A chemical treatment could help hospitals safely reuse respirator masks.

Medical respirators and masks are in critically short supply across the globe. In particular, the N95 variety (or other similar respirator masks) is in critical demand. This type of mask removes 95% of particles at diameters greater than 0.3 μm and is essential for medical workers.

However, simply disinfecting them with alcohol does not work. Studies have shown that their filtering efficiency drops dramatically (by ~40%) after even one such treatment.

Of course, production can be increased and several factories have already been repurposed to produce masks, but shortages still loom over much of the world.

A team of CalTech researchers propose a new way to clean masks, safely and efficiently, and in an inexpensive way. It starts by using ethanol instead of isopropyl alcohol.

“We have discovered a method to clean hospital-grade face masks by first soaking masks in an ethanol solution, air-drying them, then vacuum-drying them. Our study has found that this cleaning process can be used on a mask at least five times without decreasing the filter rate of the mask by more than one per cent,” the team writes.

The vacuum-drying is particularly important, the researchers stress.

“Vacuum-drying the masks removes a thin layer of water that still sticks to the fibers in the mask after air-drying. This layer of water is what causes the mask efficiency to drop (that is, how well it filters particles from the air). One worry is that this problem with moisture might come up just from wearing a mask for too long, because the moisture from a person’s breath could build up in the mask. This could also be fixed with the vacuum-drying procedure.”

The researchers also encourage hospitals and research facilities to build their own mask-testing rigs to test the filtration capacity of the equipment they have purchased and are using. A standard rig costs well over $60,000, but you can get similar results with a kit that’s 20 times cheaper.

“We built a simple mask testing rig from items that are cheap and easy to obtain, though the current design relies on a calibrated $2,500 laser particle meter. We are working to adapt cheaper laser particle meters into the design.”

It’s important to note that the study has not been peer-reviewed and has a few caveats. For instance, tap water has not been used because it might interact with microfibers and change their structures. The researchers say they aren’t sure if tap water would have an effect, but they avoided it just to be safe. They’re also not sure of how efficient this treatment would be on other types of respirator masks.

The procedure outlined here for regenerating mask filtering efficiency has not yet been approved by regulatory bodies.

Read the entire analysis here.