How We Prepare Hearing Protection for Real-World Use
By Alexandra Serban
June 06, 2019
Ask any safety manager and he’ll say that distinguishing high-quality hearing protection from the myriad options available is daunting.
We caught up with Dr. Robert Ghent, Research Audiologist and Manager of the Honeywell Howard Leight Acoustical Testing Laboratory and asked him a few questions on how hearing protection is vetted to guarantee effectiveness in everyday work situations.
Dr. Ghent, first of all, what does a research audiologist do?
Most audiologists go into clinical work, but there are other areas of specialization to explore, such as educational audiology and hearing conservation. In my case, as a research audiologist working within the hearing conservation specialty, most of what I do involves testing hearing protection products—like earplugs and earmuffs—and other solutions that help safety professionals manage their hearing conservation programs and protect their workers—like our fit-testing system, VeriPRO.
The lab’s customers are mainly internal stakeholders: Production, Quality, Regulatory, R&D, Marketing. Some departments, like Quality and Production, often need simple verification testing. Others, like R&D and Marketing, often need to run larger experiments to support product development.
Occasionally, we conduct our own research in a quest to answer ambitious questions such as “What impact do electronic earmuffs have on speech understanding in a noisy environment?” In fact, our current laboratory intern is setting up such a study with hearing-impaired workers for her doctoral dissertation.
What is the Howard Leight Acoustical Lab?
The Acoustical Lab, located in San Diego, California, resides within the walls of the facility where our foam earplugs are manufactured. Interestingly, the lab was built first and the rest of the building was constructed around it. This means the two structures are mechanically isolated from each other to avoid sound from production activities leaking into the laboratory. Construction was completed in 1998.
Howard Leight, the founder and president at the time, went to all this trouble and expense because the background noise requirements for testing are so stringent. We honor his commitment to the quality of the laboratory by maintaining his name in the title of the Honeywell Howard Leight Acoustical Testing Laboratory.
What role does an Acoustical Lab play in developing hearing protection solutions?
We are often consulted as subject matter experts early in the product development cycle. Then, as prototypes and materials are developed, the R&D department may create experiments aligned to Honeywell’s Design for Six Sigma tools to explore the acoustical characteristics of a material or design.
The laboratory also generates data to help answer research questions associated with noise attenuation.
We may perform verification testing on products to ensure R&D’s design goals are being met, and validation testing to satisfy the requirements of the marketing function but, most importantly, those of the customer, which is to provide a solution that protects workers’ hearing as appropriate to specific work environments.
As an example of testing for R&D, a chemical engineer recently requested some rudimentary testing on foam samples to see if they might make our earplugs more environmentally-friendly.
A Production example is a cost-saving effort where we are running experiments to see how a specific mold material affects the noise attenuation of earplugs.
For Retail Marketing, we tested samples of counterfeits of one of our most popular earmuffs. The data generated in the lab showed that the counterfeit products put wearers at increased risk for hearing loss compared to the genuine product. The issue wasn’t simply about lost revenue from the sale of counterfeit product, but about the idea that a counterfeit product with our name on it could be putting people at risk for hearing loss.
These are just a few examples of the internal testing role we play in the Hearing Protection Line of Business.
How are products being tested?
The lab is designed around two primary types of testing: real-ear attenuation at threshold (REAT), which is behavioral testing involving human subjects, and electroacoustic testing with an acoustical test fixture (ATF).
The ATF is anthropomorphic – a human dummy with features that are dimensional averages of real human features. In this way, the ATF disturbs the sound field in much the same way as the human head, so some correlations are possible between ATF and human measurements.
While human subject testing typically consumes more time than ATF testing, ATF testing represents by far the greatest volume of test requests coming to the lab.
What does a high-quality HPD look like?
All hearing protection devices (HPDs) sold are required to display on the package an estimate of the noise reduction a wearer might achieve if the HPD is worn correctly. That is the primary requirement of high-quality HPDs.
Secondly, the HPD must be comfortable for long-term wear. If the HPD isn’t comfortable, then it will most likely not be worn. If so, then it doesn’t matter what estimated noise reduction number is printed on the package. Those numbers are different depending on the region of world in which the HPD is being sold (NRR in North America, SNR in Europe, SLC80 in Australia, for example).
Each region that specifies such a number also publishes standards and/or regulations that dictate the testing and calculation methods. The one thing all these testing standards have in common, however, is that they all rely on REAT testing with human subjects.
How do we ensure much-needed accuracy and objectiveness?
To validate our work, we engage with external laboratories. The noise reduction label is generated by a third-party laboratory, meaning they provide the data for the numbers that are printed on the packaging. By keeping this testing at arms-length from our own laboratory, we maintain the credibility of our numbers.
Our US partner is accredited by an internationally-recognized accrediting body to carry out testing to US, European, and Australia/New Zealand standards. We oftentimes validate each other’s results by testing in each other’s lab. We also send them products for specific testing our lab may not be equipped to perform.
Every several years, the various laboratories, including ours and our partner’s, take part in a “round robin” exercise where we all run the same testing on the same products, to the same standards. We pool and analyze the data to see how much variability exists among the various laboratories. From this analysis, we calculate the uncertainty in the human subject testing procedure that can be applied to test results regardless of the lab that does the testing.
Finally, the laboratory works to maintain its own Quality Management System in accordance with ISO 17025, the international standard specifying the general competence of testing laboratories.
Dr. Robert M. Ghent, Jr. is the Research Audiologist and Manager of the Honeywell Howard Leight Acoustical Testing Laboratory at Honeywell. He oversees the testing of hearing protectors to regional test protocols, and conducts research to support product development and expand the profession’s knowledge base. He has spent over three decades on the prevention and remediation of hearing loss as an auditory researcher and clinical audiologist.
Interested in learning about hearing conservation in your work environment? Here is a list of helpful resources.