Special Incidents are incidents handled by the Chicago Fire Department that are emergencies other than fires. While a Still & Box Alarm might be used for an 'L' train derailment, a Water Rescue or a Collapse Rescue has its own assignment. Many of these assignment profiles include specialized units not ordinarily found at the scene of a fire; being part of a named preplanned response, they are not considered "Specials". However, as with fires, units not listed in the default responses below can be special-called to the incident scene, designated by their signature number (i.e., Unit 6-8-2 is one of the CFD's Air-Sea Rescue Helicopters). The additional vehicle(s) are referred to as "Specials", while the incident type is specified. Thus, if a Mobile Ventilation Unit (MVU) were called to a Building Collapse, it would be described as "Building Collapse response with one Special".