Production

• The raw carbon dioxide gas used to make dry ice is typically the byproduct from another chemical manufacturing plant. This carbon dioxide byproduct is sent from the source plant to the dry ice manufacturing plant via pipeline. Once the gas reaches the second plant, it is pumped through a series of filters to remove water vapor, volatile organic compounds (VOCs) and other impurities. The purified gas is then compressed to an extreme pressure and cooled with a freon-based refrigeration system. This combination of pressure and cooling causes the gas to condense into liquid CO2. Small amounts of liquid CO2 are then injected into a non-pressurized chamber, where the sudden decrease in pressure allows the liquid to rapidly evaporate. However, this evaporation causes the temperature to plumet. The combination of low pressure and dropping temperature causes the CO2 gas to deposit into fine, snow-like grains of solid CO2. Finally, a mechanical piston inside the chamber packs the CO2 snow into large pellets and blocks.
  
  

Applications

• Dry ice blocks are most commonly used for cooling, specifically as an alternative to electrical refrigeration systems. For example, to ship ice cream or biological specimens long distances, a freight company or courier may decide to pack them with several blocks of dry ice. Similarly, grocery stores and laboratories can use a few dozen pellets of dry ice for small-scale, temporary refrigeration projects.
  
  When placed in water, dry ice pellets create a constant stream of low-hanging fog. While the carbon dioxide that evolves from this fog is not toxic, it can become an asphyxiation risk in cramped, poorly ventilated spaces.
  
  On the industrial level, dry ice can be used as an alternative to sand- or water-blasting. Basically, small pellets of dry ice are fed into a stream of compressed air and shot out of a nozzle. The fast-moving, hard pellets break up unwanted residues and then completely sublimate into gaseous CO2.
  
  

Temperature

• Under standard temperature and pressure (STP) conditions, the surface temperature of sublimating dry ice is -78 degrees Celsius. As such, it is extremely dangerous to touch. Direct exposure to the skin, even for an instant, can cause severe frostbite.
  
  

Transporting

• When dry ice is used for shipping, the Department of Transportation (DOT) requires that both the shipping container and the cargo hull be well-ventilated. In addition to preventing accidental asphyxiation, ventilation allows the internal air pressure to equalize with the atmospheric pressure. Without this, the buildup of CO2 gas could lead to an explosion. Also, the container must have an official DOT "Carbon Dioxide" seal while in transit.
  
  

Dry Ice Bombs

• The sublimation of dry ice creates a large volume of CO2 gas. To make a "dry ice bomb," pranksters fill a screw-cap plastic container with about a pint of water, drop in a few dry ice pellets and screw the cap on tightly. A few seconds later, the pressure inside the container overpowers the plastic's shear strength, causing the container to explode. Illegal in California, Nebraska and municipalities throughout the country, dry ice bombs are notoriously loud, producing enough sonic energy to rupture ear drums within a certain range.