I'm stunned that you and your friends were the only ones who took the stairs.

As others have suggested, you might consider keeping a few more items on your person, on a keychain or in a wallet. A bandana, whistle and flashlight would be a good place to start. You might not be near your desk if it happens again.
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"2+2=4 is not life, but the beginning of death." Dostoyevsky

Bona Na Croin