NIOSH-OSHA

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 A worker collecting a sample from the open hatch of a production tank. they work on or near production and flowback tanks. This Image: J.D. Danni, OSHA. means workers can face significant health and safety risks when they manually gauge or sample tanks [Esswein et al. oxygen, creating an oxygen-deficient environment. Third, 2014; Jordan 2015]. These risks are in addition to the risk the hydrocarbon gas and vapor concentrations can of exposure to hydrogen sulfide (H2S), a well-recognized exceed 10% of the lower explosive limit (LEL), creating a chemical exposure hazard for those who work in the oil chance for fires and explosions. Exposure to hazardous and gas extraction and production industry [OSHA]. atmospheres and fire/explosion risks will vary depending on tank contents and operating conditions, the presence NIOSH and OSHA also identified nine worker fatalities of ignition sources, and other factors (Box 1, page 3). that occurred while workers manually gauged or sampled production tanks from 2010–2014 [NIOSH 2015]. What’s in this Alert? Exposures to hydrocarbon gases and vapors and/or This Hazard Alert describes the safety and health hazards oxygen-deficient atmospheres are believed to be primary when workers manually gauge or sample fluids from or contributory factors to the workers’ deaths production, flowback, or other tanks. It recommends ways [Harrison et al. 2016]. to protect workers by eliminating or reducing exposures to hazardous atmospheres, and actions employers should Working on or near oil and gas production tanks is of take to ensure that workers are properly aware of the particular concern because these tanks may contain hazards and protected from exposure to hydrocarbon concentrated hydrocarbon gases and vapors that are gases and vapors. This alert is a supplement to the OSHA under pressure. When the thief hatch is opened, the Alliance Tank Hazard Alert released in 2015 [National release of these pressurized gases and vapors can expose STEPS Network 2015]. workers. Second, the gases and vapors can displace

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. Forward-looking infrared (FLIR) photograph of the initial hydrocarbon plume Appendix B lists exposure limits for common hydrocarbon 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. 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 A worker manually gauges a flowback tank. The thief hatch is directly in front of artery disease may exacerbate the risk. These exposures his feet, and the gas and vapor released is invisible. can also have narcotic effects, causing dizziness, rapid Image: Max Kiefer, NIOSH. 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].

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

Worker Fatalities during Manual Direct-reading instruments were also used to characterize Tank Gauging and Fluid Sample peak and short-term exposures to hydrocarbon gases and Collection, 2010–2014 vapors. This study found that most workers gauging tanks (15 of 17; 88.2%) had benzene exposures exceeding the NIOSH researchers, OSHA officials, and academic NIOSH-recommended exposure limit (REL) of 0.1 parts per occupational health researchers investigated reports of million (ppm) as a time-weighted average (TWA) for a full worker deaths from 2010 through 2014 associated with shift. Some exposures also exceeded the NIOSH short- manual tank gauging and the collection of fluid samples term exposure limit of 1 ppm as a 15-minute average for (Appendix C). During the 5-year period, NIOSH researchers benzene. Worker exposures to benzene did not exceed identified nine fatalities involving these tasks. Three deaths the OSHA permissible exposure limit (PEL) criteria (1 occurred in North Dakota, three in Colorado, one in Texas, ppm as a TWA) and biological monitoring results did not one in Oklahoma, and one in Montana. exceed criteria established by the American Conference of Governmental Industrial Hygienists for benzene [OSHA All fatalities occurred at crude oil production tanks. Four 2012]. However, average benzene exposures for workers took place during tank gauging, and five happened during who gauged tanks were approximately five times greater fluid sample collection at an open thief hatch by pumpers/ than for workers not gauging tanks. In the same study, truckers. For all fatalities, the employees were working direct-reading instruments detected benzene peak alone or not being observed by a co-worker. Unprotected concentrations at open hatches exceeding 200 ppm, and exposures to high concentrations of hydrocarbon gases sustained atmospheres as high as 40% of the LEL adjacent and vapors and/or displacement of oxygen are believed to to separators and flowback tanks. Concentrations above be primary or contributory factors in each fatality [Harrison 10% of the LEL are considered a risk for fires or explosions et al. 2016]. Exposure to H2S was ruled out as a cause in and are classified as Immediately Dangerous to Life and all nine cases. A narrative description of each of the nine Health (IDLH) by OSHA and NIOSH. Workers at the sites did fatalities can be found on the NIOSH “Fatalities in the Oil not use respiratory protection while gauging tanks. and Gas Extraction Industry” (FOG) database web page (http://www.cdc.gov/niosh/topics/fog/data.html). OSHA Evaluation of Exposures to Oxygen concentrations well below normal (oxygen Workers during Tank Gauging concentration in ambient air = 21%) were documented in In 2014, OSHA industrial hygienists conducted evaluations two fatal incidents. While investigating the Case #1 death at oil and gas extraction well sites in North Dakota. The at the site, OSHA’s compliance officer measured oxygen sites were identified by observing active tank-gauging levels in the range of 11% to 12% approximately one foot operations. The evaluations characterized worker above the open hatch. A data-logging four-gas monitor exposures during manual tank gauging for full-shift, short- worn by the worker at the time of death in Case #7 term, and peak concentrations of hydrocarbon gases and recorded that the oxygen level fell to as low as 6.9%. The vapors, and flammable and oxygen-deficient environments. same worker had also worn the monitor during a previous Samples collected approximately one foot above open incident, during which the oxygen level fell to as low as hatches found IDLH concentrations of hydrocarbon gases and 9.1%, and remained consistently below 15% for a vapors, including propane, pentane, methyl butane, hexane, six-minute interval. Exposure to atmospheres with these 2-methyl pentane, and 3-methyl pentane (Table 1). low concentrations of oxygen can rapidly overcome workers and bring about unconsciousness without Worker sampling also documented overexposures warning. Also, in both incidents, the monitor worn by to benzene for short-term, ceiling, and 8-hour TWA the worker in Case #7 documented that the worker’s concentrations, based on the OSHA PELs. Potentially environment exceeded the LEL. flammable (>10% LEL) and oxygen-deficient atmospheres (<19.5% oxygen) were identified on production tanks when NIOSH Evaluation of Worker thief hatches were opened during gauging and sampling Exposures during Flowback and [Jordan 2015]. Production Activities Samples documented total hydrocarbon gas and vapor In 2013, NIOSH evaluated worker exposures to a variety of concentrations of 179,000 ppm and 219,000 ppm in the chemicals during flowback and production activities at six plumes above two thief hatches. Laboratory analyses well sites in Colorado and Wyoming [Esswein et al. 2014]. identified break-through of hydrocarbon gases in the Exposure assessments included full-shift and short-term sampling media, indicating that actual concentrations personal breathing zone (PBZ) and area air sampling. might have been greater than reported.

