Last-resort strategies during mask shortages: optimal design features of cloth masks and decontamination of disposable masks during the COVID-19 pandemic

Abstract

Face masks and respirators are the most widely used intervention measures for respiratory protection. In the wake of COVID-19, in response to shortages and lack of availability of surgical masks and respirators, the use of cloth masks has become a research focus. Various fabrics have been promoted with little evidence-based foundation and without guidelines on design principles for optimal performance. In these circumstances, it is essential to understand the properties, key performance factors, filter mechanisms and evidence on cloth masks materials. The general community might also need to decontaminate and reuse disposable, single-use devices as a last resort. We present an overview of the filter materials, filter mechanisms and effectiveness, key performance factors, and hydrophobicity of the common disposable masks, as well as cloth masks. We also reviewed decontamination methods for disposable respiratory devices. As an alternative to surgical masks and respirators, we recommend a cloth mask made of at least three layers (300-350 threads per inch) and adding a nylon stocking layer over the mask for a better fit. Water-resistant fabrics (polyesters/nylon), blends of fabrics and water-absorbing fabrics (cotton) should be in the outside layer, middle layer/layers and inside layer, respectively. The information outlined here will help people to navigate their choices if facing shortages of appropriate respiratory protection during the COVID-19 pandemic.

Keywords: equipment evaluations; infection control.

Figure 1

Schematic representation of the factors for an effective respiratory protective gear.

Figure 2

(A) Different filtration mechanisms used by the filter media. The figure depicts how particles are captured in fibres (cross-section) by electrostatic and mechanical forces. (B) Schematic filtration efficiency graph of different filtration types. (C) Real sessile drop images of cotton fabric at the intersection between the drop contour and the fabric surface. Our test revealed that water droplet rapidly absorbs into the fabric within 8 s. (D) Schematic of a preferred arrangement of fabrics recommended for cloth mask. (E) Schematic presentation of wearing a nylon stocking over face mask to improve fit.