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Health and Safety Risks for Workers Involved in Manual 

Tank Gauging and Sampling at Oil and Gas Extraction Sites

The National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety 

and Health Administration (OSHA) have identified health and safety risks to workers who manually 

gauge or sample fluids on production and flowback tanks from exposure to hydrocarbon gases 

and vapors, exposure to oxygen-deficient atmospheres, and the potential for fires and explosions.

Introduction

Workers at oil and gas extraction sites could be exposed 

to hydrocarbon gases and vapors, oxygen-deficient 

atmospheres, and fires and explosions when they open 

tank hatches to manually gauge or collect fluid samples 

on production, flowback, or other tanks (e.g., drip pots) 

that contain process fluids. Opening tank hatches, often 

referred to as “thief hatches,” can result in the release 

of high concentrations of hydrocarbon gases and vapors. 

These exposures can have immediate health effects, 

including loss of consciousness and death. 

Recent NIOSH and OSHA research showed that workers 

could be exposed to hydrocarbon gases and vapors when 

they work on or near production and flowback tanks. This 

means workers can face significant health and safety risks 

when they manually gauge or sample tanks [Esswein et al. 

2014; Jordan 2015]. These risks are in addition to the risk 

of exposure to hydrogen sulfide (H2S), a well-recognized 

chemical exposure hazard for those who work in the oil 

and gas extraction and production industry [OSHA]. 

NIOSH and OSHA also identified nine worker fatalities 

that occurred while workers manually gauged or sampled 

production tanks from 2010–2014 [NIOSH 2015]. 

Exposures to hydrocarbon gases and vapors and/or 

oxygen-deficient atmospheres are believed to be primary 

or contributory factors to the workers’ deaths 

[Harrison et al. 2016]. 

Working on or near oil and gas production tanks is of 

particular concern because these tanks may contain 

concentrated hydrocarbon gases and vapors that are 

under pressure. When the thief hatch is opened, the 

release of these pressurized gases and vapors can expose 

workers. Second, the gases and vapors can displace 

oxygen, creating an oxygen-deficient environment. Third, 

the hydrocarbon gas and vapor concentrations can 

exceed 10% of the lower explosive limit (LEL), creating a 

chance for fires and explosions. Exposure to hazardous 

atmospheres and fire/explosion risks will vary depending 

on tank contents and operating conditions, the presence 

of ignition sources, and other factors (Box 1, page 3).

What’s in this Alert?

This Hazard Alert describes the safety and health hazards 

when workers manually gauge or sample fluids from 

production, flowback, or other tanks. It recommends ways 

to protect workers by eliminating or reducing exposures 

to hazardous atmospheres, and actions employers should 

take to ensure that workers are properly aware of the 

hazards and protected from exposure to hydrocarbon 

gases and vapors. This alert is a supplement to the OSHA 

Alliance Tank Hazard Alert released in 2015 [National 

STEPS Network 2015].

A worker collecting a sample from the open hatch of a production tank. 

Image: J.D. Danni, OSHA.

NIOSH-OSHA
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Hydrocarbon Gas and Vapor Release

from Production and Flowback Tanks

Petroleum hydrocarbons can exist as liquids, gases, and vapors. Production liquids (e.g., crude oil and condensate) at 

oil and gas extraction sites can release dissolved hydrocarbon gases such as methane, ethane, propane, and butane. 

Production liquids also evaporate to produce vapors such as pentane, hexane, benzene, and xylene. Hydrocarbon gases 

and vapors are often referred to as volatile organic compounds, or “VOCs.” Hydrocarbon gases contained in crude oil are 

readily released into the air at ambient temperature and pressure. 

When a thief hatch is opened, substantial amounts of 

hydrocarbon gas and vapor (>100,000 parts per million) can 

be released [Jordan 2015], and in some cases this release 

can continue even after the initial headspace pressure is 

released. Furthermore, the composition of hydrocarbons 

in crude oil is complex, and the relative concentrations 

of specific gases and vapors are highly variable. When 

a worker opens a tank, the worker’s breathing zone can 

immediately become an acutely toxic mix of concentrated 

hydrocarbon gases and vapors. Depending on weather 

conditions, the plume may disperse or engulf workers atop 

and around tank batteries.

