# Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

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​Foreword
The National Institute for Occupational Safety and Health (NIOSH) is charged with protecting the safety and health of workers through research and training. An area of current concentration is the study of nanotechnology, the science of matter near the atomic scale. Much of the current research focuses on understanding the toxicology of emerging nanomaterials as well as exposure assessment; very little research has been conducted on hazard control for exposures to nanomaterials. As we continue to research the health effects produced by nanomaterials, particularly as new materials and products continue to be introduced, it is prudent to protect workers now from potential adverse health outcomes. Controlling exposures to occupational hazards is the fundamental method of protecting workers. Traditionally, a hierarchy of controls has been used as a means of determining how to implement feasible and effective control solutions.
* Elimination
* Substitution
* Engineering Controls
* Administrative Controls
* Personal Protective Equipment
Following this hierarchy normally leads to the implementation of inherently safer systems, where the risk of illness or injury has been substantially reduced. Engineering controls are favored over administrative and personal protective equipment for controlling existing worker exposures in the workplace because they are designed to remove the hazard at the source, before it comes in contact with the worker. However, evidence of control effectiveness for nanomaterial production and downstream use is scarce. This document is a summary of available technologies that can be used in the nanotechnology industry. While some of these have been evaluated in this industry, others have been shown to be effective at controlling similar processes in other industries. The identification and adoption of control technologies that have been shown effective in other industries is an important first step in reducing worker exposures to engineered nanoparticles. Our hope is that this document will aid in the selection of engineering controls for the fabrication and use of products in the nanotechnology field. As this field continues to expand, it is paramount that the health and safety of workers is protected.
(signature) John Howard, M.D. Director, National Institute for Occupational Safety and Health Centers for Disease Control and Prevention
​Executive Summary
The focus of this document is to identify and describe strategies for the engineering control of worker exposure during the production or use of engineered nanomaterials. Engineered nanomaterials are materials that are intentionally produced and have at least one primary dimension less than 100 nanometers (nm). Nanomaterials may have properties different from those of larger particles of the same material, making them unique and desirable for specific product applications. The consumer products market currently has more than 1,000 nanomaterial-containing products including makeup, sunscreen, food storage products, appliances, clothing, electronics, computers, sporting goods, and coatings. As more nanomaterials are introduced into the workplace and nano-enabled products enter the market, it is essential that producers and users of engineered nanomaterials ensure a safe and healthy work environment.
The toxicity of nanoparticles may be affected by different physicochemical properties, including size, shape, chemistry, surface properties, agglomeration, biopersistence, solubility, and charge, as well as effects from attached functional groups and crystalline structure. The greater surface-area-to-mass ratio of nanoparticles makes them generally more reactive than their macro-sized counterparts. These properties are the same ones that make nanomaterials unique and valuable in manufacturing many products. Though human health effects from exposure have not been reported, a number of laboratory animal studies have been conducted. Pulmonary inflammation has been observed in animals exposed to nano-sized TiO2 and carbon nanotubes (CNTs). Other studies have shown that nanoparticles can translocate to the circulatory system and to the brain causing oxidative stress. Of concern is the finding that certain types of CNTs have shown toxicological response similar to asbestos in mice. These animal study results are examples, and further toxicological studies need to be conducted to establish the potential health effects to humans from acute and chronic exposure to nanomaterials.
