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Primož HAFNER
LOTRIČ 
Metrology Ltd.

EXTRACT

Basically, face masks can be divided into three major groups: protective masks (FFP masks), medical face masks and personal face masks. For the EU market, except for personal masks, masks must conform to the legal framework requirements and must be marked with CE before being placed on the market. LOTRIČ Metrology performs medical mask tests in accordance with EN 14683:2019+AC:2019. In addition to the end products, we also test materials intended for the manufacture of masks in the development phase. LOTRIČ Metrology is a Notified body number 2897 for Personal Protective Regulation - PPE (EU) 2016/425.

INTRODUCTION

We have been calibrating and testing, with a love for metrology, for three decades. LOTRIČ Metrology is a family business with more than 170 staff members. LOTRIČ Metrology as a group consists of 10 companies operating in Slovenia, Germany, Austria, Croatia, Bosnia and Hercegovina, Serbia and N. Macedonia. Our certificates are present in 49 countries around the world, mainly in Central and Eastern Europe, where we provide 24-hour response to more than 21.000 customers. For most clients, we cover 95% of their metrology needs. In the year 2020, we performed 97.612 calibrations and tests.

MEDICAL FACE MASKS

Medical face masks on the EU market must be certified in accordance with the Medical Devices Regulation - MDR (EU) 2017/745. The harmonized technical standard for medical face mask is EN 14683:2019+AC:2019. 

Medical face masks are, in accordance with the Medical Device Regulative, a risk class I, except for masks that are sterile packaged, which are class Is. For risk class I, the manufacturer does not need a Notified body, but according to module A of the Regulative, manufacturers can make the conformity assessment themselves.

Thus, the manufacturer must meet all regulatory requirements and needs: a quality system (ISO 14385 quality management for medical devices is preferred); a risk management (ISO 14791 application of risk management to medical devices is preferred); all necessary tests performed according to EN 14683 and the requirements of the Regulation related to Health and Safety requirements; technical documentation and adequate marking, labelling and packaging, with instructions and a Declaration of conformity.

MEDICAL FACE MASK TESTING

Medical face masks according to EN 14683 should undergo different tests, depending on the type of the mask. The mandatory tests are: the Test of Bacterial filtration efficiency (BFE), where the limits are 95% for type I and 98% for type II and type IIR; the Test of Breathability (Air Permeability), where the limit is 40 Pa/cm2for type I and II, and 60 Pa/cm2 for type IIR; the Test of Biocompatibility, where the limit for Cytotoxicity is 30%; and the Test of Microbial Cleanliness (Bioburden), where the limit is 30 CFU/g. For type IIR masks, the Splash test is also required. All tests, except for Biocompatibility, should be performed on the end product.


Table 1: general requirements (source: EN 14683)

1. Test of bacterial filtration efficiency (BFE)

The BFE test method is used to measure the bacterial filtration efficiency of medical face masks. The BFE of the mask is given by the number of colony-forming units passing through the medical face mask expressed as a percentage of the number of colony-forming units present in the challenge aerosol.

The BFE test is performed with an aerosol of bacteria with an average particle size of 3,0 µm and a concentration between 1700 and 3000 CFU (colony-forming unit). The aerosol is filtered through a mask at a flow rate of 28,3 l/min. Behind the mask, the bacteria aerosol is trapped on testing plates in a six-stage cascade Andersen sampler. The plates are later incubated, and the grown colonies are counted.

The real challenge is to get the right concentration and average aerosol size, which is confirmed by the positive control, the results of which are only available after 20 hours. Everything depends on the input parameters: suspension concentration, pump flow, pressure on the nebulizer, nebulizer nozzle distance and other details. Everything needs to be balanced.

Picture 1: principle of BFE test apparatus (source: EN 14683)

LOTRIČ Metrology laboratories can also perform viral filtration efficiency, which was developed as standardized method is not available.

2. Test of breathability

In this test, we measure differential pressure at a constant flow rate of 8 l/min on a central part of the mask surface of 4,9 cm2.

The challenge is to establish a constant flow and not a constant pressure drop. Similarly, it is necessary to validate the method on an area of ​​     4,9 cm2, because testing machines do not have the ability to adjust the surface size.

Before that, the mask needs to be conditioned on temperature and relative humidity similar to those created by wearing the mask and breathing.

Picture 2: Test apparatus for breathability (source: EN 14683)

3. Test of biocompatibility

This test was developed at the Slovenian National Institute of Biology many years ago, and now the method has been adapted to samples of mask material.

The test is carried out in accordance with the requirements of EN 14683, and is prescribed as a risk assessment in accordance with ISO 10993 to analyse the mask material(s) for the health of the person wearing the mask. 

The test determines the viability of the model cell culture (cytotoxicity) which is exposed to the leaching of the material from which the mask is made. In this way, conditions are created similar to skin contact when wearing a mask.

4. Test of microbial cleanliness (BIOBURDEN)

This test determines the population of viable microorganisms on or in the product. For testing, at least 5 samples are taken from one package: one from the top, one from the bottom, and 3 randomly chosen masks. Before testing, each mask is weighed and placed in a sterile 500 ml bottle containing 300 ml of extraction liquid.

Picture 3: mask placed in extraction liquid (source: LOTRIČ Metrology)

The test is performed by extracting liquids on TSA plates for aerobic microbes, and SDA plates for fungus. The plates are incubated for 3 days at 30 °C and 7 days at 20 °C to 25 °C, after which the colonies are counted. The challenge is to keep the mask samples clean, and not contaminate it during testing.

Picture 4: plates with colonies (source: LOTRIČ Metrology)

5. Splash test

The Splash test is performed by a visual inspection of the spray resistance over 10 seconds, with 2 ml of blood from 300 mm and a speed of 550 mm/s.

The challenge is the preparation of synthetic blood or a component of blood, which must meet the criteria from the standard, and to have a constant required splash speed.

PROTECTIVE MASKS

Protective masks (FFP masks) on the EU market must be certified in accordance with the Personal Protective Regulation - PPE (EU) 2016/425. The harmonized technical standard for protective mask is EN 149:2001+A1:2009.

Protective masks are, in accordance with the Personal Protective Equipment Regulation, category III. For the category III conformity assessment, the manufacturer shall apply to a Notified body for type examination and product/quality system control.

Thus, the manufacturer must meet all regulatory requirements and needs: a quality system (ISO 9001 quality management is preferred); all necessary tests performed according to EN 149, and the requirements of the Regulation related to Health and Safety; technical documentation and adequate marking, labelling and packaging, with instructions and a Declaration of conformity.

LOTRIČ Metrology is a Notified Body with NB number 2897.


CONCLUSION

The legal framework for face masks is set down in two Regulations, and after the requirements are fulfilled by the manufacturer, a CE mark can be applied. The certification process shall be repeated in the required period, while the manufacturing process shall be permanently in accordance with all requirements.

Literatura: 

[1] EN 14683:2019+AC:2019 – Medical face masks – Requirements and test methods  

[2] EN 149:2001+A1:2009 - Respiratory protective devices - Filtering half masks to protect against particles - Requirements, testing, marking         

[3] Regulation (EU) 2016/425 of the European Parliament and of the Council of 9 March 2016 on personal protective equipment and repealing Council Directive 89/686/EEC

[4] Regulation (EU) 2017/745 of the European Parliament and of the Council of 5 April 2017 on medical devices and repealing Council Directive 90/385/EEC and 93/42/EEC