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Although noise is present in almost every workplace, preventing hearing loss remains a challenge for occupational and environmental health and safety professionals. CDC estimates, based on data from 2014, that 12 percent of U.S. workers have hearing difficulties. One in four of these workers can attribute their hearing loss to occupational noise exposures. Workers’ risk of hearing loss increases in environments with complex noise, that is, when sharp, sudden impulse noise is added to the Gaussian noise of the background. However, impulse noise, also known as impact noise, is still not fully understood within the OEHS field. Many monitoring devices on the market are incapable of accurately measuring the phenomenon.

“The current noise dosimeters, and the current way that we practice as industrial hygienists, at least in my experience, is getting an underestimation of the true value of the noise exposure out there,” said Chris Robertson, MPH, CIH, CSP, the president and CEO of the Louisiana-based consulting firm Technical Environmental Services Inc. “Therefore, we're not properly protecting people.”

Robertson and TES Senior Environmental Health and Safety Engineer Cullen Whittaker, PE, CIH, CSP, became involved in impulse noise through their OEHS work. But they found an unexpected connection with their shared hobby of hunting, since protecting one’s hearing from impulse noise is as much a challenge for hunters using rifles as it is for workers in industrial and other work environments. With Robert Agnew, PhD, CIH, CSP, who is technical director of industrial hygiene at Liberty Mutual, a former researcher at Oklahoma State University, and a firearm instructor, Robertson and Whittaker created a professional development course that allows participants to investigate impulse noise while firing various types of shotguns at a shooting range.

Participants rated their PDC, “Firearm Impulse Noise Measurement Workshop,” the top PDC of AIHA Connect 2024 after its debut at that year’s conference. In this post, Agnew, Robertson, and Whittaker relate to SynergistNOW how they developed the PDC and what they hope participants will take away when it returns to Connect 2025.

The Challenge of Inadequate Instrumentation

“Noise, in general, is already one of the most complicated things that we talk about as industrial hygienists,” Whittaker said. “It doesn't seem like it should be because it’s in every industry, basically. So we should have a really good grasp of these things, but we don't.”

Robertson and Whittaker often work with clients in industries where impulse noise is a common hazard, and they sometimes have difficulty determining whether their clients exceed occupational exposure limits for impulse noise. “There's a lot of industries in the South down here, oil and gas, petrochemical manufacturing, things like that, where they will experience high noise,” Whittaker continued. “And we need to understand how to measure it. What are the limitations of the equipment that we are using currently? If we're investigating specific things like impulse noise, what do we need to look for in the equipment we want to buy?”

Meanwhile, Agnew had also encountered the challenge of measuring impulse noise in his work at OSU. “I have a research program related to impulse noise, particularly related to firearm suppressors and their effectiveness,” he said. “And one of our key things for investigating, which is common in ballistics noise research, is the limitation of sampling rate.”

Measuring impulse noise requires monitoring devices that can sample up to one million times per second. Most devices available to OEHS practitioners are unable to do this. When assisting a student with a project on firearm suppressors, Agnew found that standard OEHS dosimeters recorded unbelievably low impulse noise measurements, even for the extremely loud noise produced by firing high-powered rifles. Agnew and his student obtained a dosimeter rated for ballistic noise but found it also unable to take accurate measurements. Finding equipment capable of meeting this challenge was like “peeling back the layers of the onion,” he said. “The more you dig in, the harder it is to measure impulse noise even in the laboratory setting.”

Robertson and Whittaker began reaching out to local OEHS professionals. With AIHA’s Deep South Local Section, they hosted a skeet shooting event. Skeet shooting is a recreational activity—and Olympic sport—in which participants fire shotguns at clay targets thrown into the air. The activity was intended to be fun, but Robertson and Whittaker also related it to the need for better understanding of impulse noise in work environments. Through the AIHA Noise Committee, they then got in touch with Agnew. From their combined expertise, practical knowledge, and hobbyist enthusiasm, Agnew, Robertson, and Whittaker developed the “Firearm Impulse Noise Measurement Workshop” PDC to draw attention to the need for instruments that can accurately measure impulse noise.

“We're doing it on a firing range because we need really loud noises,” Agnew said, “and firearms are a reliable way to do it.”

