So I get a great email today from Les.
Question:
I know how much you like science and I am a little confused about shipping the vaccine. When I was in shipping we used dry ice from time to time. Dry ice is not a hazardous chemical but the weight has to be declared because the packaging has to be able to vent (releasing CO2). DOT and FAA only allow a limited amount per flight spaced out. From what I’ve seen on the news something just doesn’t add up. Am I missing something?
Answer:
It is a great question! And while I can’t speak to the rules and regulations, I can do some back-of-the-napkin math…
Just for fun, let’s see if we can work out the numbers. It is a good question. I, too, have been curious how all of this is being transported.
As the Dry Ice turns to gas and warms up, it will take up more space. One pound brick of dry ice produces about 8 cubic feet of CO2 gas. So for every little brick you put in a case, that case needs to be – at least – 2ft by 2ft by 2ft (8 cu ft) to hold the gas that the Dry Ice will evaporate into. But as it warms, it will take up more space. If you run the quick back-of-the-napkin calculation, you find that as it warms it will take up an extra cubic foot every 20C it warms.
Dry Ice forms at about -110C, the vaccine needs to stay at -70C so we have 40C of wiggle room. That makes for easy math. Thank goodness.
So, according to our calculation we need two extra cubic feet to account for the warming from -110C to -70C before the dry ice needs to be replaced. And Dry Ice – even in a cooler – melts at 1 pound every five hours.
So the container would need to be 10 cubic feet to hold a 1 pound brick of Dry Ice. That means a container that is 2.2ft by 2.2ft by 2.2ft would be sufficient to hold all of the Dry Ice gas and account for the warming and expanding.
And the container would not “need” to be vented. Now, I know FAA rules say venting is necessary, but the chemistry, in this particular case, shows it wouldn’t be needed if things were planned properly.
Most of the stories I’ve seen, it shows the vials being transported in a medium-sized Styrofoam cooler. About 2.2ft by 2.2ft by 2.2ft in size. So perhaps, in this particular case, they are making an exception. Perhaps?
But again, I can’t answer the specifics. All I can do is the math.
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