HEPAs are great at filtering out particles, including viruses! Technically, they can be used for making masks. However there are several things you should be aware of:
1. Some types of HEPAs (e.g. fiber glass HEPAs) may not be safe for direct contact with the skin or for breathing air close to the mouth. They may irritate the skin, or release small particles that could enter your repository system.
2. A certified mask (e.g. N95, N99) is manufactured following specified guidelines such as fit and filtration efficiency, as well as breathing ability while HEPA filter manufacturers follow a different set of protocol. Your homemade HEPA filter mask therefore may not work as well as a certified mask
3. HEPA filters contain a layer of stiff PP material which gives them their rigidity. This makes them difficult to fold into shapes, or sometimes very brittle. Moulding them into effective mask shapes may be difficult.
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