Back in the early 90's in a sandy place we carried a chemical agent monitor, similar to the type used at airports these days. It sniffed the air and gave warnings when it detected dangerous levels of various "agents".
Being roughy toughy mil types we tested any number of "gasses" and you would be amazed how often we were in mortal danger! Especial after a curry night.
Surprisingly we all lived to tell the tale.