This property defines the internal security descriptor used to do access managment. The class must not be freed. 

If you intend to write or read from this class you need to do it thread safe since COM can access it from any thread.

...
  IA.CriticalSection.Enter;
  try
    access here IA.SecurityDescriptor
  finally
    IA.CriticalSection.Leave;
  end;

For more information on thread safety see property CriticalSection.

TJwServerAccessControl Properties