The National Institute for Occupational Safety and Health (NIOSH) is conducting research to identify possible workplace exposures in oil and gas extraction. This article describes results and conclusions of wellsite measurements for respirable crystalline silica associated with the use of silica sand-the primary proppant used in hydraulic fracturing. To learn more about frac sand see Well Servicing, January/February 2012, Where Does Frac Sand Come From? It is important that supervisors and employees understand that silica sand may contain up to 99 percent crystalline silica and depending on the concentration and duration of exposure, breathing fine dusts containing respirable crystalline silica can pose an occupational health hazard. Inhalation of respirable crystalline silica is associated with silicosis and lung cancer. For more information visit the OSHA-NIOSH Hazard Alert on the web and the NIOSH Science Blog. The study NIOSH partnered with operators and service companies to evaluate worker exposures to respirable silica at 11 completion sites in five states (CO, TX, ND, AR and PA). The majority of work involved slick water completions with a variety of silica sand (20/40, 40/70 and 100 mesh) and in some cases resin coated and ceramic proppant. Samples were collected in different weather conditions, altitudes and geographic locations. Workers who participated wore sampling equipment designed to collect full shift (typically 12 hours) personal breathing zone (PBZ) samples. Samples were analyzed by an American Industrial Hygiene Association accredited laboratory. Samples were analyzed first by weight for respirable dust and then by X-ray diffraction for crystalline silica. Quartz, a type of crystalline silica, was the only mineral detected above the limit of quantitation. PBZ sample results were compared to occupational exposure limits (OELs) for respirable silica exposures. The Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) is not a fixed value like hydrogen sulfide (H2S) or carbon monoxide, it is calculated for each sample based on the percentage of silica present in the dust sample using the formula: 10mg/m3 ÷(%silica + 2). As an example, if the percentage of silica is 100 percent, the PEL is 0.098 milligrams of silica per cubic meter of air (mg/m3). The NIOSH recommended exposure limit (REL) for respirable silica is a fixed value (0.05 mg/m3) and the American Conference of Government Industrial Hygienist's Threshold Limit Value (TLV) for respirable silica is fixed at 0.025 mg/ m3. Each of these exposure limits is a time-weighted average (TWA) for a work day. Summary: Exposure to respirable crystalline silica is an occupational health hazard for completions crews. Sand mover and blender operators appear to be at greatest risk for exposures but other crew members have exposure risks as well. Until a variety of engineering controls can be developed and implemented, employers and employees should: 1. Restrict access to areas with potential exposure to respirable silica to workers trained to recognize and avoid silica hazards and post signs warning of the silica hazard. 2. Conduct personal breathing zone sampling for silica. Workers should participate in all air monitoring or training programs offered by the employer. 3. Where respirators are required, workers must wear respirators approved for protection against crystalline silica-containing dust with an assigned protection factor based on the risks determined. 4. Clean contaminated work clothing using clothes cleaning booths or change into clean clothing before leaving the worksite. 5. Do not eat, drink or use tobacco products in areas where there is dust containing crystalline silica.
Exposure-levels; Risk-factors; Gas-industry; Respiratory-irritants; Respiration; Respirable-dust; Respiratory-system-disorders; Silicates; Silica-dusts; Pulmonary-system; Pulmonary-system-disorders; Silicosis; Lung-fibrosis; Lung-irritants; Lung-disease; Lung-disorders; Lung-function; Lung-cancer; Workers; Work-environment; Engineering-controls; Control-technology