UPDATE: Reports of Worker Fatalities during Manual Tank Gauging and Sampling in the Oil and Gas Extraction Industry

Posted on by Bradley King, PhD, MPH, CIH; Eric Esswein, MSPH, CIH; Kyla Retzer, MPH; John Snawder, PhD, DABT; Sophia Ridl, BS; Michael Breitenstein, BS; Marissa Alexander-Scott, DVM, MS, MPH; Ryan Hill, MPH.


Photo 1. Plume of hydrocarbon gas and vapor escaping from a flowback tank hatch

On May 19th, 2014, NIOSH posted a Science blog titled “Reports of Worker Fatalities during Flowback Operations”. This blog post provided information that NIOSH received from several sources indicating that acute exposures to hydrocarbon gas and vapors likely played a role in the deaths of at least four workers in the oil and gas extraction industry. The four workers were employed in the Williston Basin of North Dakota and Montana. Specific activities the workers had in common at the time of death included manual tank gauging of production tanks or transferring production fluids at the well site.

Since the time of the original blog posting, NIOSH researchers, along with officials from the Occupational Safety and Health Administration (OSHA) and members of the academic community, have continued to investigate these and other reports of worker deaths associated with manual tank gauging and sampling operations in the oil and gas extraction industry. Through this investigation, NIOSH researchers have now identified nine fatalities of oil and gas extraction workers from January 2010 to December 2014 associated with tank gauging or sampling. The degree of detailed information about each case varies but all have in common manually gauging or sampling production tanks at oil and gas well sites. Additionally, the possibility of death caused by exposures to hydrogen sulfide, a toxic gas commonly found in oil and gas formations, was ruled out for these cases. A tool in this ongoing investigation is NIOSH’s Fatalities in the Oil and Gas Extraction Industry (FOG) Database which collects detailed information on fatal events in this industry. NIOSH has recently updated the FOG webpage to include a report that provides further details on each case.

When hatches on production tanks are opened by a worker, a plume of hydrocarbon gases and vapors can be rapidly released due to the internal pressure present in the tank. These gases and vapors can include benzene, a carcinogen, as well as low molecular weight hydrocarbons such as ethane, propane, and butane. In addition to asphyxiation and explosive hazards, exposure to high concentrations of these low molecular weight hydrocarbons can have narcotic effects, resulting in disorientation, dizziness, light-headedness and other effects; recommendations have been made that a maximum exposure limit be set at 10% of the lower explosive limit (LEL) for light hydrocarbon gases in recognition of both the narcotic and explosive hazards.[i],[ii] Case reports of sudden death following butane and propane inhalation have suggested cardiac arrhythmia (irregular heartbeat), hypoxia (a state of insufficient oxygen supply), and respiratory depression (reduced breathing rate and inadequate ventilation of the lungs).[iii]

NIOSH researchers continue to conduct field-based exposure assessment on health risks from exposures to chemicals through the NIOSH Field Effort to Assess Chemical Exposure Risks to Gas and Oil Workers. NIOSH research investigations to evaluate worker exposures using direct-reading instruments during tank gauging activities identified instances of peak concentrations of flammable gas and vapors as high as 40% of the lower explosive limit (LEL). Peak short-term levels of total volatile organic compounds (VOCs) (measured by photoionization detectors (PIDs) in isobutylene equivalents) were above 2000 parts per million (ppm), and sustained levels as high as 500 ppm were seen to occur. These measurements were made adjacent to separators and flowback tanks.[iv] Additionally, the OSHA Health Response Team assessed concentrations of compounds such as butane, propane, and pentane at open hatches of production tanks. Data collected to date shows that concentrations of these hydrocarbons in excess of immediately dangerous to life or health (IDLH) levels can occur near open tank hatches and these concentrations can exceed the LEL presenting risks for fires and explosions. Many VOCs from hydrocarbon sources have occupational exposure limits (OELs) much lower than their LEL. NIOSH review of data collected from a multi-gas monitor worn by one decedent revealed LEL concentrations greater than 100% and simultaneous oxygen deficiency (i.e., <10%) at and around the time of the individual’s death. These conditions could occur due to high concentrations of gases and vapors inside the tank which are released in a burst of pressure as the tank hatch is opened by the worker for manual gauging or sampling operations.

Photo 2. Plume of hydrocarbon gas and vapors escaping from a production tank hatch

Photos 1 and 2 were taken by NIOSH researchers during a visit to an oil and gas well site using an infrared camera, allowing hydrocarbon gas and vapors not normally visible to be observed. The plume of gases and vapors that can be seen escaping from the tank hatches is clearly visible as a fast-moving dark cloud. White-grey portions of the cloud are steam. Note these photos are not representative of all sites and not indicative of specific hydrocarbon compounds or concentrations. These images were taken from a peak release and only represent a few seconds or minutes during a typical work day. They are included to illustrate the potential for short-term hydrocarbon releases and potential hazards for workers who may be downstream of such plumes.

