Russian roulette in the shale patch III – Exposure of oil and gas workers to silica sand | Tanja Srebotnjak’s Blog | Switchboard, from NRDC

Russian roulette in the shale patch III – Exposure of oil and gas workers to silica sand | Tanja Srebotnjak’s Blog | Switchboard, from NRDC.


This is part three in a three-part series on the occupational health and safety risks of workers in the booming oil and gas industry.

A study of oil and gas workers found unsafe exposures to a contaminant that can cause permanent lung damage. High-volume hydraulic fracturing (‘fracking’) involves pumping large amounts of water mixed with proppant and chemicals at high pressures into the wellbore to create or enlarge fractures in hydrocarbon-bearing formations and promote the flow of natural gas or oil to the surface. The proppant serves to hold the fractures open after fracturing is completed and the pumps are turned off. By far the most widely used proppant is silica sand (‘frac sand’) [1]. This sounds like a harmless ingredient in the chemical-laced fracturing fluid, but it is a major occupational hazard for workers at hydraulic fracturing sites because its inhalation can cause acute and chronic silicosis (an incurable, progressive lung disease) as well as lung cancer. Breathing in silica dust is also associated with chronic obstructive pulmonary disease (COPD), tuberculosis, kidney disease, and autoimmune diseases [2].

Each fracking operation requires one to four million pounds of silica sand and it is estimated that between 25 and 30 million metric tons of sand are used annually for fracking [3]. Moving such large amounts of sand around a drill site requires machinery that generates substantial clouds of silica dust that can be inhaled deep into the lungs. Crews employed by oil and gas servicing companies that perform hydraulic fracturing operations may, therefore, be exposed to silica dust on a routine basis. The sand is typically moved via initial transport to the site in dry-bulk heavy trucks, then onto sand movers, along transfer belts (T-belt), and into blender hoppers. All of these process stages involve dry sand and can release dust containing silica, contaminating the air nearby and even farther away depending on wind conditions [4]. Clouds of silica dust have been observed coming from frack sites and also trains and trucks transporting the sand.

The first and only study of oil and gas worker exposure to respirable silica from hydraulic fracturing operations was conducted by scientists at NIOSH in 2013 [1]. They sampled 11 sites in 5 states (Colorado, Texas, North Dakota, Arkansas, and Pennsylvania) on three consecutive days. The samples represent 12-hour, full-shift personal breathing zone measurements for 15 job titles and classifications with varying extent of involvement in handling frac sand (e.g., including Blender Operator, Sand Mover Operator, T-belt Operator, Pump Truck Operator, and Sand Coordinator). The measured silica concentrations were transformed to 8-hr time-weighted concentrations and compared with OSHA’s Permissible Exposure Limit (PEL), NIOSH’s Recommended Exposure Limit (REL) of 0.05 mg/m3, and the ACGIH Threshold Limit Value (TLV) of 0.025 mg/m3.

The results raised warning flags at all sites and for several job functions, because they frequently exceeded the established occupational exposure limits – in some cases, by 10, 20, or more times (see table).  The findings are especially worrisome because even workers who were properly using half-mask air-purifying respirators were not sufficiently protected since the measured concentrations exceeded the masks’ maximum use concentration.

The jobs with the highest relative exposures were Sand Movers and Transfer Belt Operators, who were exposed to maximum concentrations up to 55 times higher than the NIOSH REL.


% samples above ACGIH TLV

% samples above NIOSH REL

% samples above OSHA PEL

Total number of samples

Fayetteville, Arkansas





Denver-Julesburg Basin site 1, Colorado





Eagle Ford, Texas





Denver-Julesburg Basin site 2, Colorado





Marcellus, Pennsylvania





Bakken, North Dakota










Source: Adapted from Esswein et al. (2013).

The NIOSH researchers identified seven points in the handling chain of frac sand at which silica dust is generated and poses potential health hazards.

Although the sample size in the NIOSH study was relatively small, the sampling sites are broadly representative of conditions at different shale plays and raises concerns that exposures could be widespread. Moreover, although protective measures such as engineering controls, hazard warnings, training, and protective personal gear are well established in industries such as sand blasting, agriculture, and construction, silica exposure in the oil and gas sector is a relatively recent phenomenon that is not widely monitored and addressed by companies. To date no silica related disease reports are available for the oil and gas workforce [5].

Concerned by the data, NIOSH and OSHA issued a Hazard Alert to the oil and gas industry on silica exposure, which includes a number of recommendations to monitor and reduce exposure [4]. Silica related health hazards are well understood and the industry should adopt a broad range of protective measures that are both effective and economically feasible, including measures to limit dust generation and spread, replacing silica sand with less harmful proppants, reducing exposure times, and more widespread use of personal protective equipment.

On the regulatory side, OSHA can conduct more targeted, unannounced enforcement inspections and industry should fully implement the revised Hazard Communication standard that aligns chemical labeling and safety data sheets with the United Nations’ Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. In 2013 OSHA released a proposed rule to protect workers exposed to respirable crystalline silica [6].

Scientists and researchers also have an important role to fill. More high quality studies are needed to better understand exposures to silica sand in the oil and gas sector as well as of nearby communities during sand mining, transport, and fracking operations. In addition, databases on health outcomes and evaluations of the effectiveness of protective measures are needed.


[1] Eric Esswein, et al., “Occupational Exposures to Respirable Crystalline Silica during Hydraulic Fracturing,” Journal of Occupational and Environmental Hygiene 10 (7): 347–56 (2013), doi:10.1080/15459624.2013.788352.

[2] OSHA, “Chrystalline Silica,” (accessed October 16, 2014)

[3] Wall Street Daily, “Fracking Opens up an Entire New Industry,” (accessed October 14, 2014).

[4] OSHA and NIOSH, “Hazard Alert: Worker Exposure to Silica during Hydraulic Fracturing,” (accessed October 16, 2014).

[5] Roxana Z. Witter, et al., “Occupational Exposures in the Oil and Gas Extraction Industry: State of the Science and Research Recommendations,” American Journal of Industrial Medicine, March 2014, doi:10.1002/ajim.22316.

[6] OSHA, Factsheet on Proposed Crystalline Silica Rule, (accessed October 23, 2014)