GA/PA meaning in oil and gas

Relates to a system and term most commonly used in offshore installations. General Alarm is an audible claxon or horn set off either manually or automatically to alert/call personnel to muster. There then follows an initial PA by the on duty Operator advising personnel of an event and provides an initial level of instruction. This will be shortly followed by a more specific address from a member of the Installation Managemnt Response Team.