Well why can't you just talk to him for the sake of talking .. I'm sure if you say hi or something during lunch he won't be like omg he totally wants to get in my pants??
just treat it like any other person who you'd want to get to know, (to an extent..). like the above person said, even if he's not into you it's not as if he'd straight away assume that you fancy him just because you're talking to him.