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Reports of Worker Fatalities during Flowback Operations

Categories: Oil and Gas

Figure 1. Flowback Tanks

Although worker safety hazards in the oil and gas extraction industry are well known, there is very little published data regarding occupational health hazards (e.g., types and magnitude of risks for chemical exposures) during oil and gas extraction operations. To address the lack of information, NIOSH requests assistance from oil and gas stakeholders in further characterizing risks for chemical exposures during flowback operations and, as needed, develop and implement exposure controls. This blog briefly describes flowback operations and addresses reports made known to NIOSH of recent worker fatalities related to or located at flowback operations.

Worker Fatalities

Figure 2. Production Tanks

NIOSH learned about several worker fatalities associated with flowback operations through media reports, officials with the Occupational Safety and Health Administration (OSHA), and members of the academic community. According to our information, at least four workers have died since 2010 from what appears to be acute chemical exposures during flowback operations at well sites in the Williston Basin (North Dakota and Montana). While not all of these investigations are complete, available information suggests that these cases involved workers who were gauging flowback or production tanks or involved in transferring flowback fluids at the well site. Often these fatalities occurred when the workers were performing their duties alone.

Potential Exposures during Flowback Operations

Flowback refers to process fluids from the wellbore that return to the surface and are collected after hydraulic fracturing is completed. In addition to the hydraulic fracturing fluids originally pumped, returned fluids contain volatile hydrocarbons from the formation. After separation, flowback fluids are typically stored temporarily in tanks (figure 1) or surface impoundments (lined pits, ponds) at the well site. Liquid hydrocarbons from the separation process are routed to production tanks (figure 2). Workers periodically gauge the fluid levels in flowback and production tanks with hand-held gauges (sticks and tapes) through access hatches located on the top of the tank.

Hydrogen sulfide (sour gas) is well recognized as a toxic exposure hazard associated with oil and gas extraction and production (1,2). However, less recognized by many employers and workers is that many of the chemicals found in volatile hydrocarbons are acutely toxic at high concentrations. Volatile hydrocarbons can affect the eyes, breathing, and the nervous system (3,4,5,6,7) and at high concentrations may also affect the heart causing abnormal rhythms (8,9). Recently, NIOSH conducted exposure assessments to identify chemical hazards to workers involved in flowback operations. Results from initial field studies suggest that certain flowback operations/activities can result in elevated concentrations of volatile hydrocarbons in the work environment that could be acute exposure hazards. The results, conclusions, and recommendations based on these evaluations will be detailed in a peer-reviewed journal article, a future NIOSH Science Blog posting, or other communication products.

Preliminary Recommendations

Based on the limited information on fatalities and initial NIOSH exposure assessments, NIOSH researchers have identified preliminary recommendations to reduce the potential for occupational exposures:

1) Develop alternative tank gauging procedures so workers do not have to routinely open hatches on the tops of the tanks and manually gauge the level of liquid.

2) Provide hazard awareness training to ensure flowback technicians, water haulers, and drivers understand the potential hazards and risks for volatile chemical exposures when working on and around flowback and production tanks.

3) Monitor workers to determine their exposure to volatile hydrocarbons and other contaminants. Employers should consult with an occupational safety and health professional trained in industrial hygiene to ensure an appropriate sampling strategy is used.

4) Ensure workers do not work alone in potentially hazardous areas.

5) Use appropriate respiratory protection in areas where potentially high concentrations of volatile hydrocarbons can occur as an interim measure until engineering controls are implemented. Employers should consult with an occupational safety and health professional trained in industrial hygiene to determine the appropriate respirator to be used. Note that OSHA regulations (29 CFR 1910.134) require a comprehensive respiratory protection program be established when respirators are used in the workplace. NIOSH guidance for selecting respirators can be found at

6) Establish emergency procedures to provide medical response in the event of an incident.

