Isolation Levels

Running IDS 7.30 UC7-1 for Linux. I noticed whilst trawling the iiug archives two environment variables for setting default isolation levels for ACE & PERFORM, SACEISOL & SPERISOL respectively. I was wondering if there is a similar variable for setting a general isolation level? If not, what is the scope of a 'SET ISOLATION' command? If I am running a simple isql script or series of scripts through a shell programme do I have to set the isolation level in each script? Thanks in advance, Daryl.