Source: National Institute for Occupational Safety and Health (NIOSH) Science Blog

A previous NIOSH report (2016)1 described the death of nine oil and gas extraction workers that occurred during gauging or sampling activities at open thief hatches on crude oil storage tanks. Hydrocarbon gases and vapors (HGVs) and associated oxygen displacement were the primary or contributory factors in these fatalities. Additionally, wellsite exposure assessments conducted by OSHA and NIOSH identified HGVs at open thief hatches in concentrations that were immediately dangerous to life or health (IDLH) and in excess of the lower explosive limit (LEL), creating a chance for fires and explosions. It has been demonstrated that HGVs can build up under pressure and rapidly escape when thief hatches of production, flowback, and other tanks are opened, creating a highly flammable and oxygen-deficient environment, even in areas not considered to be a confined space. Acute exposure to HGVs can have narcotic effects on workers (i.e. dizziness, disorientation) as well as affect the eyes, lungs, and central nervous system. The simultaneous exposure of HGVs combined with a low oxygen atmosphere may also pose a risk for sudden cardiac death, especially in individuals with pre-existing coronary artery disease. In addition to HGVs, hydrogen sulfide (H2S), a widely recognized hazard in the oil and gas extraction industry, continues to persist as a cause of death among workers2. Hydrogen sulfide is naturally present in some oil and gas deposits and may be produced as a by-product of the desulfurization process of these fuels. Workers in all operations during oil and natural gas exploration and production may be exposed to H2S. This blog provides an update on fatalities, injuries, and exposures associated with hazardous gases and vapors (HGVs and H2S) in the oil and gas extraction industry, and alerts employers to exposures that can occur while working around oil and gas process fluids.

What’s New?

NIOSH has conducted surveillance of worker fatalities and severe injuries in the oil and gas extraction industry, including those that may be associated with exposure to or ignition of hazardous gases and vapors. Fatalities are identified using the NIOSH Fatalities in Oil and Gas Database (FOG). The federal Occupational Safety and Health Administration (OSHA) severe injury data set provides a source to identify severe non-fatal incidents among oil and gas extraction workers. In addition to fatality and injury surveillance, NIOSH has conducted additional worker exposure assessments at oil and gas worksites to examine potential hazardous exposures, including oxygen concentration and hazardous and flammable gas and vapor concentrations (HGVs and H2S) during various worker activities.


NIOSH researchers sought to determine the number of fatalities and hospitalizations with known or potential exposure to hazardous gases and vapors as well as fires and explosions while working around process fluids, including waste water, flowback, petroleum condensate, or crude oil. Waste water is also sometimes referred to as produced water, brine, salt water, etc., but often still contain hydrocarbons.

The following definition was developed to identify cases: During 2015-2016, fatalities or hospitalizations related to the ignition, inhalation, or suspected inhalation of HGVs and/or H2S while handling process fluids (e.g. fluid transfer) or working on tanks containing process fluids at oil and gas well sites or waste water disposal sites. Cases were reviewed and categorized by event type, activity type, location, and fluid type.

During 20152016, there were eight oil and gas worker fatalities during eight separate incidents that met the case definition (see cases in FOG Report ).

  • Event Type: Three workers died of sudden cardiac death with potential exposures to hazardous gases and vapors, two workers died due to fire/explosions, two workers died due to hydrogen sulfide poisoning, and one worker died due to HGV exposures.
  • Activity Type: Four workers died while transferring fluids from tanks to trucks, two workers were tank gauging or sampling, one worker was at an open tank hatch with unknown activity, and one worker was doing hotwork (grinding) on top of a tank.
  • Fluid Type: Four workers were working with produced water, three workers were working with crude oil, and one with flowback.
  • Site Type: Six workers died at well sites and two workers died at waste water disposal sites.

During 2015-2016, there were ten hospitalizations during ten separate incidents that met the case definition (see cases in FOG Report).

  • Event Type: Five workers were hospitalized due to fire/explosions, three workers hospitalized due to H2S exposure, and two workers hospitalized due to HGV exposures.
  • Activity Type: Six workers were tank gauging or sampling, one worker was transferring fluids, one worker was using a vacuum truck to remove tank bottoms, one worker was draining condensate from a separator line (i.e. heater treater), and one was transporting waste water.
  • Fluid Type: Three workers were working with produced water, one with flowback, one with tank bottoms (solids and waste), one with condensate, one with crude oil, and three were unknown.
  • Site Type: Nine workers were injured/exposed at well sites and one worker was injured at a waste water disposal site.

