How many hours ahead you order is set by the supplier's lead time; the aim is for delivery to land as close to loading as possible. Dry ice turns straight into gas at -78.5 °C, so it cannot be stocked and loses mass every hour it waits. The plan is therefore built backwards from the loading hour.
| Waiting condition | Loss per hour | Over 12 hours |
|---|---|---|
| Paper-wrapped 0.5-2.3 kg blocks, 22 °C | 14% | Gone in about 7 hours |
| 2.3 kg of pellets in a 38 mm foam box, 22-29 °C | 2% | About a quarter lost |
| Single 45 kg block | 1% | About 12% lost |
The 2% is the FAA's own 2006 measurement; the 14% and 1% are quoted in that report from earlier studies, from 1977 and 1963. Even across identical foam boxes the loss ranged from 1.6% to 2.9% an hour; it depends on piece size, container and surroundings. Weighing at delivery and again at loading on the first few orders, and noting the hours in between, gives the business its own rate.
The loss goes into the order
If the load needs 20 kg of dry ice and it will wait 10 hours in a foam box between delivery and loading, 2% an hour takes a fifth of it, so the order becomes 25 kg. If the supplier's route time does not match your loading hour, the wait goes into a container with thicker walls, because thicker walls cut the hourly loss. How many kilos a load needs is worked out in a separate article.
Waiting dry ice sits in a ventilated area, in a container that is not airtight; a cold room or a closed vehicle lets carbon dioxide build up. Because dry ice depends on the CO2 supply, a second supplier is written into the plan too.
