Image Credit: Getty Images / Melpomenem

When Mark Stenzel, FAIHA, began what would be a 30-year career in the chemical industry, he quickly encountered one of the major challenges of occupational and environmental health and safety. "We have thousands of chemicals, all kinds of mixtures, all these different scenarios, and it would be virtually impossible to measure everything," he said. "So we somehow had to have a method to estimate exposures without measurement data."

According to Stenzel, OEHS professionals can overcome this challenge by using the Structured Deterministic Model (SDM) 2.0, a tool he developed with Susan Arnold, PhD, CIH, FAIHA, Gurumurthy Ramachandran, PhD, CIH, FAIHA, and Daniel Drolet, MSc. The SDM 2.0, Stenzel explained, allows OEHS professionals to use what measurement data they have to create an algorithm that models inhalation exposures to chemicals, chemical mixtures, aerosols, particulates, and fibers. "It really is a software application that lets you use chemistry and math and industrial hygiene knowledge to estimate exposures," he said.

Developing the SDM 2.0

When Stenzel worked in the chemical industry, he and his colleagues developed a methodology for modeling inhalation exposures. Theirs was a highly technical process involving calculations performed on spreadsheets, which was not a problem for Stenzel and his colleagues because they were trained as chemists. But this is not the case for all OEHS professionals. "A lot of hygienists, they maybe have a year of college chemistry, and that's it," Stenzel said.

Stenzel, Arnold, Ramachandran, and Drolet were all members of AIHA's Exposure Assessment Strategies Committee. Over the years, they met up and discussed ways they could share their knowledge of estimating exposures. It was Arnold who came up with the idea of developing exposure monitoring software that broke down the methodology developed by Stenzel into a series of steps that would make sense to a broader set of users, Stenzel related. "Susan was able to take this very technical process and put it into what she called a checklist," he explained. "She converted what was a relatively complex topic into something that a normal, non-chemist industrial hygienist could use."

The SDM 2.0 app was developed out of this collaboration. Ramachandran, then Arnold's PhD advisor, provided the grant that enabled Arnold to evaluate her checklist. Drolet led the design of the tool and programming of the app.

According to Stenzel, the tool weighs the tendency of a chemical to evaporate and exceed acceptable exposure levels against workplace controls in place to reduce the chemical’s concentration. "That's what the model does. It balances those two, and then it can predict exposure based on potential to become volatilized and the level of control that engineering controls in the workplace will protect to," he said. "When you put it in those terms, it's not black magic. It's just chemistry and physics. But it's applied at a very simple level that the person doesn't have to be a chemist or physicist in order to use it."

The SDM 2.0 has several advantages over increased exposure monitoring, Stenzel related. Exposure monitoring is often costly and time-consuming, but employers may need OEHS professionals to make decisions about chemical exposures within minutes. However, the SDM 2.0 requires less monitoring data, is available for free online, and is able to estimate exposures quickly. "Once you're familiar with the software, you can actually do the estimates in a matter of minutes," Stenzel said.

Moreover, Stenzel’s career shows his methodology's reliability, and Arnold demonstrated the tool's effectiveness during her PhD research. "The method was calibrated and validated to show that it does really work," he said.

The SDM 2.0 app is now accessible through AIHA's website, as are other risk assessment tools.

Using the SDM 2.0

However, the tool is only helpful if OEHS professionals know it exists and how to use it. Stenzel, Arnold, and Ramachandran, with PhD candidates Ryan Hines, MS, CIH, and Puleng Moshele, MS, will also host a virtual professional development course introducing participants to the SDM 2.0. During the first half-day session, the instructors will cover the tool's theoretical and technical foundations. Then, the instructors will discuss how to use the software, including the decisions that users must make and how they can gather the information they need.

The second half-day session will be dedicated to case studies and real-world applications. The goal is to show how the tool can be applied to solve real-world problems. The instructors are "trying to make it as real as possible to participants so that they could see themselves using this in practice," Stenzel explained. These case studies will cover "a spectrum of issues that a typical IH would encounter in doing their job as a practitioner," he added. “And even if we don't hit exactly their issue, they will see how we went about solving the problem and be able to figure out, 'OK, how do I solve my specific problem?'"

OEHS professionals may apply the estimates generated by the tool to creating workplace training programs and prioritizing future monitoring efforts. The ability to prioritize is a particular benefit of exposure modeling because it allows OEHS professionals to proactively prevent exposures instead of waiting for exposures to occur and then retrofitting their programs accordingly. "Retrofitting has two big problems. One is that people have now already been exposed," Stenzel said. "And the other problem is that retrofitting tends to always be more expensive than designing it correctly."

"With this kind of tool, you don't have the overexposures in the first place," he added.

He believes that modeling and predicting exposures is a key competency that all OEHS professionals should develop. "It's our job to ensure that workers are protected. We need every tool available to make that assurance," Stenzel said. "Rather than figure out who was overexposed, what we want to know is how we can prevent that exposure and design appropriate workplaces so that the workers will not encounter these adverse risks."

From 12 to 3:45 p.m. Eastern Time on Nov. 5 and 7, AIHA University will host the live online professional development course presented by Stenzel, Arnold, Ramachandran, Hines, and Moshele, titled "Improving Professional Judgments of Inhalation Exposure and Risk Assessments Using the Structured Deterministic Model (SDM 2.0)." To learn more about the PDC or to register, visit AIHA’s website.