Knowledge of Engineering Controls Can Lead to Creative Solutions
BY BILL MELE, ROB STRODE, DANIEL HALL, CASSIDY STRODE, AND ANDREY KORCHEVSKIY
Engineering controls are one of the hierarchical priorities in managing occupational exposures and risks. Recent experience, however, indicates that the specialization of industrial hygienists may be a hindrance when considering and designing exposure controls. This article is the first in a series that will discuss how industrial hygienists and engineers can work together to better understand, implement, or improve new and existing solutions for the occupational environment.
BEHIND THE MASK A few years ago, we were called by a copper refining and casting facility where copper was being melted and cast into molds (Figure 1). The facility had identified a problem with employee overexposures to inorganic arsenic, copper fume, and copper dust. In addition, individuals working near the melting furnace and the holding furnace also had high heat and excessive noise exposures. The melting and casting process included five individuals on each shift, working at five specific tasks and work locations per shift. Personal and area sampling of metal dust and fume exposures varied from location to location and task to task, with all but one area having contaminant levels in excess of the OSHA PEL.
To address the potential exposures, the facility had established a respiratory protection program utilizing half- and full-facepiece negative-pressure air-purifying respirators. The program included all workers in the casting operation.
In addition to the respiratory protection, several engineering controls were present and operating at the facility in various states of readiness or effectiveness. One such system was general dilution exhaust ventilation, including five rooftop-mounted exhaust fans located approximately 50 feet above the casting wheels. The fans were sized to exhaust just under 250,000 cfm, but due to neglect and poor maintenance only one of them was operational. In addition, there was a clearstory with operable windows located approximately 30 feet high in one wall of the casting operation that was designed to provide some natural ventilation and make-up air to the facility. There were also numerous large openings surrounding the building perimeter consisting of bay doors, man-door openings, and equipment access doors through which natural ventilation was available, albeit not very effectively.
As might be expected, the metal fume exposures were primarily associated with the hottest process operations: in and around the melting furnace, tap-hole, launder, holding furnace, and ladle. The job task most representative of the highest exposures was that of “mold grinder.” The furnaces, launders, and ladle areas where the mold grinder worked had no mechanical exhaust. Some pedestal fans were present near the operation, but their primary intention was to deliver cooler air into these hot work zones. Unfortunately, the pedestal fans had a secondary negative effect of mixing and discharging the more contaminated air into the nearby work areas. Because the mixing increased worker exposures in the nearby areas, the fans were removed. Also, the use of the clearstory ventilation did not reduce contaminant concentrations since air entering the upper portion of the high bay simply short-circuited out through the ceiling space rather than effectively mixing with lower-level air.
These measures, with their various levels of effectiveness, had reduced the workers’ exposures “behind the mask” to concentrations below the PEL. However, area sampling still demonstrated contaminant levels above the PEL without regard to respiratory protection. Management believed these measures were in keeping with the basic tenets of good industrial hygiene practice: anticipation, recognition, evaluation, and control of occupational exposures.
But OSHA disagreed. Effectively protecting workers behind the mask was not enough.
OSHA had inspected the facility prior to our work and determined that such reliance on respiratory protection was insufficient. The inspector had written, “If one or more engineering and/or administrative controls were determined to be economically and technologically feasible, such control(s) were to be selected for implementation.”
That’s when we were asked to help. If we were going to truly control exposures, we had to go back to the drawing board.
SETTING THE PARADIGM Of the four industrial hygiene tenets, typically it’s the control aspect that becomes the tricky issue. In this case, anticipation and recognition of potential exposures were easy enough given the source materials, and the evaluation was straightforward with the use of appropriate sampling and measurement equipment. It came down to control as the real challenge.
Each industrial hygienist brings a set of knowledge and skills to a particular application, examining the problem and solutions in light of his or her own viewpoint and comfort zone. As the industry has matured, IHs have become more specialized. Undergraduate or graduate education has always been only the starting point for an IH’s knowledge base. Typically, IHs are not limited by their abilities but by their post-university experience. As a result, engineering controls are less likely to be part of an IH’s toolbox. Human nature being what it is, a lack of engineering experience may support an approach to problem solving that focuses on more immediate or temporary solutions, in contrast to the more multidisciplinary approaches that have worked in the past. There has always been pressure to implement the quickest and easiest solution, and often this approach makes the most sense, at least from a short-term or first-cost perspective. However, these solutions, although seemingly acceptable, are not necessarily the best practices OSHA is expecting to find. In keeping with the basic industrial hygiene tenets, OSHA may want to see more permanent and reliable solutions such as improved engineering controls and less reliance on respiratory protection, as it did in this case. The ultimate goal of industrial hygiene is a safe workplace, including control of exposures and risks. There are many ways to skin that cat. Industrial hygienists understand the hierarchy of exposure controls and look to apply them appropriately. In the old days, IHs had more background knowledge of engineering controls, including post-university training and experience in ventilation system design, application, assessment, and troubleshooting. Today, engineering has become another specialized area, and many IHs are more comfortable leaving it to the engineering community. The concept of attracting more engineers into the IH field has been an issue for some time. As expressed by former AIHA president Jeff Burton, the decreasing number of IHs with engineering degrees is one of the demographic trends that has altered the profession. Burton told The Synergist that when he joined AIHA in the 1960s, he was told that engineers made up approximately 25 percent of the IH community. Today, Burton