Preliminary recommendations for the oil and gas extraction industry were developed by NIOSH and listed in the original May 19, 2014, NIOSH Science Blog and these remain unchanged (with an added caution against relying on air-purifying respirators) in this update. Recommendations are provided to limit or prevent exposures to hydrocarbons and low oxygen environments and ensure worker awareness of the hazards inherent in gauging and sampling tanks:

  1. Implement alternative tank gauging procedures, including electronic (e.g., sonar or in-line fluid flow) systems that allow workers to monitor tank fluid levels remotely. Where remote gauging is not feasible or as an interim measure, establish administrative controls that reduce the number of times throughout a shift a worker is required to manually gauge tanks.
  2. Train workers on the identified hazards associated with gauging tanks, including reduced oxygen environments, flammability hazards, and the potential for concentrations of hydrocarbons that can approach and exceed IDLH concentrations when thief hatches are opened.
  3. Ensure workers are trained on and correctly and consistently use calibrated multi-gas monitors that measure percent LEL and oxygen concentration. Workers should know what actions to take whenever an alarm occurs.
  4. Ensure workers do not work alone where they may have risks for exposures to high concentrations of hydrocarbons and/or low oxygen environments.
  5. Where remote gauging is not feasible or has not yet been implemented, use of respiratory protection, including a self-contained breathing apparatus (SCBA), may be needed to protect workers. Air-purifying respirators will not protect workers from exposures to certain low molecular weight hydrocarbons such as ethane, propane, and butane and do not protect workers in oxygen deficient atmospheres. Note that OSHA regulations (29 CFR 1910.134) require a comprehensive respiratory protection program be established when respirators are used in the workplace.
  6. Establish emergency procedures to provide medical response in the event of an incident.

NIOSH is currently working with industry partners to further evaluate the magnitude of these hazards as well as evaluate the effectiveness of controls such as remote gauging systems. Additional industry assistance is requested to provide NIOSH researchers further access to sites and procedures where exposures are both controlled and uncontrolled. If you have questions or wish to provide further pertinent information, please contact us via the blog comment box below.


Bradley King, PhD, MPH, CIH; Eric Esswein, MSPH, CIH; Kyla Retzer, MPH; John Snawder, PhD, DABT; Sophia Ridl, BS; Michael Breitenstein, BS; Marissa Alexander-Scott, DVM, MS, MPH; Ryan Hill, MPH.



The objective of this blog entry is to describe an identified occupational health 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 manually gauging and sampling tanks and risks for chemical exposures. To keep the blog discussion focused on worker health, we may choose not to respond to comments that do not pertain to worker exposures.




[i] Drummond, I [1993]. Light Hydrocarbon Gases: A Narcotic, Asphyxiant, or Flammable Hazard? Applied Occupational and Environmental Hygiene, 8(2): 120-125.

[ii] NIOSH [2013]. Current intelligence bulletin 66: derivation of immediately dangerous to life or health (IDLH) values. Cincinnati, OH: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication 2014–100.

[iii] Sugie H, Sasaki C, Hashimoto C, Takeshita H, Nagai T, Nakamura S, Furukawa M, Nishikawa T, and Kurihara K [2004]. Three Cases of Sudden Death due to Butane or Propane Gas Inhalation: Analysis of Tissues for Gas Components. Forensic Science International, 143(2-3): 211-214.

[iv] Esswein EJ, Snawder J, King B, Breitenstein M, Alexander-Scott M, and Kiefer M [2014]. Evaluation of Some Potential Chemical Exposure Risks During Flowback Operations in Unconventional Oil and Gas Extraction: Preliminary Results. Journal of Occupational and Environmental Hygiene, 11(10): D174-D184.

Posted on by Bradley King, PhD, MPH, CIH; Eric Esswein, MSPH, CIH; Kyla Retzer, MPH; John Snawder, PhD, DABT; Sophia Ridl, BS; Michael Breitenstein, BS; Marissa Alexander-Scott, DVM, MS, MPH; Ryan Hill, MPH.

6 comments on “UPDATE: Reports of Worker Fatalities during Manual Tank Gauging and Sampling in the Oil and Gas Extraction Industry”

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 ».

    Such an interesting research. Thanks for sharing.

    I had involved in 1 fatality and 2 H2S knowckdowns investigations in O/G in Canada (Cross the N. Dakota Border) in past two years; we also used the Infrared Camara with hydrocarbon detector chip and saw exactly similar plumes from the top of tanks. But I did not realize that it was hydrocarbon that killed; I still believe the H2S is our primary concern for manual tank gauging and sampling operations in o/g.

    For the controls, except those mentioned in this blog, I strongly believe supplied air respirator must be used for any manual tank gauging and sampling operation (and other similar operations or tank/pipe maintanance in o/g) as H2S could kill a worker within one second (before the arlarm sounds). Nothing but a supplied air could save operator’s life in this situation.

    Thank you for your comment and sharing your expertise and experiences. In the fatalities we identified, exposure to H2S were ruled out through a review of the reported facts in the case. We plan to continue our research looking at both hydrocarbons and risks for H2S exposures

    In the eastern part of the Marcellus formation, the O&G Industry is reluctant to believe that there is sufficient carryover of hydrocarbons in the flowback to pose any degree of hazard. However, several flowback tank explosions in NEPA seem to say otherwise, even in the “dry gas” regions of the Marcellus.

    Great writing it is such a good and nice idea thanks for sharing your article .I like your post.

    My son was killed by h2s while gauging a tank in North central Texas in 2015. Thank you for this information it helps me understand why he died and gives me hope that the industry will fix. This is definitely a safety problem.

    Bradley King, Eric Esswein, Kyla Retzer, John Snawder, Sophia Ridl, Michael Breitenstein, Marissa Alexander-Scott, Ryan Hill says:

    Shellye, we are very sorry to hear of the loss of your son. We continue to work with industry to find and evaluate solutions that will prevent worker exposures to hazardous gases and vapors and protect our oil and gas workers . Thank you very much for your important comment.”

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