Figure
1. Flowback Tanks
What is flowback
Flowback
refers to process fluids from the wellbore that return to the surface and are
collected after hydraulic fracturing is completed. In addition to the hydraulic
fracturing fluids originally pumped, returned fluids contain volatile
hydrocarbons from the formation. After separation, flowback fluids are
typically stored temporarily in tanks (figure 1) or surface impoundments (lined
pits, ponds) at the well site. Liquid hydrocarbons from the separation process
are routed to production tanks (figure 2). Workers periodically gauge the fluid
levels in flowback and production tanks with hand-held gauges (sticks and
tapes) through access hatches located on the top of the tank.
MSDS for Flowback
The
Material Safety Data Sheet (MSDS) for condensate identifies it as a potentially
flammable and explosive substance with vapors that may travel long distances to
an ignition source and flash back.
Sulfur compounds in this material may decompose to release
hydrogen sulfide gas which may accumulate to potentially lethal concentrations
in enclosed air spaces. Vapor concentrations of hydrogen sulfide above 50 ppm,
or prolonged exposure at lower concentrations, may saturate human odor
perceptions so that the smell of gas may not be apparent. DO NOT DEPEND ON THE
SENSE OF SMELL TO DETECT HYDROGEN SULFIDE! IDLH for hydrogen sulfide is 100
ppm.
Hydrogen sulfide is listed as an EPA Extremely Hazardous Substance.
Contains benzene, a chemical known to cause cancer in humans. May
cause diseases of the blood forming organs, such as leukemia, adverse effects
on the immune system and adverse reproductive effects. Benzene may cause
irritation to the eyes, skin and lungs, central nervous system effects and
irregular heartbeats. IDLH for benzene is 500 ppm.
Some components of this material such as benzene, toluene and
xylene have been shown to produce fetal toxicity and/or reduce female or male
reproductive capacity in laboratory animals.
Although
worker safety hazards in the oil and gas extraction industry are well known,
there is very little published data regarding occupational health hazards
(e.g., types and magnitude of risks for chemical exposures) during oil and gas
extraction operations. To address the lack of information, NIOSH requests
assistance from oil and gas stakeholders in further characterizing risks for
chemical exposures during flowback operations and, as needed, develop and
implement exposure controls. This blog briefly describes flowback operations
and addresses reports made known to NIOSH of recent worker fatalities related
to or located at flowback operations.
Worker Fatalities
Figure
2. Production Tanks
NIOSH
learned about several worker fatalities associated with flowback operations
through media reports, officials with the Occupational Safety and Health Administration
(OSHA), and members of the academic community. According to our information, at
least four workers have died since 2010 from what appears to be acute chemical
exposures during flowback operations at well sites in the Williston Basin
(North Dakota and Montana). While not all of these investigations are complete,
available information suggests that these cases involved workers who were
gauging flowback or production tanks or involved in transferring flowback
fluids at the well site. Often these fatalities occurred when the workers were
performing their duties alone.
Potential Exposures during
Flowback Operations
Flowback
refers to process fluids from the wellbore that return to the surface and are
collected after hydraulic fracturing is completed. In addition to the hydraulic
fracturing fluids originally pumped, returned fluids contain volatile
hydrocarbons from the formation. After separation, flowback fluids are
typically stored temporarily in tanks (figure 1) or surface impoundments (lined
pits, ponds) at the well site. Liquid hydrocarbons from the separation process
are routed to production tanks (figure 2). Workers periodically gauge the fluid
levels in flowback and production tanks with hand-held gauges (sticks and
tapes) through access hatches located on the top of the tank.
Hydrogen
sulfide (sour gas) is well recognized as a toxic exposure hazard associated
with oil and gas extraction and production (1,2). However, less recognized by
many employers and workers is that many of the chemicals found in volatile
hydrocarbons are acutely toxic at high concentrations. Volatile hydrocarbons
can affect the eyes, breathing, and the nervous system (3,4,5,6,7) and at high
concentrations may also affect the heart causing abnormal rhythms (8,9).
