Introduction

Hydraulic fracturing or “fracking” is a process used 

to “stimulate” well production in the oil and gas 

industry. It is not a new process, but its use has 

increased significantly in the last 10 years because 

of new horizontal drilling and multi-stage fracking (or 

“completions”) technologies that improve access to 

natural gas and oil deposits. It involves pumping large 

volumes of water and sand into a well at high pressure 

to fracture shale and other tight formations, allowing oil 

and gas to flow into the well. 

NIOSH’s recent field studies show that workers may 

be exposed to dust with high levels of respirable 

crystalline silica (called “silica” in this Hazard Alert) 

during hydraulic fracturing. 

This Hazard Alert discusses the health hazards 

associated with hydraulic fracturing and focuses on 

worker exposures to silica in the air. It covers the 

health effects of breathing silica, recommends ways 

to protect workers, and describes how OSHA and 

NIOSH can help. Workers and employers need to be 

aware of the hazard that silica dust poses. Employers 

must ensure that workers are properly protected from 

exposure to silica. This Hazard Alert also provides a 

brief summary of other health and safety hazards to 

workers conducting hydraulic fracturing activities.

Worker Exposure to Silica during Hydraulic Fracturing

1-800-321-OSHA (6742) • www.osha.gov 1

The National Institute for Occupational Safety and Health (NIOSH) identified exposure to airborne 

silica as a health hazard to workers conducting some hydraulic fracturing operations during recent 

field studies.

Silica dust cloud by worker delivering sand from sand 

mover to transfer belt. 

Crystalline silica is a common mineral found in the 

earth's crust. It occurs primarily as quartz and is a major 

component of the sand, clay and stone materials used 

to make every day products such as concrete, brick and 

glass.

Respirable crystalline silica is the portion of crystalline 

silica that is small enough to enter the gas-exchange 

regions of the lungs if inhaled; this includes particles 

with aerodynamic diameters less than approximately 10 

micrometers (μm). 

OSHA and NIOSH have been investigating worker 

safety and health hazards in oil and gas extraction, 

including chemical exposures during hydraulic fracturing 

operations. 

OSHA has jurisdiction over the safety and health of 

workers, including workers involved in upstream oil 

and gas operations. The General Duty Clause of the 

Occupational Safety and Health (OSH) Act and OSHA’s 

General Industry Standards (29 CFR 1910) apply to 

the upstream industry. As part of the enforcement of 

these regulations, five OSHA regions located in areas of 

significant upstream activities use national, regional, and 

local emphasis programs to inspect oilfield worksites, 

including those that may have ongoing hydraulic fracturing 

operations.

NIOSH made safety and health in the oil and gas 

extraction industry a priority focus area in 2005 by 

creating the National Occupational Research Agenda 

(NORA) Oil and Gas Extraction Council, which includes 

OSHA and industry leaders in a cooperative effort to 

address occupational safety and health issues. To 

address an existing lack of information on occupational 

dust and chemical exposures associated with hydraulic 

fracturing, NIOSH established specific industry 

partnerships and initiated the NIOSH Field Effort to 

Assess Chemical Exposures to Oil and Gas Extraction 

Workers (http://www.cdc.gov/niosh/docs/2010-130/

pdfs/2010-130.pdf). Exposure to silica during hydraulic 

fracturing has been the focus of the NIOSH study to date.

OSHA•NIOSH

Photo credit: NIOSH
Why is silica a concern for workers during 

hydraulic fracturing?

Recent NIOSH field studies identified overexposure 

to airborne silica as a health hazard to workers. 

Large quantities of silica sand are used during 

hydraulic fracturing. Sand is delivered via truck 

and then loaded into sand movers, where it is 

subsequently transferred via conveyer belt and 

blended with other hydraulic fracturing fluids prior 

to high pressure injection into the drilling hole. 

Transporting, moving, and refilling silica sand into and 

through sand movers, along transfer belts, and into 

blender hoppers can release dusts containing silica 

into the air. Workers can be exposed if they breathe 

the dust into their lungs. 

NIOSH identified seven primary sources of silica dust 

exposure during hydraulic fracturing operations: 

•	 Dust ejected from thief hatches (access ports) on 

top of the sand movers during refilling operations 

while the machines are running (hot loading).

•	 Dust ejected and pulsed through open side fill ports 

on the sand movers during refilling operations.

•	 Dust generated by on-site vehicle traffic. 

•	 Dust released from the transfer belt under the sand 

movers.

•	 Dust created as sand drops into, or is agitated in, 

the blender hopper and on transfer belts.

