December 17, 2020

Inspector General to MSHA: Silica Exposure Limit Is Out of Date

MSHA needs to improve its efforts to protect coal miners from exposures to respirable crystalline silica, the U.S. Department of Labor’s Office of Inspector General (OIG) concluded following an audit of the agency. According to OIG’s report, MSHA’s current silica exposure limit is out of date, and “a significant body of evidence shows that lowering the silica limit would be a major factor in preventing coal workers’ deaths and illnesses caused by silica exposure.” OIG recommends that the agency adopt a lower legal exposure limit for silica in coal mines based on recent scientific evidence. OIG states that respirable crystalline silica may be responsible for the recent increase in black lung disease among coal miners. Its report notes that more than three times as many coal miners were found to have black lung disease during 2010–2014 compared to 1995–1999.

MSHA’s legal silica exposure limit of 100 µg/m³ for coal mines was established in 1969 and was based on a formula prescribed by the Department of Health and Human Services and a level proposed by ACGIH in the 1960s. ACGIH has lowered its limit twice since then: once in 2000 to 50 µg/m³ because it found that silica exposure near 100 µg/m³ “probably does cause silicosis and lung disease,” and again in 2006 to 25 µg/m³. In 2016, OSHA published a new final rule to protect workers from exposure to respirable crystalline silica. OSHA’s rule comprises two standards, which include a lower eight-hour time-weighted average permissible exposure limit for respirable crystalline silica of 50 µg/m3 in general industry, maritime, and construction.

“When adopting and recommending their respective 50 µg/m³ limits, both OSHA and NIOSH warned that 50 µg/m³ is the lowest feasible limit, not the safest,” the OIG report stresses. “OSHA indicated that after evaluating the best available evidence it was uncertain if there was any limit that would result in zero harm to workers; however, if such a limit existed, it would likely be lower than 50 µg/m³.”

MSHA’s exposure limit for silica remains unchanged, despite rulemaking efforts spanning more than two decades.

In a response (PDF) to OIG’s report, Assistant Secretary of Labor for MSHA David G. Zatezalo stated that MSHA will publish a proposed rule to address miners’ exposure to respirable quartz, but that the agency “cannot presume either the substance of the proposed or final rule” at this time.

OIG’s full report (PDF) can be found on its website.