Don't forget that the temperature of the day and the size of the
dry ice pieces will affect the delay length - don't assume that
delay times will be similar between bombs. A hotter day or
smaller pieces of dry ice (i.e. greater surface area) will create
a shorter delay. Remember, even though no chemical reaction
occurs you can still be legally charged with constructing a bomb.

Dry Ice: Humans will suffocate in an atmosphere with a carbon dioxide
concentration of 10% or more. Use in a well-ventilated area. Dry ice
typically has a temperature of about -75 degrees C, so do not
allow it to come into contact with the skin, as freezer burns
and frostbite will occur. Always use gloves or tongs when
handling dry ice.


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