The study showed that one-third of workers achieve attenuation higher than published NRR for their earplugs, and another third achieve attenuation within 5 dB of those ratings. Only the remaining third had attenuation that was more than 5 dB below published NRRs.
A recent field attenuation study conducted by the Howard Leight Acoustical Laboratory on the performance of hearing protection devices shows that individual, one-on-one training was the most significant factor in predicting good earplug performance.
The study, which was conducted on more than 100 workers at 8 facilities, showed that one-third of workers achieve attenuation higher than published Noise Reduction Ratings (NRR) for their earplugs, and another third achieve attenuation within 5 dB of those ratings. Only the remaining third had attenuation that was more than 5 dB below published NRRs.
"This reinforces the need for individual fit testing of earplugs, especially in light of the Environmental Protection Agency’s proposed labeling changes," said Brad Witt, MA, CCC-A, director of hearing conservation for Sperian Hearing Protection LLC, and a principal author of the study. "No generalized rating scheme for hearing protectors can be effective without knowing how much attenuation individual workers actually attain.
"If a safety manager were to supply earplugs based on the assumption that all earplugs only achieve half of their published NRR in the field, then clearly two-thirds of the workers in this study would be seriously overprotected, since they are achieving much higher protection than 50%," he said.
In the study, workers were tested during standard work shifts. They were not pre-screened, and were tested with their own earplugs that they routinely wear on the job, with no modifications. The tested earplugs were from four different hearing protection device manufacturers, and workers received no training or coaching as part of the test, they were simply asked to insert the earplugs as they normally did on the job. No feedback or correction was offered if they fit the earplug incorrectly.
A wide range of HPDs is available today, including different materials and styles designed for specific applications and/or worker preferences.
Witt says the purpose of the study was to identify factors that contributed to good earplug fit, and good attenuation in use. "A variety of personal as well as program factors were evaluated to determine which factors would correlate the best to a good earplug fit among these 100 workers," he said. Factors included: gender, age, years working in a hazardous-noise environment, ear canal size, familiarity with hearing protection devices, model of product used, amount of group training received, amount of individual training received, and enforcement.
Of all these factors, says Witt, "only one stood out as having a strong correlation: one-on-one training. That is, the more often a worker had received individual training in the proper use of hearing protectors, the higher the probability of a good fit." The same could not be said for group training, he says. "It appeared to make no difference at all whether a worker had attended zero, five, or 10 group training sessions in hearing protection, when measuring good attenuation in the field."
Enforcement, he added, was also a good predictor of good earplug performance, but only when it was coupled with one-on-one training. Another question posed by the study was whether workers who achieved low attenuation with one type of earplug would also attain low attenuation with all types of earplugs. "We tested this by inviting some workers to try a second pair of earplugs—different earplugs, perhaps a model they had never tried before," Witt says. Workers who tried a second pair of earplugs often had major leaps in attenuation, bringing them closer to the published NRR.
"Field testing of hearing protectors bridges the gap between the laboratory estimates of attenuation and the
real-world attenuation achieved by workers as they normally wear the protectors," Witt concluded. "This test
confirmed the value of individual, one-on-one training, and the wisdom of offering workers a variety of
suitable hearing protectors."