estimates that only five percent of IHs have engineering degrees. In addition, many industrial hygiene programs may have only one course, or at most a few courses, in ventilation, and very few IHs get on-the-job post-university training in engineering controls. But leaving engineering controls solely to the engineers begets a potential philosophical problem: engineers tend to perceive mechanical solutions in mechanical terms, and might not have a good feel for how exposures are affected by human behavior. On the other hand, IHs tend to gravitate toward procedures, training, and behavior modification. In the past, IHs would combine exposure assessment with an engineering assessment to reach a combined control solution. Today, many IHs are more comfortable leaving engineering to the engineering community (see Figure 2). At the facility in our story, addressing the first elements of the hierarchy of controls (elimination and substitution) was not an option since eliminating or substituting for copper as a contaminant source is impossible when the product being produced is copper. So what’s next? ADMINISTRATIVE AND ENGINEERING PROPOSALS In response to OSHA’s requirement, administrative controls were a logical control approach since they were immediately available for implementation. Our theory was that the TWA exposures could be reduced by limiting the time each worker spent in high potential exposure areas. Thus, part of our proposed solution was to reduce task-specific durations by rotating workers through the various job functions. To make this control more effective, we also recommended that a sixth employee be trained and added to the work force to further reduce each individual’s TWA exposure. This plan effectively resulted in an “equality of outcomes” for worker exposures. While this strategy helped reduce employee TWA exposures, it wasn’t capable of lowering TWA exposures below the PEL without regard to respiratory protection. Also, to implement this strategy, each employee needed to be cross-trained in all of the production tasks, incurring initial and ongoing training costs. As noted above, PPE was already being provided in the form of respiratory protection, along with heat-resistant suits and hearing protection. For industrial hygienists, the use and implementation of respiratory protection is generally well understood and straightforward. However, the issuance of respiratory protection is not as simple and inexpensive as might be presumed. It entails a range of additional administrative efforts and costs associated with an effective respiratory protection plan, not to mention the issues associated with individual compliance with the program. Based on OSHA’s requirement that engineering controls be considered, and since the in-place controls were not effectively protecting workers without regard to respiratory protection, it was time to look at existing engineering controls. This discussion only concerns ventilation, but engineered solutions can also reduce heat and noise exposures. In consideration of this combined IH/engineering approach, and to achieve reduced exposures and comply with OSHA’s requirements, we made several recommendations related to engineering controls in addition to our administrative recommendations. One recommendation was to refurbish the rooftop fans. This “fix” provided a significant up-flow of contaminant-laden air from the casting wheel, reducing the fume and dust exposures at the holding furnace, ladle, and casting wheel work locations. To enhance the displacement ventilation above the casting wheel, we also recommended closing the clearstory windows. This would allow fresh make-up air to enter the facility from all sides of the casting wheel, and would draw hot contaminated air off the holding furnace, ladle, and casting wheel up through the rooftop fans. Because of these changes, workers experienced an inflow of fresh outside air at their backs, and the airflow drew contaminants away from the workers and up to the rooftop exhaust. (The airflow pattern after refurbishment is depicted by the arrows in Figure 2.) THE REST OF THE STORY Before facility management made any changes to the engineering controls, we collected personal and area air samples for inorganic arsenic and copper dust and fume over the course of three days. Results were reported together with the control recommendations. Approximately 15 months later, after the engineering control improvements and administrative controls had been implemented, we returned to the site and repeated the air monitoring. For the job function with the highest initial exposure (mold grinder), it was determined that the engineering control improvements reduced the copper fume exposures by approximately 56 percent. Other job tasks at the various monitored locations demonstrated similar reductions to both copper and arsenic exposures, with some tasks achieving somewhat more or less improvement. While the TWA exposures for the rotating team members were reduced by as much as 64 percent, one of the positions still required respiratory protection to maintain actual exposures below the PEL. However, these pre- and post-control measurements demonstrated the effectiveness of the integrated approach to exposure control (that is, combined engineering and administrative controls). Nevertheless, management continued the use of respiratory protection. Among the questions that could be asked about this project, one concerns the meaning of “economically and technologically feasible.” The answer, like beauty, is in the eyes of the beholder—in this case, OSHA. While it appeared technologically feasible to implement best-practice engineering controls that would reduce all worker exposures below the PEL without regard to respiratory protection—and we did recommend additional engineering controls to this end—these controls were not considered economically feasible. As is evident in this story, an IH’s understanding of engineering controls can play an important role in addressing compliance issues, enhancing worker protection, and satisfying OSHA’s requirements. While no new engineering equipment was installed in our example, the IH team’s ability to identify, assess, troubleshoot, and modify existing engineering controls, in combination with administrative controls, was vital to recommending a solution that was acceptable to OSHA and which measurably decreased worker exposures and risks. However, without basic knowledge of engineering controls, the IH’s ability to provide creative and complete solutions, especially engineering solutions, is constrained. We encourage all IHs to embrace engineering controls in their practice and endeavor to make them part of their knowledge base. THE AUTHORS are members of the staff of Chemistry & Industrial Hygiene, Inc., a consultancy based in Wheat Ridge, Co. They can be reached through Bill Mele at (303) 420-8242 or firstname.lastname@example.org.
Suggested Readings The Synergist: “An Engineer at Heart: AIHA Past President Seeks a Bigger Tent for IH,” May 2015. The Synergist: “The Ventilation Guru,” April 2014.