Worker Exposure to Crystalline Silica During Hydraulic FracturingPosted on by
Hydraulic fracturing or “fracking” is the process of injecting large volumes of water, sand, and chemicals into the ground at high pressure to break up shale formation allowing more efficient recovery of oil and gas. This form of well stimulation has been used since the late 1940s, but has increased substantially over the last 10 years with the advent of horizontal drilling technology that greatly improves access to gas deposits in shale. Approximately 435,000 workers were employed in the US oil and gas extraction industry in 2010; nearly half of those workers were employed by well servicing companies, which includes companies that conduct hydraulic fracturing (BLS).1
To date, most of the attention on the safety and health implications of hydraulic fracturing has been related to impacts on the environment, primarily the potential for ground water contamination by hydraulic fracturing fluids. Although worker safety hazards in the oil and gas extraction industry are well known, there is very little data regarding occupational health hazards during hydraulic fracturing operations; for example, whether workers are exposed to toxic chemicals at hazardous concentrations. To investigate potential worker health hazards in this rapidly expanding industry and address the existing lack of information on occupational dust and chemical exposures associated with hydraulic fracturing, NIOSH initiated the NIOSH Field Effort to Assess Chemical Exposures in Oil and Gas Extraction Workers. Initial hazard assessments identified exposure to crystalline silica during hydraulic fracturing as the most significant known health hazard to workers and this has been the focus of the NIOSH study to date.
Crystalline silica, in the form of sand (“frac sand”), plays a major role in the hydraulic fracturing process. Each stage of the fracking operation typically involves hundreds of thousands of pounds of “frac sand.” The sand is used as a proppant to hold open the fissures created by hydraulic fracturing and allow the gas to flow out of the shale into the well. Moving, transporting and refilling thousands of pounds of sand onto and through sand movers, along transfer belts, and into blenders generates considerable dust, including respirable crystalline silica, to which workers can be exposed.
Inhalation of fine dusts of respirable crystalline silica can cause silicosis.2 Silicosis is an incurable but preventable lung disease. Mortality statistics undercount silicosis cases. Still, death certificates document that an average of 162 individuals died annually from or with silicosis in the U.S. over the period 2000-2005.3 The disease typically develops after long periods of exposure and progresses gradually. However, rapidly fatal cases of acute silicosis resulting from very intense exposures over only a few months or years are well documented among sandblasters, tunnelers, miners, and some other occupational groups.2 Crystalline silica has also been determined to be an occupational lung carcinogen4,5 and there is evidence that inhaling respirable silica dust causes chronic obstructive pulmonary disease (COPD), chronic renal (kidney) disease and various autoimmune diseases. Individuals with silicosis are known to be at higher risk of tuberculosis and several other respiratory infections.
Silica Dust Levels
NIOSH recently collected 116 air samples at 11 different hydraulic fracturing sites in five different states (AR, CO, ND, PA and TX) to evaluate worker exposure to crystalline silica. At each of the 11 sites, full-shift personal-breathing-zone (PBZ) exposures to respirable crystalline silica consistently exceeded relevant occupational health criteria (e.g., the Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL), NIOSH Recommended Exposure Limit (REL), and the American Conference of Governmental Industrial Hygienist’s (ACGIH) Threshold Limit Value (TLV®)). At these sites, 54 (47%) of the 116 samples collected exceeded the calculated OSHA PELs; 92 of 116 (79%) exceeded the NIOSH REL and ACGIH TLV. The magnitude of the exposures is particularly important; 36 of the 116 (31%) samples exceeded the NIOSH REL by a factor of 10 or more. The significance of these findings is that even if workers are properly using half-mask air-purifying respirators, they would not be sufficiently protected because half-mask air-purifying respirators have a maximum use concentration of 10 times the occupational health exposure limit.
Based on these results, NIOSH concluded that an inhalation health hazard existed for workers exposed to crystalline silica at the evaluated hydraulic fracturing sites. NIOSH notified company representatives of these findings and provided reports with recommendations (listed below) to control exposure to crystalline silica. We recommend that all hydraulic fracturing sites evaluate their operations to determine the potential for worker exposure to crystalline silica and implement controls as necessary to protect workers.
