Gases and vapors continue to pose hazards on oil and gas well sites during gauging, fluid transfer, and disposal

Posted on by Kyla Retzer, MPH; Emily Schmick, MSPH, CIH; Alejandra Ramirez-Cardenas, MPH; Bradley King, PhD, MPH, CIH; and John Snawder, PhD, DABT


1) The worker peers down an open hatch of the oil tank. 2) In some regions, workers gauge oil tanks by opening tank hatches, visually observing liquid levels, and then manually measuring liquid oil levels. 3) As commonly designed, fixed oil tanks often are interconnected for both liquid and vapor, allowing contents to equalize over multiple tanks. Equalization of tanks can result in a high volume of off-gassed vapors when a tank hatch is opened. 4) The windsock is a visual indicator for the worker to stay positioned upwind while gauging. Photo courtesy of OSHA

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


Gas/Vapor Concentration (ppm) IDLH (ppm) Severity (Concentration/IDLH)
Methane** 141,000 5,000* 28
Ethane** 62,600 3,000* 21
Propane** 59,100 2,100* 28
Butanes** 50,900 1,600* 31
Pentanes** 25,500 1,500* 17
Benzene 175 500 0.35
Toluene 6.8 500 0.01
Ethylbenzene Not Detected 800* 0.0
Xylenes 0.5 900 0.0
Hexane 6,000 1,100* 5.5
Heptane 3,510 750 4.7
Octane Not Detected 1,000* 0.0
Nonane 0.8 800* 0.0
Hydrogen Sulfide 450 100 4.5

* 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

Kyla D. Retzer, MPH, is an Epidemiologist in the NIOSH Western States Division. 

Emily Schmick, MSPH, CIH, is an ORISE Research Fellow in the NIOSH Western States Division.

Alejandra Ramirez-Cardenas, MPH, is a Research Assistant in the NIOSH Western States Division.

John Snawder, PhD, DABT, is a Research Toxicologist in the NIOSH Division of Applied Research and Toxicology.

Bradley King, PhD, MPH, CIH, is an Industrial Hygienist in the NIOSH Western States Division.


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.

Posted on by Kyla Retzer, MPH; Emily Schmick, MSPH, CIH; Alejandra Ramirez-Cardenas, MPH; Bradley King, PhD, MPH, CIH; and John Snawder, PhD, DABT

19 comments on “Gases and vapors continue to pose hazards on oil and gas well sites during gauging, fluid transfer, and disposal”

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 ».

    I want to thank John Snawder and Bradley King for their tireless efforts. As I left my prior employer in the Oil and Gas Exploration Industry in 2015, it appears the pace of risks and unwanted fatalities has still not abated.
    I expected more of a push towards automated gauging, sight glass use and a full consolidation of LACT- Lease Acquisition Custody Transfer on BLM and Tribal sites.

    It has been in the interest of many stakeholders including oil and gas surface engineers, industrial supply firms of gauging equipment and LACT technology and the American Petroleum Institute, the major O&G companies and government agencies to improve the health and safety requirements for tank gauging and thieving as a part of petroleum measurement, but still much more needs to be done.

    It’s truly horrible to read about those who have lost their lives or have been injured while working in the oil and gas industry. While we have relied upon oil and gas for such a long time to help create the modern world we live in, we must begin to transition to a society that is not nearly as reliant upon them. Electric vehicles and wind and solar power will take us a long way in this transition. For those who site cost as a deterrent, this is not an obstacle anymore. Many websites show how the cost of solar, for example, is now economically viable. Leaders of industry must finally see the writing on the wall and begin the cost effective switch to a clean energy economy.

    The Oil and Gas Extraction Program provides leadership to control or eliminate occupational injuries, illnesses and fatalities among workers in the oil and gas extraction industry — a workforce critical to the energy infrastructure of the nation. This includes establishments engaged in operating and/or developing onshore oil and gas fields, sometimes referred to as exploration and production or upstream oil and gas. The Oil and Gas Extraction Program works with partners in industry, other government agencies, academia, trade associations, professional organizations, and labor to address the leading causes of work-related injury, illness and fatality to improve the health and well-being of oil and gas extraction workers.

    The use of “green” energy technologies would eliminate the risks from oil and gas industry technology, however the green technologies introduce their own set of hazards that require attention to safety and health concerns. See: and

    Thank you for your comment. Explosion proof cameras and remote visual monitoring can provide numerous safety and security applications within the oil and gas industry.

    My husband is ill, he did not know, he had no idea what he was being exposed to, he worked at a produced water injection well with tanks that also had up to four feet of crude oil accumulated on the top of the tanks.
    He has a very bad prognosis, one of his co workers died, and two others had cardiac events. Very bad, my husband almost died, he’s alive but has very bad illness due to NO protection he had no idea he even needed it.
    We have now found out there were rules and they were not ever explained to him, thank you however mynheart is heavy reading this because I am so sad that I’m loosing him too soon. And it could have been prevented. If you have any help to offer please help,us.

    Dear Cheryl,

    We are very sorry to hear about your husband’s illness and his coworker’s death. You may consider contacting OSHA (Occupational Safety & Health Administration) where you live to report your husband’s illness. The OSHA 24-hour hotline is 1-800-321-6742. I also hope you have considered taking him to an occupational health clinic in your area to help you determine the best actions to take. We continue to monitor hospitalizations and fatalities reported to OSHA on oil and gas well sites that may be related to exposures to harmful gases and vapors and work with our partners to raise awareness of this hazard and how to protect workers. Thank you for your heartfelt comment.