Help Wanted

NIOSH continues to work with OSHA to obtain additional information about these fatalities. We request assistance from our occupational safety and health stakeholders for information on other potentially related incidents or fatalities related to acute exposures during such flowback operations. NIOSH is looking for additional industry partners to work with us to further characterize worker exposures during flowback operations and to develop and evaluate controls, as needed. If you have questions or wish to provide further pertinent information, please contact us via the blog comment box below or by e-mail at


John Snawder, Ph.D, DABT; Eric Esswein, MSPH, CIH; Bradley King, MPH, CIH; Michael Breitenstein, BS; Marissa Alexander-Scott, DVM, MS, MPH; Kyla Retzer, MPH; Max Kiefer, MS,CIH and Ryan Hill, MPH.
John Snawder, Michael Breitenstein, and Marissa Alexander-Scott are with the NIOSH Division of Applied Research and Technology (DART) in Cincinnati, OH. Eric Esswein, Bradley King, Kyla Retzer and Max Kiefer are with the NIOSH Western States Office in Denver, CO. Ryan Hill is with NIOSH, Office of the Director, Morgantown, West Virginia



The objective of this blog entry is to describe a potential emerging occupational hazard in the oil and gas extraction industry. Additionally, it is meant to request help from stakeholders for more information related to fatalities associated with flowback operations. To keep the blog discussion focused on worker health, we may choose not to respond to comments that do not pertain to worker exposures.


1. NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149 Hydrogen Sulfide:

2. OSHA Oil and Gas Well Servicing eTool: General Safety and Health: Hydrogen Sulfide Gas

3.NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. Benzene:

4. NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. N-Pentane:

5. NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. N-Hexane:

6. NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. N-Heptane:

7. NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. Petroleum distillates:

8. Adgey A.A., Johnston P.W., McMechan S. Sudden cardiac death and substance abuse. Resuscitation. (1995)Jun;29(3):219-21.

9. Sugie, H., Sasakia C. Hashimotoa, C., Takeshita, H. et al. Three cases of sudden death due to butane or propane gas inhalation: analysis of tissues for gas components. Forensic Science International (2004) 143:211–214.

Public Comments

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this site is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

  1. May 20, 2014 at 3:24 pm ET  -   Safety Engineer

    There was a fatality at a crude oil tank battery in Oklahoma, March 20. Suspiciously similar to these fatalities. OSHA still waiting for ME report.

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  2. May 20, 2014 at 5:01 pm ET  -   vishal

    great article…
    information was given in good manner.
    thanks for sharing it with us :)

    Link to this comment

  3. May 21, 2014 at 2:10 pm ET  -   Kim Feil

    I have repeatedly begged our Arlington TX City Council to mandate pressurized, ventless, flowback tanks because Urban Drilling risks the fenceline folks too! Nobody is watching out for us….I fear for my familys health. I have blogged on these guys deaths here ..

    Link to this comment

  4. May 21, 2014 at 2:27 pm ET  -   Robert Schmetzer

    There are many reference articles that can be goggled. Flow back from the hydraulic fracturing comes with a list of natural and manmade toxins. Radio active isotopes come in different uranium based numbers. U 234, u235, u236, etc. Radon gas and depleted uranium are burnt off with flaring, ponds spilling, dumping on roadways and unlined garbage dumps. The VA has multiple examples of veterans coming home with severe illnesses because of exposure to depleted uranium. Halliburton has a patient on the perf gun used in every well to blow a hole in the steel pipe and shale. It has depleted uranium disks according to the US Patient office. The drillers know when they are in the Marcellus shale when the radiation alarms go off. Radon gas originates from the shale and works itself into aquifers and cellars of homes. Our government who is trusted with protecting the public has sold permits to harm the public. This is not a good idea.

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  5. May 21, 2014 at 5:45 pm ET  -   Jeremy

    Rule #4, Ensure workers do not work alone in potentially hazardous areas, will help insure that more than one person can be killed at a time.

    Link to this comment

  6. May 21, 2014 at 8:23 pm ET  -   Paul Schmidt

    Flowback after an acid stimulation or fracture stimulation carries the same produced fluids as a well that is naturally flowing. Most deaths are from H2S which is produced regardless of fracture stimulation of the well. No volatile chemicals are used to fracture that would potentially cause a fatality during flowback. There are many parts of the world where formation pressures and geology allows for naturally flowing wells where just a hole has to be drilled and casing run. In the US we have to extract the oil where a pathway is made artificially by either pumping acid or fracturing. An average citizen does not understand these processes, unfortunately and hence this has caused a furore in the country where public is protesting against these processes. The acid pumped in these wells is 15% acid the rest is water and other chemicals that inhibit corrosion etc contrary to public belief that alien slime is pumped down these wells. Similarly the main constituent of Hydraulic Fracturing is gel made from guar gum which is a common food additive and then sand is used as a proppant. This man made fracture just allows for oil to flow to the well and there are thousands of feet of vertically impermeable rock that separate these fractures and any cross-flow from the upper aquifer or potable water bearing formations. If our citizenry does not educate themselves on these methods and the public protests and votes against these processes we will be paying 10 bucks a gallon for a gallon. We cannot import all the oil from the middle-east. Let us incorporate science and good common sense into the masses so they can make educated decisions about all of our futures and those of our children.

