On Sat, 9 Jan 2021 08:41:19 +0000 Ian Jackson
Post by Ian Jackson Post by Joe
I wouldn't personally expect the typical 'virus-filtering' mask
to keep out brick dust.
I was unaware that people exhale brick dust.
Not generally, no. But a basic mask can't tell whether things are
going in or out.
Post by Ian Jackson
The main purpose of the typical man-in-the-supermarket mask is
not so much to filter the outgoing breath, but instead it is to
impede it, and slow it down so that it doesn't project very far
from the exhaler.
No, it will reduce the projection distance for coughing and
sneezing, something many people can achieve without a mask.
The most common mask type has a bit of bent wire to shape around
the nose, but no provision for any kind of fitting around the
bottom or sides. And many people don't bother shaping the bit of
wire, unless they wear glasses.
You might also look up the very few studies of the effectiveness
of these simple masks in reducing the spread of Covid. Here's a
The following article from one of the editors of the BMJ commenting
on the same study puts the comment you linked into a wider
DANMASK-19, the first trial of mask use during covid-19, was
"negative." Masks didnt work. We knew this before the trial was
published because we were told so on social media. The authors
were reported by the media to be struggling to find a major
journal for their trial. Journals weren't proving brave enough
to publish the study, said the authors, and they didnt make a
When the mythical trial was finally published last week in the
Annals of Internal Medicine we didnt need to read it. We
already knew its damning verdict on mask wearing. Social media
told us as much. Eminent professors of evidence based medicine,
Carl Heneghan and Tom Jefferson, confirmed this in an article for
Except that if you read the published paper you find almost the
exact opposite. The trial is inconclusive rather than negative,
and it points to a likely benefit of mask wearing to the
wearerit did not examine the wider potential benefit of reduced
spread of infection to othersand this even in a population where
mask wearing isnt mandatory and prevalence of infection is low.
This finding is in keeping with summaries of evidence from
A disagreement among experts, especially about interpretation of
a study, is a common occurrence. It is the usual business of
science. Only, Facebook didnt see it that way.
This article from Nature may be more useful:
Face masks: what the data say. The science supports that face
coverings are saving lives during the coronavirus pandemic, and
yet the debate trundles on. How much evidence is enough?
https://www.nature.com/articles/d41586-020-02801-8 (Oct 2020)