Appendix A shows how hydrocarbon gases and vapors 

behave when they are released from a production tank. 

Appendix B lists exposure limits for common hydrocarbon 

gases and vapors.

Health Hazards of Hydrocarbon 

Gases and Vapors

Acute exposures to hydrocarbon gases and vapors can 

affect the eyes, lungs, and central nervous system. If 

present in sufficient concentrations to displace oxygen, 

this exposure can sensitize the heart to stress hormones, 

such as catecholamines, causing abnormal rhythms and 

ventricular fibrillation that can lead to sudden death 

[Adgey et al. 1995; Bass 1970; Martinez et al. 2012; NIOSH 

2005a,b,c; Poklis 1976; Reinhardt et al. 1971; Riihimäki 

and Savolainen 1980]. Even a brief exposure (30 seconds 

or less) to high concentrations of hydrocarbons and a 

low-oxygen atmosphere can result in the rapid onset 

of respiratory depression, hypoxia, and fatal cardiac 

arrhythmias [Miller and Mazur 1984]. Pre-existing coronary 

artery disease may exacerbate the risk. These exposures 

can also have narcotic effects, causing dizziness, rapid 

disorientation, and confusion that could lead to loss of 

judgment, narcosis, and incapacitation [Drummond 1993; 

Sugie et al. 2004]. Some hydrocarbons are also known carcinogens (e.g., benzene) [ATSDR 2007].

Forward-looking infrared (FLIR) photograph of the initial hydrocarbon plume 

after a thief hatch on a production tank battery is opened. The plume later 

expands to many times its initial size. Image: John Snawder, NIOSH.

A worker manually gauges a flowback tank. The thief hatch is directly in front of 

his feet, and the gas and vapor released is invisible. 

Image: Max Kiefer, NIOSH.
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Box 1.

Factors that may increase worker exposure to hydrocarbon 

gases and vapors and flammable atmospheres

1. Produced Fluid and Reservoir Characteristics

• Condensate and lighter crude (versus heavy crude)

• Unstabilized (non-degassed) crude oils

• High gas to oil ratio fluids 

• High temperature fluids

• High production volumes/early in production 

2. Operational and Task-related Factors 

• Drilling out plugs during completion operations

• Tanks that are not isolated prior to opening hatch

• Interconnected tanks (tank batteries)

• Tanks using flare systems with backpressure on the vapor space

• Flowback operations

• Working around tanks with vapor recovery units 

• Maintenance work

• Working around separators/enclosed spaces

3. Environmental Factors

• Higher temperatures

• Weather inversions

• Higher altitude

• Low wind speed

Factors that may decrease worker exposure to hydrocarbon 

gases and vapors and flammable atmospheres

1. Engineering Controls

• Remote or automatic gauging and sampling

• Blowdown valves

• Tank sampling taps

• Thief hatch pressure indicators, etc. 

2. Work Practices 

• Working upwind and at a distance from open hatches

3. Personal Protective Equipment (PPE)

• Flame retardant clothing

• Appropriate respiratory protection

• Impermeable gloves
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Worker Fatalities during Manual 

Tank Gauging and Fluid Sample 

Collection, 2010–2014

NIOSH researchers, OSHA officials, and academic 

occupational health researchers investigated reports of 

worker deaths from 2010 through 2014 associated with 

manual tank gauging and the collection of fluid samples 

(Appendix C). During the 5-year period, NIOSH researchers 

identified nine fatalities involving these tasks. Three deaths 

occurred in North Dakota, three in Colorado, one in Texas, 

one in Oklahoma, and one in Montana.