A Practical PDC

The course will start with a general overview of noise physics. Then Robertson and Whittaker will share their field research on noise dosimeter screening thresholds for impulse noise, including their solutions for when impulse noise exceeds the devices’ screening limits. This part of the PDC will offer “practical solutions to industrial hygienists on how to continually evaluate or seek out impulse and impact noise,” Robertson said.

Then, Agnew will walk participants through an inventory of impulse noise. His presentation will convey the differences between impulse and Gaussian noise, similar to the educational session he delivered on this topic at AIHA Connect 2024. “If you were in a continuous noise environment that was 110 dB, you’d just lose your mind how loud that is,” Agnew said. “But that's opening a can of coke. That impulse is 110. So there's a real big difference in power.” He will also address the differences between sound pressure and power, mechanisms for hearing damage, and various sound level measurement systems and instruments.

These presentations will prepare participants for the third part of the PDC, in which they will leave the classroom for the firing range. Monitoring equipment will be set up to measure noise levels as participants fire at targets under instructor supervision. Participants will compare noise measurements taken by standard dosimeters, a dosimeter marketed for ballistic noise monitoring, and laboratory-grade noise measuring equipment. They will also evaluate noise levels produced by different types of shotguns and the effects of engineering controls, such as suppressors.

According to Robertson, a key difference between this year’s PDC and last year’s will be the inclusion of noise dosimeters. “I think it's really going to show how noise dosimeters are a great screening tool, but we need to use a sound level meter, and an appropriate sound level meter, to actually look for impulse and impact noise,” he said.

“When you have the lab equipment there, you can see the difference in the waveforms right there on the screen in front of everybody. It's really dynamic learning,” Agnew said. “And then we're going to go back into the classroom, then try to start figuring out how we interpret what the dosimeters are telling us when it comes to evaluating occupational disease risk for people using firearms or other impulse sources.”

Wide Applications of Impulse Noise Research

The excursion to the firing range will provide a unique interactive element to the PDC, which the instructors hope will be fun for participants. But they also stressed that the experience will be applicable to a range of industries—wherever impulse noise can be found. “Almost every work environment has complex noise, meaning that it has impulse and impact sound,” Robertson stressed. “And that's why this particular PDC is so important because we're underestimating the true concentration out there. So that's why people are still at risk of hearing loss.”

His intent is that participants will come away understanding what impulse noise is and that it’s likely present in their work environments. They will also leave the PDC knowing how to use a dosimeter to screen for impulse noise, how to achieve accurate measurements, and how to overcome the limitations of their equipment.

Better awareness of the limitations of noise monitoring equipment was also a major concern for Agnew. “Our standard tools give us a false sense of security because they're reading impulses, but they're really underestimating them,” he said. Through the PDC, he aims not only to increase awareness of this problem but also to move the OEHS field, including practitioners and manufacturers, toward solutions. “And hopefully, in the future, we'll start working on understanding hearing protection devices and impulse noise.”

Whittaker agreed with the need to involve manufacturers of noise monitoring and hearing protection devices, as well as other OEHS professionals, in discussions of impulse noise. “It's taken me a long time to really get to the point where I feel like I have a decent understanding of regular noise exposures,” he said. “We're not going to get to that point with impact and impulse noise unless we start having these conversations and having these learning events where we're actually figuring things out together.”

“I want to help people retire healthy and happy so they can play with their grandbabies, and that's what, I think, we're starting to do with this PDC,” Robertson said. “And it's fun at the same time.”

The professional development course “Firearm Impulse Noise Measurement Workshop,” led by Robert Agnew, Christopher Robertson, and Cullen Whittaker, will occur Thursday, May 22, from 7 a.m. to 6 p.m. Central time, in association with AIHA Connect 2025. Participants of this PDC will be provided boxed lunches and transportation to and from the offsite firing range. AIHA Connect 2025 will be held from May 19 to 21 in person at the Kansas City Convention Center in Kansas City, Missouri, and virtually. To view the conference agenda, visit the AIHA Connect website.

Related:

The Synergist: "A Day at the Range: Controlling Impulsive Noise in a Tactical Training Environment" (April 2015).

The Synergist: "A Deaf Spot for Industrial Hygiene: The Problem of Impulse Noise" (January 2017).

The Synergist: "Noise Limits for Warfighting: Recently Revised Standard Addresses Noise from Military Operations" (November 2016).