Dry ice is solid carbon dioxide (CO2), made by compressing and cooling gaseous CO2 until it liquefies. Expansion converts the liquid into the solid state which is compressed by a hydraulic press into dry ice blocks, slices or pellets.
Before handling and using dry ice it is important that you understand its properties, potential hazards and measures to be taken to reduce risk.
Two key precautions that must be followed by those using or handling dry ice are:
- Do not put dry ice in a gas tight container. Excess pressure build up can cause containers to explode!
- Do not store dry ice in cold rooms or any other unventilated room
The following represent generic safety measures to be applied for all workers involved in the handling, use, storage and transport of dry ice to minimise risk of harm. Further, more detailed consideration on suitable ventilation systems and possible need for dioxide monitors is required for activities involving the use / storage of large quantities of dry ice.
Many factors can affect the rate at which dry ice sublimes from the sold state into gaseous carbon dioxide. These include ambient temperature and humidity, the quality of the storage container, the number of times the container is opened and closed. The better the insulation, the slower the sublimation rate and the longer the quality of the product will be maintained.
Storage practices to be followed by all users of dry ice include:
Transport practices to be followed by all users of dry ice include:
|In general, oxygen deficiency leads to a loss of mental alertness and a distortion of judgement and performance. This happens within a relatively short time, without the person's knowledge and without prior warning.|
|21 - 14%||Increasing pulse rate, tiredness|
|14 - 11%||Physical movement and intellectual performance becomes difficult|
|11 - 8%||Possibility of headaches, dizziness and fainting after a fairly short period of time|
|8 - 6%||Fainting within a few minutes, resuscitation possible if carried out immediately|
|6 - 0%||Fainting almost immediate, death or severe brain damage|
|The UK has assigned an 'workplace exposure limit' of 5,000 ppm (0.5%) over 8 hours and 15,000 ppm (1.5%) for 10 minutes. Carbon dioxide vapour is not truly inert. It is mildly toxic.|
|1%||Slight, and un-noticeable, increase in breathing rate|
|2%||Breathing becomes deeper, rate increase to 50% above normal. Prolonged exposure (several hours) may cause headache and a feeling of exhaustion|
|3%||Breathing becomes laboured, rate increases to 100% normal. Hearing ability reduced, headache experienced with increase in blood pressure and pulse rate|
|4 - 5%||Symptoms as above, with signs of intoxication after 30 minute exposure and slight choking feeling|
|5 - 10%||Characteristic pungent smell noticeable. Breathing very laboured, leading to physical exhaustion. Headache, visual disturbance, ringing in the ears, confusion probably leading to loss of consciousness within minutes|
|10 - 100%||Loss of consciousness more rapid, with risk of death from respiratory failure. Hazard to life increased with concentration, even if no oxygen depletion. Concentrations of 20-30% and above are immediately hazardous to life.|
|The gasping reflex is triggered by excess carbon dioxide and not by shortage of oxygen.|
Using this calculation, if the oxygen concentration can fall to, or below, 18% then action needs taking to minimise risks. For this reason the use or storage of liquid nitrogen or solid carbon dioxide is prohibited in cold rooms.