Powered Air-Purifying Respirator (PAPR) uses a blower to force the ambient atmosphere through air-purifying cartridges into a respirator (either hood or full-face piece).
The PAPR motor-blower draws surrounding air through the filters which capture the contaminant. Air pressure in the face piece/hood is higher than the surrounding air which is referred to as a positive pressure. This means that if a leak occurs, air will flow from inside the face piece/hood to the outside air.
PAPRS protect the user, as the battery pack and motor blower unit are fully operational. However, if the battery pack fails or the unit becomes inoperable, this respirator becomes negative-pressure. You must leave the area when the PAPR fails.