Frack sand: An easily overlooked occupational hazard

by Elizabeth Grossman

Tap water bursting into flame, water sources contaminated with toxic chemicals, once-pastoral rural hillsides turned over to industrial fossil fuel extraction, and unprecedented earthquake activity. These are among the environmental health concerns commonly associated with the extraction of natural gas by the method known as hydraulic fracturing – or fracking. But one of the more pernicious and pervasive potential occupational fracking hazards may come from sand. Not just ordinary sand, but sand that is nearly 100% crystalline silica and specially produced to play a key role in every fracking operation. The National Institute for Occupational Safety and Health (NIOSH) has recently reported that this use of industrial sand is likely exposing large numbers of workers to unacceptably high levels of silica exposure, putting them at risk for developing the incurable lung disease silicosis, lung cancer, chronic obstructive respiratory disease, bronchitis, tuberculosis, scleroderma, renal disease, and respiratory failure.

Sand’s role in fracking has received relatively little attention outside of industry circles, but it’s vital to these operations. Frack sand gets pumped into wells along with the chemicals known as proppants to stabilize the wells in preparation for injection of water and other fracking chemicals. Sand is also used in well-site cementing jobs. As described by Well Servicing Magazine, a fracking operation depending on its size and complexity may use anywhere from a few tons to more than two million pounds of sand. U.S. production volumes of this sand have soared in the past few years to tens of millions of tons annually, prompting industry publications describe this as equivalent to a “gold rush.” In February, US Silica went public on the NY Stock Exchange with the first-ever IPO by a frack sand company.

Much of this sand is mined in open-pit quarries that can produce nearly pure silica or quartz sand then transported to processing plants by rail or truck for screening and washing. Mine development has become an environmental health and safety issue for a number of communities. Fracking sand (for which the American Petroleum Institute sets specifications) is typically delivered to wellsites by truck and then transferred to various pieces of equipment. According to the Well Servicing account, a typical truckload is about 25 tons, and many operations require more than one such truckload.  At the well site, sand is transferred to various pieces of equipment, often releasing dust in the process, for example when sand is moved into bins and special conveyors used to take the sand from delivery trucks to the machinery that will pump it into the well. The sites and vehicles themselves also stir up dust.

Alarming air sampling results

NIOSH recently reported the result of its air sampling to evaluate worker exposure to crystalline silica at 11 different fracking sites in five states – Arkansas, Colorado, North Dakota, Pennsylvania, and Texas. At each site, exposures to respirable crystalline silica “consistently exceeded relevant occupational criteria” established by NIOSH, the Occupational Safety and Health Administration (OSHA), and the American Conference of Governmental Industrial Hygienists (ACGIH). Ninety-two (79%) of the 116 samples exceeded the NIOSH recommended exposure level (REL) and ACGIH threshold limit value, and  54 or 47% exceeded OSHA permissible exposure levels. NIOSH notes that the magnitude of exposures measured is particularly important: 36 or 31% of these samples exceeded the NIOSH REL by a factor of 10 or more. This means that even if workers are using half-mask purifying respirators properly, they would not be sufficiently protected.

“If you can see silica-containing dust in the air, exposures can be a problem,” said NIOSH in its April 30 presentation on fracking’s occupational health hazards, which was part of an Institute of Medicine workshop on unconventional gas extraction. While it’s hard to know if what’s pictured in the NIOSH slides contains silica, numerous photos of different steps of a fracking operation involving sand all showed plumes, clouds, and trails of pale gray or white dust coming off equipment being used in various stages of the mining, processing, and delivery.

The sites NIOSH sampled were in the DJ Basin in Colorado (in the Niobrara shale that extends across the intersection of Colorado, Wyoming, Nebraska and Kansas), the Fayetteville shale in Arkansas, the Marcellus shale in Pennsylvania, the Baaken formation in North Dakota, and the Eagle Ford shale in Texas. Asked in a phone interview to name the companies working at these sites, NIOSH senior industrial hygienist Eric Esswein declined, saying it “wouldn’t be productive.” He also said he could not provide the exact locations for the sampling sites as NIOSH researchers were driven to the locations by “industry partners” and because the closest address for many is a GPS coordinate.

NIOSH’s National Occupational Research Agenda Oil & Gas Extraction Council members and partners lists include BP, El Paso Energy, ExxonMobil, Halliburton, Schlumberger, and a number of other drilling companies, but a numberof other well-known companies associated with fracking operations (Chesapeake Energy, Shell, and MarkWest, for example) are not listed, nor is the American Petroleum Institute.

Widespread exposures

Using Bureau of Labor statistics figures, NIOSH estimates that in 2010, approximately 435,000 workers were employed in what’s called the “upstream end” – exploration and production segment –  of US oil and gas extraction. Nearly half of these workers were employed by well servicing companies, including companies conducting hydraulic fracturing. But exactly how many workers are employed in what’s called “completion”  – the drilling phase of fracking operations – or in jobs that could put them at risk for exposure to silica dust in fracking operations or in mining fracking sand, NIOSH could not say. “I don’t think anyone yet as a grip on the exact number of workers in fracking operations,” said AFL-CIO industrial hygienist Bill Kojola.