Based on workplace observations at each of the 11 hydraulic fracturing sites, NIOSH researchers identified seven primary points of dust release or generation from hydraulic fracturing equipment or operations. These included the following locations or equipment:
- Dust emitted from “thief” hatches (open ports on the top of the sand movers used to allow access into the bin)
- Dust ejected and pulsed through side fill ports on the sand movers during refilling operations
- Dust generated by on-site vehicle traffic, including sand trucks and crew trucks, by the release of air brakes on sand trucks, and by winds
- 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
- Dust released from the top of the dragon’s tail (end of the sand transfer belt) on sand movers
Given the magnitude of silica-containing, respirable dust exposures measured by NIOSH, personal respiratory protection alone is not sufficient to adequately protect against workplace exposures. A combination of product substitution (where feasible), engineering, administrative, and personal protective controls, along with worker training, is needed to control workplace exposure to respirable silica during hydraulic fracturing. Working with industry partners, NIOSH researchers have identified the following controls, some simple, and some more complex, that can be implemented in a variety of ways.
- Use a less hazardous non-silica proppant (e.g., ceramic) where feasible.
- Use local exhaust ventilation for capture and collection. Cyclones dust collectors and a portable baghouse connected to thief hatches can capture dusts as they are generated. NIOSH researchers have developed two conceptual phase controls for this source of dust generation. The first is a mini-baghouse assembly that could be retro-fitted over the existing thief hatch openings. The baghouse takes advantage of the positive pressure generated by sand filling which inflates the bag and dust control is achieved as a filter cake develops on the inside the baghouse fabric. The design is envisioned to be self-cleaning as the filter cake would fall back into the sand container as the fabric collapses when air pressure is released after bin filling.
- Use passive enclosures at points of dust generation. Install stilling curtains (also called staging curtains) around the bottom sides of the sand movers to limit dusts released from belt operation. Stilling curtains can be made of clear thick plastic (including heavy plastic strips) or other appropriate materials to contain dusts. Enclosures can also be considered along and at the ends of the sand transfer belt (dragon tail).
- Minimize distances between the dragon tail and T-belts and blender hoppers. Minimizing the distance that sand falls through the air can help minimize dust generation.
- Replace transfer belts with screw augers on sand movers. This involves Prevention-through-Design considerations for engineers and equipment designers when new sand movers are manufactured or are rebuilt and will require more extensive engineering and mechanical retrofitting. 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.
- Use amended water (e.g., containing chloride and magnesium salts) to reduce dust generation on roads into and at the well site. Do not use well brines for dust control.
- Mandate use of cam-lock caps for fill ports on sand movers. When sand mover bins are being filled, sand dust is pulsed from the fill port on the opposite side of the sand mover. Mandating that cam lock caps be secured in place can help minimize dust generation.
- Use administrative controls. Limit the number of workers, or the time workers must spend, in areas where exposure to high concentrations of silica can occur. Consider options for remote operations to remove employees from areas where exposures can occur.
- Provide worker training. Hydraulic fracturing workers should be trained on the hazards of crystalline silica and the steps they should take to limit dust generation and reduce the potential for exposure.
- Monitor workers to determine their exposure to crystalline silica. Conduct PBZ air sampling on workers engaged in activities where “frac” sand is used. Documenting worker exposures is important to verify the need for controls, determine the efficacy of controls that have been implemented, and ensure that the appropriate respiratory protection is used as an interim control until engineering controls can be implemented. This information is also useful for worker training and informing workers about their exposures. Employers should consult with an occupational safety and health professional trained in industrial hygiene to ensure an appropriate sampling strategy is used.
- Use appropriate respiratory protection as an interim measure until engineering controls are implemented. As discussed above, a half-mask air-purifying respirator may not provide sufficient protection. As an interim measure until engineering controls are implemented and evaluated, a higher level of respiratory protection should be used. Employers should consult with an occupational safety and health professional (industrial hygienist) to determine the appropriate respirator to be used. Employers should establish a comprehensive respiratory protection program that adheres to OSHA regulations (CFR 29 1910.134) and ensure that workers who wear respiratory protection are medically cleared, properly trained and fitted, and are clean shaven each day. The NIOSH policy on respiratory protection for crystalline silica can be found at: http://www.cdc.gov/niosh/docs/2008-140/.NIOSH guidance for selecting respirators can be found at http://www.cdc.gov/niosh/docs/2005-100/default.html.
The NIOSH document Best Practices for Dust Control in Metal/Nonmetal Mining discusses dust control in underground mining operations. Research results from this document have direct relevance for minerals handling operations in hydraulic fracturing operations.
