In This Issue
Summer Issue of The Bridge on Shale Gas: Promises and Challenges
June 15, 2014 Volume 44 Issue 2

Occupational Health and Safety Considerations in Oil and Gas Extraction Operations

Friday, June 27, 2014

Author: Karen B. Mulloy

The onshore oil and gas industry has experienced rapid growth in upstream extraction production, in part due to the use of hydraulic fracturing (fracking) in unconventional wells. Although hydraulic fracturing is not a new process, its use has increased significantly in the past decade with the introduction of horizontal drilling and multistage fracking technologies. With the rise in production has come an escalation in risks of occupationally related injury, illness, and fatality. These risks are described together with some approaches to risk reduction and remediation.

Employment in the US Oil and Gas Extraction Industry

Employment in the US oil and gas extraction industry has grown dramatically in recent years. The Energy Information Agency reports that in 2012 the industry employed approximately 579,000 workers in drilling, extraction, and support activities, an increase of more than 162,000 jobs or 40 percent since 2007.[1] The North American Industry Classification System (codes 21111, 213111, 213112) characterizes these jobs as follows[2]:

  •  drilling, completing, servicing, and equipping wells;
  • operating separators, emulsion breakers, de-silting equipment, and field gathering lines for crude petroleum and natural gas; and
  • performing other activities in preparing oil and gas up to the point of shipment from the producing property.

Occupational Injuries and Fatalities

The National Institute for Occupational Safety and Health (NIOSH), in an analysis of the Bureau of Labor Statistics (BLS) Census of Fatal Occupational Injuries, reported an annual occupational fatality rate of 27.5 per 100,000 workers in the oil and gas extraction industry from 2003 to 2009[3]—seven times higher than the rate for all US workers, which was 3.9 per 100,000 workers.[4] More than half (53 percent) of all fatalities among oil and gas workers were of those who had less than one year on the job (Hill 2012).

Correlating Factors

The industry’s fatality rate correlates directly with the level of drilling activity, as measured by the number of active rotary rigs3: as the number of drilling and workover rigs increases, so does the fatality rate. The reported fatality rate controls for the number of workers in the industry, so changes in the rate are also related to other factors, such as an increase in the number of inexperienced and inadequately trained workers and longer work hours (associated with worker fatigue) (Retzer et al. 2012a). Moreover, in times of high demand older rigs with fewer safety guards may be brought back into service as well as small companies that typically don’t operate during a downturn.3

Oil and gas extraction industry fatality rates are further correlated with both the type (drilling, well servicing, and operation) and size of the establishment (small, medium, large).3 NIOSH analysis of fatality rate by company type and size showed that workers employed by drilling companies had the highest fatality rate, followed by workers in well servicing companies, and then operators, irrespective of establishment size (Hill 2012).

Small companies had the highest fatality rate for all three company types. There are several possible reasons for this correlation. In NIOSH’s work with industry, discussions have indicated that small companies may not have health and safety staff, staff may have competing responsibilities, and health and safety programs may not be as well developed as at medium and large companies. In addition, small drilling contractors may lack the technologies (e.g., top drive, power tongs, pipe handling) that isolate workers from hazardous tasks, and small operators may have different safety expectations from those of large operators (Hill 2012).

Types of Injuries

The relative frequency of different types of fatalities in the US oil and gas extraction industry is shown in Table 1 (Hill 2012).[5] Transportation incidents are the most frequent, followed by contact with objects or equipment, fires and explosions, exposure to harmful substances/environments, and falls. The motor vehicle fatality rate for workers in the oil and gas industry subsector was more than eight times higher than that of private workers in all other industry sectors (Hill 2012). Fatigue associated with long hours (8- or 12-hour shifts for 7 or 14 days in a row) is believed to be a significant contributor to the motor vehicle crashes.[6]

Table 1

In contrast to fatal injuries, most segments of the oil and gas extraction industry report a lower nonfatal injury rate than the average for private industry. For example, in 2010 the estimated annual rate of nonfatal work-related injuries for all job categories was 1.2 per 100 full-time workers, 1.9 for workers in support activities for oil and gas extraction, and 3.3 for drilling oil and gas wells.3 During the same year the annual rate for all private industries was 3.5 nonfatal injuries per 100 full-time workers.3 Whether due to underreporting or other recordkeeping issues, the reason for the lower reported injury rate for oil and gas extraction workers is not clear.