    We are the family of Dennis Mason who died October 1, 2016 on the Cerny well site in Kingfisher, Oklahoma . He was found directly by an open Getty box. His death was ruled “hypertensive heart disease” yet he had never had high blood pressure, never had heart problems and was very healthy. For those of you going through a similar situation – don’t ever give up – I know we will not . I wish the CDC would have gotten involved but we never heard from them.

    Ms. Mason, we are very sorry for your loss. NIOSH referenced this fatality in our 2018 blog and noted the death was a cardiac event: possible work exposure. We have consulted with OSHA and health professionals on this case and others. The investigations of the deaths associated with tank gauging and fluid transfer were conducted by OSHA, medical examiners, and others and subsequently reviewed by NIOSH for inclusion in our reports. We continue to try and alert employers and workers of hazards and make recommendations to the industry to stop these types of events.

    Hi I am in Australia and was potentially exposed to crude oil vapors whilst transferring from a tank to my road tanker.
    The Niosh video of the driver being exposed to harmful gases is exactly how it happened, loading with no vapour recovery hose, vapours pouring into the work area on a still day, and this happened on at least 5 occasions over 4mths. PPE was long sleeve, trouser, glasses, boots and hardhat.
    I am told that being exposed to these vapours for 3.5 hrs per loading of a quad road train each time would not be enough to have long term effects. Healthy prior to this??
    As I was not being monitored or tested : eg urine and blood I have no idea how exposed I have been. Except that I have some CNS issues now. It’s been 4mths since last exposure.
    In Australia there hasn’t been or only minimal exposure reported and acted on. I am having a hard time proving my medical condition is related to exposure.
    Occupational physician’s only compare two of the chemical’s in crude as being the worst benzene and toluene an don’t expect the other chemicals to cause damage. I find this unbelievable as there is so much been recorded globally.
    My Question is where can I find information and studies done to the effects of exposure to hydrocarbons, b-tex, and crude oil vapors in detail.
    Thank you for all your input into Health and Safety in this industry

    Thank you for your comment. The following blogs (Reports of Worker Fatalities during Flowback Operations, Preliminary Field Studies on Worker Exposures to Volatile Chemicals during Oil and Gas Extraction Flowback and Production Testing Operations, and UPDATE: Reports of Worker Fatalities during Manual Tank Gauging and Sampling in the Oil and Gas Extraction Industry), and the NIOSH-OSHA Hazard Alert: Health and Safety Risks for Workers Involved in Manual Tank Gauging and Sampling at Oil and Gas Extraction Sites will provide more information.

    In this blog, Table 1 above reports results for select gases and vapors collected during petroleum condensate transfer near the venting point behind the tanker truck. Note the IDLH column. The Immediately dangerous to life or health air concentration values (IDLH values) developed by the National Institute for Occupational Safety and Health (NIOSH) characterize these high-risk exposure concentrations and conditions and are used as a component of respirator selection criteria first developed in the mid-1970s. IDLH values are established (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) to indicate a maximum level above which only a highly reliable breathing apparatus, providing maximum worker protection, is permitted. During some fluid transfer activities without proper engineering controls or respiratory protection workers may be exposed to some chemicals many times greater than the IDLH and for many chemicals with defined short term limits (never to exceed 15 minutes) or ceilings (should never be exceeded) by multiple times. Gas and vapors associated with petroleum products may contain chemicals that are carcinogenic, effect the nervous system, multiple organs including the lungs, liver, kidneys, digestive system, skin etc.

    The ATSDR Toxic Substances Portal has some information on Total Petroleum Hydrocarbons (ATSDR – Toxic Substances – Total Petroleum Hydrocarbons (TPH) ( and the NIOSH Pocket Guide has a few substances relevant to these exposures (CDC – NIOSH Pocket Guide to Chemical Hazards – Petroleum distillates (naphtha), CDC – NIOSH Pocket Guide to Chemical Hazards – Kerosene, CDC – NIOSH Pocket Guide to Chemical Hazards – L.P.G.). The New Jersey right to know sheet is pretty helpful too (Right to Know Hazardous Substance Fact Sheet ( Benzene and toluene are not the only hazards.

    Thank you for your comment. Explosion proof cameras and remote visual monitoring can provide numerous safety and security applications within the oil and gas industry.Working with the Explosion-proof camera and the ATEX-rated camera has become crucial for success in an industry-filled world with a hundred faces.

    Thank you for your comment. Explosion-proof or intrinsically safe cameras for remote video monitoring of oil and gas facilities can improve safety and security. While it is difficult to monitor at all times, visual monitoring when alerted that individuals are on location can serve as another level of safety. Many of the workers harmed are working alone and technology that can reduce the time for help to arrive may improve outcomes.

    Amazing Blog! Safety training drives down the number of accidents, injuries, illnesses, near-misses and property damage in oil and gas industry. It’s really great information

    I admire the valuable information you offer in your articles. Thanks for posting it. Nice post.

Post a Comment

Your email address will not be published. Required fields are marked *

All comments posted become a part of the public domain, and users are responsible for their comments. This is a moderated site and your comments will be reviewed before they are posted. Read more about our comment policy »

Page last reviewed: May 14, 2019
Page last updated: May 14, 2019