Personal attenuation ratings versus derated noise reduction ratings for hearing protection devices

Abstract

National and international regulatory and consensus standards setting bodies have previously proposed derating hearing protector ratings to provide a better match between ratings determined in a laboratory and the real-world measurements of attenuation for workers. The National Institute for Occupational Safety and Health has proposed a derating scheme that depends upon the type of protector. This paper examines four real-world studies where personal attenuation ratings (PARs) were measured at least twice, before and after an intervention in earplug fitting techniques. Results from these studies indicate that individualized earplug fitting training dramatically improves a worker's achieved PAR value. Additionally, derating schemes fail to accurately predict the majority of achieved PARs. Because hearing protector fit testing systems are now readily available for use in the workplace, personal attenuation ratings provide a better estimate of worker noise exposures and are able to identify those persons who need additional instruction in fitting hearing protection devices.

Figure 1.

(Color online) Sorted PAR chart from the NIOSH Advanced Hearing Protector study (Murphy et al., 2007). Fit testing was accomplished with the original FitCheck system modified to test four subjects simultaneously. The open symbols represent the initial fit tests conducted in February 2004. The solid symbols represent the fit tests conducted during the fourth visit to the factory in February 2005. Red symbols are the right ear and blue symbols are the left ear. The gray bars are the range of the NRR values (dBC) for the earplugs worn by the subjects. The magenta bars are the range of the derated NRRs (dBA).

Figure 2.

(Color online) Sorted PAR charts from the Chinese worker studies (Gong et al., 2019; Liu et al. 2020; Gong et al. 2021a; Gong et al., 2021b). The different panels separate the results from the subjects based upon the earplugs and fit-test systems used in these studies. The solid lines in the panels indicate the respective NRR and the dashed lines indicate the derated, C-A corrected NRR for each earplug tested. The E-A-Rfit^™ system was used to test the workers in the two panels on the left. The FitCheck Solo system was used to test the workers in the other six panels. Initial fit tests are indicated with blue circles and the final fit tests are indicated with gold diamonds.

Figure 3.

(Color online) Sorted PAR charts from the USMC fit testing study (Federman and Duhon, 2016). For each section of this plot, the initial fit test is shown as the blue circles. The expert fit PARs are shown in orange squares and self-refit PARs of the earplug are displayed as gold diamonds. The horizontal solid lines are the NRR (33 dBC) of the Moldex Camo Plugs^® and the dashed lines are the derated NRRs (13 dBA). The PAR results measured with 3-, 5-, and 7-frequencies are separated with a vertical line from 0 to 60 dBA.

Figure 4.

(Color online) Sorted PAR charts from the USMC fit testing study (Federman et al., 2021). The three panels illustrate the result of the different training methods. The upper panel used the current video-based instruction. The middle panel shows the results for the experiential (eHPD) training protocol. The lower panel shows the results from the integrated fitting protocol that combined the video and experiential training. For each panel, the initial fit test is shown as blue circles. For the experiential and integrated protocols, the subjects were tested immediately after having been fit by the experimenter (orange squares), and then the subjects were asked to remove the earplug and self-refit the earplug (gold diamonds). The horizontal solid lines are the NRR (33 dBC) of the Camo Plugs^® and the horizontal dashed lines are the derated NRRs (13 dBA).

Figure 5.

(Color online) Pre-training and Post-training swarm plots illustrate the effect (or lack of effect) of training on the PARs relative to the derated NRR. OSHA derating and C-A correction was applied. The blue symbols are the initial fit tests before training. The gold symbols are the post-training PARs.