•	 Dust released from operations of transfer belts 

between the sand mover and the blender; and

•	 Dust released from the top of the end of the sand 

transfer belt (dragon’s tail) on sand movers. 

1-800-321-OSHA (6742) • www.osha.gov 2

Silica dust clouds from delivery trucks loading into sand 

movers. 

Fracturing fluid is made up of a base fluid, proppant, and chemical additives. Water accounts for about 90 percent of 

the fracturing mixture and sand accounts for about 9.5 percent. Chemicals account for the remaining one half of one 

percent of the mixture. The base fluid applies pressure to the formation and delivers the proppant to the fractures.

The base fluid is usually water, but can include methanol, liquid carbon dioxide, and liquefied petroleum gas.

Proppant consists of particles that hold open the fractures created by hydraulic fracturing, allowing the oil and gas 

to flow out of the formation and into the well bore. Silica sand is frequently used as a proppant. Other proppants can 

include sintered bauxite or ceramics, and resin-coated sand.

Chemical additives include friction reducers, scale inhibitors, solvents, acids, gelling agents, and biocides that are 

added to protect equipment, reduce pumping requirements, and maintain the integrity of the oil or gas formation. 

An Overview of the "Fracking" Process

The process known as "fracking" has long been used to extract oil from depleted wells. It is now widely used 

across the country to tap previously unreachable oil and natural gas locked within deep rock formations. Graphic: Doug Stevens

Copyright 2012, Los Angeles Times.Reprinted with permission.

Photo credit: NIOSH
NIOSH Findings on Worker 

Exposures to Silica

In cooperation with oil and gas industry partners, NIOSH 

collected 116 full shift air samples at 11 hydraulic 

fracturing sites in five states (Arkansas, Colorado, North 

Dakota, Pennsylvania and Texas) to determine the 

levels of worker exposure to silica at various jobs at the 

worksites. Many air samples showed silica levels for 

workers in and around the dust generation points above 

defined occupational exposure limits.1

Of the 116 samples collected:

•	 47% showed silica exposures greater than the 

calculated OSHA PEL. 

•	 79% showed silica exposures greater than the 

NIOSH REL of 0.05 milligrams per cubic meter 

(mg/m3

). 

•	 9% of all samples showed silica exposures 10 or 

more times the PEL, with one sample more than 

25 times the PEL.

•	 31% of all samples showed silica exposures 10 or 

more times the REL, with one sample more than 

100 times the REL.

Determining worker exposure levels is important 

for selecting the right type of control measures, 

including engineering controls and respiratory 

protection. For example, half-face respirators are 

not protective for silica levels over 10 times the 

exposure limit.

NIOSH found that sand 

mover and blender 

operators, and workers 

downwind of these 

operations (especially 

during hot loading), 

had the highest silica 

exposures. Workers 

upwind and not in the 

immediate area of sand 

movers (sand delivery 

truck spotters) also had 

exposures above the 

NIOSH REL, possibly

from the dust created 

by traffic at the well site. 

1-800-321-OSHA (6742) • www.osha.gov 3

The OSHA general industry PEL for quartz, the 

common form of crystalline silica found in sand, is an 

8-hour time-weighted average exposure to respirable 

dust calculated using the following formula:

 PEL =

 

The PEL is approximately equal to 0.1 mg/m3 for pure 

quartz silica.

The PEL is outlined in 29 CFR 1910.1000 Table Z-3. 

If other forms of crystalline silica are present, the PEL 

calculation must be modified as per Table Z-3.

The NIOSH REL is a fixed value of 0.05 mg/m3.

10

(% Silica) + 2

Silica dust by worker conducting 

sand transfer operations. Photo 

shows sand mover and transfer 

system. 

Worker and area samples collected in enclosed but 

non-filtered cab vehicles (e.g., chemical and blender 

trucks) were above the REL, even when spending 

most of the day in the cab. Worker and area samples 

collected in enclosed vehicles with air conditioning 

and filtration (e.g., data vans) had silica exposures 

below the NIOSH REL. 

Health Hazards of Silica

Hydraulic fracturing sand contains up to 99% silica. 

Breathing silica can cause silicosis. Silicosis is a 

lung disease where lung tissue around trapped silica 

Photo credit: NIOSH

1 Employers are required to take actions to reduce worker 

exposures if air samples show levels above OSHA’s calculated 

Permissible Exposure Limit (PEL). The OSHA PEL is the 

legally enforceable regulatory limit. The NIOSH Recommended 

Exposure Limit (REL) is a non-mandatory, recommended 

occupational exposure limit. However, because OSHA recognizes 

that many of its PELs are outdated and inadequate measures of 

worker safety, both OSHA and NIOSH recommend that employers 

take actions to keep worker exposures below the NIOSH REL.