The US Energy Information Administration explained that there is really no comprehensive tally of the number of current US hydrofracking operations. But a typical fracking crew has 10 to 20 workers, with as many as 10 different job titles, explained Esswein. Additional workers are involved with site preparations and deliveries, tasks that include construction and cementing work, along with well drilling and related activity. Typically, only one person employed directly by the oil or gas company that owns or leases the well will be working at a particular site. Everything else is contracted out. NIOSH’s assessment of silica exposure did not include workers involved in the sand extraction and processing or transport to well sites – and in an additional complication for fracking-related occupational health efforts, silica mining falls under the Mine Safety and Health Administration (MSHA) jurisdiction while other stages of the process are within OSHA’s purview.

Esswein explained that NIOSH’s silica exposure sampling was undertaken as part of the “NIOSH Field Effort to Assess Chemical Exposures in Oil and Gas Extraction Workers.” “The companies working with us, stepped up to the plate” and said “we want to work with you on this,” Esswein recounted. “We see them as leaders in the field,” he said.

Esswein described a recent call to discuss silica exposures in which about 150 industry representatives participated. “If any industry can get a grip on this problem, it’s oil and gas,” he said. “This caught people by surprise,” he explained, although, “Why this is, we don’t know.” But, he said, “people are moving very fast in response,” initiating retrofits and other control measures.

There is currently no NIOSH medical surveillance or health hazard evaluation work underway to assess silica or other fracking-related chemical exposures. Esswein described this research as in its infancy and acknowledged there are many data gaps in addition to those on silica exposures. Among these are exposure to diesel particulates and hydrocarbons, biocides, and to metals, solders and epoxies, and as Dr. Aubrey Miller, NIEHS and US Health Service senior medical advisor, noted, also to mixtures of these substances. Esswein called exposure to silica “an occupational hazard of antiquity,” and encouraged me not to write something that would reflect negatively on industry.

Concerned by what they had learned from NIOSH, on May 22 the AFL-CIO, United Mine Workers of American and United Steelworkers wrote to OSHA, NIOSH, and MSHA asking that OSHA and NIOSH jointly issue a “hazard alert,” identifying occupational hazards in fracking operations, with a special focus on silica exposures; that NIOSH expand its field work in fracking to include medical surveillance; that MSHA evaluate mines producing fracking sands and assess worker exposure at these mines; that OSHA develop a National Emphasis Program for training and outreach around fracking work; and that OSHA “immediately initiate rulemaking on a new silica standard and issue a proposed rule that includes and training” along with “a protective permissible exposure limit.” A revised OSHA silica exposure standard has been under review at the Office of Management and Budget for the past year.


Elizabeth Grossman is the author of Chasing Molecules: Poisonous Products, Human Health, and the Promise of Green Chemistry, High Tech Trash: Digital Devices, Hidden Toxics, and Human Health, and other books. Her work has appeared in a variety of publications including Scientific American, Salon, The Washington Post, The Nation, Mother Jones, Grist, and the Huffington Post. Chasing Molecules was chosen by Booklist as one of the Top 10 Science & Technology Books of 2009 and won a 2010 Gold Nautilus Award for investigative journalism.


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Thank you for this, Lizzie, well done. It begs the question: if the drilling companies (BP, El Paso Energy, ExxonMobil, Halliburton, Schlumberger, and others) are as proactive on identifying and preventing silica exposures at their operations--as NIOSH's Esswein describes--and have "stepped up to the plate," have they also stepped up to the plate and called for OMB to move forward with the extraordinarily overdue revision of the OSHA silica exposure standard? What position have they taken on this? It's disingenuous, of course, for these companies to be framed as "industry leaders" if they are "stepping up" on one foot to clean up their operations (along with their image) while also "stepping down" on the effort to update the Standard, right? I suspect they are "stepping up" because silica doesn't fall into the category of "unknown" fracking chemicals whose identity these companies have shielded from the public view. The health effects of silica can't be obscured by "doubt" and industry assurances of safety as can "unknown" or "confidential" fracking chemicals.

By Mike Wilson (not verified) on 04 Jun 2012 #permalink

Great point Mike! They step up the plate when its convenient----maybe because they get some free consulting help from NIOSH. If NIOSH would disclose the names of these firms, we could very well ask them if they would write to OMB and ask for a release of the OSHA draft proposed rule. I think that would be very "productive."

Fracking poses so many risks, but I never really thought that long about the risks of silica sand. Great article!

Good article! One minor correction: in the second paragraph."Frack sand gets pumped into wells along with the chemicals known as proppants to stabilize the wells in preparation for injection of water and other fracking chemicals."

The sand grains, not the chemicals are the proppants, so called because they PROP the fractures to keep them open.

By Kelvin Rodolfo (not verified) on 05 Jun 2012 #permalink

Thanks for the clarification on proppants. Do you know if there are additional substances mixed in with the sand when it's used as a proppant?

Important point.


If you're working the oil patch, your big risk is still injury from the heavy equipment. Keep your eyes open.

@ Elizabeth--By volume, sand is a minor component. Here's an article that gives some info on the other ingredients, as well as a link to “Chemicals Used in Hydraulic Fracturing,” prepared by the United States House of Representatives Committee on Energy and Commerce.

By Jim Tittle (not verified) on 07 Jun 2012 #permalink