Enhancing and sustaining noise attenuation from hearing protection devices: A mixed methods review of fit testing and instruction approaches

Extensive training has been shown to improve the effectiveness of hearing protection devices (HPDs) in reducing noise exposure for workers. This study aimed to (1) assess the evidence for short- and long-term effectiveness of HPD fit testing paired with extensive instructions and (2) identify the type and frequency of refresher instruction associated with maintaining its effectiveness. A literature search was completed on February 5, 2025. The inclusion criteria focused on uncontrolled before-and-after (UBA) studies that reported personal attenuation ratings (PARs) provided by HPDs in the field. A total of 23 UBA studies involving 5,575 workers were included, meta-analyses were performed when multiple comparable studies were located. For earplugs, retesting immediately after extensive training increased the mean PAR by 12.88 dB (13 studies) compared with the pre-intervention PARs without instructions. The improvement decreased to 8.84 dB (2 studies) within 6 months and further reduced to 4.46 dB (2 studies) at 12 months. For earmuffs, only one study reported increase in PARs of 5, 2, and 3 dB for immediate, short-term, and long-term assessment, respectively. Introducing extensive refresher training within a 6-month interval increased the mean PAR from earplugs by 1.53 dB (2 studies) compared with the post-intervention PAR retested immediately after extensive training, with a further increase of 3.45 dB (1 study) following annual extensive instruction. Simple refresher instructions within a 6-month interval maintained the PAR values (1 study). However, without any refresher training, the PAR decreased by 2.64 dB (2 studies) within 6 months and 3.09 dB (2 studies) over 6 months or longer. Refresher training may increase the probability that workers receive efficient protection from their HPDs. However, more high-quality studies could help inform the optimal type and frequency of refresher training.