First off, good for you for volunteering!
You ask a very good question!
The answer is yes, you can
transmit things to your own cats - bacteria, fungus, fleas. But please don't let that stop you from volunteering!
I work at a retirement home for cats on the weekends and we have been dealing with several cases of ringworm. So the precautions I take are as follows:
I have a separate set of shoes I only use for there (just an old set of tennies that I throw in the wash with bleach once a month).
I bring a change of clothes and change before going home (or if you have a garage that works well to change there). Then I throw my old clothes in a bag. When I get home I go STRAIGHT to the washer, throw my clothes in with some bleach for colors and then jump in the shower. My keeties get to see me after that.
Probably for you, just changing your clothes and shoes and washing your hands/arms/face really well before and after getting home would be fine. It's a bit of a pain, but I figure better safe than sorry!
Good luck and let us know how it works out!!