All fatalities occurred at crude oil production tanks. Four 

took place during tank gauging, and five happened during 

fluid sample collection at an open thief hatch by pumpers/

truckers. For all fatalities, the employees were working 

alone or not being observed by a co-worker. Unprotected 

exposures to high concentrations of hydrocarbon gases 

and vapors and/or displacement of oxygen are believed to 

be primary or contributory factors in each fatality [Harrison 

et al. 2016]. Exposure to H2S was ruled out as a cause in 

all nine cases. A narrative description of each of the nine 

fatalities can be found on the NIOSH “Fatalities in the Oil 

and Gas Extraction Industry” (FOG) database web page 

(http://www.cdc.gov/niosh/topics/fog/data.html).

Oxygen concentrations well below normal (oxygen 

concentration in ambient air = 21%) were documented in 

two fatal incidents. While investigating the Case #1 death 

at the site, OSHA’s compliance officer measured oxygen 

levels in the range of 11% to 12% approximately one foot 

above the open hatch. A data-logging four-gas monitor 

worn by the worker at the time of death in Case #7 

recorded that the oxygen level fell to as low as 6.9%. The 

same worker had also worn the monitor during a previous 

incident, during which the oxygen level fell to as low as 

9.1%, and remained consistently below 15% for a 

six-minute interval. Exposure to atmospheres with these 

low concentrations of oxygen can rapidly overcome 

workers and bring about unconsciousness without 

warning. Also, in both incidents, the monitor worn by 

the worker in Case #7 documented that the worker’s 

environment exceeded the LEL. 

NIOSH Evaluation of Worker 

Exposures during Flowback and 

Production Activities

In 2013, NIOSH evaluated worker exposures to a variety of 

chemicals during flowback and production activities at six 

well sites in Colorado and Wyoming [Esswein et al. 2014]. 

Exposure assessments included full-shift and short-term 

personal breathing zone (PBZ) and area air sampling. 

Direct-reading instruments were also used to characterize 

peak and short-term exposures to hydrocarbon gases and 

vapors. This study found that most workers gauging tanks 

(15 of 17; 88.2%) had benzene exposures exceeding the 

NIOSH-recommended exposure limit (REL) of 0.1 parts per 

million (ppm) as a time-weighted average (TWA) for a full 

shift. Some exposures also exceeded the NIOSH shortterm exposure limit of 1 ppm as a 15-minute average for 

benzene. Worker exposures to benzene did not exceed 

the OSHA permissible exposure limit (PEL) criteria (1 

ppm as a TWA) and biological monitoring results did not 

exceed criteria established by the American Conference 

of Governmental Industrial Hygienists for benzene [OSHA 

2012]. However, average benzene exposures for workers 

who gauged tanks were approximately five times greater 

than for workers not gauging tanks. In the same study, 

direct-reading instruments detected benzene peak 

concentrations at open hatches exceeding 200 ppm, and 

sustained atmospheres as high as 40% of the LEL adjacent 

to separators and flowback tanks. Concentrations above 

10% of the LEL are considered a risk for fires or explosions 

and are classified as Immediately Dangerous to Life and 

Health (IDLH) by OSHA and NIOSH. Workers at the sites did 

not use respiratory protection while gauging tanks. 

OSHA Evaluation of Exposures to 

Workers during Tank Gauging

In 2014, OSHA industrial hygienists conducted evaluations 

at oil and gas extraction well sites in North Dakota. The 

sites were identified by observing active tank-gauging 

operations. The evaluations characterized worker 

exposures during manual tank gauging for full-shift, shortterm, and peak concentrations of hydrocarbon gases and 

vapors, and flammable and oxygen-deficient environments. 

Samples collected approximately one foot above open 

hatches found IDLH concentrations of hydrocarbon gases and 

vapors, including propane, pentane, methyl butane, hexane, 

2-methyl pentane, and 3-methyl pentane (Table 1). 

Worker sampling also documented overexposures 

to benzene for short-term, ceiling, and 8-hour TWA 

concentrations, based on the OSHA PELs. Potentially 

flammable (>10% LEL) and oxygen-deficient atmospheres 

(<19.5% oxygen) were identified on production tanks when 

thief hatches were opened during gauging and sampling 

[Jordan 2015]. 

