Silica exposure -- an old and deadly hazard -- is common at frack sites, researcher says

Gayathri Vaidyanathan, E&E reporter

Published: Tuesday, May 1, 2012

Oil and gas workers carrying out hydraulic fracturing are often exposed to levels of fine sand dust, sometimes at more than 10 times the recommended safe limit, according to a researcher with the Centers for Disease Control and Prevention (CDC)

Sand dust contains silica or quartz that can penetrate the lungs and cause a fatal disease called silicosis. The disease is irreversible, and a low to moderate exposure can result in illness even 20 years after exposure. Silica has also been linked to lung cancer.

"It is probably one of the oldest known occupational hazards, from a lung disease perspective," said Eric Esswein, senior industrial hygienist from the National Institute for Occupational Safety and Health (NIOSH). "Two hundred workers die every year still from silicosis. The thing about silicosis is, by preventing the exposure you can prevent the disease."

He was speaking at an Institutes of Medicine roundtable in Washington, D.C., presenting results from yet-to-be-published research. 

So much airborne silica hangs over some unconventional gas fields that even the half-mask respirators that workers wear may not be sufficient for protection, Esswein said. 

The research was conducted between 2010 and 2011 at 11 oil and gas sites in Colorado, Arkansas, Texas, North Dakota and Pennsylvania. The scientists gathered about 225 hours of data in total and sometimes stayed on sites for 18 hours a day to get representative samples. 

The scientists measured the exposures by collecting air samples within a worker's immediate vicinity. The samples are called "personal breathing zone" measurements. 

They collected data at various elevations and temperatures and included workers' exposure to silica, particulate matter emissions from diesel engines, emissions of volatile organic compounds (VOCs), hydrogen sulfide, aldehyde and other chemicals. 

Of all the chemicals, the one of greatest concern was silica. 

Sand is a key component in hydraulic fracturing, with nearly 4 million pounds getting pumped underground together with water and chemicals to crack shale and release natural gas. 

Hundreds of trucks transport the material in and out of the sites, and the sand is stored in bins called "sand masters." Exposure can occur during any part of the operation, such as when sand masters are refilled under pressure and sand dust laden with silica gets airborne. 

The National Institute for Occupational Safety and Health's recommended exposure limit for silica is 0.05 milligram per cubic meter of air, which means that the average worker can safely inhale about 500 micrograms of silica each day. 

The Occupational Safety and Health Administration sets a safe limit for respiratory dust containing silica at 10 milligrams per cubic meter of air. 

While oil and gas workers typically wear half-mask respirators when handling sand, these protect up to only 10 times the NIOSH limit. The scientists found that at least a fraction of the workers on most sites are exposed beyond this limit. 

Out of the 11 sites the researchers studied, 10 sites were in violation of OSHA safe limits for silica.

In the Denver-Julesburg basin in Colorado, the researchers collected 21 personal breathing zone samples from six drilling sites. They found that 71 percent of the workers were exposed to silica above the NIOSH-recommended exposure limit. And 55 percent of those exposures were above 10 times the NIOSH limits, meaning that face masks would be ineffectual. 

On another site in the same basin, researchers collected 18 samples and found 95 percent above the NIOSH safe limit. 

In the Fayetteville Shale, the researchers collected 26 samples from one site and found 81 percent of the exposures were greater than the NIOSH limit. 

In the Marcellus, they collected 27 samples from one site and found 92 percent of the samples above the NIOSH limit. 

In the Eagle Ford in Texas, they collected eight samples from one site and found 62 percent of the samples above safe limits. 

Cumulatively, out of 11 sites and 116 samples, 79 percent were above NIOSH safe limits, and 31 percent of those were at least 10 times higher. 

And 47 percent of the samples were higher than the OSHA safe limit for respiratory dust.

The only site where researchers did not find silica exposures above the OSHA limit was located on the Bakken Shale. At that site, operators used a ceramic, man-made proppant instead of sand while hydraulic fracturing. 

NIOSH has conveyed these results to both industry and OSHA, and controls are being designed to prevent exposures at the source, said Esswein. It would be up to OSHA to require controls on sites after first recording a violation, he said. 

The research will soon be published in both an academic journal and a trade journal, Esswein said.