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.

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 oxygen- deficient 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 air- purifying 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.

NIOSH & OSHA Recommendations for Manual Tank Gauging and Fluid Sample Collection 1. Implement alternative tank gauging and 6. Ensure that workers are trained on — and correctly sampling procedures that enable workers to and consistently use — calibrated multi-gas and monitor tank fluid levels and take samples oxygen monitors that measure percent LEL and without opening the tank hatch. oxygen concentration. Workers should understand the limitations of these monitors as well as appropriate 2. Retrofit existing tanks with dedicated sampling actions to take whenever an alarm occurs or ports (i.e., tank sampling taps [American Petroleum they experience health symptoms (e.g., leave the Institute 2013]) that minimize worker exposures to hazard area, report symptoms to supervisors). hydrocarbon gases and vapors, thereby eliminating the need to routinely open thief hatches to 7. Do not permit employees to work alone sample. These sampling taps should minimize the when tank gauging or working around tanks, magnitude of hydrocarbon plumes and should limit thief hatches, or other areas where they may the need for workers to access the top of tanks. encounter process fluids. Observers should be trained on proper rescue procedures and be 3. Install thief hatch pressure indicators to provide stationed outside potentially hazardous areas. an immediate visual indicator of tank pressures and potential hazards. Pressure indicators can 8. As an interim measure, where remote gauging or show workers the pressure in the tank and sampling is not feasible or engineering controls allow a trained worker to follow appropriate are not implemented, (a) train workers in proper procedures, such as actuating a blowdown work practices, such as tank-opening procedures, valve, venting gas to a flare, or using appropriate that can minimize risks for exposures, (b) ensure respiratory protection, such as a self-contained intrinsic safety by proper grounding and prohibiting breathing apparatus or an air-line respirator. the use of spark producing devices or equipment, (c) establish administrative controls to reduce 4. Conduct worker exposure assessments to the number of times throughout a shift a worker determine exposure risks to volatile hydrocarbons is required to manually gauge tanks, (d) safely and other contaminants. Employers may consult reduce tank pressure prior to gauging, and (e) use an occupational safety and health professional appropriate respiratory protection, including a trained and certified in industrial hygiene and who supplied air respirator (SAR) and/or self-contained has knowledge and experience with combined breathing apparatus (SCBA) in areas where IDLH flammable gas and vapor exposures to ensure that VOC exposures may occur (i.e., during manual tank an appropriate air-sampling strategy is used. gauging/sampling). Employers should consult with a 5. Provide hazard communication training in a language trained occupational safety and health professional that employees understand to ensure that general to determine the appropriate respirator to be used. site workers, tank gaugers and samplers, water NIOSH guidance for selecting respirators is at: http:// haulers, drivers, and others who open tank hatches www.cdc.gov/nioshdocs/2005-100/default.html. understand the hazards associated with opening 9. Wear flame-resistant clothing to protect against tanks and the precautions necessary to conduct burns from fires and explosions. Also, use this work safely. These hazards include reduced appropriate impermeable gloves to limit risks for oxygen environments, flammability hazards and skin exposures to chemicals (e.g., benzene). possible ignition sources, and the potential for concentrations of hydrocarbons that can approach 10. Establish and practice emergency procedures or exceed IDLH concentrations. Post hazard signage to provide on-scene, immediate medical at access stairs, catwalks, and/or tanks to alert response in the event of an incident, such as workers about the hazards associated with opening a collapsed worker, or workers experiencing thief hatches and precautions that must be taken. symptoms of chemical overexposures or exposure to an oxygen-deficient atmosphere.