As noted above, NIOSH is designing conceptual engineering controls to minimize exposure to silica during hydraulic fracturing. NIOSH hopes to have a working prototype in the next month and is looking for industry partners to help us test this engineering control. If you are interested, please contact us via the blog comment box below or by e-mail at firstname.lastname@example.org. NIOSH is also looking for additional partners in drilling and well servicing to work with us to evaluate worker exposures to other chemical hazards and develop controls as needed. Other potential workplace exposures can include hydrocarbons, lead, naturally occurring radioactive material (NORM) and diesel particulate matter which have not been fully characterized. Please refer to the document NIOSH Field Effort to Assess Chemical Exposure Risks to Gas and Oil Workers for details and contact us if you have questions or wish to participate.
—Eric Esswein, MSPH; Max Kiefer, MS; John Snawder, PhD; and Michael Breitenstein, BS
Capt. Esswein is a Senior Industrial Hygienist in the NIOSH Western States Office.
Mr. Kiefer is the Director of the NIOSH Western States Office.
Dr. Snawder is a Research Toxicologist in the NIOSH Division of Applied Research Technology.
Mr. Breitenstein is a Research Biologist in the NIOSH Division of Applied Research Technology
Note: The objective of this blog entry is to describe workers’ exposures to respirable crystalline silica during hydraulic fracturing operations, discuss potential controls, and request help from industry partners to work with us on methods to reduce worker exposure. Hydraulic fracturing is a topic fraught with many environmental and general public health questions. To keep the blog discussion focused on worker health, we may choose not to post comments that do not pertain to worker exposures.
- BLS, Quarterly Census of Employment and Wages: http://www.bls.gov/cew/.
- Davis GS . Silica. In: Harber P, Schenker MB, Balmes JR, eds. Occupational and environmental respiratory disease. 1st ed. St. Louis, MO: Mosby—Year Book, Inc., pp. 373–399.
- National Occupational Respiratory Mortality System (NORMS). http://webapp.cdc.gov/ords/norms.html
- NIOSH Hazard Review, Health Effects of Occupational Exposure to Respirable Crystalline Silica. http://www.cdc.gov/niosh/docs/2002-129/pdfs/2002-129.pdf.
- National Toxicology Program . Report on carcinogens 12th ed. U.S. Department of Health and Human Services, Public Health Service. http://ntp.niehs.nih.gov/?objectid=03C9AF75-E1BF-FF40-DBA9EC0928DF8B15
27 comments on “Worker Exposure to Crystalline Silica During Hydraulic Fracturing”
Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this site is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».
In what counties in these States were these 11 sites located?
Thank you for your comment. The NIOSH study regulations that guide our research, 42.CFR 85a.8 (c), limit us from identifying specific places of employment when reporting overall study results from multiple sites. Revealing information at the county level could indirectly reveal the identity of individuals or companies studied.
You also should be aware of a recent NIOSH publication, Dust Control Handbook for Industrial Minerals Mining and Processing, Report of Investigations 9689/2012, NIOSH Pub. No.2012-112. It can be accessed through the following hyperlink: http://www.cdc.gov/niosh/mining/pubs/pubreference/outputid3675.htm. Many of the dust controls identified for the industrial minerals industry potentially could be applied to this industry sector . . . perhaps with some modification.
In a letter dated May 22, the labor organization requested that the Occupational Safety and Health Administration (OSHA), the National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MHSA) begin to work with the industry to implement policies and procedures.
The letter was in reaction to a NIOSH study that determined a hazard existed for fracking workers. The report said that NIOSH “concluded that an inhalation health hazard existed for workers exposed to crystalline silica at the evaluated hydraulic fracturing sites.”
Most silica sand is transported by rail, often in open cars. Does NIOSH have any recommended controls for silica sand being transported in open rail cars?
Thank you for your question. Although we have no specific recommendations for dust control during open rail car transport of silica, there are a number of general recommendations that would apply to reduce emissions from the source (use of covers/tarps) and to protect workers (enclosed cabs).
Thanks for your help, great work here.
The article is vague to the point of being misleading. Did you map the sampling locations and distances from point sources? The article seems to indicate that workers anywhere on the sites were over-exposed. How does the exposure at fracking sites compare with the myriad of other silica generation-use sites such as quarry, playground sand, cement/concrete, diatomaceous earth processing? The statement that personal protection equipment for employees is not sufficient is a regulatory issue requiring engineering controls and is not stated as such. Or do you have exposure evidence showing that employees are overexposed and are at risk while wearing PPE? Who took the data? Usually these data are taken by the site to ensure efficacy/need of control measures.
