Medical face masks that meet the Australian Standards are measured in accordance with three performance metrics:
- Bacterial Filtration Efficiency (BFE)
- Differential Pressure (Delta P)
- Synthetic Blood Penetration
Bacterial Filtration Efficiency (BFE)
EN 14683:2014 Annex B
– Method for in-vitro determination of bacterial filtration efficiency (BFE)
This test determines the ability of a face mask to filter an aerosol (stream of liquid droplets carried in an air steam) containing bacteria (Staphylococcus aureus). The percentage of bacteria filtered is calculated to determine its Bacterial Filtration Efficiency (BFE). (TGA, 2021)
The bacteria-containing aerosol is carried in a stream of air flowing at 28.3 L/min (1 cu.ft/min) through a mask specimen (Rengasamy et al., 2017) . After the aerosol passes through the mask, the air steam goes through a special apparatus known as an impactor, which separates the droplets into groups with different sizes (diameter). Each group (fraction) is then collected on nutrient-rich agar-filled Petri dishes (Zhou et al., 2018) which are incubated for two days, allowing the bacterial colonies to grow to a size that can be counted (Zhou et al., 2018). The BFE percentage is calculated from the number of colonies that develop when the aerosol is passed through a mask, compared to when no mask is present (Rengasamy et al., 2017).
Inspecting an agar-filled Petri dish for Staphylococcus aureus colonies to determine bacterial filtration efficiency in accordance with EN 14684:2014 Annex B.
Bacterial Filtration Efficiency (BFE) test is performed on filtration materials and devices that are designed to provide protection against biological aerosols, such as face masks, surgical gowns, caps, and air filters.
Differential Pressure (Delta P)
EN 14683:2014 Annex C – Method for determination of breathability (differential pressure)
This test measures the differential pressure of air on either side of the test material. It determines the breathability of a mask (whether a wearer will be able to breathe comfortably while wearing it).
A device that measures the differential pressure required to draw air through a measured surface area at a constant airflow rate is used to measure the air exchange pressure of the medical face mask material. The test is performed in accordance with the requirement of Annex C of EN 14683:2019.
The breathability performance of a mask is determined by the difference in pressure across a specimen when air at a defined flow rate (8 L/min) is passed through it (Tcharkhtchi et al., 2021)). The measured differential pressure is divided by the area of the mask through which the air is passed, providing a measurement in units of mmH2O/cm2 (Eurofins Medical Device Testing, 2020).
Level 1 masks are required to not exceed 4 mmH2O/cm2, ensuring that they have the highest level of breathability. In comparison, mask types that provide higher resistance to blood penetration and bacterial efficiency filtration (Levels 2 and 3) may have slightly reduced breathability.
Testing the differential pressure across a mask specimen to determine Breathability performance in accordance with EN 14684:2014 Annex C.
ISO 22609:2014 – Test method for resistance by synthetic blood
The Synthetic Blood Penetration Test determines the ability of a face mask to act as a barrier against blood-borne pathogens from a stream of (synthetic) blood. A volume of synthetic blood is sprayed at the centre of the mask at high velocity (Rengasamy et al., 2015), mimicking what may happen during a surgical procedure. Masks that claim higher protection levels are required to resist penetration by correspondingly high-velocity streams. This measures the mask’s ability to stop blood from penetrating through the mask or its fluid splash resistance. The table below lists the various stream velocities which must be resisted for each protection level.
Synthetic bloodstream striking a mask specimen in the ISO 22609 Resistance to Blood Penetration test.
