It sounds like it's over and above your contract of work, however maybe don't worry too much or dismiss it yet.
The fire wardens at my work, all they have to do is check designated areas are empty should the fire alarm go - and they get to wear a very fetching yellow jacket, the sort you can buy in the poundshop.

Feather in your cap for your yearly appraisals (If you get them - you can say you have taken on this extra responsibility).
See what they say