Thank you for your comment. Since you posed multiple questions I we will address each of your concerns separately.
Q : “Did you map the sampling locations and distances from point sources?”
A: Your question implies that we used fixed point area sampling – we did not. We followed standard industrial hygiene practice and collected the majority of the samples as full-shift personal breathing zone samples (PBZ); collected on workers while they were doing their normal jobs. This gives a time-weighed average measurement of each worker’s actual shift exposure. Workers usually perform functions at different locations during a shift, and that is taken into account in computing the time-weighted average exposure; however the concept of distance from point source is not meaningful with personal sampling as workers are inherently mobile.
Q: “The article seems to indicate that workers anywhere on the sites were over-exposed.”
A: Workers whose jobs were in close proximity to sand handling equipment, such as Sand mover, Transfer belt and Blender operators generally had the highest measurements for respirable dust containing crystalline silica. Sand mover operators and Transfer belt operators frequently exceeded the calculated OSHA PEL as a time weighted average for a given work day.
Q: “How does the exposure at fracking sites compare with the myriad of other silica generation-use sites such as quarry, playground sand, cement/concrete, diatomaceous earth processing?”
A: Because sand used for hydraulic fracturing can contain up to 99% silica, dusts formed during the handling of the product may contain more respirable crystalline silica than other silica generating industries. Certain areas at quarries, diatomaceous earth processing and cement plants may have similar exposure potential if the ore contains crystalline silica and the material is being mechanically ground or fractured. Grinding and breaking up the source material creates the “respirable size” particles that make the dust hazardous. Most mines, quarries and other sites with potential crystalline silica exposures modify processes, use engineering controls, or use other handling methods that reduce worker exposure below occupational exposure limits. Those that do not control dust put their workers at risk and may not be in compliance with regulations. No matter which industry is in question, if the exposure is at or above the exposure limits, controls would be required. Playground sand typically is not hazardous because the particles are too large to become airborne and those that do are filtered by the nose and upper airways and do not reach the lower lung where lung damage occurs. Respirable dust samplers such as those we used would not likely have measured excess exposure from playground sand.
Q: “The statement that personal protection equipment for employees is not sufficient is a regulatory issue requiring engineering controls and is not stated as such. Or do you have exposure evidence showing that employees are overexposed and are at risk while wearing PPE?”
A: Yes, we do have exposure evidence showing that some of the employees we measured were overexposed at levels that exceeded ten times (10x) the occupational exposure limit. You are correct that using the hierarchy of controls, employers should use engineering controls first to reduce exposures before resorting to Personal Protective Equipment (PPE). In our blog, we noted that when exposures exceed 10x the exposure limit that a half-mask respirator does not provide adequate protection. That class of respirator is rated with an Assigned Protection Factor (APF) of 10. That means it is rated to reduce exposure (inside the mask) by a factor of 10. Therefore the Maximum Use Concentration (MUC) is 10x the exposure limit. You are correct that this is a regulatory issue. In 29 CFR 1910.134 (d)(3)(i) (A and B), the regulations define the APFs and MUCs for the various classes of respiratory protection, and define the limitations for their use when exposure limits are exceeded.
Not to go too far off topic, but what of the other chemicals being used in fracking? Are any of their transport/application methods exposing workers unsafely? Hard to find a good source of data but I found [http://pivotupstreamgroup.com/D-FRAC.aspx] and another at [FracFocus.org].
Some of the chemicals being used are certainly not benign. Have there been many independent studies of worker protection for these?
Thank you for your comment. NIOSH has just begun to characterize potential chemical exposures to workers in upstream oil and gas industries. While we have limited knowledge of any specific exposures, we have observed that most handling of chemical additives are specific to certain job titles and are usually short term. Our observations to date indicate that many chemicals arrive in bulk tanks and connections/disconnections to mixing and blending equipment or tanks are done with workers in appropriate personal protective equipment.
Were the workers at the specific sites where NIOSH sampled and found exposure levels exceeding safety limits informed that they had been exposed at these levels? If so, were they informed directly by NIOSH or did NIOSH ask employers to communicate this information? Has any medical follow-up been undertaken for or recommended to workers exposed at these levels, and if so what form did that follow-up take? Since many workers employed by companies that perform these services that involve fracking sand at hydraulic fracturing operations move from site to site as jobs are completed and new wells drilled elsewhere, is any program in place to monitor these workers’ health with regard to silica exposures over the long term – that is, beyond exposure at a single drilling site?
