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

In 2013, an occupational medicine physician from the University of California, San Francisco, contacted CDC’s National Institute for Occupational Safety and Health (NIOSH), and the Occupational Safety and Health Administration (OSHA) about two oil and gas extraction worker deaths in the western United States. The suspected cause of these deaths was exposure to hydrocarbon gases and vapors (HGVs) and oxygen (O₂)-deficient atmospheres after opening the hatches of hydrocarbon storage tanks. The physician and experts from NIOSH and OSHA reviewed available fatality reports from January 2010 to March 2015, and identified seven additional deaths with similar characteristics (nine total deaths). Recommendations were made to industry and regulators regarding the hazards associated with opening hatches of tanks, and controls to reduce or eliminate the potential for HGV exposure were proposed. Health care professionals who treat or evaluate oil and gas workers need to be aware that workers might report symptoms of exposure to high concentrations of HGVs and possible O₂ deficiency; employers and workers need to be aware of this hazard and know how to limit exposure. Medical examiners investigating the death of oil and gas workers who open tank hatches should consider the contribution of O₂ deficiency and HGV exposure.

Workers at oil and gas well sites often manually gauge the level of fluid or collect a sample from storage tanks containing process fluids. These workers climb to the top of the tanks, open a “thief” hatch (a closable aperture on atmospheric tanks, used to sample the tank contents) (Figure), and either place a device into the hatch to measure the fluid level or lower a “thief” sampler (a hollow tube) into the tank to collect liquid samples. In 2013, an occupational medicine physician from the University of California, San Francisco, received a report of a 2012 oil and gas worker fatality in North Dakota; that state’s medical examiner attributed death to the inhalation of petroleum hydrocarbons. The male worker, aged 21 years, was gauging crude oil production tanks on the well site, at night and alone. A coworker found the victim unconscious near the open hatch. Colleagues initiated cardiopulmonary resuscitation, and the worker was transported to the hospital where he was pronounced dead approximately 2 hours later. An autopsy found no obvious signs of traumatic injury. Toxicology testing identified detectable quantities of low–molecular weight hydrocarbons (propane and butane), and evidence of heavier molecular weight hydrocarbons. No indication of exposure to hydrogen sulfide (H₂S) was identified. Initially, the death was attributed to cardiovascular disease and later to hydrocarbons. The occupational medicine physician subsequently identified a second worker who died from a sudden cardiac event in 2010 while performing tank gauging; H₂S was excluded as a factor. The physician contacted NIOSH and OSHA about these two deaths.

To identify other oil and gas extraction worker fatalities associated with exposure to HGVs, the physician and experts from NIOSH and OSHA reviewed media reports, OSHA case files, and the NIOSH Fatalities in Oil and Gas database. Cases were defined as nontraumatic oil and gas extraction worker deaths occurring during January 2010–March 2015, in which the workers were 1) performing tank gauging, sampling, or fluid transfer activities at oil and gas well sites; 2) working in proximity to a known and concentrated source of HGVs (e.g., an open hatch); 3) not working in a confined space; and 4) not exposed to H₂S, fires, or explosions. All available information on identified fatalities was reviewed, including OSHA investigations, coroner and toxicology reports, gas monitor data, and exposure assessment data.

Nine deaths, occurring from January 2010 to March 2105, were identified (Table); six of the deaths occurred during 2014. Three deaths occurred in Colorado, three in North Dakota, and one each in Montana, Oklahoma, and Texas. The median age of workers was 51 years (range = 20–63 years), and all were male. All of the victims were working alone at the time of the incidents and were found collapsed on a tank or catwalk, or at the base of the catwalk stairs. In at least five cases, the hatch was open when the worker was found. Five of the fatalities occurred during the collection of a fluid sample, and four occurred during tank gauging. Toxicologic data on HGVs were not consistently collected during autopsy, but petroleum hydrocarbon vapors were noted as a cause of death for three workers.

Only one of the nine workers was known to have been provided a respirator, but fit-testing had not occurred, and the air-purifying respirator was not suitable for high concentrations of HGVs or O₂ deficiency. The exposure assessment conducted by OSHA following the 2010 case found O₂ concentrations as low as 11% at 1 foot above the open thief hatch (O₂ concentrations in ambient air = 21%). In addition, HGV concentrations were in excess of the lower-explosive limit (minimum concentration of a gas necessary to support its combustion in air), suggesting exposures high enough (>10,000 parts per million [ppm]) to cause acute central nervous system symptoms. In case number seven, the worker wore a data-logging, continuous multi gas monitor as a regular work practice. Three weeks before the fatal event, he was examined in an emergency department after experiencing altered consciousness while gauging a tank. Gas monitor data during this event revealed a 5-minute interval, concurrent with his symptoms, when O₂ concentrations were in the range of 10% to 15% and flammable HGVs exceeded the lower-explosive limit. On the day of his death, the gas monitor again indicated that the lower-explosive limit had been exceeded, with O₂ concentrations as low as 7%.

