In this sort of context you can only delete elements which are identical in both clauses.
Your two clauses are
I have OSHA
I am certified ...
You may therefore delete the second I, but must retain the verb am:
I have OSHA and am certified ...
If your two clauses are
I have OSHA
I have a certificate ...
you may delete the second I have:
I have OSHA and a certificate ...
Note, however, that this is true only if the two haves are identical in sense and syntactical role. If your two clauses are
I have OSHA
I have earned a certificate ...
the second have cannot be deleted, because in the first clause have is a lexical verb and in the second have is an auxiliary:
I have OSHA and have earned a certificate ...