In early 2020 there were critical supply shortages of PPE; 20/30 Labs were awarded a grant for face mask reprocessing (FRR decontamination and re-use) by Innovate UK. We were able to utilise our normal laboratory activities of verifying and validating the reprocessing of medical devices for manufacturers, as well as research we completed at the time on filter integrity and efficacy.
By the middle of 2020, we were inundated by medical face mask manufacturers wanting to get a classification under EN 14683: 2019, but unable to find a testing site. 20/30 Labs were able to quickly mobilise and repurpose some of the equipment from the grant, as well as assemble and validate a testing rig, to put together the full testing suite for medical face mask classification. At the height of the pandemic, we were able to offer a service that enabled supply of much needed PPE at the correct quality, to reach the NHS, other healthcare settings and the public.
A medical face mask is a Class I medical device, generally composed of a filter layer that is placed, bonded or moulded between layers of fabric. They must meet the design and safety requirements of the UK Medical Device Regulations 2002 (SI 2002 No 618, as amended), and be CE or UKCA marked before being sold in the UK.
The purpose of medical face masks is to limit transmission of infectious elements from staff to patients during surgical procedures in operating theatres, and other similar conditions. A secondary purpose is to reduce the transmission of infectious elements from the nose and mouth of an asymptomatic carrier or a patient with clinical symptoms, particularly in epidemic or pandemic situations. They can also protect the wearer against splashes of potentially contaminated liquids.
Medical face masks are classified into two types (Type I and Type II) according to bacterial filtration efficiency, and Type II is further divided according to splash resistance (Type IIR for ‘resistance’). The efficiency of a mask depends on several factors such as the filtration capability, material quality and the fit on the wearer’s face (loops, tie bands, nose clamps).
Stage 1 : Scope
The five markers for classification as per EN 14683: 2019 are: Bacterial Filtration Efficacy, Breathability (Differential Pressure), Microbial Cleanliness (Bioburden as per ISO 11737-1:2018), Splash Resistance (as per ISO 22609:2004), and Biocompatibility (ISO 10993-1:2009).
Stage 2 : Sample Preparation
For each test, samples should be conditioned at 21°C ±5 and 85% ±5 relative humidity for a minimum of 4h (room temperature) to bring them into equilibrium with atmosphere prior to testing.
Each test marker has different criteria for sample size (mm), minimum quantity and composition (i.e., when a mask consists of two or more areas with different characteristics or different layer composition, each panel or area shall be tested individually, and the lowest performing panel used). All tests must be carried out on finished products or samples cut from finished products.
Stage 3 : Test Methods
BFE: Bacterial Filtration Efficacy
A sample of the mask material is clamped between a six-stage cascade impactor and an aerosol chamber. An aerosol of Staphylococcus Aureus ATCC 6538 is introduced into the aerosol chamber by a BLAM nebuliser and drawn through the mask material and the impactor under vacuum, at a flow rate of 28.3L/min. The bacterial challenge is delivered for 1minute. The bacterial filtration efficiency (BFE) of the mask is given by the number of colony forming units passing through the medical face mask material and captured at each stage of the impactor (onto Tryptone Soya Agar) expressed as a percentage of the number of colony forming units present in the challenge aerosol (Mean particle size 3.0μm ± 0.3)
ΔP: Differential Pressure
Face masks are required to show that when challenged with of flow of air equivalent to 8L/min that the pressure difference between one side of the mask and the other falls under required limits. This ensures that the material of the mask is sufficiently breathable for its intended use.
MC: Microbial Cleanliness
Face masks are required to show that when in their final packaging, the bioburden present on the masks does not exceed 30 CFU/g. Recovery from the mask/sample(s) is undertaken using a modified, UKAS-accredited method, according to ISO 11737-1: 2018 (Bioburden SOP L053) and as per EN 14683 requirements. Samples are aseptically taken out of packaging in a Class II laminar flow cabinet, weighed and visually examined for any damage. The samples are then placed into 300ml sterile recovery diluent containing a surfactant and sonicated for five minutes. The eluent is tested for viable aerobic bacteria and yeast/moulds. The total bioburden is expressed by addition of the TSA and SDA CFU counts at the end of the incubation period.
SR: Splash Resistance
Face masks classified as Type IIR intended for surgery are required to show that when challenged with a splash of blood, simulating an arterial flow, that the blood does not penetrate the mask to the users face and mouth. The principle of the test is that the velocity of blood leaving a canula of a defined diameter can be controlled to the same as the velocity produced by normal human blood pressure in a severed artery by controlling the volume of blood delivered over specific time frame. Using the standard canula, 2ml of blood delivered over 0.66 seconds gives a velocity of 550cm/s, which is equivalent to a blood pressure of 16kPa. Type IIR face masks are required to resist this equivalent pressure.
Stage 4 : Acceptance Criteria
Stage 5 : Stage 5: Results
Lab reports are issued, in alignment with EN 14683: 2019 acceptance and reporting criteria.
Medical Face Masks classified as per EN 14683: 2019 from 2020 – 2021.
Pass rate, with classification Type II or Type IIR
Turnaround time on each project
Routine Monitoring Projects; Microbial Cleanliness
20/30 lab were able to meet the growing demand of Medical Face Mask testing at the height of the pandemic, turning around every project within 8 – 14 days (incubation periods of 7 days). This testing was integral to getting more PPE to the public and the NHS, and additionally removing non-compliant masks from selling in stores.
20/30 Labs has been able to use the skills gained through the Innovate UK grant and Medical Face Mask testing and apply it to new areas. We have carried out several projects on bacterial filtration efficacy of biocidal aerosols, filter penetration testing and barrier mask testing. Some of our work on barrier mask testing also made the news!
Accredited to BS EN ISO 13485 for “The provision of microbiological testing and consultancy for the medical device industry” we can offer a wide range of microbiological validation services for medical devices including proof of concept, product design & compliance and performance qualification.
- BS EN 14683:2019 Medical face masks. Requirements and test methods
- BS EN ISO 11737-1: 2018 +A1: 2021 Determination of a population of microorganisms on products
- ISO 22609:2004 Clothing for protection against infectious agents — Medical face masks — Test method for resistance against penetration by synthetic blood