Recently, NIOSH conducted exposure assessments to identify chemical hazards to
workers involved in flowback operations. Results from initial field studies
suggest that certain flowback operations/activities can result in elevated
concentrations of volatile hydrocarbons in the work environment that could be
acute exposure hazards. The results, conclusions, and recommendations based on
these evaluations will be detailed in a peer-reviewed journal article, a future
NIOSH Science Blog posting, or other communication products.
Preliminary
Recommendations
Based
on the limited information on fatalities and initial NIOSH exposure
assessments, NIOSH researchers have identified preliminary recommendations to
reduce the potential for occupational exposures:
1)
Develop alternative tank gauging procedures so workers do not have to
routinely open hatches on the tops of the tanks and manually gauge the level of
liquid.
2)
Provide hazard awareness training to ensure flowback technicians, water haulers, and
drivers understand the potential hazards and risks for volatile chemical
exposures when working on and around flowback and production tanks.
3)
Monitor workers to determine their exposure to volatile hydrocarbons and other
contaminants. Employers should consult with an occupational safety and health
professional trained in industrial hygiene to ensure an appropriate sampling
strategy is used.
4)
Ensure workers do not work alone in potentially hazardous areas.
5)
Use appropriate respiratory protection in areas where potentially high concentrations
of volatile hydrocarbons can occur as an interim measure until engineering
controls are implemented. Employers should consult with an occupational safety
and health professional trained in industrial hygiene to determine the
appropriate respirator to be used. Note that OSHA regulations (29
CFR 1910.134;)
) require a comprehensive
respiratory protection program be established when respirators are used in the
workplace. NIOSH guidance for selecting respirators can be found at http://www.cdc.gov/niosh/docs/2005-100/default.html
6)
Establish emergency procedures to provide medical response in the event of an
incident.
NIOSH
continues to work with OSHA to obtain additional information about these
fatalities. We request assistance from our occupational safety and health
stakeholders for information on other potentially related incidents or
fatalities related to acute exposures during such flowback operations. NIOSH is
looking for additional industry partners to work with us to further characterize
worker exposures during flowback operations and to develop and evaluate
controls, as needed. If you have questions or wish to provide further pertinent
information, please contact us via the blog comment box below or by e-mail at nioshblog@cdc.gov.
Notes
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 fatalities
associated with flowback operations. To keep the blog discussion focused on
worker health, we may choose not to respond to comments that do not pertain to
worker exposures.
References
1.
NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention National Institute for Occupational
Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149 Hydrogen
Sulfide: http://www.cdc.gov/niosh/npg/npgd0337.html
2.
OSHA Oil and Gas Well Servicing eTool: General Safety and Health: Hydrogen
Sulfide Gas
https://www.osha.gov/SLTC/etools/oilandgas/general_safety/h2s_monitoring.html
3.NIOSH
POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention National Institute for Occupational
Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. Benzene: http://www.cdc.gov/niosh/npg/npgd0049.html
4.
NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention National Institute for Occupational
Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. N-Pentane:
http://www.cdc.gov/niosh/npg/npgd0486.html
5.
NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention National Institute for Occupational
Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. N-Hexane: http://www.cdc.gov/niosh/npg/npgd0322.html
6.
NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention National Institute for Occupational
Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. N-Heptane: http://www.cdc.gov/niosh/npg/npgd0312.html
7.
NIOSH POCKET GUIDE TO CHEMICAL HAZARDS, DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention National Institute for Occupational
Safety and Health. (2007)DHHS (NIOSH) Publication No. 2005-149. Petroleum
distillates: http://www.cdc.gov/niosh/npg/npgd0492.html
8.
Adgey A.A., Johnston P.W., McMechan S. Sudden cardiac death and substance
abuse. Resuscitation. (1995)Jun;29(3):219-21.
9.
Sugie, H., Sasakia C. Hashimotoa, C., Takeshita, H. et al. Three cases of
sudden death due to butane or propane gas inhalation: analysis of tissues for
gas components. Forensic Science International (2004) 143:211–214.