Evaluation of PPE for medical personnel to combat COVID -19

Dr Subrata Das

By guest author Dr Subrata Das, Professor (Fashion Technology) Bannari Amman Institute of Technology, Sathyamangalam, Erode District, Tamil Nadu 638401, India. The author can be contacted via E-mail: subratactl@gmail.com

TextileFuture is very proud to present this excellent technical paper to our readers.

Personal protective equipment (PPE) is used in a wide range of industries to protect workers from exposure to workplace hazards and is designed to address requirements specific to the context of its use. In healthcare, the goal of PPE is to protect healthcare personnel (HCP) from body fluids and infectious organisms via contact, droplet, or airborne transmission.

The ideal face mask blocks large respiratory droplets from coughs or sneezes – the primary method by which people pass the coronavirus to others – along with smaller airborne particles, called aerosols, produced when people talk or exhale. The World Health Organisation recommends medical masks for healthcare workers, elderly people, people with underlying health conditions, and people who have tested positive for the coronavirus or show symptoms.

Two medical-grade masks, N99 and N95, are the most effective at filtering viral particles. N99 masks reduced a person’s risk of infection by 94 to 99 percent after 20 minutes of exposure in a highly contaminated environment. N95 masks offered almost as much protection – the name refers to its minimum 95 percent efficiency at filtering aerosols. N95 masks offered better protection than surgical masks. Disposable surgical masks are a close second. Surgical masks are made of nonwoven fabric, so they’re usually the safest option for healthcare workers who don’t have access to an N99 or N95 mask. Surgical masks reduced the transmission of multiple human coronaviruses through both respiratory droplets and smaller aerosols. In general, surgical masks are about three times effective in blocking virus-containing aerosols than homemade face masks. Hybrid masks – combining two layers of 600-thread-count cotton with another material like silk, chiffon, or flannel – filtered more than 80 percent of small particles (less than 300 nanometres) and more than 90 percent of larger particles (bigger than 300 nanometres). A combination of cotton and chiffon offered the most protection, followed by cotton and flannel, cotton and silk, and four layers of natural silk. These options may even be better at filtering small particles than an N95 mask, though they weren’t necessarily better at filtering larger particles. Two layers of 600-thread-count cotton or two layers of chiffon might be better at filtering small particles than a surgical mask. Three layers of cotton or silk are also highly protective. WHO recommends that fabric masks have three layers: an inner layer that absorbs, a middle layer that filters, and an outer layer made from a non-absorbent material like polyester. Three layers of either a silk shirt or a 100 percent cotton T-shirt may be just as protective as a medical-grade mask. Silk in particular has electrostatic properties that can help trap smaller viral particles.

Masks have very specific performance requirements. Standard Test Method for Evaluating the Bacterial Filtration Efficiency (BFE) of Medical Face Mask Materials, using a Biological Aerosol of Staphylococcus aureus by using ASTM F2101 has been summarised below: 

This test method offers a procedure for evaluation of medical face mask materials for bacterial filtration efficiency. This test method does not define acceptable levels of bacterial filtration efficiency. Therefore, when using this test method it is necessary to describe the specific condition under which testing is conducted. This test method has been specifically designed for measuring bacterial filtration efficiency of medical face masks, using Staphylococcus aureus as the challenge organism. The use of S. aureus is based on its clinical relevance as a leading cause of nosocomial infections. This test method has been designed to introduce a bacterial aerosol challenge to the test specimens at a flow rate of 28.3 L/mm. (1 ft3/min). This flow rate is within the range of normal respiration and within the limitations of the cascade impactor. Unless otherwise specified, the testing shall be performed with the inside of the medical face mask in contact with the bacterial challenge. Testing may be performed with the aerosol challenge directed through either the face side or liner side of the test specimen, thereby, allowing evaluation of filtration efficiencies which relate to both patient-generated aerosols and wearer-generated aerosols. Degradation by physical, chemical, and thermal stresses could negatively impact the performance of the medical face mask material. The integrity of the material can also be compromised during use by such effects as flexing and abrasion, or by wetting with contaminants such as alcohol and perspiration. Testing without these stresses could lead to a false sense of security. If these conditions are of concern, evaluate the performance of the medical face mask material for bacterial filtration efficiency following an appropriate pre-treatment technique representative of the expected conditions of use. Consider preconditioning to assess the impact of storage conditions and shelf life for disposable products, and the effects of laundering and sterilization for reusable products. If this procedure is used for quality control, perform proper statistical design and analysis of larger data sets. This type of analysis includes, but is not limited to, the number of individual specimens tested, the average percent bacterial filtration efficiency, and standard deviation. Data reported in this way help to establish confidence limits concerning product performance. Examples of acceptable sampling plans are found in references such as ANSI/ASQ Z1.4 and ISO 2859-1.


