As you noted, the straps need to have elasticity to allow for head motion. If they don't stretch, the mask becomes too tight and too loose depending on your head position. Having a good stretch factor helps keep the tension even.
For me, the answer is turning out to be yes. That could just be something to do with my skin and the elastic, but I don't know for sure. It would take larger data sets with more people to really know for sure. Replacing the harness, and/or elastics is not something that dentec accounts for in their cost benefit analysis of the NxMD over N95s. The dentec NxMD feels like a minimum viable product in some ways. But when the elastics are fresh, it's a comfortable mask that fits well on me. When the elastics are old, the mask does stay sealed well on me, and they slip. I think the harness design and construction could use improvement, but any change to the design of an elastomeric mask that is not approved would require NIOSH approval.
@@jhellier I don't actually wear the mask that much these days, and even when I did, I was only using it intermittently during the day, not for a whole work shift and was always stored inside away from sunlight. It didn't get that much UV so if it is a UV issue, it would have to be extremely sensitive.
Watch the video to see that I compared the worn out elastics to the elastics on an unused mask that has the same kind of harness to verify the stretch ratio as well as the tension. I confirmed that the stretch ratio of the worn out elastic was half that of the stretch ratio of the elastic in the unused mask harness. The deterioration of the elastic is confirmed by measurement.
Thank you for this information!
I'm not sure I understand, wouldn't we want the headstraps in a respirator to be less flexible so that it doesn't loosen up during wear?
oh nvm, i guess it's to adapt to head movement
As you noted, the straps need to have elasticity to allow for head motion. If they don't stretch, the mask becomes too tight and too loose depending on your head position. Having a good stretch factor helps keep the tension even.
Does the elastic need replacing every few months?
For me, the answer is turning out to be yes. That could just be something to do with my skin and the elastic, but I don't know for sure. It would take larger data sets with more people to really know for sure. Replacing the harness, and/or elastics is not something that dentec accounts for in their cost benefit analysis of the NxMD over N95s.
The dentec NxMD feels like a minimum viable product in some ways. But when the elastics are fresh, it's a comfortable mask that fits well on me. When the elastics are old, the mask does stay sealed well on me, and they slip. I think the harness design and construction could use improvement, but any change to the design of an elastomeric mask that is not approved would require NIOSH approval.
@@gerardhughes do you spend alot of time in the sun? Perhaps that degrades the rubber? Do you wash it daily?
@@jhellier
I don't actually wear the mask that much these days, and even when I did, I was only using it intermittently during the day, not for a whole work shift and was always stored inside away from sunlight. It didn't get that much UV so if it is a UV issue, it would have to be extremely sensitive.
I think something streatch too easily may not get a good seal.
Watch the video to see that I compared the worn out elastics to the elastics on an unused mask that has the same kind of harness to verify the stretch ratio as well as the tension.
I confirmed that the stretch ratio of the worn out elastic was half that of the stretch ratio of the elastic in the unused mask harness. The deterioration of the elastic is confirmed by measurement.
@@gerardhughes However, I don't know the range of tension suit for the half face masks 🤔