Beta ratio filter efficiency

It follows that the higher the value of the beta ratio, the more particles of the specified size, or greater, are retained on the filter. The filter efficiency at this particle size can then be determined from the beta ratio ... 

The beta ratio and the corresponding efficiency are illustrated in Table 1.5 in a test where the filter was challenged with 1 million particles per unit volume (the numbers in Table 1.5 refer, of course, to the same particle size). 

The nominal rating of a filter can be expressed by means of this efficiency fignre. Given as a percentage, it can be calculated from the beta ratio, or directly from the particle number count ... 

The classic method of determining filter efficiency is by the bead challenge test, with a rating expressed as a beta ratio, thus a beta ratio > 75 specifies a filter efficiency of 98.6% or better relative to a particle size of x pm. 

In the past, several terms have been coined to describe the retention efficiency of the filter system beta value, microbiological safety index, reduction ratio, and titer reduction ratio [64,68,72], The log reduction value (LRV) is a filter retention efficiency term that is the logarithm to the base of 10 of the ratio of the number of organisms in the challenge suspension to the number of organisms in the filtrate. 

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