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  7. May 23, 2014 at 10:25 am ET  -   John Puskar, P.E.

    The entire oil and gas industry, in my opinion, is missing a central piece of their safety puzzle. API 76 recommended practice for contractor safety management references 68 other documents, 114 training programs and asks 430 safety program questions of contractors. Guess how much of this directly relates to the core activity of handling flammable gas? NONE, Nothing, nada. Hard to believe. I am a founding member of NFPA 56, Standard for fire and explosion prevention during the cleaning and purging of flammable gas piping systems. This standard actually directly speaks to many of the root causes of oil & gas related fires and explosions. The oil & gas industry knows nothing of this standard although its been out now for nearly 3 years. I am presenting a paper on the topic at the upcoming asse meting in Orlando in June. If anyone wants a copy, email me at

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  8. May 27, 2014 at 3:15 pm ET  -   M. Sweeney

    If some of the volatile hydrocarbons at fracking sites can cause the death of workers, I am wondering what the short- and long-term effects may be for residents living on the gas fields who may be repeatedly exposed to these volatile hydrocarbons (albeit at lower levels than the workers). I have seen fracked gas wells in Northeast PA that are only a few hundred feet from homes and I have seen neighborhoods where there are many, many gas wells–what are the cumulative effects? What about the long-term effects of living near the wells? What about the effects on infants, young children, and pregnant women? What effects might the local weather have (e.g. what if the wind is blowing from a fracking site toward nearby residences)? Is anyone modeling any of this and calculating what the local effects would be at various gas well setbacks and gas well densities?

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    • AUTHOR COMMENT May 28, 2014 at 9:49 am ET  -   John Snawder, Eric Esswein, Bradley King, Michael Breitenstein, Marissa Alexander-Scott, Kyla Retzer, Max Kiefer, and Ryan Hill

      Thank you for your comment. NIOSH researchers can not address potential community exposures because our research and findings are specific to occupational exposures at a work site, and should not be extrapolated to communities or other areas beyond the specific activities we are monitoring. This is because exposures to the community cannot be predicted from worker exposures. We do not have the mandate or authority to research community and environmental issues. For more information on the effects of oil and gas extraction on communities, please visit the websites for CDC’s National Center for Environmental Health and the Agency of Toxic Substances and Disease Registry.

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  9. June 14, 2014 at 10:30 pm ET  -   O E Smith

    Oil drilling deaths have reached 545 since 2008 in the U S because of the fracking frenzy that has taken off in North Dakota. The American people over all hears little about this among other things. We have heard the dispute about whether or not it is healthy for our environment but rarely how dangerous this type of operation is. With so many people out of work I have heard many claim they are going to work the oil fields in North Dakota because they are always hiring. I see now why that is.

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  10. August 9, 2014 at 2:34 pm ET  -   Sokolov

    Yes, I fully support the statement of other commentator, everybody talks about ecological costs of new fracking boom, nobody mentions decreased safety levels on some of the new fields.


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  11. August 21, 2014 at 1:09 am ET  -   kasey johnson

    I work on a drilling rig and its funny how no one metions the dangers of over heating because of frc’s.

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  12. November 12, 2014 at 9:52 pm ET  -   Dave

    I recently did some work in flowback and my job was to strap or measure the tanks. I did this 1 2 3 times and hour sometimes and the fumes from the flowback water and from the condensate were very overpowering sometimes gave me headaches, made my stomach upset and I felt dizzy and tired. The fumes got so bad one night I almost puked passed out and couldnt breath and my supervisor thought it was funny I didnt. Being a firefighter/EMT with hazmat training I went over the MSDS sheets for the stuff and its suggested to wear splash protection, rubber gloves for handling and a respirator because its some bad stuff. My company and the oil company we were working for just didnt seem to care and my concerns fell on deaf ears and I am glad I quit because I could forsee something bad happening to myself.

