December 7, 2023

NIOSH: IEQ, Noise Among Concerns in Underground Warehouse Facility

Employees’ exposures to wood dust and noise were among the concerns identified by NIOSH during a health hazard evaluation (HHE) of a warehouse facility located in a former underground limestone quarry. The employer representative who requested the evaluation asked the agency to also assess potential exposures to carbon monoxide and radon, and to explain the mineral fibers and oil-like residue found on some of the rock walls in the cavern. NIOSH’s HHE report describes the facility as a 33,000-square-foot space located within a four-million-square-foot underground cavern, which housed multiple other businesses. The workspace NIOSH evaluated had a 1,200-square-foot woodshop with a table saw, miter saw, router, and handheld power tools as well as a small painting area. People traveled between businesses in the cavern by driving vehicles on a paved concrete road.

During two visits to the facility, NIOSH staff assessed exposures and health concerns by measuring carbon monoxide, carbon dioxide, temperature, and relative humidity throughout the workspace, and by taking sound level measurements while the woodshop was in use. Agency personnel also collected full-shift personal air samples for wood dust and noise for workers who performed woodworking and painting tasks as well as area air samples for wood dust, noise, and other airborne particles. They used tracer gas to measure the air exchange rate in the workspace and collected bulk samples of the fibrous material and residue from the cavern walls.

Levels of carbon monoxide and radon were below occupational exposure limits, according to NIOSH’s findings. But the agency report raises concerns about employees’ wood dust and noise exposures in the woodshop and about low air exchange rates in the warehouse. For example, workers’ exposures to wood dust varied depending on how much time woodworking equipment was in use. During NIOSH’s evaluation, employees did two hours of administrative work before beginning work in the woodshop. For the six hours that woodworking equipment was in use, time-weighted average exposures to wood dust were at the NIOSH recommended exposure limit of 1 milligram per cubic meter (mg/m3) of air. If the workers were not exposed to wood dust during the two hours of administrative work they did at the start of their shift, their full-shift personal wood dust exposure would be 0.73 mg/m3. None of the wood dust exposures measured by NIOSH were at or above OSHA’s permissible exposure limit of 15 mg/m3. Workers’ noise exposures were above NIOSH’s REL for noise of 85 A-weighted decibels (dBA) as an eight-hour TWA; sound levels were sometimes above 95 dBA, occasionally reaching 100 dBA. NIOSH’s report also describes concerns related to the warehouse’s very low air exchange rates: about one air exchange every 13 hours.

Elemental analysis of the mineral fibers from the cavern walls indicated the presence of magnesium, sulfur, and oxygen. The proportional average calculated atomic weight concentrations for four samples suggested that the fibers contained a compound consisting of magnesium sulfate called epsomite, which can form on the internal surface of cave walls, particularly in limestone caves.

“Because the warehouse has relatively limited amounts of these fibers present on the cavern walls, and typical workplace conditions would not cause fibers to become airborne, the fibers should not present a risk to employees,” NIOSH’s report states. “However, if fibers needed to be removed from the wall, use a high efficiency particulate air (HEPA)-filtered vacuum for removal tasks.”

Analytical laboratory analysis of the oil-like residue from the cavern walls was inconclusive. According to NIOSH, it’s possible that the residue was a remnant from activities related to the workspace’s former use as a limestone quarry. Another potential explanation is that the residue “could be leaching through the cavern rock from an underground or above ground source,” the agency report explains.

Recommendations for improving workplace health and safety at the facility include reducing wood dust exposures in the woodshop by improving dust capture at the saws and reducing workers’ hearing loss risk by including woodshop employees in a hearing loss prevention program. NIOSH also urges the employer to supply outdoor air to the cavern warehouse following specifications for ventilation rates outlined in the standard ANSI/ASHRAE 62.1-2022, Ventilation and Acceptable Indoor Air Quality. While workers were not found to be overexposed to carbon monoxide, NIOSH warns that low air exchange rates could lead to a buildup of pollutants in the workspace from the vehicles used in the area.

For more information, read the HHE report (PDF). Other HHE reports are available from the NIOSH website.