Efficiency Of COVID Masks
The last few Months have been dominated by Coronavirus whether in social settings, work or in the media. You are constantly reminded about the threat the virus poses, and rightly so. A lot of discussions have centred on preventative measures and PPE with a focus on masks and the level of real protection they offer. I had an interesting discussion recently where I was told that N95 masks offer filtration efficiencies of 95%. To the average person this seems like a very high efficiency value but to an engineering professional looking at providing filtration for a safety critical process this efficiency rating could be deemed too low for the task at hand e.g. filters used within offshore seal gas applications requiring filtration efficiencies of 99.9% at 1 micron.
Filtration media used in critical applications are normally assigned an absolute rating for a given particle size, an absolute rated filter offers the reassurance of downstream protection for any critical equipment or final product. This rating is issued on the basis of test data used to calculate a defined efficiency or beta ratio. The higher the beta ratio or efficiency of the filter the more particles of the given size and above the filter will capture. Acceptable beta ratio values differ between industry to industry, so it wise to become familiar with the beta ratio and efficiency’s that are used in your industry or application as they can often be an inflexible part of a spec that have to be adhered to in order to comply with a given standard or regulation.