During the COVID-19 pandemic, 2,500 factories were converted to produce 116 million daily. During the COVID-19 pandemic, people in the United States, and in a lot of countries in the world, were urged to make their own cloth masks due to the widespread shortage of commercial masks. See also (PPE) References Bibliography Nancy Bollinger, Robert Schutz et al. NIOSH Guide to Industrial Respiratory Protection. — NIOSH. — Cincinnati, Ohio: DHHS (NIOSH) Publication No. 87-116, 1987. — 305 p. Linda Rosenstock et al. TB Respiratory Protection Program In Health Care Facilities. Administrator's Guide. — DHHS (NIOSH) Publication No. 99-143. — Cincinnati, Ohio, 1999. — 120 p. Nancy Bollinger et al. NIOSH Respirator Selection Logic. — DHHS (NIOSH) Publication No. 2005-100. — Cincinnati, Ohio, 2004. — 39 p Respiratory protective equipment at work. A practical guide. 4 ed. — HSE (UK). — Norwich: Crown, 2013. — 59 p. — . BGR/GUV-R 190 Benutzung von Atemschutzgeräten. — Deutsche Gesetzliche Unfallversicherung e.V. (DGUV), Medienproduktion. — Berlin (BRD), 2011. — 174 p. Jaime Lara, Mireille Vennes. Guide pratique de protection respiratoire. — Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST). — Montréal (Canada), 2002. — 56 p. — Further reading NIOSH respirators main page NIOSH respirator fact sheet What's Special about Chemical, Biological, Radiological, and Nuclear (CBRN) Air-Purifying Respirators (APR)? NIOSH Fact Sheet NIOSH-Approved Disposable Particulate Respirators (Filtering Facepieces) TSI Application note ITI-041: Mechanisms of Filtration for High Efficiency Fibrous Filters British Standard BS EN 143:2000: Respiratory protective devices – Particle filters – Requirements, testing, marking British Standard BS EN 149:2001: Respiratory protective devices – Filtering half masks to protect against particles – Requirements, testing, marking External links 3M Safety Respirator Classification Guide 3M.com Mine Safety Appliance Company (MSA) Respirator Classification Guide MSA.com CDC Protective Masks Fact Sheet cdc.gov/niosh Canadian Centre for Occupational Health and Safety (CCOHS) Respirator Selection ccohs.ca The following links are respirator selection logic and competitive bid research information pages for Chemical, Biological, Radiological, and Nuclear (CBRN) defense responders: Air-Purifying Respirators (APR): cdc.gov/niosh. Respirator manufacturer approvals for NIOSH-certified air-purifying respirator with CBRN Protections (CBRN APR). This link covers APR and Air-Purifying Escape Respirators (APER) certified by the NIOSH's National Personal Protective Technology Laboratory (NPPTL), Pittsburgh, PA, to CBRN protection NIOSH standards. CBRN APR are tight-fitting, full-face respirators with approved accessories and protect the user breathing zone by relying on user negative pressure, fit testing and user seal checks