3 ms·
You'll have seen the memes about people wearing a mask and then coughing onto an agar plate. Here's a study where they did that properly. It suggests that peo
by DanBC 6y ago
You'll have seen the memes about people wearing a mask and then coughing onto an agar plate.
Here's a study where they did that properly.
It suggests that people should be changing their masks every two hours.
https://www.ijic.info/article/download/10788/7862/ https://www.ijic.info/article/download/10788/7862/
> This study was conducted to check the efficacy of face masks in limiting bacterial dispersal when worn continuously in Operation Theater. A comparison was done to find out difference between fabric and two ply disposable masks. The first sample was collected prior to wearing the mask, using cough plate method holding a blood agar plate approximately 10 -12 centimeters away from the mouth. The personnel were asked to produce “ahh” phonation. Participants were then asked to don the face mask, continue routine work and report to the study center located inside the theater for further sample collections at designated intervals of 30, 60, 90, 120 and 150 minutes after wearing the fabric mask made of cotton. The study was replicated on immediate next day using two ply disposable mask keeping all the other conditions and personnel exactly the same. Bacterial counts before wearing the mask were 5.36±4.38 and 5.7±2.99 on day 1 and day 2 of study. Bacterial counts were 0.96±1.06 (P<0.001) and 0.7±0.87 (P<0.001) at 30 min; 2.33±1.42 (P<0.001) and 2.36±1.03 (P<0.001) at 60 min; 3.23±1.54 (P=0.007) and 4.16±1.78 (P=0.011) at 90 min; 5.63±4.02 (P=0.67) and 4.9±1.98 (P=0.161) at 120 min and 7.03±4.45 (P=0.019) and 5.6±2.21 (P=0.951) at 150min respectively for fabric and two ply disposable mask. Counts were near pre-wear level in about two hours irrespective of the type of mask. There was no significant difference between cotton fabric and two ply disposable masks. Face masks significantly decreased bacterial dispersal initially but became almost ineffective after two hours of use.
- jgalt212 6y ago> Face masks significantly decreased bacterial dispersal initially but became almost ineffective after two hours of use. That statement is logically hard to swallow as it's just as hard to breath through a face mask during minute 1 as it is during minute 121.
- tzs 6y agoThere are at least 5 mechanisms by which filters can filter out particles. Four of them are explained in this document [1]. Some filter materials also trap particles electrostatically. but I have no idea if that is relevant for masks filtering viruses. For at least some of the four mechanisms covered in that document (inertial impaction, diffusion, and interception) it seems plausible that once you have a particle caught that way any other similar particle that otherwise might have been caught at the same spot the same way might either bounce off the first particle or dislodge the first particle. This could eventually reach a steady state where as many particles are coming out as are coming in the other side, just with the individual particles being delayed. If the particles are small enough so that sieving isn't significant, then there would probably be little change in the ability of air molecules to get through regardless of whether or not the filter is in the early, nearly clean stage or is in the steady state late stage where there are plenty of particles trapped. [1] http://donaldsonaerospace-defense.com/library/files/documents/pdfs/042665.pdf http://donaldsonaerospace-defense.com/library/files/document...