What are the symptoms of silicosis?

Silicosis is classified into three types: chronic/classic, 

accelerated, and acute.

Chronic/classic silicosis, the most common type, 

occurs after 10-20 years of moderate to low exposures 

to respirable crystalline silica. Symptoms associated 

with chronic silicosis may or may not be obvious; 

therefore, workers need to have a chest X-ray to 

determine if there is lung damage. As the disease 

progresses, the worker may experience shortness of 

breath when exercising and have clinical signs of poor 

oxygen/carbon dioxide exchange. In the later stages, 

the worker may experience fatigue, extreme shortness 

of breath, cough, and, in some cases, respiratory 

failure.

Accelerated silicosis can occur after 5-10 years of 

high exposures to respirable crystalline silica. It is 

similar to chronic silicosis, but progresses more rapidly. 

Acute silicosis occurs after only a few months or a few 

years following exposures to extremely high levels of 

respirable crystalline silica. Symptoms of acute silicosis 

include rapidly progressive and severe shortness of 

breath, weakness, and weight loss. Though much less 

common than other forms of silicosis, acute silicosis 

nearly always leads to disability and death.
What can be done at hydraulic 

fracturing worksites to protect workers 

from exposure to silica?

Under the Occupational Safety and Health Act of 1970, 

employers are responsible for providing safe and 

healthy working conditions for their workers. Employers 

must determine which jobs expose workers to silica 

and take actions to control overexposures and protect 

workers. A combination of engineering controls, work 

practice, protective equipment, and product substitution 

where feasible, along with worker training, is needed 

to protect workers who are exposed to silica during 

hydraulic fracturing operations.

One way to reduce silica exposure is to use alternative 

proppants (e.g., sintered bauxite, ceramics, resincoated sand) where feasible. However, before using 

other proppants, it is important to evaluate the health 

hazards associated with them. If safe proppant 

alternatives are not feasible, then employers should 

monitor worker exposures, take measures to prevent 

exposures to silica, and inform workers of hazards, as 

described below. 

Several OSHA standards and directives cover 

operations that may expose workers to silica, 

including:

• Air Contaminants (29 CFR 1910.1000)

• Hazard Communication (29 CFR 1910.1200)

• Respiratory Protection (29 CFR 1910.134)

OSHA’s Directive CPL 03-00-007, titled National 

Emphasis Program – Crystalline Silica, has detailed 

information on silica hazards, guidelines for air 

sampling, guidance on calculating PELs for dust 

containing silica, and other compliance information.

1-800-321-OSHA (6742) • www.osha.gov 4

particles reacts, causing inflammation and scarring 

and reducing the lungs’ ability to take in oxygen.2

Workers who breathe silica day after day are at greater 

risk of developing silicosis. Silica can also cause lung 

cancer and has been linked to other diseases, such as 

tuberculosis, chronic obstructive pulmonary disease, 

and kidney and autoimmune disease.3

Monitor the air to determine worker exposures 

to silica

• Collect respirable dust samples to determine 

which jobs expose workers to silica above exposure 

limits. Employers should consult with a trained 

occupational safety and health professional, such 

as a certified industrial hygienist, or contact OSHA’s 

free on-site consultation service. 

• If air samples show levels above OSHA’s calculated 

PEL, employers are required to take actions to reduce 

worker exposures. However, both OSHA and NIOSH 

recommend that employers take the actions below 

to keep worker exposures below the NIOSH REL.

Control dust exposures by improving existing 

engineering controls and safe work practices

Engineering controls and work practices provide the 

best protection for workers and must be implemented 

first, before respiratory protection is used. Working with 

industry partners, NIOSH has identified the following 

control options for hydraulic fracturing operations:

Short-term work practice and procedural changes 

that can be implemented quickly:

•	 Mandate the capping of unused fill ports (e.g., 

cam lock caps) on sand movers. Securing 

unused fill ports can help reduce the dust released, 

especially during filling. 

• Reduce the drop height between the sand 

transfer belt and T-belts and blender hoppers.

Limiting the distance that sand falls through the air 

can help reduce dust. 

• Limit the number of workers, and the time 

workers must spend in areas where dust and 

silica levels may be elevated, and consider ways to 

perform dusty operations remotely to completely 

remove employees from these areas. 

• Apply fresh water to roads and around the well 

site to reduce the dust.