AS 4381: 2015 Single-use Face Masks
|(AS) 4381: 2015 SINGLE USE FACE MASKS - Characteristics of Level1, Level 2 and Level 3 Face Masks|
|Levels||Level 1||Level 2||Level 3|
|Characteristics||Low Barrier Protection||Moderate Barrier Protection||Maximum Barrier Protection
|Definition||Low barrier protection. general use for short procedures and exams that do not involve aerosols, sprays, or fluids. Materials evaluated for resistance to penetration by synthetic blood at minimum velocity||Moderate barrier protection: for low to moderate levels of aerosols, sprays and/or fluids. Materials evaluated for resistance to penetration by synthetic blood at the middle velocity.||Maximum barrier protection: for heavy levels of aerosols, sprays and/or fluids. Materials evaluated for resistance to penetration by synthetic blood at the maximum velocity.|
|Application||For general purpose medical procedures, where the wearer is not at risk of blood or bodily fluid splash or to protect staff and/or patient from droplet exposure to microorganisms (e.g. patient with upper respiratory tract infection visits General Practitioners||For use in emergency departments, dentistry, changing dressings on small wounds or healing wounds where minimal blood droplet exposure may possibly occur (e.g. endoscopy procedures)||For all surgical procedures, major trauma first aid or in any area where the healthcare worker is at risk of blood or body fluid splash (e.g. orthopaedic, cardiovascular procedures).|
|Bacterial Filtration Efficiency (BFE) %||≥ 95%||≥ 98%||≥ 98%|
|Differential Pressure (Delta P) Differential Pressure mm H2O/cm2||<4.0||<5.0||<5.0|
|Resistance to penetration by synthetic blood, minimum pressure in mmHg for pass result||80 mmHg||120 mmHg||120 mmHg|
|Source: Standard AS 4381:2015|
Level Rating that meets ASTM Standards
Barrier protection levels are defined by the Australian standard AS 4381:2015 Single-Use Face Masks and classifies face masks based on the results of the above three tests.
LEVEL 1 – Low Barrier Protection
Fluid Resistance: 80mm Hg, low fluid exposure.
Applications: Mostly worn by nurses and doctors performing general practise procedures where there is little to no risk of blood or bodily fluid droplet exposure from the patient seeking medical attention.
LEVEL 2 – Medium Barrier Protection
Fluid Resistance: 120mm Hg, moderate fluid exposure.
Applications: Widely accepted in emergency departments, frontline medical and dental settings where the risk of minimal droplet contamination is present during patient treatment procedures.
LEVEL 3 – High Barrier Protection
Fluid Resistance: 160mm Hg, high fluid exposure.
Applications: Providing the highest level of protection in medical settings, these masks are worn by first responders and healthcare clinicians as a barrier against blood and bodily fluid splashes, resulting from surgical procedures and major trauma first aid situations.
Level 2 & 3 surgical masks are constructed with 3-4 layers of material for moderate to maximum fluid barrier protection.
It’s essential to remember that not all face masks are performance and quality standards-rated so it’s important to confirm your level of protection before you purchase.
Eurofins Medical Device Testing. (2020). Medical face masks on the market: Review of materials, characteristics and performed tests (p. 4). Eurofins. Retrieved from https://cdnmedia.eurofins.com/european-west/media/12146819/medical_face_mask_report_v13.pdf
Rengasamy, S., Shaffer, R., Williams, B., & Smit, S. (2017). A comparison of facemask and respirator filtration test methods. Journal of occupational and environmental hygiene, 14(2), 92–103. https://doi.org/10.1080/15459624.2016.1225157
Rengasamy, S., Sbarra, D., Nwoko, J., & Shaffer, R. (2015). Resistance to synthetic blood penetration of National Institute for Occupational Safety and Health-approved N95 filtering facepiece respirators and surgical N95 respirators. American Journal Of Infection Control, 43(11), 1190-1196. doi: 10.1016/j.ajic.2015.06.014
Tcharkhtchi, A., Abbasnezhad, N., Zarbini Seydani, M., Zirak, N., Farzaneh, S., & Shirinbayan, M. (2021). An overview of filtration efficiency through the masks: Mechanisms of the aerosols penetration. Bioactive Materials, 6(1), 106-122. doi: 10.1016/j.bioactmat.2020.08.002
Zhou, S. S., Lukula, S., Chiossone, C., Nims, R. W., Suchmann, D. B., & Ijaz, M. K. (2018). Assessment of a respiratory face mask for capturing air pollutants and pathogens including human influenza and rhinoviruses. Journal of thoracic disease, 10(3), 2059–2069. https://doi.org/10.21037/jtd.2018.03.103
For More Information:
- ISO 22609 Clothing for protection against infectious agents — Medical face masks — Test method for resistance against penetration by synthetic blood (fixed volume, horizontally projected)
- EN14683 Medical face masks – Requirements and test methods
- AS 4381 Single-use face masks for use in health care