Right, a reset in this discussion might be in order.
There are basically two types of respiratory protective equipment (RPE); those that rely on a close-fitting and effective face seal, and those that do not.
The ones that do not rely on a close-fitting face seal protect the wearer by means of powered air supply into the wearer's breathing zone; the idea is that the air is supplied at a rate that exceeds the demand of the wearer. Like the hoods that some wear. Like this:
The supplied air is delivered via a hose (by compressor) to the wearer, having been filtered on the way.
These hoods are more comfortable, are suitable for those who sport beards, or have skin complaints / scarring that precludes them wearing close-fitting face pieces.
They are however more impractical in many settings (you have to have a compressor and hose), are more expensive, and offer no protection in event of power failure.
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Respirators that rely on a close face seal can be powered as above (with the same advantages and disadvantages), supplied with air from tanks (like firefighters' BA equipment (good, but heavy, expensive, and only good for a limited period of time), powered with battery-packed motors, or be unpowered.
Those with battery packs are more practical than hose-and-compressor ones, and cheaper, but the wearer can "outbreathe" the motor (you can't "outbreathe" a compressor), and thus will be absolutely reliant on the face seal being totally intact.
Unpowered "face-fitted" respirators rely on the wearer to inhale air through the filter. As the inhaled air will take the path-of-least-resistance, it will only come through the filter (as intended) if the face seal is very good; otherwise, it will leak around the mask, and the wearer will breathe "normal", unfiltered, "dirty" air.
As @conny correctly said earlier, the purpose of the (exhalation) valve is to make the respirator more comfortable for the wearer (by letting the moist breath out). It also stops the moist air dampening the filter material (which both reduces its effectiveness, and contaminates it with bugs and germs that the wearer is exhaling).
Also, what comes in, must come out. Without an exhalation valve, the air has to get out somehow; either back through the filter (not desirable, and therefore prevented by an inhalation valve in non-disposable facepieces), or back through the face-seal (again, not desirable; you don't want to keep breaching your face seal with every exhaled breath).
The exhalation valve is often not positioned to direct exhaled air downwards, as that is not its purpose. My own respirators direct exhaled air directly forwards, for example.
All of the above is regarding RPE, with the P standing for "protection" (for the wearer).
Where the water is muddied is the change of emphasis on exactly who is being protected, and how.
Typically, the medical profession (with rare exceptions) wore their masks not to protect themselves from their patients, but their patients from them.
With CV, this is no longer the case.
Hence, the current situation where the medical profession is wearing RPE to protect themselves, and the general public asked to wear masks (or headscarves, repurposed t-shirts, and the like) to protect "everyone else".
There are basically two types of respiratory protective equipment (RPE); those that rely on a close-fitting and effective face seal, and those that do not.
The ones that do not rely on a close-fitting face seal protect the wearer by means of powered air supply into the wearer's breathing zone; the idea is that the air is supplied at a rate that exceeds the demand of the wearer. Like the hoods that some wear. Like this:
The supplied air is delivered via a hose (by compressor) to the wearer, having been filtered on the way.
These hoods are more comfortable, are suitable for those who sport beards, or have skin complaints / scarring that precludes them wearing close-fitting face pieces.
They are however more impractical in many settings (you have to have a compressor and hose), are more expensive, and offer no protection in event of power failure.
____________
Respirators that rely on a close face seal can be powered as above (with the same advantages and disadvantages), supplied with air from tanks (like firefighters' BA equipment (good, but heavy, expensive, and only good for a limited period of time), powered with battery-packed motors, or be unpowered.
Those with battery packs are more practical than hose-and-compressor ones, and cheaper, but the wearer can "outbreathe" the motor (you can't "outbreathe" a compressor), and thus will be absolutely reliant on the face seal being totally intact.
Unpowered "face-fitted" respirators rely on the wearer to inhale air through the filter. As the inhaled air will take the path-of-least-resistance, it will only come through the filter (as intended) if the face seal is very good; otherwise, it will leak around the mask, and the wearer will breathe "normal", unfiltered, "dirty" air.
As @conny correctly said earlier, the purpose of the (exhalation) valve is to make the respirator more comfortable for the wearer (by letting the moist breath out). It also stops the moist air dampening the filter material (which both reduces its effectiveness, and contaminates it with bugs and germs that the wearer is exhaling).
Also, what comes in, must come out. Without an exhalation valve, the air has to get out somehow; either back through the filter (not desirable, and therefore prevented by an inhalation valve in non-disposable facepieces), or back through the face-seal (again, not desirable; you don't want to keep breaching your face seal with every exhaled breath).
The exhalation valve is often not positioned to direct exhaled air downwards, as that is not its purpose. My own respirators direct exhaled air directly forwards, for example.
All of the above is regarding RPE, with the P standing for "protection" (for the wearer).
Where the water is muddied is the change of emphasis on exactly who is being protected, and how.
Typically, the medical profession (with rare exceptions) wore their masks not to protect themselves from their patients, but their patients from them.
With CV, this is no longer the case.
Hence, the current situation where the medical profession is wearing RPE to protect themselves, and the general public asked to wear masks (or headscarves, repurposed t-shirts, and the like) to protect "everyone else".
They'll be envied by many teachers.
Found some I hope
I take an XXL hat size so should be ok for all. Slight resistance to breathing but no intention of wearing them for long periods. OTT for preventing spread really.
