N95 respirators are respiratory protective devices that are engineered to achieve a very close facial fit and efficient filtration of airborne particles as shown in Figure 5.
N95 respirators are made of a material that filters most of the particles from the air when it passes through the face mask – as long as the respirator is correctly fitted. Most air being taken in passes through the face mask and is thus filtered, removing most or all virus particles.
Figure 5. N95 respirator
Reuse of respirators
Ideally, respirators should be disposed of after each use, however, under certain conditions, they can be reused by the same person. These respirators should not be used when it is crushed, torn or creased, soiled or splashed with potentially infectious secretions or wet – no matter which liquid it has been wet with, or when it becomes difficult to breathe while wearing it.
Respirators may be reused, only if they are in short supply.
They can be reused by the same person, not shared among different people. If properly cared for, respirators can last one week or more. It must not be cleaned. They should be stored in a clean and dry location when not in use. They may be wrapped with a dry cloth or tissue. These should not be wrapped in plastic as this tends to retain moisture and reduce the face mask’s efficacy. Exposing used N95 masks to the right spectrum of UVC can help sanitise the mask in between use. [6, 7].
Face mask: how to wear
While wearing a face mask is essential, wearing them with proper precautions is also important:
- Hands should be properly cleaned with soap and water or hand sanitiser before and after the process of removing the mask
- Mask should be checked for any tears or holes before being used
- The coloured side of the mask is usually in the front and away from the face while the white side faces towards the face.
- Hands should be thoroughly cleaned before and after the process of removing the mask. Touching the front face of the mask should be avoided. Mask should be properly discarded in the trash.
- The mask should fit snugly, without wide gaps at the sides or under the eyes. Masks that incorporate a bendable wire over the nose often fit better.
Key issues and concerns
People are advised to cover their nose and mouth while roaming around in public, as donning of face masks has proven to be important to help curb COVID-19. Other barriers like social distancing, personal hygiene can also help in creating a combined effective method to reduce the spread and chances of getting infected as can be shown in Figure 6. 
Figure 6. The Swiss cheese model showing various layers to prevent infectious diseases and control transmission risks
Correct methods on how to use masks and strict control by the governments not only on wearing masks but also on how they should be worn and handled can further reduce the spread of COVID-19. The Public must be trained about the correct way of putting on, wearing, removing, and disposing of face masks for face masks to be effective .
Although the SARS-COV-2 virus is very small it is contained in respiratory fluids which means that particles are larger than the virus alone. Particles in the submicron region (d p between 0.25 and 1.0 μm) and super micron region (d p > 2.5 μm), can be effectively filtered out from the inhaled air by either surgical masks or N95 masks. A recent COVID-19 dynamic modelling study also suggested that broad adoption of even relatively ineffective non-medical grade “social” masks may meaningfully reduce the community transmission and decrease peak hospitalizations and deaths during the current COVID-19 pandemic .
Homemade face masks
A study conducted on the effectiveness of homemade masks as an alternative to commercial masks concluded that surgical masks are more effective in preventing microorganisms than homemade masks.
Nevertheless, in short of supply scenarios, homemade cloth masks are better than no protection and 100% cotton is the best material to use while making them. The use of double-layer cotton masks reduces the emission of larger particles [14,16].
Face masks: shedding fibres
While utilising cloth masks, care must be taken while removing and cleaning the masks as cloth masks can be prone to shedding fibres and in turn lodge deposited micro-organisms . Few tips for cloth masks are shown in Figure 7.
Figure 7: Good practices while using facemasks 
Section 5 References
- Tang, J. W., Noakes, C. J., Nielsen, P. V., Eames, I., Nicolle, A., Li, Y., & Settles, G. S. (2011). Observing and quantifying airflows in the infection control of aerosol-and airborne-transmitted diseases: an overview of approaches. Journal of Hospital Infection, 77(3), 213-222.
- WHO – Use of facemasks
- Wei, J., & Li, Y. (2016). Airborne spread of infectious agents in the indoor environment. American journal of infection control, 44(9), S102-S108.
- Kai, D., Goldstein, G. P., Morgunov, A., Nangalia, V., & Rotkirch, A. (2020). Universal masking is urgent in the COVID-19 pandemic: Seir and agent-based models, empirical validation, policy recommendations. arXiv preprint arXiv:2004.13553
- Schünemann, H. J., Akl, E. A., Chou, R., Chu, D. K., Loeb, M., Lotfi, T., ... & Mertz, D. (2020). Use of facemasks during the COVID-19 pandemic. The Lancet Respiratory Medicine, 8(10), 954-955
- Godoy, L. R. G., Jones, A. E., Anderson, T. N., Fisher, C. L., Seeley, K. M., Beeson, E. A., ... & Sullivan, P. D. (2020). Facial protection for healthcare workers during pandemics: a scoping review. BMJ global health, 5(5), e002553.
- Chughtai, A. A., Seale, H., & Macintyre, C. R. (2020). Effectiveness of cloth masks for protection against severe acute respiratory syndrome coronavirus 2. Emerging infectious diseases, 26(10).
- "Transmission-Based Precautions". U.S. Centers for Disease Control and Prevention. 2016-01-07. Retrieved 2020-03-31.
- Guidance on the use of masks to control influenza transmission.
- Engineers design a reusable alternative to N95 face mask.
- Jefferson, T., Foxlee, R., Del Mar, C., Dooley, L., Ferroni, E., Hewak, B., ... & Rivetti, A. (2008). Physical interventions to interrupt or reduce the spread of respiratory viruses: systematic review. Bmj, 336(7635), 77-80.
- Cumbo, E., & Scardina, G. A. (2020). Management and use of filter masks in the “none-medical” population during the COVID-19 period. Safety Science, 104997
- Davies, A., Thompson, K. A., Giri, K., Kafatos, G., Walker, J., & Bennett, A. (2013). Testing the efficacy of homemade masks: would they protect in an influenza pandemic?. Disaster medicine and public health preparedness, 7(4), 413-418.
- Why plastic face shields aren’t a safe alternative to cloth masks.
- Asadi, S., Cappa, C. D., Barreda, S., Wexler, A. S., Bouvier, N. M., & Ristenpart, W. D. (2020). Efficacy of masks and face coverings in controlling outward aerosol particle emission from expiratory activities. Scientific Reports, 10(1), 1-13.
- A user’s guide to masks: What’s best at protecting others and yourself. https://www.npr.org/sections/goatsandsoda/2020/07/01/880621610/a-users-guide-to-masks-what-s-best-at-protecting-others-and-yourself?t=1603376612321.
- Mantzari, E., Rubin, G. J., & Marteau, T. M. (2020). Is risk compensation threatening public health in the COVID-19 pandemic?. BMJ, 370.
- Coronavirus is not canceled: Wear your mask.