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  13. November 20, 2014 at 8:50 am ET  -   Mert Soylu

    Great Post, provided information indicates a lot of details. Thanks!

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  14. November 29, 2014 at 1:16 am ET  -   qdc Qatar

    Thanks For sharing information its use for us.

    Best Engineering Consultant

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  15. December 10, 2014 at 7:47 am ET  -   Carreira

    Great Post, provided information indicates a lot of details. Thanks!


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  16. May 17, 2015 at 3:34 pm ET  -   miekacorporation

    Enjoyed the reading the post!

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  17. June 9, 2015 at 2:34 pm ET  -   Jose E. Pena

    I am a driling fluids engineer, My specialty is drilling and treating H2S formations in
    South Texas, IE: Ramondville, La Grulla, Rio Grande City, and Zapata areas. The gas
    samples from different formations, are tested, and gas sample bottles, are shipped
    of and tested for H2S,C02, Methane, and other gases. As these wells are produced
    Dehydration, and Amine Seperator units are installed to treat out poisionous gasses
    depending on what the field is producing by the Reservour Engineers Calculations.

    The other side Condensate Tanks are vented to atmosphere, it is not dangerous as
    long as the wind is blowing, and vent gasses flow away from you.

    Frac Tanks with degrading Chemical Drilling Fluids, should be drained and shipped
    to storage locations.

    Link to this comment

    • AUTHOR COMMENT June 10, 2015 at 11:11 am ET  -   Eric Esswein and Bradley King

      Thank you for your comment and expertise. Dilution ventilation (i.e., wind) may reduce concentrations of hydrocarbons in some cases but relying solely on the wind as an exposure control mechanism is not recommended. Standing upwind of tank hatches may also help to reduce exposures but neither natural dilution ventilation nor standing upwind should be relied upon to completely reduce risks. We encourage the development and use of engineering controls such as remote gauging and remotely venting tanks before workers are present on tank platforms to help control the multiple safety risks that can be encountered during manual tank gauging including: oxygen deficient atmospheres, the presence of acutely toxic gases and vapors, and the flammability hazards.

      Link to this comment

  18. September 25, 2015 at 2:14 pm ET  -   Marissa Cortese

    It is my great pleasure to visit your website and to enjoy your excellent Blog Commenting Sites post here.
    Thanks.. :)

    Link to this comment

  19. November 22, 2015 at 11:30 am ET  -   Steven Jahn

    Has NIOSH issued a summary report as to the investigation of fatalities and the near misses that have been reported in this blog? Awareness at the worker level is lacking, but it should not be for the owners of the wells… is possible that simple awareness will not solve the problem, unless monitoring instrument use is coupled with a good understanding of the timing and initiation of the gas releases.
    Thanks Steve

    Link to this comment

    • AUTHOR COMMENT November 27, 2015 at 7:17 am ET  -   John Snawder, Eric Esswein, Bradley King, Michael Breitenstein, Marissa Alexander-Scott, Kyla Retzer, Max Kiefer, and Ryan Hill

      Thank you for your comment. Yes, NIOSH has provided more information about those cases. On April 10th, 2015, NIOSH published an updated science blog that identified a total of nine fatalities associated with tank gauging or sampling ( We also provided more information about those nine cases, including a narrative description of each event, on our website ( With regards to preventing additional fatalities, NIOSH agrees that relying solely on raising awareness of the hazard is not the most effective strategy. In our updated blog, we recommend the use of alternative tank gauging and sampling procedures, that would allow workers to remotely gauge and sample oil and gas production tanks. NIOSH also collaborated with OSHA and the National STEPS Network to develop a tank hazard infographic and supporting materials that are available for download ( These materials not only serve to raise awareness, but they also promote engineering and administrative controls, and PPE considerations. We are continuing our work to more fully characterize the hazards associated with manual tank gauging and sampling and to promote effective strategies to protect workers; we will continue to seek additional input and collaboration from stakeholders as we conduct that work.

      Link to this comment

  20. March 14, 2016 at 4:58 am ET  -   Marissa

    Awesome post Thanks for sharing this information.

    Link to this comment

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