Accident Prevention Programs

To address the high fatality rate, safety training specific to the oil and gas industry has been developed by the Occupational Safety and Health Administration (OSHA)[7] and NIOSH.[8] In addition, some companies have initiated in-vehicle monitoring programs that record date, time of day, speed, acceleration, deceleration, and safety belt use. It is estimated that these programs can lead to a 50–93 percent reduction in motor vehicle crash rate (Retzer et al. 2012b).

Wyoming provides an example of a state-based accident prevention program. In June 2011 the Wyoming Oil and Gas Safety Alliance ( and Wyoming OSHA entered into a formal collaboration to foster a safer workplace and healthier workers. One important measure is the Stop Work Authority, which establishes the responsibility and obligation of any individual to suspend a work task or group operation when one of the following occurs: the control of a health, safety, and/or environment risk is not clearly determined or understood, or a previously unforeseen hazard or risk is recognized and, if left uncorrected, may result in injury or damage.

Exposure to Toxic Agents

The second broad category of health risks in the oil and gas industry, after injury or fatality, involves acute and long-time exposures to toxic agents. NIOSH (2010) has created a program to assess exposure risks to oil and gas workers, with the following goals:

  • identify processes and activities where chemical exposures could occur;
  • characterize potential exposures to vapors, gases, particulates, and fumes; and
  • recommend safe work practices and/or propose and evaluate exposure controls (e.g., engineering controls, substitution, and personal protective equipment). 


A number of specific agents have been evaluated—respirable crystalline silica, diesel particulates, hydrogen sulfide, volatile organic compounds (e.g., benzene), acid gases (HCl) and caustic compounds (NaOH), aldehydes used as biocides, heavy metals (e.g., lead), radioactive materials (e.g., uranium, thorium, radon), and noise. These agents are not unique to the oil and gas industry, and there is significant experience in the occupational health and safety field in understanding and reducing or eliminating their impacts on workers’ health.

Benzene, for example, is a carcinogen that can cause aplastic anemia and leukemia, and exposure to it is regulated by OSHA standards. But the oil and gas extraction industry is exempted from the national benzene standard. Historically, OSHA has based the rationale for this exemption on data showing that “average worker exposures would be well below the action level” (OSHA 1995). There has been increasing concern, however, that the benzene levels may be higher than previously thought. NIOSH is involved in a study of volatile organic compound exposures in the oil and gas extraction industry.

Silica Exposure

Of all the agents listed above, silica is receiving the most attention in the oil and gas industry. A large quantity of silica sand is commonly used as a proppant to hold open cracks and fissures during hydraulic fracturing. Exposure to respirable crystalline silica particles (less than 5 micrometers) occurs during blending and sand loading operations, sand truck refilling, and sand mover operations, all of which produce freshly fractured quartz (Figure 1; Esswein et al. 2013), which has been shown to have greater toxicity than aged quartz (Castranova et al. 1996; Shoemaker et al. 1995). Such exposure induces an inflammatory reaction in the lung and causes diseases such as silicosis (acute, accelerated, chronic) (Banks 2005) and chronic obstructive pulmonary disease (Möhner et al. 2013). Workers with silicosis also have a greater risk of tuberculosis.

Figure 1

The International Agency for Research on Cancer evaluated the carcinogenicity of respirable crystalline silica and concluded that inhaled quartz and cristobalite were carcinogenic in occupational settings (IARC 2012). Silica exposure has also been linked with autoimmune diseases (Miller et al. 2012) that are related to chronic inflammatory effects; these diseases include rheumatoid arthritis (Rosenman and Zhu 1995), scleroderma (Sluis-Cremer et al. 1985), systemic vasculitis (Gómez-Puerta et al. 2013), systemic lupus erythematosus (Brown et al. 1997), and chronic renal disease (Vupputuri et al. 2012).

