A small insight into Masks- A vital part of PPE


Masks- A vital part of PPE

Sayak Nandi

Department of Textile Technology

Government College of Engineering and Textile Technology, Serampore,WB, India

Introduction

In the current situation, when the world is facing a major pandemic without a certified cure; PPE seems to be the last resort. Mask is a part of PPE, which has become possibly the most vital part of it. So, I have tried to give a little more insight into masks also sighting some recent developments and common mistakes etc.

Reason why mask is so essential in this pandemic

When we consider the mode of transmission by COVID-19, it is contact, droplet or airborne [1]. Hence the PPE designed should be effective in preventing these three modes as shown in Table. 1.


Mode of Transmission

PPE to be used

Guidelines and advices to Prevent these modes

Contact

Gloves, Apron

Washing hands frequently with soaps or use of at least 60% alcohol based sanitizers

Droplet

Gloves, Apron, Fluid Resistant Mask, Eye Protection

Use of Masks and maintaining social distancing

Airborne

Gloves, Fluid repellent gown, Eye Protection, Mask

Use of Masks and maintaining social distancing

Table 1: Modes of transmission and their match type PPE [1] and Guidelines for common people [2]

Hence, Masks have been the most crucial part of PPE with very little knowledge to common people. However we go by the initial guidelines provided by Government [3], it doesn’t recommend the use of PPEs for common people. However certain international research [4] claims, use of N95 masks reduces infection.  Later the use of masks was made mandatory.

Mechanism of Filtration

The filters used in modern surgical masks and respirators are generally made from nonwovens- fibre porosity, diameter and thickness of filter determines the efficiency of a mask. Generally there are 4 types of filter mechanism shown in Fig. 1.


Fig. 1: Filter mechanisms [5]

Inertial impaction: Filtration for large particles; the large particles diverted around a filter fibre structure due to its size.

Interception: Filtration for large particles; the intercepted particle can be prevented by fine filter fibres.

Diffusion: Filtration for small particles; the small particles that are bombarded by air molecules, causing it to deviate from air stream and come in contact with filter fibre.

Electrostatic attraction: Filtration for oppositely charged particles; If the charge of filter fibre is opposite to the charge of particle, it causes attraction. This mechanism doesn’t favor any particular particle size.

More about N95 masks and Multi layered Masks

In a PPE use of N95 masks or multilayered masks (minimum 3 layers) are recommended [6], since it provides maximum protection against COVID-19. [5] [7].

N95 masks: The word N signifies “Nonresistant to oil” and “95” signify 95% filtration to aerosols. The masks are generally made from fibres of diameter 1 micron of thermoplastic like polypropylene, polyester etc. using melt blown technique.

Respirator filters are rated as N, R or P for their level of protection against oil and aerosols. Where “R” is little oil resistant and “P” is strongly oil resistant. The oil removes the electrostatic charges from the filter media, hence greater the oil resistance greater the filtration.

Multilayered masks: Generally made from non-woven thermoplastic like polypropylene, polyester etc. using melt blown technique. The masks are generally 3-4 layered for better filtration. Even FFP2 and FFP3 masks are also recommended in certain parts. (Filtration 94% and 99% respectively).Researches regarding usage of FFP2 and FFP3 and N95 is shown, though the masks have a high filtration rate; however particle influx through face shield leakage of the N95 respirators far exceeds the influx through the filter. The ratio of face seal leakage to filter leakage is in range of 7-20:1, so it is advisable to dispose these respirators and not reusing it multiple times [8]

General mistakes by common people

In common it is seen people using surgical masks, home-made masks and paper masks in spite of guidelines. It is known that home-made masks and paper masks cannot provide the same degree of protection. A study shows choice of material might affect the filtration, use of silk shows higher filtration (approx. 90%) than coarse cotton (70%)[9].This might be due to silk forms strong electrostatic charges and enhances filtration.

Even in a study shows protection factor of surgical mask against particle 0.04-1.3 μm was on average of 8 to 12 times less than N95 masks [10]. Another study also suggests surgical mask filters ranges from 10% to nearly 90% [5]. Hence N95 respirator and multilayered masks must be used for better protection. A better difference for surgical mask, paper mask and N95 mask is provided in Fig. 2.


Fig. 2: Difference between surgical mask, paper mask and N95 mask [11]


Some extra information about Masks

Researches have also been conducted to achieve reusable N95 masks with flexible nonporous Si-based replaceable membrane to enhance filtration efficiency [12].

Certain researches involves the comfort perspective of the masks, the use of atraumatic silicon border dressing to prevent skin injuries due to use of tight masks for long hours was carried out for the front line warriors [13].

Recent Trends and Conclusion

Certain companies have recently been manufacturing reusable masks with antimicrobial finishing. These masks retains its anti-microbial efficacy upto certain washing cycles, these masks are highly recommended and might be a useful weapon in this situation. However certain fashionable masks that don’t provide adequate safety are also available in market. So it is advisable to buy and use masks that are effective, rather than only fashionable ones. Since masks and PPEs might be our “Last Resort” in this pandemic till any proper medication is available.

References:

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3 Comments

  1. Very informative and useful article. Thanks to the author .

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  2. Nice one....too much informative

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  3. Useful and very much relevant in the present context

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