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HSE collaborates on FFP3 mask re-use research

18 February 2021

THE THREAT of COVID means that healthcare workers (HCW) in the NHS and other clinical care settings must wear respiratory protection while treating infected patients for their own protection.

This includes single use filtering facepiece respirators (FFP3) if undergoing aerosol generating procedures. However, especially at the beginning of the pandemic, there was a shortage of FFP3 masks. Although new masks are now becoming available, any way to maximise use safely should be considered.  

One possible solution is for FFP3 masks to be re-used. However, as they have only been tested for single use it is unclear if decontaminating the masks will be effective or alter the structural integrity of the masks making them unable to protect the wearer. In a Canadian study, decontaminating mask material with vaporised hydrogen peroxide (VHP) proved effective, although the material they tested was from US as standard N95 masks are not generally used in the UK or EU. 

In a cross-disciplinary project involving microbiology and PPE teams, HSE collaborated with Bioquell, a leading UK supplier of hydrogen peroxide fumigation systems. The project aimed to build on the Canadian research using the same basic methodology, but with FFP3 respirators. 

Five different types of commonly used FFP3 masks were sourced from the NHS, two with valves and three without. Biological indicators (bacterial spores more resistant to decontamination than SARS-CoV-2) and chemical indicators were inserted into each type of the sample masks to test efficacy of the fumigation process. The results were compared with unexposed controls and showed that the fumigant penetrated the mask and killed the bacteria dried onto the biological indicators. The results showed four to six log reduction in numbers, which means a reduction rate of bacteria of ten thousand to ten million from the original sample. 

Each mask type was subjected to both 10 fumigation cycles and 20 fumigation cycles, with visual checks carried out to determine if there were any apparent changes to the mask material or their structure. Masks were also checked for residual hydrogen peroxide. Some off-gassing was evident shortly after fumigation but dissipated with time to a level that would not significantly expose the wearer to risks such as skin irritation or breathing difficulties.

No significant structural changes were observed in the masks compared to unexposed controls, other than some wear and tear associated with repeated handling, so volunteer fit testing was conducted by experienced qualified fit testers to determine if they still offered protection to the user.  This showed there to be no significant deterioration in fit compared to unexposed controls.  

The results were sufficiently promising as an option for re-use of FFP3s to warrant a pilot study to be conducted at an NHS Trust using similar technology, but with masks previously used in healthcare.

More information can be found on the Solutions from HSE website at solutions.hse.gov.uk