Silica Contamination Control: A Gathering Storm?
- Jeremy M. Slagley (Indiana University of Pennsylvania)
- Document ID
- American Society of Safety Engineers
- Professional Safety
- Publication Date
- November 2015
- Document Type
- Journal Paper
- 35 - 37
- 2015. American Society of Safety Engineers
- 0 in the last 30 days
- 61 since 2007
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- Silica is a known health hazard, and unconventional oil and gas development has placed it in the public eye.
- OSHA’s proposed standard includes provisions for regulated areas, cross-contamination and decontamination. HEPA vacuuming and wet methods are prescribed in the proposed standard, but air showers are another viable method.
- Direct-reading instruments may be part of employers’ arsenal for decontamination procedures.
Unconventional (horizontal) drilling, while used in the oil and gas industry for decades, has unleashed an explosion of natural gas development across the U.S. in the past several years (Stevens, 2012). The affected states have benefited enormously from this renewed economic activity due to the presence of the various shale layers underlying their land. State and federal regulators have been working with industry to responsibly develop the resource while protecting safety, health and the environment.
However, not all associated hazards were well understood from the beginning of the boom. NIOSH released a report in 2013 on its 2-year effort to analyze the degree of airborne silica health hazards for workers conducting hydraulic fracturing operations at oil and gas wells. NIOSH reported 111 personal breathing zone samples for various jobs, with some exposures several times the proposed OSHA permissible exposure limit (PEL) of 0.05 mg/m3.
Table 1 (p. 36) shows some of the 8-hour time weighted average (TWA) full-shift samples reported in the study. In some cases, the exposures exceeded the protection factor afforded by the select respirators worn by the workers. According to OSHA’s Respiratory Protection Standard, a half-face elastomeric air-purifying respirator has an assigned protection factor of 10. Any exposure above 0.50 mg/ m3 would exceed the maximum use concentration at the proposed PEL.
The researchers also found some high exposures for workers less involved with handling silica, such as the chemical truck operator who had a maximum measured TWA of 0.319 mg/ m3 (Table 1). This suggests that environmental silica release could contribute significantly to bystander exposures (Esswein, Breitenstein, Snawder, et al., 2013). Oliver and Miracle-McMahill (2006) discovered high silica exposures among bystanders in their study of silica exposures and health effects among tunnel construction workers.
Silica is a known occupational health hazard (OSHA, 2013), particularly related to the risk of silicosis, a lung disease. Silica exposures are linked to other adverse health outcomes as well. While Oliver and Miracle-McMahill (2006) found no silicosis by chest X-ray in their epidemiological study, they found chronic bronchitis, symptoms consistent with asthma, shortness of breath and physician-diagnosed asthma at a prevalence of 10.7%, 25%, 29% and 6.6%, respectively. Forty-four of the 70 air samples collected were above the current OSHA PEL.
Finkelstein (2000) reports that exposures at the current OSHA PEL give a lifetime risk of 5% to 10% for silicosis and a 30% risk for lung cancer. He advocates for reducing the PEL to the current NIOSH recommended exposure limit of 0.05 mg/ m3, with an accompanying risk below 5% (Finkelstein, 2000). While the hazard of silica exposure is not disputed, workers may view silica as a familiar hazard and, thus, give less attention to following prescribed preventive measures (Haas & Cecala, 2015).The advent of widespread hydraulic fracturing means that exposures to silica have likely increased (Cyrs, Le, Hollins, et al., 2014). OSHA’s proposed rulemaking activity has heightened silica awareness as well. The proposed regulation would apply to the natural gas industry and reduce the allowable exposure as well as require expanded ancillary occupational health measures.
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