Incident response team members ideally are trained and prepared to fulfill the roles required by the specific situation (for example, to serve as incident commander in the event of a large-scale public emergency). As the size of an incident grows, and as more resources are drawn into the event, the command of the situation may shift through several phases. In a small-scale event, usually only a volunteer or ad hoc team may respond. In events, both large and small, both specific member and add hoc teams may work jointly in a unified command system. Individual team members can be trained in various aspects of the response, either be it medical assistance/first aid, hazardous material spills, hostage situations, information systems attacks or disaster relief. Ideally the team has already defined a protocol or set of actions to perform to mitigate the negative effects of the incident.