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PAPR (Powered Air-Purifying Respirator) is not necessarily negative pressure. It can be designed as either positive pressure or negative pressure. These two modes have significant differences in working principle, protection level, and applicable scenarios:
Positive pressure PAPR: Provides higher protection
By continuously supplying air to the mask through an electric fan at a pressure higher than the external environment, the mask maintains positive pressure inside.
Due to the higher internal pressure than the external environment, even if there is a slight leakage in the mask, air will flow outwards, effectively preventing external contaminants from entering, thus having a higher protection level.
Protection Factor (APF): For example, the APF of a full face mask of positive pressure PAPR can reach 1000, while that of a half mask is 50.
Notes: At extremely high breathing rates, if the instantaneous inhalation volume exceeds the supply capacity of the fan, a brief negative pressure may still form inside the mask.
Negative pressure PAPR: Focuses on assisting breathing
It relies on the expansion of the lungs during inhalation to generate negative pressure, thereby drawing in external air through the fan and filter into the mask.
Main functions: More focused on assisting breathing, that is, by the fan helping to overcome the resistance of the filter, reducing the breathing burden of the user. Its air supply volume is lower than that of positive pressure type.
Protection Factor (APF): Due to the negative pressure environment, any leakage may cause external contaminated air to be sucked in, and its protection level is relatively lower. For example, the APF of a full face mask of negative pressure PAPR is 100, and that of a half mask is 10.
Standard marking: According to the national standard GB30864-2014, positive pressure and negative pressure PAPR have different markings. For example, the positive pressure type of a close-fitting half mask is PHF, and the negative pressure type is NHF.
