"AIM a. This document is to provide guidance on methods@ procedures@ and documentation for assessing the fit and protection levels of negative-pressure respirators used by NATO armed forces through various mechanisms@ thereby achieving common understanding between NATO armed forces whenever fit and protection factors are discussed. This will serve as an indicator on the protection afforded by a properly selected@ fit-tested@ and functioning respirator when properly worn and used in an environment where the oxygen content is not less than 20%. b. This document is prepared for negative-pressure respirators@ sometimes referred to as air purifying respirators (APR)@ but may apply to other types of respirators such as positive-pressure respirators@ including powered air-purifying respirators (PAPR)@ supplied-air respirators (SAR) and self-contained breathing apparatus (SCBA)@ or other types of respirators such as an ""escape hood"" with suitable modifications and adapters."