Maintenance downtime and overheads for applying patches are major concerns for systems requiring round the clock availability. Hence, methods for carrying out dynamic updates are needed. However, correctness of the system during and after every dynamic update needs to be ensured. This paper defines two safety criteria, type consistency and isolation of process execution for dynamic software update. Updates involving one or more insertions of new classes, removals of old classes and replacements of old classes are considered. The condition for producing a type safe update schedule is defined. The parts of the program whose execu- tions have to be isolated from process update are annotated by the user. Conditions are also provided for ensuring isola- tion of the update process from execution of annotated parts of the program.