In the case of infectious diseases like COVID-19, hospitals have to make sure that their patient-facing employees are safe by using Personal Protective Equipment, in particular, N95 masks. N95 masks can stop up to 95% of particles that are as small as 0.3 microns. Yet, not only are N95 masks expensive, they also cannot easily be reused immediately. A collaboration between Mumbai-based institutions, Tata Institute of Fundamental Research (TIFR) and Tata Memorial Hospital, has spawned a workable solution to the problem of expense and decontamination.
Moist heat
Chance and a shared interest in optimising the use of N95 masks brought together Arnab Bhattacharya, a TIFR professor, and C.S. Pramesh, the director of Tata Memorial Hospital. After discussing various routes for decontamination of the masks, such as the use of UV radiation, hydrogen peroxide and so on, they concluded that using moist heat was a good bet. They realised that heat treatment at temperatures beyond 65-70 degrees C for about 60 minutes in dry air or for just about 30 minutes in moist air with humidity over 50% was sufficient to decontaminate the masks, even with SARS-CoV-2 virus. In this method of decontamination, the pathogen is reduced by 99.9%. “We play safe and use 70 degrees C for more than 60 minutes, with some humidity anyway,” says Prof. Bhattacharya. “We have checked that the filtration efficiency of various masks is not impacted over five such one-hour decontamination cycles.”
Time, a decontaminant
If the used N95 mask is left alone and exposed to air for 96 hours, it will get decontaminated. If a person had five masks to use, and used a different one each day, then by the sixth day, the mask used on day one will be decontaminated. As Prof. Pramesh explains, in TMH, they use a combination of the two approaches for best results. “To date over 6,500 N95 masks have been decontaminated using this method at our hospital. Not only has this resulted in a huge saving, the integrity and reliability of the masks are not compromised,” says Prof. Pramesh. Before using the masks, the group ascertained that the right temperature and right duration of heating eliminated the viral load, and the mask was decontaminated and its integrity intact.
The TIFR group also tests the masks beforehand to make sure that they indeed qualify to be called N95. As Prof. Pramesh explains, “This is because as the pandemic grew in impact, we needed many more masks than our usual suppliers could provide. We had to purchase them from new manufacturers and needed to check the quality.” This has two aspects – checking the filtration capacity and also the fit, and the TIFR team obliged.
Low-cost solution
In fact, Prof. Bhattacharya and coworkers have developed, in collaboration with Manu Prakash’s team from Stanford, a low-cost method of decontamination of the masks that simply uses two vessels, one of which fits into the other, and a cotton cover that insulates the outer vessel. Water is placed in the outer vessel, heated and then the smaller vessel with the mask in it is placed within and the moist air works its magic. “The outer vessel a 5 l capacity aluminium one, and the inner one an approximately 2 l capacity stainless steel one. A Venus 4400 N95 respirator, one of the most common brands used in India, was chosen for the experiments,” says Prof. Bhattacharya. “COVID-19 has brought people together in amazing ways to try to tackle problems in a constrained environment.”