1. https://www.who.int/news-room/detail/03-03-2020-shortage-of-personal-protective-equipment-endangering-health-workersworldwide
2. https://www.fda.gov/medical-devices/letters-health-care-providers/surgical-mask-and-gown-conservation-strategies-letterhealthcare-providers
3. https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/index.html
4. Interpretation of inhalation airflow measurements for respirator design and testing;Janssen LL;J Int Soc Respir Prot,2005
5. https://www.astm.org/READINGLIBRARY/VIEW/F2100.html