Carbon Dioxide


Chemical Symbol:   CO2
DOT Proper Shipping Name:               

Carbon Dioxide, Carbon Dioxide, Refrigerated Liquid Carbon Dioxide, Solid or Dry Ice

TC Shipping Name:

Carbon Dioxide / Carbon Dioxide, Refrigerated Liquid  Carbon Dioxide, Solid or Dry Ice

UN Number:    UN 1013 (for compressed gas)


  U.S. Units      SI Units      
Chemical formula:  CO2 CO2
Molecular weight  44.01 44.01
Vapor pressure at 70oF (21.1oC)                  838 psig 5778 kPa
Specific gravity of the gas 1.38 1.38
at 70oF (21.1oC) and at 1 atm 1.522 1.522
at 70oF (21.1oC) and at 1 atm -188.1oF -122.3oC



Carbon dioxide is a compound of carbon and oxygen in proportions by weight of about 27:3. A gas at atmospheric temperatures and pressures; carbon dioxide is colourless, odourless, and acid gas. It is considered by some people to have a slightly pungent odour and biting taste.


Carbon dioxide gas is relatively non-reactive and non-toxic. It will not burn and it will not support combustion or life. Carbon dioxide may exist simultaneously at its triple point as a solid, liquid and gas at a temperature at -69.9°F (-56.6°C) and a pressure of 60.4 psig (416 kPa). At temperatures and pressures below the triple point, carbon dioxide may be either a solid (dry ice) or a gas, depending upon temperature conditions. Solid carbon dioxide at a temperature of -109.3°F (-78.5°C) and 1 atmosphere, transforms directly to a gas (sublimes without passing through the liquid phase). Lower temperatures will result if solid carbon dioxide sublimes at pressures less than 1 atmosphere. Thermodynamic properties of saturated carbon dioxide in the solid, liquid, and vapour phases are given in table 1A and IB.


At temperatures and pressures above the triple point and below 87.9°F (31.1°C), carbon dioxide liquid or gas may exist in equilibrium in a closed container. Within this temperature range, the vapour pressure in a closed container holding carbon dioxide liquid or gas in equilibrium bears a definite relationship to the temperature. Above the critical temperature, which Is 87.9°F (31.1°C), carbon dioxide cannot exist as a liquid regardless of the pressure.





Solid carbon dioxide is used quite extensively to refrigerate dairy products, meat products, frozen foods, and other perishable foods while in transit. It is also used as a cooling agent in many industrial processes, such as grinding heat-sensitive materials, rubber tumbling, cold-treating metals, shrink fitting of machinery parts, vacuum cold traps, and so on. Gaseous carbon dioxide is used to carbonate soft drinks, for pH control in water treatment, in chemical processing, as a food preservative, as an inert blanket in chemical and food processing and metal welding as a growth stimulant for plant life, for hardening moulds and cores in foundries, and in pneumatic devices. Liquid carbon dioxide is used as an expendable refrigerant for freezing and chilling food products; for low-temperature testing of aviation, missile, and electronic components; for stimulation of oil and gas wells; for rubber tumbling; and for controlling chemical reactions. Liquid carbon dioxide is also used as a fire extinguishing agent in portable and built-in fire extinguishing systems.





Carbon dioxide is normally present in the atmosphere at about 0.035% by volume. It is also a normal and end product of human and animal metabolism. The exhaled breath contains up to 5.6% carbon dioxide. The greatest physiological effect of carbon dioxide is to stimulate the respiratory center, thereby controlling the volume and rate of respiration. It is able to cause dilation and construction of blood vessels and is a vital constriction of blood vessels and is a vital constituent of the acid-base mechanism that controls the pH of the blood. Carbon dioxide acts as a stimulant and a depressant on the central nervous system, Increases in heart rate and blood pressure have been noted as a concentration of 7.6% , and dyspnea, headache, dizziness, and sweating occur if exposure at that level is prolonged. At concentrations of 10% and above, unconsciousness can result in 1 minute or less. Impairment in performance has been noted during prolonged exposure to concentrations of 3% carbon dioxide even when the oxygen concentration was 21% . Inhalation of gaseous carbon dioxide can adversely affect body function. Skin, eye, or mouth contact with dry ice or compressed carbon dioxide can cause freeze burns or tissue damage.





Gaseous carbon dioxide is an asphyxiant. Concentrations of 10% or more can produce unconsciousness or death. Lower concentration may cause headache, sweating, rapid breathing, increased heartbeat, shortness of breath, dizziness, mental depression, visual disturbances, and shaking.





Dry carbon dioxide liquid and gas is compatible with most metallic piping materials. The primary hazards are elevated pressure and the loss of piping ductility at low temperature. Low pressure liquid carbon dioxide is typically stored at temperature ranging form 0°F to -20°F (- 1 7.8°C to -28,9°C). Rapid depressurisation will cause the liquid to auto refrigerate.


Piping materials acceptable for insulated bulk liquid service include:


1. carbon steel schedule 80 threaded forged steel fitting rated at a minimum of 2,000.

2. carbon steel schedule 40 butt or socket weld forged steel fitting rated at a minimum of 2,000.

3. stainless steel schedule 40 threaded

4. copper tube type K silver brazed with wrought fittings.





Carbon dioxide is contained, shipped, and stored in either liquefied or solid form. Additional information regarding the safe storage, handling, and use of carbon dioxide can be found in CGA G-6 Carbon Dioxide [6]. Applications using gaseous carbon dioxide are supplied by gas converted from liquid or solid carbon dioxide. Carbon dioxide is one and a one-half times heavier than air and tends to accumulate in low or confined areas. Positive ventilation may be required with the gas being exhausted near floor level where the carbon dioxide concentrates. Appropriate warning signs should be affixed outside those areas where high concentrations of carbon dioxide gas may accumulate. Suggested wording for such a sign is:





Ventilate before entering. When entering low and confined areas where a high concentration of carbon dioxide gas may be present, use a self-contained breathing apparatus (SCBA) or supplied-air respirator. Do not use a cartridge-type respirator.