Samples documented total hydrocarbon gas and vapor 

concentrations of 179,000 ppm and 219,000 ppm in the 

plumes above two thief hatches. Laboratory analyses 

identified break-through of hydrocarbon gases in the 

sampling media, indicating that actual concentrations 

might have been greater than reported. 
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Table 1. Hydrocarbon Gas and Vapor Concentrations Measured by OSHA

Approximately 1 Foot Above Open Production Tank Hatches (North Dakota, 2014).

Gas or Vapor Concentration (average ppm) IDLH* (average ppm) Severity**

Propane 43,000 2,100 >20 x

Butane(s) 100,000 1,900 >50 x

Pentane(s) 28,000 1,500 >20 x

n-Hexane 4,500 1,100 >4 x

Benzene 100-400 500 <1 x

 *Immediately Dangerous to Life or Health concentrations expressed as 10% of the LEL

**Severity = Airborne Concentration Expressed as ppm / IDLH (ppm)

Appropriate Respiratory Protection

Although air-purifying respirators with organic vapor cartridges can protect against vapors (such as benzene, hexane, 

toluene, and xylene), they are ineffective against light hydrocarbon gases (such as methane, ethane, propane, butane, 

and pentane) because these gases quickly pass through the activated charcoal sorbent in respirator cartridges [Freedman 

et al. 1973; 3M 2013]. Air-purifying respirators also have other important limitations. They do not protect against oxygendeficient atmospheres or concentrations of hydrocarbons exceeding the maximum use concentration (Occupational 

Exposure Limit X the Assigned Protection Factor) for the respirator/cartridge ensemble. 

Workers using half-face or full-face air-purifying respirators while tank gauging will not be protected against exposures to 

light hydrocarbon gases and vapors and oxygen-deficient atmospheres. At least one worker who died was wearing an airpurifying respirator at the time of his death. Supplied air respirators (e.g., air-line or self-contained breathing apparatus 

[SCBA]) can protect workers from toxic exposures and oxygen-deficient atmospheres — provided the user is wearing the 

respirator correctly in accordance with the OSHA Respiratory Protection Standard (29 CFR 1910.134) [OSHA 2006].

Conclusions

Exposure assessment studies conducted by NIOSH and OSHA have identified worker health and safety risks that 

occur when workers open thief hatches and manually gauge and sample fluids from production and flowback tanks. 

Toxicological data, inherent factors from the oil collection process, and exposure assessments provide evidence that 

gauging and sampling tanks present significant hazards to workers, including risks for exposures to oxygen-deficient 

atmospheres, inhalation exposures to concentrated petroleum hydrocarbon gases and vapors, and fires and explosions. 

Moreover, nine fatalities identified over five years were associated with working close to open hatches of crude oil 

production tanks. Exposures to hydrocarbon gases and vapors and/or oxygen-deficient atmospheres are believed to be 

primary or contributory factors to these workers’ deaths. 

Hydrocarbon gas and vapor emissions from production and flowback tanks are wide-ranging. Consequently, it is difficult 

to predict the magnitude of risk from any specific gauging or sampling task. Factors that can affect the extent of the 

occupational exposures are presented in Box 1, page 3. These factors should be considered as part of worker exposure 

assessments. 

NIOSH and OSHA recommend that employers take the following steps to ensure that workers are properly aware of the 

hazards and protected from exposure to hydrocarbon gases and vapors.

Sample collection methods are under development to more accurately assess hydrocarbon gas and vapor concentrations 

during manual thieving (i.e., sampling) and gauging. Consistent with the NIOSH field research, the OSHA evaluations 

identified worker exposure risks for hydrocarbon gases and vapors, and fires and explosions.
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1. Implement alternative tank gauging and

sampling procedures that enable workers to

monitor tank fluid levels and take samples

without opening the tank hatch.

2. Retrofit existing tanks with dedicated sampling

ports (i.e., tank sampling taps [American Petroleum

Institute 2013]) that minimize worker exposures to

hydrocarbon gases and vapors, thereby eliminating

the need to routinely open thief hatches to

sample. These sampling taps should minimize the

magnitude of hydrocarbon plumes and should limit

the need for workers to access the top of tanks.

