NIOSH: Protect Forestry Employees from Exposures to Erionite, Silica
Following a recent health hazard evaluation of employees’ exposures to erionite mineral fibers during forestry activities, NIOSH recommended controlling dust exposures with ventilated vehicle cabs, wet methods, and other engineering and administrative controls. The evaluation was conducted by the NIOSH Health Hazard Evaluation (HHE) Program in response to a request from a federal government agency concerned about employees working in areas where erionite had been confirmed or was suspected to be present. According to the HHE report, which is available as a
, exposure to erionite fibers is associated with health effects similar to those typically seen with asbestos exposure, including malignant mesothelioma.
NIOSH staff observed employees performing tasks such as thinning, felling, and bucking trees; digging fireline; spraying invasive plant species; mowing campgrounds; and using a Bobcat to masticate timber, grade roads, and fill in push pits, which were dug in the late 1950s and early 1960s to explore for uranium. During the agency’s evaluation, NIOSH personnel took personal air samples for erionite mineral fibers as well as respirable crystalline silica, which is commonly found in many geologic formations, usually as quartz. They also took rock and soil samples to analyze for erionite.
One of NIOSH’s objectives was to develop a revised approach to more accurately detect and measure erionite in air samples.

One of NIOSH’s objectives was to develop a revised approach to more accurately detect and measure erionite in air samples from the location. The agency’s revised method involved first identifying an erionite mineral fiber and then evaluating its elemental makeup using electron dispersive spectroscopy. More information regarding the sampling and analytical methods used during the evaluation is available in the appendices of the NIOSH report.
NIOSH staff found that all employees were exposed to erionite mineral fibers and confirmed that erionite was also present in the bulk rock and soil samples collected from rock formations in the forest. The agency recommended against repairing roads with aggregate containing erionite and encouraged the employer to take further steps to protect workers such as regularly maintaining air filters in the equipment and washing personal protective equipment to remove dust and dirt.
“Although OELs specific to erionite have yet to be developed, and toxicological studies of the health effects of the various forms of erionite are ongoing, health hazards of erionite exposure have been identified elsewhere,” the NIOSH report reads. “Characterizing and minimizing potentially hazardous exposures until an evidence-based OEL for erionite is developed is necessary.”
Detectable silica concentrations were also found in several task-based personal air samples; the report notes that quartz was the only form of crystalline silica detected. While none of the measurements identified overexposures to respirable crystalline silica, the authors of the report caution that NIOSH has previously identified overexposures among employees performing similar tasks on other federal land. A 2014 NIOSH report (
) found that certain tasks performed by employees working to maintain dirt roads for a federal government agency disturbed dust that contained crystalline silica, and that area air samples indicated a high percentage of quartz—up to 100 percent. Due to the variable environmental and geological conditions that employees may encounter, the 2014 report highlights the importance of minimizing exposures during dust-generating activities.
“Because of the variability in job tasks, including tasks that aerosolize dust particles,” the 2014 report reads, “the potential for exposure to erionite and silica dust exists.”