Dry ice turns straight into gas at -78.5 °C and leaves no liquid behind. One kilogram releases about half a cubic metre of CO2. The gas is colourless and odourless and about 1.5 times heavier than air; in the open it disperses, but in a closed load space, a cold room or a basement it collects at floor level and displaces oxygen.
| CO2 concentration | Meaning |
|---|---|
| 5000 ppm (0.5%) | 8-hour average limit (OSHA, NIOSH) |
| 30,000 ppm (3%) | 15-minute short-term limit (NIOSH) |
| 40,000 ppm (4%) | immediately dangerous to life or health (IDLH) |
So before working with dry ice in an enclosed space the air is ventilated and a CO2 meter and alarm are used. Carrying it in a load space that is not separated from the driver's cab is unsafe. Dry ice is never kept in a sealed container, because the subliming gas builds pressure; the packaging must let the gas escape.
If headache, dizziness or shortness of breath begins, or the alarm sounds, leave the area, keep others out and do not go in to rescue anyone; that is a job for the trained team. A -78 °C surface on bare skin causes cold burns, so dry ice is handled with insulated gloves.