Practices that involve equipment changes:

• Enclose points where dust is released. Install 

thick plastic stilling or staging curtains around the 

bottom sides of the sand movers to limit dusts 

released from belt operation. Enclosures can also 

be added along and at the ends of the sand transfer 

belt. 

• Where possible, use enclosed cabs or booths.

Consider configuring operator cabs and booths with 

HEPA filtration and climate controls to further protect 

workers.

• Use local exhaust ventilation to collect silicacontaining dusts and prevent dust escape. Install 

dust collection systems onto machines or equipment 

that can release dust. 

2

 NIOSH [1986]. Occupational respiratory diseases. Cincinnati, 

OH: U.S. Department of Health and Human Services, Public 

Health Service, Centers for Disease Control, National Institute 

for Occupational Safety and Health, DHHS (NIOSH) Publication 

No. 86-102.

3

 NIOSH [2002] Hazard Review, Health Effects of Occupational 

Exposure to Respirable Crystalline Silica. Cincinnati, OH: U.S. 

Department of Health and Human Services, Public Health 

Service, Centers for Disease Control, National Institute for 

Occupational Safety and Health, DHHS (NIOSH) Publication 

No. 2002-129.
• Replace transfer belts with screw augers on 

sand movers in new designs or retrofits. Dust 

can be released from the sand moving belt under 

the sand movers from the actions of belt movement 

or vibration. Moving sand through an auger system 

rather than a belt will help contain the sand and 

reduce dust release.

1-800-321-OSHA (6742) • www.osha.gov 5

Provide respiratory protection when it is 

needed to protect workers

When engineering and work practice controls are not 

feasible, while they are being implemented, or when 

they do not reduce silica levels below OSHA PELs, 

employers must provide workers with respirators. 

Whenever respirators are used, the employer must 

have a respiratory protection program that meets 

the requirements of OSHA’s Respiratory Protection 

standard (29 CFR 1910.134). This program must 

include proper respirator selection, fit testing, medical 

evaluations, and training. 

•	 If respirators are 

provided, use at least 

a NIOSH-approved 

N95 respirator. If the 

silica level is more 

than 10 times the PEL, 

a half-face respirator 

is not protective and a 

respirator that offers 

a greater level of 

protection (e.g., a 

full-facepiece 

respirator, which will 

protect workers at 

silica levels up to 50 

times the PEL) must 

be used. Full-face 

powered air-purifying 

respirators (PAPR) 

provide more protection than half-face air-purifying 

respirators. In general, workers find PAPRs to be 

more comfortable.

For more information, see OSHA’s Safety and Health 

Topics page and eTool on respiratory protection. 

Provide training and information to workers 

about the hazards of silica and other chemicals

OSHA’s Hazard Communication standard requires 

that employers provide their workers with training and 

information about hazardous chemicals used in the 

workplace. Employers must provide training and 

information to workers in a manner and language 

that the worker understands. Employers must: 

•	 Prepare and implement a written hazard 

communication program.

•	 Provide training and information on the hazards of 

silica and other chemicals used in the workplace.

•	 Provide workers access to Safety Data Sheets 

(SDSs) on silica sand and other hazardous 

chemicals they are exposed to during hydraulic 

fracturing operations.

NIOSH-approved N95 filtering 

facepiece (top) and elastomeric 

(bottom) half-face respirators 

can be used only if silica 

concentrations are less than 10 

times the PEL. 

A conceptual example of a screw auger retrofit assembly. Image credit: NIOSH

A conceptual example of a baghouse assembly on the 

back of a truck. 

Image credit: NOV Appco

A conceptual example of dust control technologies 

being used by industry. 

Image credit: Frac Sand Dust Control LLC
1-800-321-OSHA (6742) • www.osha.gov 6

Consider medical monitoring for workers who 

are exposed to silica

As part of its National Emphasis Program on Silica, 

OSHA recommends that employers medically monitor 

all workers who may be exposed to silica dust levels 

at or above one-half the PEL. Recommended medical 

tests include: 

•	 A medical exam that focuses on the respiratory 

system and includes a work and medical history. 

•	 A chest X-ray, evaluated by a qualified professional 

as described in Directive CPL 03-00-007.

OSHA recommends that these tests be repeated every 

three years if the employee has less than 15 years 

of silica exposure, every two years if the employee 

has 15 to 20 years of exposure, and every year if the 

employee has 20 or more years of exposure.

What additional health and safety 

hazards exist during hydraulic 

fracturing?