Thank you for your questions,
Q. Were the workers at the specific sites where NIOSH sampled and found exposure levels exceeding safety limits informed that they had been exposed at these levels? If so, were they informed directly by NIOSH or did NIOSH ask employers to communicate this information?
A. NIOSH provided sampling results to the employer in individual site reports by job title, but not by personal identifiers. We requested that the employer communicate these environmental survey findings to the workforce to raise awareness of the silica exposure hazard and the administrative and interim controls necessary to reduce exposure. The site reports provided results of samples whether they were above or below occupational exposure limits and, where applicable, recommendations to reduce or control exposures. Currently, NIOSH policies for individual worker notification cover only communication of future risk as determined from epidemiologic cohort studies. However, NIOSH is currently reviewing its policies and procedures for communicating exposure results to individual workers in all its field investigations, including environmental exposure sampling.
Q. Has any medical follow-up been undertaken for or recommended to workers exposed at these levels, and if so what form did that follow-up take? Since many workers employed by companies that perform these services that involve fracking sand at hydraulic fracturing operations move from site to site as jobs are completed and new wells drilled elsewhere, is any program in place to monitor these workers’ health with regard to silica exposures over the long term – that is, beyond exposure at a single drilling site?
A. The findings reported in the above blog represent the first study to assess worker exposures to respirable silica during hydraulic fracturing and did not include medical monitoring of workers. The site visit reports did not make recommendations regarding medical monitoring. The OSHA-NIOSH Hazard Alert (http://www.osha.gov/dts/hazardalerts/hydraulic_frac_hazard_alert.html) includes information on worker monitoring, respiratory protection, controls, and medical monitoring, including OSHA and NIOSH references detailing what specific monitoring should be conducted.
Thank you for the information about exposure to silica containing dust. I hope your studies are expanded to improve our understanding of the hazards of silica. Other than the use of water for road dust control I was surprised that your recommendations did not include any of the wet suppression methods that are commonly used at quarries and other material handling operations to reduce exposure to airborne dust. I would think that water spray systems, fog fans and a variety of similar technologies could easily be adapted for use at drill sites. Does NIOSH feel that wet suppression systems would not be useful or has their use simply not been investigated?
Thank you for your comment. The sand needs to be kept dry until it enters the wet section of the blender. This is due to the way the machines handle the sand.
Guidelines for Minimizing Respirable Silica Exposure in Hydraulic Fracturing.
Are these guidelines reasonable or will they restrict fracturing as it is now being done?
What will be the effect of these guidelines for Arctic oilfield conditions?
Thank you for your questions.
The recommendations above and also presented in the OSHA-NIOSH Alert (http://www.osha.gov/dts/hazardalerts/hydraulic_frac_hazard_alert.html) vary in complexity and cost. Some control measures are very simple, would not be restrictive, and require no expense. Keeping thief hatches and unused fill-ports closed/capped during filling of sand movers, reducing drop heights or installing chutes from sand coveyors to transfer belts and blenders, and using wet methods to control dust from wind and traffic can reduce exposures at little or no expense. Reducing the number of workers in and around sand moving equipment and locating dust producing equipment downwind of prevalent winds where possible will also reduce the potential for exposure. If workers must work in proximity to equipment that generates respirable dust containing silica, they should be trained, medically cleared and provided with properly fitted NIOSH-approved respirator suitable for exposures encountered. More expensive controls include: replacing or installing shields or stilling curtains on transfer belts and chutes to blenders, installing local dust controls such as the NIOSH prototype baghouse retrofit or a centralized dust collection system. Most of these controls would be effective in most any climate or season.
The Oil and Gas industry, equipment manufacturers, the National STEPS Network, OSHA and NIOSH have formed a focus group to address silica exposures during hydraulic fracturing. This group is developing solutions that range from retrofits and modifications of existing equipment to prevention through design of new equipment so dust emissions are reduced at the source.
Because NIOSH is a part of CDC whose mandate extends to the entire population of the US and in view of the proliferation of fracking, it would seem urgent to assess the level of exposures resulting from fracking not only of industrial workers but also to the public, particularly vulnerable subpopulations such as the very young, very old, and persons medically compromised by pre-existing conditions who live in the proximity of fracking operations.
