The development and testing of a prototype mini-baghouse to control the release of respirable crystalline silica from sand movers

ABSTRACT

Inhalation of respirable crystalline silica (RCS) is a significant risk to worker health during well completions operations (which include hydraulic fracturing) at conventional and unconventional oil and gas extraction sites. RCS is generated by pneumatic transfer of quartz-containing sand during hydraulic fracturing operations. National Institute for Occupational Safety and Health (NIOSH) researchers identified concentrations of RCS at hydraulic fracturing sites that exceed 10 times the Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) and up to 50 times the NIOSH Recommended Exposure Limit (REL). NIOSH research identified at least seven point sources of dust release at contemporary oil and gas extraction sites where RCS aerosols were generated.

 NIOSH researchers recommend the use of engineering controls wherever they can be implemented to limit the RCS released. A control developed to address one of the largest sources of RCS aerosol generation is the NIOSH mini-baghouse assembly, mounted on the thief hatches on top of the sand mover. This article details the results of a trial of the NIOSH mini-baghouse at a sand mine in Arkansas from November 18–21, 2013.

 During the trial, area air samples were collected at 12 locations on and around a sand mover with and without the mini-baghouse control installed. Analytical results for respirable dust and RCS indicate the use of the mini-baghouse effectively reduced both respirable dust and RCS downwind of the thief hatches. Reduction of airborne respirable dust ranged from 85–98%; reductions in airborne RCS ranged from 79–99%. A bulk sample of dust collected by the baghouse assembly showed the likely presence of freshly fractured quartz, a particularly hazardous form of RCS.

 Planned future design enhancements will increase the performance and durability of the mini-baghouse, including an improved bag clamp mechanism and upgraded filter fabric with a modified air-to-cloth ratio. Future trials are planned to determine additional respirable dust and RCS concentration reductions achieved through these design changes.

KEYWORDS:

• Baghouse
• engineering controls
• hydraulic fracturing
• oil and gas extraction
• respirable crystalline silica

Acknowledgments

NIOSH thanks and acknowledges Southwestern Energy (SWN) for their demonstrated leadership in occupational health and safety by agreeing to partner with NIOSH in safety and health research as part of the NIOSH Field Effort to Assess Chemical Exposures in Oil and Gas Workers. The authors further express their sincere gratitude to Jim Bolander, Allen Green, Ted Hunter, Tom Huetter, and others at SWN for their support of the field evaluation of the mini-baghouse retrofit assembly. The authors thank Mr. Kenneth Strunk (NIOSH, Spokane) for his computer-generated rendering of a sand mover used in this article.

Additional information

Funding

Funded by internal NIOSH funds.