Editor’s note: this post is part of a series on exposure assessment sessions held at AIHce EXP 2018 in Philadelphia. For information about the upcoming AIHce EXP 2019 in Minneapolis, visit the conference website.

Audience members at AIHce EXP 2018 were treated to a fascinating look at the exposure assessment challenges facing the U.S. Air Force during both ground and airborne operations.

“In the Air Force, a lot of our assets have advanced materials in them, and in the event of a mishap there are unique emissions that we have to consider for first responders, follow-on support, bystanders, and the general population,” said Christin Grabinski, a research chemical engineer for the U.S. Air Force School of Aerospace Medicine, 711th Human Performance Wing Air Force Research Laboratory, at Wright-Patterson Air Force Base in Ohio.

Grabinski leads the hazard detection and control engineering team, whose mission is to apply advanced technologies for characterizing and mitigating exposures to chemical hazards. He revealed that ultrafine particles can make exposure assessment of small-arms training a challenge.

“The main issue is that lead ammunition was replaced with lead-free frangible ammunition quite a long time ago,” Grabinski said. “But we still need to take it seriously as a potential hazard. Right away there started to be respiratory irritation complaints filed. But lead-free frangible is primarily copper, and copper doesn't exceed the occupational exposure limit very often. It's not predictive of respiratory irritation. We need to have an exposure standard and a sampling method that's predictive of the symptoms.

“Actual firing emissions are composed of gases, vapors, and aerosols. Aerosols are primarily in the ultrafine size range, so we're talking about very, very tiny particles that dominate the emissions from firing. So that's what we want to make sure that we capture in our exposure assessments.”

Grabinski investigated five small-arms firing ranges—some fully enclosed, others partially enclosed.

“We know that if particles are that small—in the 16 to 28 nanometer size range—the surface area per mass is very large. We know from toxicity studies that surface area is more often correlated with pulmonary toxicity than mass. The particles are very small. In one cell you could have hundreds of particles enter, so we were worried about translocation issues and types of toxicity that aren't traditionally assessed.”

To determine relevant exposure standards and assessment methodologies, Grabinski’s team needed to complete a follow-up research and development study, including toxicity and health evaluation in small-arms training instructors, to identify the correlation between specific components of firing emissions and health outcomes. That comprehensive evaluation of emissions properties and health effects to support new exposure standards is expected to wrap up this year.

The exposure assessment challenges aren’t limited to ground operations. While presenting on pilot breathing air, Daniel Mackenzie-Smith, a bioenvironmental engineer, explained that the complex environments inside aircraft often require the development of specialized monitoring equipment.

“Evidence showed that engine bleed air, which can carry chemical contaminants, is getting into the supplied breathing air to the pilots,” Mackenzie-Smith said. “So, our short-term objective was to characterize the pilot breathing air, which is supplied by the onboard oxygen-generating system. Since there are no readily available commercial instruments or devices that are solely intended to meet this objective, what we had to do is essentially engineer our own device.”

Sampling focused on Air Force cargo aircraft: the C-17 and C-130. The aircraft posed several challenges for the researchers and their equipment, including elevated oxygen levels and intense vibration.

“We deal with a lot of unique exposure environments that require us to engineer various interfaces as well as develop correction factors and tools to help meet the objectives that we are presented with,” Mackenzie-Smith said. “The key research gaps we have currently are not only finding intrinsically safe devices and instruments to use, but also ones that are safe to fly and can accommodate those unique environments.”