From Boot by Daniel Da Cruz:

The next day brings classes on weapons that may decide future wars - NBC (Nuclear, Biological and Chemical). These horrors are not always or totally without a defense, however. Heat, blast and radiation effects of atomic explosives are, to be sure, deadly except for those very distant. Biological agents-viruses, bacteria and toxins-are slower and more insidious, but quite as lethal. But against chemical attack - nerve, blood, blister and choking agents - there is some chance of survival, if immediate measures are used. Men trained in NBC techniques will, ironically, be better equipped to survive future wars than the civilian populations whom they are fighting to protect.

NBC instruction ends as do many protest demonstrations in a cloud of CS riot gas. Recruits are led into the gas chamber and don their masks. They make sure their masks are tight and the airways clear. The integrity of the mask is tested when the instructor pulls the ring on a canister of CS, filling the room with almost impenetrable fumes. Recruits are then ordered to remove their masks. They are made to stand fast for fifteen seconds, choking and weeping and itching, before being given the signal to grope their way to the hatch.

"That was the longest fifteen seconds of my life," gasps Recruit Garcia as he stumbles out the hatch into the sunlight, his face streaming tears, his eyes red and puffy, his skin blotched from the stinging gas.

*****

Effective observation often depends on good night vision. After one minute of darkness, the eyes' sensitivity to light increases 10 times; after 20 minutes 6,000 times, and after 40 minutes it achieves the maximum sensitivity, 25,000 times. Human eyesight is so sensitive that it is possible, from a mountaintop at night, to detect the flare of a match 50 miles away. On the other hand, if that match is used to light a cigarette, the smoker's night vision is cut by 50 percent after just a few puffs.