Immunity from prosecution may be granted at the grand jury stage, CPL 190.45, as well as elsewhere in a criminal proceeding, typically at trial. Immunity is covered by article 50 of the Criminal Procedure Law and in article 190, regarding grand jury proceedings.
A louver (American English) or louvre (British English) is a window blind or shutter with horizontal slats that are angled to admit light and air, but to keep out rain and direct sunshine. The angle of the slats may be adjustable, usually in blinds and windows, or fixed.
If you are going to do anything, install a fan at one end of the building and a gravity backdraft louver at the other end. This way, if you ever want to close your shop doors and just exhaust the shop, it will work properly. If you have the shop door open, the louver does nothing.