Back in the days when I served Uncle Sam in the U.S. Air Force (that was in the bad old days of the Cold War and the Soviet 'Evil Empire'), one of the first things we did in our inprocessing at the base I was stationed at in Europe was go to a mandatory NBC (nuclear, biological, chemical, not the TV network

) warfare briefing. We were told that the nearest Warsaw Pact air bases were only about fifteen minutes' flying time away and that any attack by them would assume to use chemical weapons, at the very least.
We were briefed on the effects of chemical weapons and learned the strange alphabet that identified the various deadly chemical concoctions... VX, GB, Tabun, Sarin, mustard gas, etc. and how to recognize the symptoms of a chemical attack. You gotta be very quick with that atropine injector... and you learned how to pack the gas mask for quick donning -- if it took you more than ten seconds to put it on, you're as good as dead. They didn't go too much into detail with biological agents.
After the briefing was the mandatory trip to the gas chamber, to experience the effects of CS riot control (tear) gas. Not a very pleasant experience with your eyes tearing, your nose running and hacking and puking your guts inside out. Once you get out of the chamber and into fresh air, the symptoms subside, though we were instructed to make sure we thoroughly washed our clothing afterward, since leftover particles of CS tend to be a little persistent.
Almost every month we practiced a chemical warfare exercise code-named 'Salty Nation'. It usually started in the wee hours of o-dark-thirty and lasted for 18-24 hours. Occasionally, the exercise would start with the playing of the 'William Tell Overture' (the Lone Ranger theme), which to this day I can't listen to without reminding me of these exercises. Luckily, when I reported in, the base had just ended a two-week long chem warfare exercise called 'Salty Demo'. Not fun.
To reinforce the fact that it was an exercise and not the real thing, the alarm signals were always prefixed with the word 'EXERCISE'; for example, the warning signal was called 'ALARM YELLOW'. The signal for an air raid in progress was 'EXERCISE ALARM RED'. (Don't ask me why, but it's called 'ALARM BLUE' in U.S. military bases in South Korea.) Whenever chemical agents were detected, 'ALARM BLACK' was issued. There was one time during an exercise that for some unknown reason the speaker cut off the word 'EXERCISE'; all we heard was 'ALARM RED'. You've never seen so many people grabbing for their gas masks so quickly.
The exercises were played in deadly seriousness and the chem suits were hot and downright uncomfortable when worn for long periods of time. Not to mention that the charcoal lining of the suit dirtied up your uniform. I was glad when the loudspeaker system on the base announced 'ALARM WHITE'; that was the all-clear signal and usually signaled the end of the exercise.