My specific question is this: what steps are being taken, perhaps in cooperation with other agencies of CDC, to ensure that in parallel to your study, the risks to non-employees living in proximity of fracking operations (particularly densely concentrated fracking operations) are determined? This appears vital since the numbers of such non workers are far larger and their vulnerability to even lower exposures than industry workers might well be substantial because of differences in age distribution and levels of pre-existing illness.
Finally, what is the preferred method of signing up to receive information on your commendable efforts to assess the medical consequences of fracking as well as similar efforts within and outside of the Federal government?
Thank you for your comment and question,
As NIOSH deals specifically with worker safety and health, we asked our colleagues at CDC’s National Center for Environmental Health (NCEH) and CDC’s sister agency, the Agency for Toxic Substances and Disease Registry (ATSDR), to respond to your question.
Jointly managed under one director, NCEH and ATSDR are the primary groups within the Department of Health and Human Services (HHS) working to address community-level exposure and health issues associated with hydraulic fracturing and unconventional gas activities. Working closely with NIOSH and other partners, NCEH/ATSDR is working to better define a framework for research and public health response in the area of unconventional gas activities. Toward this goal, in spring 2012, NCEH/ATSDR and George Washington University brought together experts on environmental health and on hydraulic fracturing in order to identify public health concerns, data gaps, methodologies, and next steps to inform and address these concerns. Additionally, ATSDR is collaborating with EPA on its national study to understand the potential impacts of hydraulic fracturing on drinking water resources (http://www.epa.gov/hfstudy/index.html).
ATSDR has also been requested by EPA and state agencies to evaluate the quality of drinking water and air in several areas where hydraulic fracturing is occurring. So far, ATSDR has examined exposures in six communities. In these evaluations, ATSDR has focused on whether any harmful exposures are occurring, but not whether they may be directly related to unconventional gas activities. ATSDR/NCEH activities related to hydraulic fracturing can be found on the ATSDR website (http://www.atsdr.cdc.gov/), including previously completed health consultations.
Updates on NIOSH efforts to evaluate worker exposure in the hydraulic fracturing industry and other projects in the oil and gas extraction industry can be found on the NIOSH oil and gas extraction program web site (http://www.cdc.gov/niosh/programs/oilgas/).
I want to commend the researchers involved in the studies related to fracking. They have created some excellent resources about a growing industry for which relatively little process specific occupational health information has been available and for which silica hazards may have been underestimated otherwise.
The OEM of the Frac Sanders (Hogs) has a fantastic dust collector that simple mounts on the truck. It is very effective and can be fit onto new equipment as well as existing equipment. The amount of airborne silica particles is virtually eliminated when the collector is used. It is a fantastic technology.
sad no one thinks of the sewer workers who breathe in lots of strange stuff that treatment plants get yet never seems to care for them.
How much of an impact does the length of exposure have on total respirable silica dust levels? In other words, would there be a concern for overexposure for individuals whom visit frac sites for 3-4 hours at a time a few days a week? Also, which job titles had exposures that were below the NIOSH REL for a full-shift workday?
Each exposure to crystalline silica increases your lifetime risk of silicosis and other silica-related diseases. The incremental increase in risk is determined by: (1) the concentration of respirable crystalline silica during the exposure; (2) the duration of exposure during each work shift; and (3) the number of times you are exposed during your lifetime. For some locations on the work sites, an individual could be exposed over the REL in minutes. For example at a location that is 10x the REL, it would take only (480 minutes / 10x) = 48 minutes to exceed the 8-hr time weighted average.
Of the 15 job titles that we sampled 1 or more times, operators in the data van, pump truck operators, QC Tech, sand truck driver, and wireline operator did not have samples above the REL.
Nice article. Hydraulic fracturing began as an experiment in 1947, and the first commercially successful application followed in 1949. As of 2012, 2.5 million hydraulic fracturing operations had been performed worldwide on oil and gas wells; over one million of those within the U.S.
Thanks for sharing!
Thanks for writing about fracking and the problems associated with it. One of the major problems was the security and health issues of the workers working in these environment.
Nice article.Thank you for the information about exposure to silica containing dust and Other than the use of water for road dust control I was surprised that your recommendations did not include any of the wet suppression methods that are commonly used at quarries and other material handling operations to reduce exposure to airborne dust.
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