As the Coronavirus pandemic continues, it has been well publicised that there is a shortage of vital respiratory protective equipment, in both the NHS and private sectors. Until a reliable supply can be re-established, governments and other bodies are looking to alternatives and methods to increase longevity of their supplies. One such method is the sterilisation and re-use of disposable respirator masks. (There are a number of different mask types being used to help protect from and limit coronavirus transmission. You can read more about the different types of disposable mask here.) The cleaning of re-usable equipment prior to sterilisation is recommended however there is no data on both effective and non-damaging cleaning methods for disposable equipment.
A number of groups have been investigating the use of different types of sterilisation on disposable masks in terms of how effective the process is and if the masks protective effects become compromised following this. A technical report (1) has also been issued by the European Centre for Disease Control and can be accessed here, with details of some of the methods listed below. We have also researched some different methods used by various groups around the world which we have summarised.
Steam sterilisation (i.e autoclaving)
A number of attempts at steam sterilisation have been made to differing success. A group in the Netherlands use steam sterilisation of FFP2 masks at 134°C and masks showed signs of deformation in some masks(2), whereas another group used steam sterilisation at 121°C and their testing indicates that repeated sterilisation did not significantly influence the filter efficiency of the masks (they repeated the sterilisation process 5 times, but their sample size was very small and only focused on a single type of mask) (3).
Hydrogen Peroxide Vapour Sterilisation
An FDA commisioned study showed the use of hydrogen peroxide vapour (HPV) to be effective in decontaminating N95 respirators and the respirator maintained its functions even after 10-20 cycles, but after this showed signs of degradation (1). A study in the Netherlands suggested only up to 2 cycles of HPV on FFP2 masks is effective before they fail fit testing. This study did not completely consider filtration ability of the masks after processing and was only tested on a single type of mask not containing cellulose (cellulose containing masks may negatively affected by HPV)(2).
Dry Heat Sterilisation
Dry heat sterilisation has also been suggested as a possible methods for respirator reprocessing. The German Ministry of Work & Social Affairs (Bundesministeriums für Arbeit und Soziales) and the Ministry of Health (Bundesministerium für Gesundheit), BMAS/BMG have suggested the following method for FFP2, FFP3 and other face masks : dry heat between 65-70°C for 30 minutes. The use of the Memmert SF110plus is recommended as it is a certified medical device, and the set temperature will be able to be accurately held within tolerance with confidence. (4) The temperature exposure over time set, i.e. cycle parameters are recorded and filed by Memmert Medical Devices precisely. It could be possible to carry this process out with other devices (i.e. drying ovens), however you would want to be confident the temperature is held accurately for the set cycle.
Many groups around the world are carrying out further research into these methods to fully investigate their efficacy. The above methods are only to be considered as a last-resort measure and due to the limited data availability, any chosen methods should be fully evaluated, along with fit tests being carried out.
You can read our Corona Virus advice page here, where we link you to any bits of useful information and also to our current high demand in stock items. If you have a specific PPE requirement, you can fill out our request form here.
(1) Cloth masks and mask sterilisation as options in case of shortage of surgical masks and respirators. European CDC Technical Article, 2020. Available from: https://www.ecdc.europa.eu/sites/default/files/documents/Cloth-face-masks-in-case-shortage-surgical-masks-respirators2020-03-26.pdf
(2) Hergebruik FFP2 mondmaskers 2020. Bilthoven: RIVM, 2020. Available from: https://www.rivm.nl/documenten/hergebruik-ffp2-mondmaskers.
(3) Sterilization of disposable face masks by means of standardized dry and steam sterilization processes; an alternative in the fight against mask shortages due to COVID-19. The Journal of Hospital Infection, 2020. Available from: https://www.journalofhospitalinfection.com/article/S0195-6701(20)30176-6/fulltext
(4)A method for reprocessing of face masks, ﬁltering facepiece respirators, respirators (respirators hereafter). Memmert GmbH, 2020. Available from: https://www.memmert.com/fileadmin/products/documents/downloads-divers/Statement_of_reprocessing_of_respirators_EN_-_signed.pdf