This
Good News article made me think of my varsity days in the chemistry lab doing practicals and seeing little smudges of colour appearing on blotting paper. All I remember is that it was a paper chromatography experiment and my partner seemed to know a lot more about it than I did.
But in this case it's the thread that changes colour after detecting certain dangerous gases in the air.
I can just imagine going off to work at the local chemical plant wearing a blue shirt and finding halfway through the morning that it's turning brown, or yellow. And if you're not sure whether you are imagining it, taking out a smartphone camera. Apparently it can tell you of even small amounts of harmful gases in the air. Isn't science amazing?
I wonder if embroidering a shirt or a badge with this type of thread would be sufficient to let you know that the air you were breathing was becoming hazardous.