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I found this pic here. Aren't these Koreans overkilling by wearing half face disposable respirators, inside their 3M powered air respirators? Isn't a 3M powered air respirator enough?

enter image description here

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Raymond J. Roberge (2008) discusses the rationale for concurrent use of N95 FFR masks and PAPR hoods. The primary benefit is to reduce the number of particles the wearer inhales, and secondarily to provide backup protection in the event of power loss in the PAPR.

PDF link: https://www.ajicjournal.org/article/S0196-6553(07)00594-9/pdf

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  • Your answer would be greatly improved by a supporting reference.
    – Carey Gregory
    Commented Apr 11, 2020 at 0:33
  • 1
    Thanks — I edited the answer and added support from published literature
    – goodside
    Commented Apr 11, 2020 at 0:59
  • It would be called "defense in depth" in other contexts. Commented Apr 21, 2020 at 21:40
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It's not clear that they are actually wearing a 3M powered air purifying respirator system as those have a valve and filter at the front of the mask.

Anyway, even if it is a 3M PAPR the data suggests you get a lot more protection

Objective: To determine if using an N95 filtering face-piece respirator concurrently with a loose-fitting powered air-purifying respirator (PAPR) offers additional protection to the wearer.

Methods: We used a breathing mannequin programmed to deliver minute volumes of 25 L/min and 40 L/min. We measured the baseline protection factor of the PAPR with its motor operational and then deactivated (to simulate mechanical or battery failure). We tested 3 replicates of 3 different N95 models. We glued each N95 to the breathing mannequin and obtained a minimum protection factor of 100 at 25 L/min. We then placed the PAPR on the mannequin and took protection factor measurements with the N95-plus-PAPR combination, at 25 L/min and 40 L/min, with the PAPR operational and then deactivated.

Results: The N95 significantly increased the PAPR's protection factor, even with the PAPR deactivated. The effect was multiplicative, not merely additive.

Conclusions: An N95 decreases the concentration of airborne particles inspired by the wearer of a PAPR.

https://pubmed.ncbi.nlm.nih.gov/19025703/

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Just to add a component not otherwise mentioned: The Powered Air Purifying Respirator (PAPR) only filters air coming into the PAPR, i.e., the wearer is protected at an N95 level assuming an N95 filter is being used.

However, the exhaled air of the wearer is not filtered. So if the PAPR wearer unknowingly has COVID, there is some small potential for contaminated air to be exhaled into the airspace, thus potentially infecting others (patients).

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  • Welcome to MedicalSciences.SE. We work differently to many SE sites, where we have a strict policy that all answers should be backed up with reliable references so that the answer can be independently verified, regardless of the reader's background. See this list of reliable sources. Unreferenced claims can be challenged and lead to deletion of your answer. Commented Dec 28, 2022 at 4:18

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