I don't think it will help the OP, but a good approach when visiting
anywhere new, including a music session you haven't previously visited,
is to watch first and gauge how other people behave before stepping in
yourself. (It's often said about fora such as this as well. I'm definitely
not trying to make a point there)

The problem with most of the sessions I have found in Ireland is that
most people are visitors, and probably visitors with less knowledge of
session etiquette than I have, so you can understand some breaches. I
have no doubt I'm going to the wrong ones and might benefit from advice
on finding more "authentic" sessions in Ireland.

Then again, it's not usual to lay down the rules explicitly. At best it
spoils the flow of the session and at worst it'll offend someone and
they'll never want to attend a session again.