Is it likely that a first aid provider will cause further injury to a casualty?

It is absolutely possible for a first aid provider to cause further injury to a casualty. For this reason, it is recommended that one only provide care that they are comfortable giving. For example, someone trained in basic first aid should never attempt to give an emergency tracheotomy in order to provide an airway. However, under normal situations, it is not uncommon for procedures such as CPR to dislocate or break ribs, even if done properly.