Moose is correct. It is used by the incident commander at an incident to maintain accountability of personnel on scene. Depending on the department and incident type they are usually conducted at specific times frames or when there is significant changes that happen, a collapse or as in going from and offensive mode(fighting the fire inside) to a defensive mode(evacuating the building and fighting it from the outside). Also depending on the department PAR can be done by the Incident commander, the Incident Safety Officer or dispatch. When a PAR is called it is the duty of the officer or senior member of the crew being called to check his personnel and to inform whoever is calling for PAR that they have PAR(all members of their crew accounted for) or that someone is missing or unaccounted for and where and what there last assignment was.