An unexploded chemical weapon... I wish it could be explained away with something like that. Considering our throughput, our hands are full with just the crater incident. Snowfield has a population of eighty thousand... We’ve made arrangements so that we can deal with matters even if all of them were to disappear... But, if possible, I’d like to avoid anything so troublesome.
Or so Faldeus thought, when he noticed that his hand was clenched tight on something. It was a balled up scrap of notepaper covered in fragmentary writing. When Faldeus carefully spread it out, he saw that it was a message clearly addressed to himself.
Do you not notice?
The barrier walls of this facility are thick.
Therefore, it does not enter here.

Fate/Strange Fake: Volume 3, Chapter 7 ("Day 1, Afternoon")