Plants use light energy to photosynthesize carbohydrate from carbon dioxide and water which generates oxygen as a waste product. During night plants breathe out some carbon dioxide. Carbon dioxide is heavier than air, about 1.67 times. Carbon dioxide turns to solid below −78.5 °C at 1 atm, and in this state it is called dry ice. At −56.6 °C and pressure above 5.1 atm carbon dioxide turns to liquid.

There are various uses of carbon dioxide in food, oil, chemical industry, medical field etc. In food industry carbon dioxide is used as an acidity regulator, propellant, in carbonated beverages, wine making etc.  In medical field carbon dioxide is used for respiratory therapy and pulmonary function testing.

Carbon dioxide is a non-flammable, nontoxic gas classified as Class 2.2 in transport regulations. Higher concentration of carbon dioxide in shipping containers and ship’s cargo hold lead to oxygen depleted atmosphere

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Transport regulations list carbon dioxide as below

1. UN 1013, CARBON DIOXIDE, Class 2.2
2. UN 1845, CARBON DIOXIDE, SOLID (DRY ICE), Class 2.2
3. UN 2187, CARBON DIOXIDE, REFRIGERATED LIQUID, Class 2.2

UN 1013 can be stowed on or under deck on a cargo ship however UN 1845 & UN 2187 is authorized for on deck stowage only.