This test method is used to measure the bacterial filtration efficiency (BFE) of medical face mask materials, employing a ratio of the upstream bacterial challenge to downstream residual concentration to determine filtration efficiency of medical face mask materials. This test method is a quantitative method that allows filtration efficiency for medical face mask materials to be determined. The maximum filtration efficiency that can be determined by this method is 99.9 %. This test method does not apply to all forms or conditions of biological aerosol exposure. Users of the test method should review modes for worker exposure and assess the appropriateness of the method for their specific applications. This test method evaluates medical face mask materials as an item of protective clothing but does not evaluate materials for regulatory approval as respirators. If respiratory protection for the wearer is needed, a NIOSH-certified respirator should be used. Relatively high bacterial filtration efficiency measurements for a particular medical face mask material does not ensure that the wearer will be protected from biological aerosols, since this test method primarily evaluates the performance of the composite materials used in the construction of the medical face mask and not its design, fit, or facial-sealing properties. The values stated in SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance of the standard. This test method does not address breathability of the medical face mask materials or any other properties affecting the ease of breathing through the medical face mask material. This test method may also be used to measure the bacterial filtration efficiency (BFE) of other porous medical products such as surgical gowns, surgical drapes, and sterile barrier systems. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

There are some other methods which are also useful for combating COVID – 19 virus for medical professionals. This may be either in form of medical gowns or other protective textiles useful for doctors, nurses and other staff members associated with the profession.

BS EN 149:2001+A1:2009 Respiratory protective devices.  Filtering half masks to protect against particles.
BS EN 166:2002 Personal eye protection. Specifications
BS EN 14126:2003  Protective clothing.
BS EN 14605:2009+A1:2009 Protective clothing against liquid chemicals. (Types PB [3] and PB [4])
BS EN 13795-1:2019 Surgical clothing and drapes. Requirements and test methods. Surgical drapes and gowns
BS EN 13795-2:2019 Surgical clothing and drapes. Requirements and test methods. Clean air suits
BS EN 455-1:2000 Medical gloves for single use. Requirements and testing for freedom from holes
BS EN 455-2:2015 Medical gloves for single use.
BS EN 455-3:2015 Medical gloves for single use.
BS EN 455-4:2009 Medical gloves for single use.
BS EN 14683:2019 Medical face masks.
BS EN ISO 10993-1:2009 Biological evaluation of medical devices.
BS EN ISO 374-5:2016 Protective gloves against dangerous chemicals and micro-organisms.
BS EN ISO 13688:2013  Protective clothing. General requirements

Some of the testing equipment which is useful for this purpose is also shown in Figure 1 to Figure 9.

PPE use in healthcare involves 3 phases: (1) donning, (2) while providing patient care, and (3) doffing. Issues or errors during any of these phases can lead to a risk of contamination to the HCP.  Incorrect technique or sequence in donning can expose HCP during patient care, or sets HCP up for a doffing failure. Contamination of HCP can occur during patient care if PPE is damaged, has design flaws, or if HCP circumvent protection (i. e, reaching under PPE). Risks of contamination during doffing can be due to an incorrect removal technique, improper handling and disposal of PPE, or by damaging PPE to expose HCP.