Medical Mask Testing
Testing for performance
The Barrier Protection Level is defined by AS 4381:2015 in terms of the performance that a mask demonstrates in response to three tests:
Blood Penetration ISO 22609:2014 – Test method for resistance by synthetic blood
Synthetic blood stream striking a mask specimen in the ISO 22609 Resistance to Blood Penetration test.
This test determines the ability of a mask to resist a stream of (synthetic) blood through. Mask specimens are required to prevent full-thickness penetration of the blood stream after it is directed onto the outer (coloured) layer of the mask, as may happen during surgery. The selected velocity of the blood stream is determined through correspondence to different levels of (human) blood pressure. Masks which claim higher protection levels are required to resist penetration by correspondingly high velocity streams. The table below lists the various stream velocities which must be resisted for each protection level.
Bacterial Filtration Efficiency EN 14683:2014 Annex B – Method for in-vitro determination of bacterial filtration efficiency (BFE)
Inspecting an agar-filled Petri dish for Staphylococcus aureus colonies to determine bacterial filtration efficiency in accordance with EN 14684:2014 Annex B.
The test determines the ability of a mask to filter an aerosol (stream of liquid droplets carried in an air stream) containing bacteria (Staphylococcus aureus). The percentage of bacteria filtered is calculated and termed Bacterial Filtration Efficiency (BFE).
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. After the aerosol passes through the mask, the air steam is passed 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. The Petri dishes are incubated for two days, allowing the bacterial colonies to grow to a size that are able to be counted. 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. The table below lists the BFE percentage required to meet each protection level. Higher protection level masks are required to filter more of the bacterial aerosol.
Breathability / Differential Pressure EN 14683:2014 Annex C – Method for determination of breathability (differential pressure)
Testing the differential pressure across a mask specimen to determine Breathability performance in accordance with EN 14684:2014 Annex C.
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. The measured differential pressure is divided by the area of the mask through which the air is passed, providing a measurement in units of Pa/cm2 (or mmH2O/cm2).
The differential pressure provided by a mask, or in other words, its resistance to air flow, corresponds to the ease of breathing through it. A mask that provides a reduced differential pressure is therefore easier to breath through compared to a mask that produces a higher differential pressure.
The table below lists the different values of differential pressure which are required to not be exceeded for various Protection Levels. 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.
The different levels of Protection level are described in AS 4381 as follows:
Level 1
For general purpose medical procedures, where the wearer is not at risk of blood or body fluid splash or to protect staff and/or the patient from droplet exposure to microorganisms (e.g. patient with upper respiratory tract infection visits General Practitioner).
Level 2
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).
Level 3
For all surgical procedures, major trauma first aid or in any area where the health care worker is at risk of blood or body fluid splash (e.g. orthopedic, cardiovascular procedures).
The performance of each Barrier Protection Levels are defined are as follows:
| AS 4381:2015 Barrier Protection Level |
Resistance to Blood Penetration (at specified blood pressure) |
Breathability (Differential Pressure / specimen area) |
Bacterial Filtration Efficiency |
|---|---|---|---|
| ISO 22609:2014 | EN 14683:2014 Annex B | EN 14683:2014 Annex C | |
| 1 | 80 mmHg (10.6 kPa) | < 4.0 mmH2O/cm2 (39.2 Pa/cm2) | ≥ 95% |
| 2 | 120 mmHg (16.0 kPa) | < 5.0 mmH2O/cm2 (49.0 Pa/cm2) | ≥ 98% |
| 3 | 160 mmHg (21.3 kPa) |
Some masks in Australia are registered on the basis of claims of a Declaration of Conformity to EN 14683 in its entirety (rather than the test methods and protection levels nominated by AS 4381 as described above). The requirements for protection level of EN 14683 are different than those of AS 4381, and are summarised in the table below.
| EN 14683 Mask Type |
Resistance to Blood Penetration (at specified blood pressure) |
Breathability (Differential Pressure / specimen area) |
Bacterial Filtration Efficiency |
|---|---|---|---|
| ISO 22609:2014 | EN 14683:2014 Annex B | EN 14683:2014 Annex C | |
| I | Not required to be tested | < 3.0 mmH2O/cm2 (29.4 Pa/cm2) | ≥ 95% |
| II | ≥ 98% | ||
| IIR | 120 mmHg (21.3 kPa) | < 5.0 mmH2O/cm2 (49.0 Pa/cm2) |