These incidents illustrate that hazardous gas and vapor exposures while handling process fluids continue to occur, either through the inhalation or ignition of hazardous gases and vapors.

Exposure assessments

In July 2017, NIOSH conducted air monitoring while a trucker was transferring petroleum condensate from a storage tank onto his truck. As hydrocarbon fluids were transferred, gases and vapors that were previously in equilibrium within the storage tank released into the belly of the truck’s tank. To prevent over pressuring of the truck tank as liquid was transferred, the gases and vapors were vented directly to the outside of the back of the truck; no vent line was used to direct the gases and vapors away from the trunk at a distance. Direct reading instrument data and bulk air samples were collected at and around the tanker trunk and later analyzed to determine HGV and H2S concentrations in the air during this activity. Forward-looking Infrared (FLIR) video was used to visualize and record the plume of hazardous gases and vapors that surrounds the tanker truck during the fluid transfer (click for video).

While performing this fluid transfer, hazardous gases and vapors were measured in concentrations over 348,000 parts per million, or 34.8% of the air volume. The full analysis of this air sample is shown in Table 1.

Table 1. Results for select gases and vapors collected during petroleum condensate transfer near the venting point behind the tanker truck


Concentration (ppm)

IDLH (ppm)

Severity (Concentration/IDLH)






























Not Detected
















Not Detected







Hydrogen Sulfide




* Immediately Dangerous to Life or Health (IDLH) values are based on the NIOSH Current Intelligence Bulletin 663, which states “In the event that the derived health-based IDLH value exceeds 10% of the LEL concentration for a flammable gas or vapor, the air concentration that is equal to 10% of the LEL will become the default IDLH value for the chemical.”

** Analysis Method- Gas chromatography-flame ionization detector (GC-FID)

† Analysis Method- Gas chromatography-photoionization detector (GC-PID)

‡ Analysis Method- Direct reading instrument with electrochemical sensor

Recommendations for Employers, Workers, and Incident Investigators

Oil and gas worker fatalities and hospitalizations due to ignition or inhalation of hazardous gases and vapors and associated oxygen deficiency are preventable. There are a number of resources available that employers and workers can use to prevent these incidents.


Implement recommendations contained in the following relevant resources to prevent exposures to hazardous gases and vapors:


Comply with all employer policies and hazard assessments to ensure you are protected from hazardous gases and vapors. Always wear required personal protective equipment and your multi-gas monitor and heed all alarms. Review the videos listed above and each of the National STEPS Network Hazard Alerts to learn more ways to protect yourself.

Incident investigators

Medical examiners and coroners investigating oil and gas worker fatalities need to be aware of the possibility of hazardous gas and vapor exposures and request appropriate lab tests. Exposure to high concentrations of HGVs and oxygen-deficient atmospheres can result in sudden cardiac death in oil and gas extraction workers. Analysis of ante-mortem or postmortem blood for documentation of HGV exposure (2139B) as well as H2S (thiosulfate in blood) is available from clinical toxicology laboratories.

Help Wanted!

NIOSH is working with industry partners to continue to evaluate the magnitude of hazards and effectiveness of controls in the oil and gas industry. We are looking for industry partners who are interested in participating in studies and/or providing access to sites to assess exposures. If you have questions, or would like to provide pertinent information on this topic, please contact us via the blog comment box or by email at

Note:  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 illnesses, injuries, and fatalities associated with fluid transfer. To keep the blog discussion focused on worker health, we may choose not to respond to comments that do not pertain to worker exposures.


Ted Teske, Ryan Hill, Robert Harrison (California Department of Public Health), Michael Hodgson (OSHA), J.D. Danni (OSHA), Mike Marshall (OSHA), Barbara Alexander


Esswein EJ, Retzer K, King B, Cook-Shimanek M. Environmental and Health Issues in Unconventional Oil and Gas Development. Kaden DA, Rose TL, eds. Waltham MA: Elsevier, 2016 Jan: 93-105.
Harrison RJ, Retzer K, Kosnett MJ, et al. Sudden Deaths Among Oil and Gas Extraction Workers Resulting from Oxygen Deficiency and Inhalation of Hydrocarbon Gases and Vapors — United States, January 2010–March 2015. MMWR Morb Mortal Wkly Rep 2016;65:6–9. DOI:

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.

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