Invisible Dust, Lasting Impact: Silica Exposure Risks in Trona Mining

The following article is an Industrial Hygiene in the Workplace exclusive about the respirable crystalline silica (RCS) exposure workers face when mining trona (natural soda ash).

Bernard L. Fontaine, Jr., D.B.A., M.Sc., CIH, CSP, FAIHA, Contributor

Background: Trona, or natural soda ash, is a sodium sesquicarbonate mineral found in the Wilkins Peak Member of the Eocene Green River Formation in southwest Wyoming. Comprising approximately 70% sodium carbonate, trona is used in manufacturing glass, detergents, chemicals, and consumer products. However, trona mining poses a persistent occupational hazard: respirable crystalline silica (RCS)—fine dust particles that can scar lungs, shorten lives, and challenge even robust safety systems.

Objective: This paper reviews occupational exposure to RCS during trona mining activities, which employ approximately 2,300 U.S. workers.

Methods: Case examples were drawn from published reports and peer-reviewed studies analyzing RCS exposure during drilling, blasting, crushing, conveyor transfer and maintenance tasks.

Results: Workers engaged in these activities often experience RCS levels at or above the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL).

Conclusions: Trona mining operations face silica exposure risks similar to other metal and non-metal mining sectors. Continued vigilance, exposure monitoring, and implementation of engineering controls are essential to protect miner health and safety.

Introduction

Trona deposits occur globally, including in the United States (Wyoming and Utah), Botswana, Egypt, Turkey, China, and Namibia. The largest deposits are located in Wyoming’s Green River Basin, where trona formed 48–53 million years ago in the ancient Lake Gosiute. As the lake expanded and contracted through climatic cycles, thick trona beds accumulated, now lying 600–2,000 feet underground (Wyoming Mining Association [WMA], 2017). Modern trona mines resemble underground cities, complete with lighting, ventilation systems, workshops, and roadways. The mineral itself is white to gray, glassy in appearance, and soft (2.5–3 on the Mohs scale). It dissolves readily in water or weak acid and is composed of sodium carbonate, sodium bicarbonate, and water—a mineral of both historical and modern industrial significance.

Industrial and Historical Uses

Trona has been valued for millennia. Ancient Egyptians used it in mummification and in the manufacture of soap and glass. The Romans used soda ash derived from trona to make bread, glass, and medicines. Historically, trona symbolized purification and transformation and was integrated into spiritual rituals (Helvaci, 1998). In the modern era, trona-derived soda ash remains indispensable. It is used in the manufacture of glass, detergents, and industrial chemicals, and appears in household items such as toothpaste, paper, and baking soda. Soda ash also helps neutralize acidity in water and industrial processes (MSHA, 2020).

Mining and Processing

Wyoming’s Green River Basin contains an estimated 127 billion tons of trona, with roughly 40 billion tons recoverable using conventional methods (WMA, 2017). The room-and-pillar mining technique is used, leaving large pillars of mineral to support the ceiling while removing ore from adjacent rooms. After extraction, trona ore is crushed, heated, dissolved, filtered, crystallized, and dried into soda ash. However, this process releases fine dust.

Figure 1 – Trona Mining Operation in Wyoming

Source: Wyoming Mining Association

Trona ore naturally contains silica-bearing minerals, which, when disturbed, generate respirable crystalline silica particles smaller than 10 micrometers. These particles can penetrate deep into the lungs, where they may cause long-term respiratory damage (NIOSH, 2021).

A Hidden Threat Underground

The Mine Safety and Health Administration (MSHA) and the National Institute for Occupational Safety and Health (NIOSH) have documented RCS concentrations in trona mines that exceed the OSHA and MSHA PEL of 50 µg/m³ (8-hour time-weighted average) (MSHA, 2020; NIOSH, 2021). Depending on ventilation and control measures, exposures in Wyoming’s Green River Basin have ranged from 20 µg/m³ to more than 120 µg/m³. Even with improved control technologies, high-risk operations such as drilling, blasting, crushing, and conveyor transfers continue to present significant exposure potential.

Figure 2 – Estimated RCS Dust Concentration in Trona Mines

Source: Hypothetical illustration based on data trends reported by NIOSH (2021) and MSHA (2020).

Health Implications

Chronic exposure to respirable crystalline silica can result in silicosis, an irreversible and potentially fatal lung disease. Even at low concentrations, prolonged exposure can lead to measurable declines in lung function and increased susceptibility to chronic obstructive pulmonary disease (COPD) and lung cancer. The International Agency for Research on Cancer (IARC, 2012) classifies respirable crystalline silica as a Group 1 human carcinogen. A 2020 NIOSH surveillance study reported elevated rates of lung abnormalities among trona miners with long work histories, suggesting that cumulative exposure continues to pose a significant health risk (NIOSH, 2021).

Exposure Control and Prevention

Reducing RCS exposure requires adherence to the hierarchy of controls, prioritizing engineering and administrative strategies before reliance on personal protective equipment (PPE). Engineering controls include wet drilling, water sprays, enclosed cabs with filtered air, and local exhaust ventilation. Administrative controls involve regular maintenance of dust systems, worker rotation, hazard communication, and air monitoring. Properly fitted respirators should be used where other controls are insufficient. Periodic medical surveillance, including lung function tests and chest radiographs, aids in early disease detection.

Conclusion

Respirable crystalline silica exposure remains a significant occupational health challenge in trona mining. Despite advances in regulation and control technologies, overexposures persist in certain operations. Preventing silicosis and related diseases demands continuous air monitoring, strong regulatory enforcement, thorough worker training, and a proactive safety culture that treats exposure prevention as both an ethical obligation and a core operational priority. IHW

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