Workplace exposure limits have been established to address the dangers of silica. The current OSHA permissible exposure limit (PEL) for respirable crystalline silica (quartz) is approximately equivalent to 100 μg/m3 as an 8-hour time-weighted average (TWA),[9] but a more protective PEL is being proposed[10] in line with the NIOSH recommended exposure limit (REL) for respirable silica of 50 μg/m3 (NIOSH 2002). The American Conference of Governmental Industrial Hygienists recommends the most protective threshold limit value (TLV), 25 μg/m3 for a TWA exposure based on an 8-hour workday (ACGIH 2012).

However, research has shown silica levels for oil and gas workers in and around dust generation points to be above the recommended occupational exposure limits. In a recent study NIOSH collected 111 personal breathing zone (PBZ) samples from workers with 15 different job titles at 11 well sites in 5 states (Arkansas, Colorado, North Dakota, Pennsylvania, and Texas) under all conditions to evaluate worker exposures to respirable crystalline silica during fracking (Esswein et al. 2013). Of the 111 samples 83.8 percent exceeded the TLV, 68.5 percent exceeded the REL, and 51.4 percent exceeded the PEL for respirable silica. The jobs most at risk were sand mover operators and T-belt operators—their PBZ exposures exceeded the REL or PEL by a factor of 10 or more.

Prevention of Exposure to Silica: Hierarchy of Controls

Protection of workers who are exposed to silica during hydraulic fracturing operations will require a combination of engineering controls, product substitution where feasible, improved work practices, worker training, and proper protective equipment. Table 2 shows a hierarchy of controls recommended to eliminate or reduce exposure to silica (Esswein and Hill 2013).

Table 2

Elimination of the toxic agent is always the first and best approach. In this regard, proper engineering design of processes and equipment is key. Such design measures may involve incorporation of skirting, filters, and shrouds by retrofitting existing equipment (Esswein and Hill 2013).

Even better is building these protections into the original engineering design.[11] Some operators have substituted manufactured ceramics (Esswein et al. 2013; NIOSH/OSHA 2012) as the proppant instead of silica sand to reduce respirable crystalline silica exposure. Other means for reducing exposure involve strong administrative control over operations, such as limiting the number of workers and time spent in areas of high dust.

In addition, OSHA’s Hazard Communication standard requires that employers provide training and information in a manner and language that each worker understands to ensure that informed workers engage in safe work practices.


Although the high fatality rate among oil and gas extraction workers has been noted for more than a decade, the rapid increase in the number of workers in the past five years and the expansion of the industry to a greater number of states has brought the issue to the forefront. Research findings showing that fatality rates are highest among small companies (those with fewer than 20 employees) and workers with less than one year of experience, and that transportation incidents are the most frequent fatal event type, have spurred efforts for improved safety.

Novel intervention programs are needed to reduce the fatality rate in the oil and gas extraction industries. Reducing the exposure of workers to silica and other chemical agents is a complex, multifaceted problem that can best be addressed through principles of prevention through design. Improved occupational health and safety surveillance will help to capture the effectiveness of injury and illness prevention interventions.

Overall, a sustained, concerted effort by those in industry, public health, regulatory agencies, and academia is needed to identify potential risks and significantly reduce illness and fatalities in the oil and gas extraction industries.


The author thanks Eric Esswein, Ryan Hill, and others at the NIOSH Western States Office for sharing their research results and insights into the health and safety issues in the oil and gas extraction industry.


ACGIH [American Conference of Governmental Industrial Hygienists]. 2012. TLVs and BEIs: Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati.

Banks DE. 2005. Silicosis. In: Textbook of Clinical Occupational and Environmental Medicine, 2nd ed. Rosenstock L, Cullen MR, Brodkin CA, Redlich CA, eds. Philadelphia: Elsevier Saunders. pp. 380–392. 

