Noise reduction under the hood of a portable air‐purifying respirator system by means of a muffler insert.

Speech intelligibility is probably never more important than in emergency situations. Recently a manufacturer of a portable air‐purifying respirator system requested assistance in lowering the noise level that users were encountering under the hood. In operation, the noise level and sound quality in the hood were reported to be objectionable and concern about the ability of personnel to communicate effectively was expressed. Typically, choosing quieter components would be the first step in evaluating various acoustical treatment packages. However, since the components of the blower exposed to the air path were already NIOSH approved, choosing an alternate blower was not a viable option. Polymer Technologies embarked on a study that evaluated the blower and the paths to the receiver, successfully providing attenuation options that could be easily implemented. Prototype testing proved that substantial acoustical attenuation could be achieved by utilizing an in‐line muffler lined with acoustical absorption material. The maximum benefit achieved was in excess of a 14 dBA reduction in the overall sound pressure level under the hood at ear level and resulted in what was considered to be a more “acceptable” sound.