As is well known and understood, it is not unusual to find several crews of firemen from different fire companies at an emergency scene.  As is equally well known, it is not unusual, either, to find several crews utilizing different rigs of the same Fire Company at the emergency.  Even though someone is charged with the responsibility of separating "filled" and "emptied" pressurized air-pak bottles at the scene, experience has shown that "empties" do get mixed-in with "fresh" bottles, and the emergency firemen oftentimes have to search for pressurized bottles to be used as replacements.  Typically used procedures of dumping empties near a designated tree, and retrieving "fresh" bottles at the truck simply do not do the job of keeping them segregated.