5 ms·
the ones without exhalation valves do. the barrier is bidirectional. the ones with valves bypass this which is why those shouldn't be used for source control bu
by sterlind 6y ago
the ones without exhalation valves do. the barrier is bidirectional. the ones with valves bypass this which is why those shouldn't be used for source control but are popular for wildfires etc.
- __blockcipher__ 6y agoThanks. That was my thinking but glad to see it confirmed. Kind of ironic that you’re not allowed to wear an N95 with an exhale valve, but are encouraged to wear a surgical mask, bandana, cloth mask, or dirty T-shirt, none of which provide any source control. Again, the elephant in the room is respiratory viruses in general, and SARS-2 in particular, spread via aerosols. Non-N95 face coverings cannot block aerosols. Indeed mask wearing leads to deeper breaths to maintain homeostasis (this has been studied), therefore lead to a greater net volume of air, therefore lead to increased aerosol emission before even accounting for the potential to nebulize large droplets into a shower of tiny aerosol particles. But I digress.
- loosescrews 6y agoA surgical mask, bandana, cloth mask, or dirty T-shirt over a particulate mask (e.g. N95) is typically allowed. There are serious benefits to the wearer to having an exhaust valve. Wearing a second, less effective face covering over the particulate mask retains the benefits of the particulate mask and exhaust valve while maintaining the same level of source control as without the particulate mask.