What the water test means

Of course, I was on a PPE Zoom meeting when I first heard of the water test. Someone said their mask was validated because it held water…. “What does that prove?” I thought to myself. Turns out nothing. It means absolutely nothing.

So I set out to do my own Myth Busters of sort and tested 5 masks against the water challenge.

What it showed was that mask was not a piece of paper. That’s about it. The criteria for a surgical mask is to create a water barrier. So that if you get splashed with blood during the operation, you don’t get it in your mouth or nose. Even the simple cheap patient mask I had, held water as well.

Water has a high surface tension which means it takes a much bigger hole than 0.3 microns for water to seep through or a higher pressure gradient.

Here’s the video of the test. From left to right I tested two 3M NIOSH N95s, a KN95 with measured filtration of 50% at 0.3 microns, a procedural mask, and a flimsy paper patient mask which apparently still has a water resistant layer in it.

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