3. Install thief hatch pressure indicators to provide

an immediate visual indicator of tank pressures

and potential hazards. Pressure indicators can

show workers the pressure in the tank and

allow a trained worker to follow appropriate

procedures, such as actuating a blowdown

valve, venting gas to a flare, or using appropriate

respiratory protection, such as a self-contained

breathing apparatus or an air-line respirator.

4. Conduct worker exposure assessments to

determine exposure risks to volatile hydrocarbons

and other contaminants. Employers may consult

an occupational safety and health professional

trained and certified in industrial hygiene and who

has knowledge and experience with combined

flammable gas and vapor exposures to ensure that

an appropriate air-sampling strategy is used.

5. Provide hazard communication training in a language

that employees understand to ensure that general

site workers, tank gaugers and samplers, water

haulers, drivers, and others who open tank hatches

understand the hazards associated with opening

tanks and the precautions necessary to conduct

this work safely. These hazards include reduced

oxygen environments, flammability hazards and

possible ignition sources, and the potential for

concentrations of hydrocarbons that can approach

or exceed IDLH concentrations. Post hazard signage

at access stairs, catwalks, and/or tanks to alert

workers about the hazards associated with opening

thief hatches and precautions that must be taken.

6. Ensure that workers are trained on — and correctly

and consistently use — calibrated multi-gas and

oxygen monitors that measure percent LEL and

oxygen concentration. Workers should understand the

limitations of these monitors as well as appropriate

actions to take whenever an alarm occurs or

they experience health symptoms (e.g., leave the

hazard area, report symptoms to supervisors).

7. Do not permit employees to work alone

when tank gauging or working around tanks,

thief hatches, or other areas where they may

encounter process fluids. Observers should be

trained on proper rescue procedures and be

stationed outside potentially hazardous areas.

8. As an interim measure, where remote gauging or

sampling is not feasible or engineering controls

are not implemented, (a) train workers in proper

work practices, such as tank-opening procedures,

that can minimize risks for exposures, (b) ensure

intrinsic safety by proper grounding and prohibiting

the use of spark producing devices or equipment,

(c) establish administrative controls to reduce

the number of times throughout a shift a worker

is required to manually gauge tanks, (d) safely

reduce tank pressure prior to gauging, and (e) use

appropriate respiratory protection, including a

supplied air respirator (SAR) and/or self-contained

breathing apparatus (SCBA) in areas where IDLH

VOC exposures may occur (i.e., during manual tank

gauging/sampling). Employers should consult with a

trained occupational safety and health professional

to determine the appropriate respirator to be used.

NIOSH guidance for selecting respirators is at: http://

www.cdc.gov/niosh/docs/2005-100/default.html.

9. Wear flame-resistant clothing to protect against

burns from fires and explosions. Also, use

appropriate impermeable gloves to limit risks for

skin exposures to chemicals (e.g., benzene).

10. Establish and practice emergency procedures

to provide on-scene, immediate medical

response in the event of an incident, such as

a collapsed worker, or workers experiencing

symptoms of chemical overexposures or

exposure to an oxygen-deficient atmosphere.

NIOSH & OSHA Recommendations for Manual 

Tank Gauging and Fluid Sample Collection
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How Can OSHA and NIOSH Help?

OSHA has compliance assistance specialists throughout the nation who can provide information to employers and 

workers about OSHA standards, short educational programs on specific hazards or OSHA rights and responsibilities, and 

information on additional compliance assistance resources. Contact your local OSHA office for more information.

OSHA’s On-site Consultation Program offers free and confidential safety and health services to small and mediumsized businesses in all states and territories across the country, with priority given to high-hazard worksites. On-site 

Consultation services are separate from enforcement and do not result in penalties or citations. Consultants from state 

agencies or universities work with employers to identify workplace hazards, provide advice on compliance with OSHA 

standards, and assist in establishing and improving their safety and health management systems. To locate the OSHA 

On-site Consultation Program nearest you, call 1-800-321-6742 (OSHA) or visit http://www.osha.gov/dcsp/smallbusiness/

index.html.

