Rapid quantitative measure of speech intelligibility through personal protective equipment facemasks using two head & torso simulators

Abstract

A test method has been developed that provides a rapid and quantitative measure of speech intelligibility via speech transmission index (STI) through personal protective facemasks using two Brüel & Kjær Head and Torso Simulators (HATS) under a variety of acoustical environmental conditions. STI measurements were made using this new Test Method (TM) on a collection of 3M prototype and production facemasks and respirators, a competitor facemask, and a “no mask” baseline. This new TM enables rapid differentiation among facemask designs. Comparisons among the set of face coverings shows a clear tradeoff of filtration level for STI. New 3M prototypes with 90% filtration achieved an Excellent STI of 0.85, only 0.03 below a perfect no mask baseline. There is a dramatic step from maximum STI with no filtration at all to Excellent STI with 90% filtration. Most of the 95% filtration masks had STIs clustered near the lower end of the Excellent band at 0.78. P100 filtration significantly compromised speech intelligibility in the 3M 6300 half facepiece reusable respirator with a Fair quality rating on the STI scale at 0.60.