DRY ICE/CARBON DIOXIDE CYLINDERS - Safe Use & Storage
1. Physical Properties and Handling
Gaseous state
At normal temperature (+15°C) and atmospheric pressure CO2 has a density of 1.87
kg/m3 and is 1.5 times heavier than air. It is a colourless and odourless gas (with a slightly
pungent odour at high concentrations) and spreads along the ground collecting in low-
lying areas such as pits and cellar.
Carbon dioxide is classified as a nontoxic gas but it does start to affect breathing at
concentrations of about 1%, with affects becoming more serious with increasing
concentrations.
Carbon dioxide is a non-flammable gas.
Liquid State
Carbon dioxide can exist as a liquid below the critical temperature of 31°C and above the
triple point with a temperature of -56.6°C and 4.18 bar gauge (bar).
CO2 is transported, stored and handled in liquid form, either at ambient temperature (in
cylinders or not insulated storage tanks at a pressure of 45 - 65 bar) or refrigerated (in
insulated tankers and storage tanks) at a temperature range of -35°C to 15°C and a
pressure of 12 to 25 bar. The CO2 in this state, is a liquid at its boiling point.
Below the triple point CO2 can only exist in the solid and gas phase. Therefore the liquid
CO2 cannot exist at atmospheric pressure. When the liquid CO2 is depressurised below
the triple point pressure of 4.18 bar to atmospheric pressure it is transformed to dry ice
and gas. Consequently when the liquid CO2 is released to the atmosphere a dense white
fog of powdery solid carbon dioxide particles and vapour is produced.
Solid state (Dry ice)
The expansion of liquid CO2 to atmospheric pressure is used to produce CO2 snow at a
temperature of -78.5°C. The snow is pressed to dry ice blocks or pellets.
Dry ice is handled in insulated containers.
Chemical Properties
Carbon dioxide does not support combustion. When dissolved in water, carbonic acid
(H2CO3) is formed. The pH - value of carbonic acid varies from 3.7 at atmospheric
pressure to 3.2 at 23.4 bar.
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