OSHA’s and NIOSH’s Cooperative Initiatives: OSHA, NIOSH, and the National STEPS Network have formed an Alliance 

(http://www.osha.gov/dcsp/alliances/steps_niosh/steps_niosh.html) to develop products that will reduce fatalities and 

injuries in this industry. Additionally, OSHA, NIOSH, and several U.S. onshore exploration and production industry trade 

associations, companies, and individual experts have formed an Emerging Issues Focus Group to further explore worker 

hazards during oil and gas extraction and to develop practical short- and long-term solutions to protect worker safety and 

health. Look for products and updates from these groups.

NIOSH can help characterize exposures at your workplace and is looking for industry partners to evaluate engineering 

controls that may reduce exposure to hydrocarbon gases and vapors. NIOSH is also looking for additional partners in 

drilling and well servicing to help evaluate worker exposures to other chemical hazards and develop controls as needed. 

Please refer to the document NIOSH Field Effort to Assess Chemical Exposure Risks to Gas and Oil Workers: (http://www.

cdc.gov/niosh/docs/2010-130/) for details and contact information if you have questions or wish to participate. 

In addition, NIOSH has an active program that encourages Prevention through Design considerations so that occupational 

health and safety aspects are built into equipment during the design phase.

Employers and workers can always request a NIOSH Health Hazard Evaluation. For more information about this program, 

please visit the website - (http://www.cdc.gov/niosh/hhe/HHEprogram.html).

Worker Rights

Workers have the right to:

• Working conditions that do not pose a risk of serious harm. 

• Receive information and training (in a language and vocabulary they understand) about workplace hazards,

methods to prevent them, and the OSHA standards that apply to their workplace. 

• Review records of work-related injuries and illnesses. 

• Get copies of test results that find and measure hazards. 

• File a complaint asking OSHA to inspect their workplace if they believe there is a serious hazard or that their

employer is not following OSHA’s rules. OSHA will keep all identities confidential.

• Exercise their rights under the law without retaliation or discrimination.

For more information, see OSHA’s page for workers (https://www.osha.gov/workers/index.html).
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Contact OSHA

For questions or to get information or advice, to report an emergency, fatality, inpatient hospitalization, amputation or 

loss of an eye, or to file a confidential complaint, contact your nearest OSHA office, visit www.osha.gov, or call OSHA at 

1-800-321-OSHA (6742), TTY 1-877-889-5627.

There are 28 OSHA-approved occupational safety and health State Plans. State Plans are required to have standards and 

enforcement programs that are at least as effective as federal OSHA’s and may have different or more stringent standards. 

More information about State Plans is available at: http://www.osha.gov/dcsp/osp/index.html

Contact NIOSH

To receive documents or more information about occupational safety and health topics, please contact NIOSH at 

1-800-CDC-INFO (1-800-232-4636), TTY 1-888-232-6348, email: cdcinfo@cdc.gov or visit the NIOSH web site at: http://

www.cdc.gov/niosh/.

Suggested Citation:

NIOSH [2016]. NIOSH/OSHA Hazard Alert. Health and Safety Risks for Workers Involved in Manual Tank Gauging and 

Sampling at Oil and Gas Extraction Sites. U.S. Department of Health and Human Services, Centers for Disease Control and 

Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2016-108.

Acknowledgements: 

NIOSH and OSHA acknowledge Robert Harrison, MD, (University of California, San Francisco) for his valuable assistance 

in identifying worker fatalities related to tank gauging and sampling. NIOSH and OSHA gratefully acknowledge Michael 

Kosnett, MD, MPH, and Margaret Cook-Shimanek, MD, MPH (University of Colorado, Denver and Colorado School of 

Public Health) for their expertise and counsel in medical toxicology relating to hydrocarbon exposures and risks for sudden 

death, and their discussions of a specific fatality investigation. 

NIOSH and OSHA also thank and acknowledge Rick Ingram of the National STEPS Network for his enduring leadership at 

the National STEPS Network and the recently formed OSHA Alliance, along with his support of the NIOSH Field Effort to 

Assess Chemical Exposures in Oil and Gas Workers. 

