I volunteer @ my local Humane League. I think it's really great that your thinking of volunteering.
I have not heard or had anything happen like that to me or any other volunteer that I know of. I like Catholic said, take my shoes off in the garage before I come into the house. I also change my clothes and take a shower almost right away when I get home.
I really love volunteering there.
It makes me feel so good to know I'm doing something little to help. The shelter workers always are grateful for volunteers and any help they can give.