Brown LM, Gridley G, Olsen JH, Mellemkjaer L, Linet MS, Fraumeni JF Jr. 1997. Cancer risk and mortality patterns among silicotic men in Sweden and Denmark. Journal of Occupational and Environmental Medicine 39:633–638. 

Castranova V, Pailes WH, Dalal NS, Miles PR, Bowman L, Vallyathan V, Pack D, Weber KC, Hubbs A, Schwegler-Berry D, Xiang J, Dey R, Blackford J, Ma JYC, Barger M, Shoemaker DA. 1996. Enhanced pulmonary response to the inhalation of freshly fractured silica as compared with aged dust exposure. Applied Occupational and Environmental Hygiene 11:937–941.

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Esswein EJ, Breitenstein M, Snawder J, Kiefer M, Sieber K. 2013. Occupational exposures to respirable crystalline silica during hydraulic fracturing. Journal of Occupational and Environmental Hygiene 10:347–356.

Gómez-Puerta JA, Gedmintas L, Costenbader KH. 2013. The association between silica exposure and development of ANCA-associated vasculitis: Systematic review and meta-analysis. Autoimmunity Reviews 12:1129–1135.

Hill R. 2012. Improving safety and health in the oil and gas extraction industry through research and partnerships. Presentation at the MAP ERC Energy Summit, April 12, Denver.

IARC [International Agency for Research on Cancer]. 2012. Silica dust, crystalline, in the form of quartz or cristobalite. In: A Review of Human Carcinogens, Part C: Arsenic Fibers, Metals, and Dusts, pp. 355–405. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Lyon, France. Available at 14.pdf.

Miller FW, Alfredsson L, Costenbader KH, Kamen DL, Nelson LM, Norris JM, De Roos AJ. 2012. Epidemiology of environmental exposures and human autoimmune diseases: Findings from a National Institute of Environmental Health Sciences expert panel workshop. Journal of Autoimmunity 39:259–271.

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NIOSH [National Institute for Occupational Safety and Health]. 2002. NIOSH Hazard Review: Health Effects of Occupational Exposure to Respirable Crystalline Silica. Available at

NIOSH. 2010. Fact sheet: NIOSH field effort to assess chemical exposure risks to gas and oil workers. DHHS (NIOSH) Publication No. 2010-130. Available at

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Shoemaker DA, Pretty JR, Ramsey DM, McLaurin JL, Khan A, Teass AW, Castranova V, Pailes WH, Dalal NS, Miles PR, Bowman L, Leonard S, Shumaker J, Vallyathan V, Pack D. 1995. Particle activity and in vivo pulmonary response to freshly milled and aged alpha quartz. Scandinavian Journal of Work, Environment and Health 21:15–18.

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[1] “Oil and Gas Industry Employment Growing Much Faster Than Total Private Sector Employment.” US Energy Information Agency, August 2013. Available at

[2] NAICS information is from the US Census Bureau, available at

[3] Information about Oil and Gas Extraction: Occupational Health and Safety Risks is available from NIOSH at

[4] Data from the BLS Census of Fatal Occupational Injuries Charts, 1992–2012, available at

[5] Ryan D. Hill, Manager, NIOSH Oil and Gas Safety and Health Program, personal correspondence, February 14, 2014.

[6] Ryan D. Hill, Manager, NIOSH Oil and Gas Safety and Health Program, personal correspondence, April 26, 2013.

[7] OSHA information about safety and health topics related to oil and gas extraction is available at

[8] NIOSH information about Oil and Gas Extraction Outputs: Products is available at

[9] OSHA regulations for occupational exposures to crystalline silica are available at standards_silica.html.

[10] OSHA’s Proposed Rule on Occupational Exposure to Respirable Crystalline Silica (09/12/2013) is available in the Federal Register at 20997/occupational-exposure-to-respirable-crystalline- silica.

[11] NIOSH provides online guidance on “prevention through design” (PtD) at

About the Author:Karen B. Mulloy is an associate professor in the Departments of Environmental Health Sciences and Family Medicine and Community Health, School of Medicine, Case Western Reserve University, Cleveland, Ohio.