Liquefied carbon dioxide is stored at ambient temperatures in high pressure uninsulated and non-refrigerated cylinders manufactured from steel or aluminium. Caution must be taken that cylinders and high pressure tubes charged with liquid carbon dioxide not be allowed to exceed a temperature of 125°F. Cylinders should never be stored near furnaces, radiators or other sources of heat. Storage areas should be designed to prevent heavy objects from accidentally shearing piping, valve, or pressure relief devices. Cylinders should be properly secured using safety chains, nesting, or other protective devices to prevent them from over-turning.


Cylinders are filled by weight either by pressure or by using a pump.


Larger users of liquid carbon dioxide typically use insulated bulk containers. These range in capacity from 400-lb vacuum-insulated non-refrigerated containers to 100-ton (90,718-kg) urethane-insulated, mechanically refrigerated fixed storage units.


The bulk storage container should be located in an area that is not subject to unusually high temperatures. If the ambient is above 110°F (43.3°C) for long periods of time, it may be necessary to provide additional refrigeration capacity. Ambient temperatures below 0°F (-17.8°C) for prolonged periods may cause the container pressure to decrease and require the use of a pressure building vaporiser.


Dusty, oily locations should be avoided because of the tendency of dust and oil to collect on the refrigerator condenser and thus reduce its efficiency. A dry, well-ventilated location is preferable.


All liquid carbon dioxide piping should be designed to compensate for shrinkage, which occurs at liquid temperatures. The discharge of liquid to the atmosphere will cause a significant thrust force that the piping must be able to safely withstand. A pressure relief valve must be placed between each positive shut-off point in the system to compensate for the rapid pressure increase caused by thermal expansion.


The rapid discharge of liquid carbon dioxide through a line that is not grounded will result in a build-up of static electricity, which may be dangerous to operating personnel. Such line should, therefore, be grounded before use.


Flexible loses used with low pressure liquid carbon dioxide should have a minimum working pressure at 500 psig (3450 kPa) and be design for low-temperature operation.





Solid carbon dioxide (dry ice) has a temperature of -109.3°F (-78.5°C) at 1 atmosphere and must be protected during storage with thermal insulation in order to minimise loss through sublimation. Dry ice should be stored in well-insulated storage containers, preferrably in a cool, non-confined, or ventilated area. Protection from airborne dust and insects should be provided since carbon dioxide vapours naturally attracts insects, which will suffocate and contaminate dry ice storage.


Care should be taken when handling dry ice. Use heavy gloves or ice tongs; do not handle dry ice with bare hands. Blocks of dry ice may weigh up to 50 lb (22.7kg) and can cause injury if dropped, See CGA G-6.9 for more information.


A suggested wording for a caution label for dry ice follows:






Avoid contact with skin and eyes; use gloves.

Do not taste.

Keep out of children’s reach.

Liberates gas that may cause asphyxiation.

Do not put in stoppered or closed containers.






Slowly vent the carbon dioxide to a well-ventilated outdoor location away from inhabited areas and building air intakes. Venting liquid is preferred to eliminate the foundation of dry ice inside the storage container or cylinder. The resulting cloud or cold gas may drift across highways, sidewalks and other public areas. Venting should be done on a clear day with the moderate winds if possible.





Vent slowly from the liquid phase of the cylinder to a well-ventilated outdoor location away from personnel for work areas. This typically requires inverting the cylinder. Venting vapour could self-refrigerate the cylinder to a hazardously low temperature, Return the emptied cylinders to the supplier with some residual pressure, with the cylinder valve tightly closed and with the valve protective cap(s) in place.





Ventilate adjacent enclosed area to prevent the formation of dangerous concentrations of carbon dioxide. Personnel, including rescue workers, should not enter area in which the carbon dioxide content exceeds about 3% by measurement unless wearing a SCBA or supplies air-respirators.


Avoid contact of the skin or eyes with solid carbon dioxide (dry ice) or objects cooled by solid carbon dioxide.





Skin Contact- In case of frostbite of contact with solid carbon dioxide (dry ice) or cold gases, place the frostbitten part in warm water. If warm water is not available or is impractical to use, wrap the affected part in blankets. Do not rub. Consult a physician.


Eye Contact- If the eyes are involved, obtain prompt medical attention. The only appropriate first aid measure is a soft sterile pad held in place over both eyes.








Portable Tanks


Liquefied carbon dioxide is also authorised for shipment In portable tanks conforming to specification DOT 51. The minimum design pressure is the same as for cargo tanks.


Cargo Tanks


Liquefied carbon dioxide is also authorised for shipment in cargo tanks complying with DOT specifications MC-330 and TC/MC-331. The minimum design pressure for these tanks must be 200 psig or, if built to requirements in “Low Temperature Operation” of the ASME Boiler and Pressure Vessel Code.




Large quantities of carbon dioxide for commercial use are primarily obtained from geological reserves or from by-product gas streams from one of the following processes:

1. Ammonia Production

2. Ethyl Alcohol Production

3. Hydrogen Production

4. Ethylene Oxide Production

5. Synthetic Natural Gas Production

6. Acid Neutralisation

7. Power Plant Combustion


Solid carbon dioxide or dry ice is typicality produced in three forms-block, pellets, or bulk “snow.” It is manufactured by decreasing the pressure of the liquid below its triple point, forming a mixture of dry ice (snow) and cold vapours. The solid may then be compressed into blocks or pellets. Dry ice blocks are generally available in 10-inch cubed while pellets are available in various sizes.