The U.S. National Fire Protection Association (NFPA) 1981 standard covers self-contained breathing apparatus (SCBA) for emergency services. It requires a minimum STI of 0.55 for non-electronic systems, and 0.60 for supplementary systems. The test methods for both non-electronic and supplementary systems are similar. Both require a hemi-anechoic chamber and a Head and Torso Simulator (HATS)…