How do I determine the additions and deletions from Safari MARC Records update file?

To see if a record is an addition or deletion, check in the LDR field, the 5th bit triggers an add or delete (the count starts at 0).

For example:
=LDR 01158nam 2200313Ia 4500
05 - Record status
a - Increase in encoding level
c - Corrected or revised
d - Deleted
n - New
p - Increase in encoding level from pre-publication

You can load the Safari MARC record file you have into your loader program which will identify the record either as an addition or deletion.

Learn more information about indicators definition.