In addition to silica hazards, workers may be exposed 

to other worksite health hazards that can include 

exposure to diesel particulate and exhaust gases from 

equipment, high or low temperature extremes, high 

noise levels, and overexertion leading to sprains and 

strains. In addition, fatigue may be a concern due to 

long working hours.

Hydraulic fracturing sites also have safety hazards

similar to those at other oil and gas drilling sites, 

including:

•	 Being struck by moving equipment, including motor 

vehicle accidents (primarily when traveling to and 

between well sites), tools, and falling objects.

• Poor lighting.

• Being caught in pinch points (such as hammer union 

wings and hammers, pump iron, and racks).

• Falling from heights.

• Being struck by high-pressure lines or unexpected 

release of pressure (for example, mismatched or 

worn hammer unions, line failure).

• Fires or explosions from flowback fluids containing 

ignitable materials (e.g., methane) and other 

flammable materials stored or used at the well site.

• Working in confined spaces, such as sand storage 

trailers, frac tanks, and sand movers without taking 

the required precautions.

See OSHA’s Oil and Gas Well Drilling and Servicing 

eTool website (http://www.osha.gov/SLTC/etools/

oilandgas/index.html) for more information on safety 

and health hazards at oil and gas extraction sites.

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 advice for small businesses with fewer 

than 250 employees at a site (and no more than 500 

employees nationwide) to help identify and correct 

hazards at your worksite. On-site consultation services 

are separate from enforcement and do not result in 

penalties or citations. To locate the OSHA Consultation 

Office nearest you, visit OSHA’s website at www.osha.

gov or call 1-800-321-OSHA (6742).

OSHA’s Cooperative Initiatives: OSHA, NIOSH, 

and several U.S. onshore exploration and production 

industry trade associations, companies, and individual 

experts have formed a Respirable Silica Focus Group 

to further explore silica exposure during hydraulic 

fracturing and to develop practical short- and long-term 

solutions to protect worker safety and health.

NIOSH is designing conceptual engineering controls to 

minimize exposure to silica during hydraulic fracturing. 

NIOSH is looking for industry partners to help test 

these engineering controls. If you are interested, 

please contact NIOSH at westernstatesoffice@cdc.

gov. NIOSH is also looking for additional partners 

in drilling and well servicing to help evaluate worker 

exposures to 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/

pdf) for details and contact us 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 (such as dust control) are built into equipment 

during the design phase.

See “A Guide to Working Safely With Silica. If It’s Silica, 

It’s Not Just Dust” (U.S. Department of Labor and 

NIOSH) for more information about the hazards of silica 

and protecting workers from silica exposures. 

OSHA recently revised the Hazard Communication 

standard to conform with the Globally Harmonized 

System of Classification and Labeling of Chemicals 

(GHS). "Material Safety Data Sheets" (MSDSs) are now 

referred to as SDSs, and the information on SDSs will 

be presented in the standard 16 section format. Refer to 

OSHA's Hazard Communications webpage to get more 

information.
DTSEM 6/2012 7

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 OSHA-approved 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.

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. 

NIOSH recommendations for preventing silicosis, 

including dust control, sampling and analysis methods, 

medical monitoring of workers, training, and respiratory 

protection, can be found at the Silica Topics webpage 

at http://www.cdc.gov/niosh/topics/silica. 

For more information, see Best Practices for Dust 

Control in Metal/Nonmetal Mining (www.cdc.gov/

niosh/mining/pubs/pubreference/outputid3388.htm), 

which discusses dust control in underground mining 

operations. Research results from this document have 

direct relevance for minerals handling operations in 

hydraulic fracturing operations. 

Worker Rights

Workers have the right to:

• Working conditions that do not pose a risk of serio

 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 

(http://www.osha.gov/workers.html).

Contact OSHA

For questions or to get information or advice, to report 

an emergency, to report a fatality or catastrophe, to 

order publications, to file a confidential complaint, or 

to request OSHA’s free on site-consultation service, 

contact your nearest OSHA office, visit www.osha.gov, 

or call OSHA at 1-800-321-OSHA (6742), TTY 1-877-

889-5627. 

Many states operate their own occupational safety and 

health programs approved by OSHA. States enforce 

similar standards that may have different or additional 

requirements. A list of state plans is available at www.

osha.gov/dcsp/osp/index.html.

Contact NIOSH

To receive documents or more information about 

occupational safety and health topics, please contact 

NIOSH: 1-800-CDC-INFO (1-800-232-4636); TYY: 

1-888-232-6348; email: cdcinfo@cdc.gov or visit the 

NIOSH web site at www.cdc.gov/niosh.