When the contaminant is not known or if the oxygen content in the air is too low, compressed air is the alternative that provides the right protection. The air is taken from a compressor and must be cleaned via a compressed air filter. A feeder hose between the filter and the user is needed and it must be CE-certified together with the compressed air fed respiratory protection device. With this respiratory protection device you don't have to think about changing any filter. Simple and safe.