NIOSH acknowledges our industry partners (and especially their workers) for their leadership in occupational health and safety, 

as demonstrated by their participation in the NIOSH Field Effort to Assess Chemical Exposures in Oil and Gas Workers.

Appendix A.

Behavior of Hydrocarbon Gases and Vapors in a Production Tank

1. Hydrocarbon gases and vapors exist in equilibrium with liquid hydrocarbons (e.g., crude oil) in a 

production tank.
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2. Gases (previously in equilibrium with crude oil in a pressurized tank) release to the atmosphere 

when the tank lid is opened.

3. Vapors form when liquid hydrocarbons inside the tank evaporate.

4. Hydrocarbon gases and vapors are generated at a slower pace as tank pressure decreases. Lighter 

hydrocarbon gases and vapors stay aloft; denser gases and vapors seek the ground.

Graphics: Cindy Striley, NIOSH. Photographs: John Snawder, NIOSH.
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Appendix B.

Examples of Volatile Hydrocarbons Commonly Present in Oil and Gas Process Fluids,

 NIOSH Recommended Exposure Limits (RELs), OSHA Permissible Exposure Limits (PELs), 

Lower and Upper Explosive Limits (LEL and UEL).

Compound REL PEL IDLH LEL UEL

Methane None (asphyxiant) 5,000 ppm

(10% LEL)

5.00%

50,000 ppm

15.00%**

150,000 ppm

Ethane None (asphyxiant) 3,000 ppm

(10% LEL)

3.00%

30,000 ppm

12.50%**

125,000 ppm

Propane 1,000 ppm 1,000 ppm 2,100 ppm

(10% LEL)

2.10%

21,000 ppm

9.50%***

95,000 ppm

n-Butane 800 ppm none 1,600 ppm

(10% LEL)

1.60%

16,000 ppm

8.40%***

84,000 ppm

i-Butane 800 ppm none 1,600 ppm

(10% LEL)

1.60%

16,000 ppm

8.40%***

84,000 ppm

n-Pentane 1120 ppm 

(610 ppm 15-minute 

ceiling limit)

1,000 ppm 1,500 ppm

(10% LEL)

1.50%

15,000 ppm

7.80%***

78,000 ppm

n-Hexane 50 ppm 500 ppm 1,100 ppm

(10% LEL)

1.10%

11,000 ppm

7.50%***

75,000 ppm

Benzene  0.1 ppm

(1 ppm STEL)

1 ppm 500 ppm 1.20%

12,000 ppm

7.80%** *

78,000 ppm

Heptane 85 ppm 

(440 ppm 

15-minute ceiling 

limit)

500 ppm 750 ppm 1.00%

10,500 ppm

6.70%***

67,000 ppm

Ethyl Benzene 100 ppm

(125 ppm STEL)

100 ppm 800 ppm

(10% LEL)

0.80%

8,000 ppm

6.70%***

67,000 ppm

Toluene 100 ppm

(150 ppm STEL)

200 ppm 500 ppm 1.10%

11,000 ppm

7.10%***

71,000 ppm

Xylenes 100 ppm

(150 ppm STEL)

100 ppm 900 ppm 0.90%

9,000 ppm

7.00%**

70,000 ppm

Mixed Petroleum 

Hydrocarbons/

Distillates 

(naphthas)

350 mg/m3 (1800 

mg/m3 15-minute 

ceiling limit)

500 ppm 1100 ppm 1.10%

11,000 ppm

5.90%**

59,000 ppm

* When the health-based immediately dangerous to life or health (IDLH) values are greater than 10% of the lower explosive limit 

(LEL) of the air contaminant, the IDLH value is set at 10% LEL, because explosive hazards are deemed a greater risk than toxicity—

NIOSH, Current Intelligence Bulletin 66 (http://www.cdc.gov/niosh/docs/2014-100/). An IDLH is a maximum airborne concentration 

above which only a highly reliable breathing apparatus providing maximum worker protection is permitted [NIOSH 2004]. IDLH 

values are based on a 30-minute exposure duration. Upper explosive limit (UEL) is the highest concentration (%) of a gas or a vapor 

in air capable of producing a flash or fire in the presence of an ignition source. Concentrations higher than the UEL are “too rich” to 

burn.