Discussion

During January 2010–March 2015, at least nine deaths of oil and gas workers occurred in the United States, with exposure to HGVs a confirmed or suspected factor. Oil and gas extraction is a high-risk industry, with overall occupational fatality rates seven times the national average (1). Although safety hazards in the industry are well-known, few published reports address chemical exposures and acute occupational illness associated with oil and gas extraction. Recent exposure assessments have identified that opening thief hatches and manual gauging or sampling from hydrocarbon-containing tanks, outdoors in nonconfined spaces, is widely practiced and poses substantial and potentially lethal hazards to workers (2–4). These hazards include sudden exposure to high concentrations (>100,000 ppm) of low–molecular weight HGVs, accompanied by displacement of air, resulting in O₂ deficiency. Inhaled O₂ concentrations of <15% can significantly impair central nervous system function, and concentrations of <10% can result in loss of consciousness and possible death within seconds to minutes (5). Low O₂ blood levels (hypoxemia) can exacerbate cardiac ischemia and increase the release of epinephrine (adrenalin). High concentrations (i.e., 50,000 ppm to ≥100,000 ppm) of low–molecular weight hydrocarbons, particularly butane, have been shown in animal studies and human reports to sensitize the heart to epinephrine-induced ventricular fibrillation, a lethal cardiac arrhythmia (6–8). The simultaneous exposure to high levels of low–molecular weight HGVs and a low O₂ atmosphere above an open tank hatch poses a risk for sudden cardiac death. Preexisting coronary artery disease can exacerbate that risk. In addition, high levels of low–molecular weight HGVs can exert anesthetic effects that contribute to central nervous system depression (9). The exposure-assessment samples also showed concentrations of propane, butane, pentane, and 2-methylbutane exceeding 100% of the lower-explosive limit (3). Concentrations of explosive gases in excess of 10% of the lower-explosive limit are considered immediately dangerous to life or health. Because of the nine identified fatalities, the exposure-assessment findings, and the potential mechanism for sudden cardiac death, OSHA, NIOSH and multiple industry stakeholders collaboratively issued a hazard alert on tank gauging at oil and gas well sites (10). In addition, the Bureau of Land Management has proposed changes to current federal regulations* that replace outdated technology and practices with remote tank gauging technologies, reducing or eliminating the need for manual tank gauging.

Health professionals need to recognize the signs and symptoms of exposure to high concentrations of HGVs and possible O₂-deficient atmospheres in oil and gas workers. Health and safety professionals need to recognize and act on nonfatal warning signs and symptoms, such as dizziness, confusion, immobility, and collapse in oil and gas workers who might have been exposed to high concentrations of HGVs and to O₂-deficient atmospheres. As required by OSHA regulations, employers should reduce or eliminate the hazard; this can include practices that allow for alternative fluid sample collection points, remote monitoring of fluid levels, proper use of gas monitors, respiratory protection meeting OSHA requirements, and worker training. Employers also need to ensure that workers do not work alone where they might have risks for exposures to high concentrations of hydrocarbons and low-O₂ environments. Having automated external defibrillators available at worksites is also important. Medical examiners and coroners investigating workplace fatalities need to be aware of the possibility that exposure to high concentrations of HGVs and O₂-deficient atmospheres can result in sudden cardiac death in oil and gas extraction workers. Analysis of antemortem or postmortem blood for documentation of HGV exposure is available from clinical toxicology laboratories.

Acknowledgments

Maggie Cook-Shimanek, Eric Esswein, Ryan Hill, Bradley King, John Snawder, Ann Krake.

Corresponding author: Robert J. Harrison, [email protected], 415-885-7580.

¹Division of Occupational and Environmental Medicine, University of California, San Francisco; ²National Institute for Occupational Safety and Health, Western States Division, CDC; ³Division of Clinical Pharmacology and Toxicology, University of Colorado School of Medicine; ⁴Department of Environmental and Occupational Health, Colorado School of Public Health; ⁵Office of Occupational Medicine and Nursing, Occupational Safety and Health Administration, Washington, DC; ⁶Health Response Team, Occupational Safety and Health Administration, Salt Lake City, Utah.

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FIGURE. An oil field worker manually gauges the level of process fluid in a fixed production oil tank* — United States

Photo/Todd Jordan, Occupational Safety and Health Administration

*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.

TABLE. Sudden deaths caused by inhalation of hydrocarbon gases and vapors and oxygen deficiency among oil and gas extraction workers — United States, January 2010–March 2015