** International Chemical Safety cards: http://www.cdc.gov/niosh/ipcs/

***NIOSH Pocket Guide to Chemical Hazards: http://www.cdc.gov/niosh/npg/npgd0524.html

**** Upstream oil and gas operations are exempt from the OSHA Benzene standard, 1910.1028.
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Appendix C.

Worker Fatalities Related to Oxygen Deficiency and Inhalation of Hydrocarbon 

Gases and Vapors Among Oil and Gas Extraction Workers—Multiple States,

2010 to 2014

Year of 

death

Age, in 

years

State Job Title Job Task Description of how 

person was found

Time of day 

found

Coroner’s stated cause of death

1 2010 30 MT Crew 

Worker

Gauging Slumped over on the 

catwalk

3:00 a.m. Hypertensive and atherosclerotic 

cardiovascular disease

2 2012 21 ND Flow 

Tester

Gauging On catwalk next to 

open hatch

12:30 a.m. Hydrocarbon poisoning due to inhalation of 

petroleum vapors

3 2013 39 ND Truck 

Driver

Collecting 

Sample

Slumped over catwalk 

railing on knees in 

front of open hatch

10:20 a.m. Sudden cardiac arrhythmia (primary), morbid 

obesity and arteriosclerotic heart disease 

(contributory)

4 2014 57 OK Truck 

Driver

Collecting 

Sample

On catwalk next to 

tank, slumped over

10:12 a.m. 

(time of 

death)

Undetermined (no autopsy performed)

5 2014 51 CO Truck 

Driver

Collecting 

Sample

Hanging from 

guardrail, hooked by 

clothing

10:39 a.m.

(time of 

death)

Sudden cardiac death due to ischemic heart 

disease

6 2014 57 CO Truck 

Driver

Collecting 

Sample

Collapsed over open 

hatch

10:30 a.m. Atherosclerotic cardiovascular disease

7 2014 59 CO Truck 

Driver

Collecting 

Sample

Collapsed over open 

hatch

1:40 p.m. Toxic gas inhalation and oxygen displacement 

by volatile hydrocarbons (primary), 

atherosclerotic cardiovascular disease and 

sudden cardiac death (contributory)

8 2014 63 TX Tank 

Gauger

Gauging At the bottom of 

catwalk stairs

4:14 a.m. Arteriosclerotic and hypertensive 

cardiovascular disease

9 2014 20 ND Flow 

Tester

Gauging Face down, over open 

hatch

5:00 a.m. Cardiac arrhythmia, with cardiac 

hypertrophy, coronary artery hypogenesis, 

obesity and petroleum hydrocarbon vapors
1-800-321-OSHA (6742) • www.osha.gov 12 1-800-CDC-INFO (1-800-232-4636) • www.cdc.gov/niosh

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Disclaimer

This Hazard Alert is not a standard or regulation, and it creates no new legal obligations. It contains 

recommendations as well as descriptions of mandatory safety and health standards [and other regulatory 

requirements]. The recommendations are advisory in nature, informational in content, and are intended to assist 

employers in providing a safe and healthful workplace. The Occupational Safety and Health Act requires employers 

to comply with safety and health standards and regulations promulgated by OSHA or by a state with an OSHAapproved State Plan. In addition, the Act’s General Duty Clause, Section 5(a)(1), requires employers to provide 

their employees with a workplace free from recognized hazards likely to cause death or serious physical harm. 

The mention of any non-governmental organization or link to its website in this Hazard Alert does not constitute an 

endorsement by OSHA or NIOSH of that organization or its products, services, or website.

*Accessibility Assistance: Contact OSHA’s Directorate of Technical Support and Emergency Management at (202) 693-2300 for assistance accessing PDF materials.

All other documents, that are not PDF materials or formatted for the web, are available as Microsoft Office® formats and videos and are noted accordingly. If additional 

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can download the MOBI file format.

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DHHS (NIOSH) Publication Number 2016-108 │ OSHA-HA-3843-2016

02/2016