Currently, there are no established regulatory occupational exposure limits (OELs) for nanomaterials in the United States; however, other countries have established standards for some nanomaterials, and some companies have supplied OELs for their products. In 2011, NIOSH issued a recommended exposure limit (REL) for ultrafine (nano) titanium dioxide and a draft REL for carbon nanotubes and carbon nanofibers. Because of the lack of regulatory standards and formal recommendations for many nanomaterials in the United States, it is difficult to determine or even estimate a safe exposure level. Many of the basic methods of producing nanomaterials occur in an enclosure or reactor, which may be operated under positive pressure. Exposure can occur due to leakage from the reactor or when a worker’s activities involve direct manipulation of nanomaterials. Batchtype processes involved in the production of nanomaterials include operating reactors, mixing, drying, and thermal treatment. Exposure-causing activities at production plants and laboratories employing nanomaterials include harvesting (e.g., scraping materials out of reactors), bagging, packaging, and reactor cleaning. Downstream activities that may release nanomaterials include bag dumping, manual transfer between processes, mixing or compounding, powder sifting, and machining of parts that contain nanomaterials. ​Hazards involved in manufacturing and processing nanomaterials should be managed as part of a comprehensive occupational safety, health, and environmental management plan. Preliminary hazard assessments (PHAs) are frequently conducted as initial risk assessments to determine whether more sophisticated analytical methods are needed. PHAs are important so that the need for control measures is realized, and the means for risk mitigation can be designed to be part of the operation during the planning stage.
Engineering controls protect workers by removing hazardous conditions or placing a barrier between the worker and the hazard, and, with good safe handling techniques, they are likely to be the most effective control strategy for nanomaterials. The identification and adoption of control technologies that have been shown effective in other industries are important first steps in reducing worker exposures to engineered nanoparticles. Properly designing, using, and evaluating the effectiveness of these controls is a key component in a comprehensive health and safety program. Potential exposure control approaches for commonly used processes include commercial technologies, such as a laboratory fume hood, or techniques adopted from the pharmaceutical industry, such as continuous liner product bagging systems.
The assessment of control effectiveness is essential for verifying that the exposure goals of the facility have been successfully met. Essential control evaluation tools include time-tested techniques, such as airflow visualization and measurement, as well as quantitative containment test methods, including tracer gas testing. Further methods, such as video exposure monitoring, provide information on critical task-based exposures, which will help to identify high-exposure activities and help provide the basis for interventions.
​Contents
* Foreword................................................................................................................................................................................................................................................................................................................................................................................................iii
* Executive Summary................................................................................................................................................................................................................................................................................................................................................................................................iv
* List of Figures................................................................................................................................................................................................................................................................................................................................................................................................x
* List of Tables................................................................................................................................................................................................................................................................................................................................................................................................xi
* List of Abbreviations................................................................................................................................................................................................................................................................................................................................................................................................xii
* Acknowledgements................................................................................................................................................................................................................................................................................................................................................................................................xiv
* 1 Introduction................................................................................................................................................................................................................................................................................................................................................................................................1
* 1.1 Background................................................................................................................................................................................................................................................................................................................................................................................................1
* 1.2 Industry Overview................................................................................................................................................................................................................................................................................................................................................................................................3
* 1.3 Occupational Safety and Health Management Systems................................................................................................................................................................................................................................................................................................................................................................................................3
* 1.3.1 Prevention through Design (PtD)................................................................................................................................................................................................................................................................................................................................................................................................6
* 1.3.2 OELs as Applied to Nanotechnology................................................................................................................................................................................................................................................................................................................................................................................................7
* 1.3.3 Control Banding................................................................................................................................................................................................................................................................................................................................................................................................7
* 2 Exposure Control Strategies and the Hierarchy of Controls................................................................................................................................................................................................................................................................................................................................................................................................9
* 2.1 Elimination................................................................................................................................................................................................................................................................................................................................................................................................9
* 2.2 Substitution................................................................................................................................................................................................................................................................................................................................................................................................10
* 2.3 Engineering Controls................................................................................................................................................................................................................................................................................................................................................................................................10
* 2.3.1 Ventilation................................................................................................................................................................................................................................................................................................................................................................................................11
* 2.3.1.1 Local Exhaust Ventilation................................................................................................................................................................................................................................................................................................................................................................................................12
* 2.3.1.2 Air Filtration................................................................................................................................................................................................................................................................................................................................................................................................14
* 2.3.2 Nonventilation Engineering Controls................................................................................................................................................................................................................................................................................................................................................................................................16
* 2.4 Administrative Controls................................................................................................................................................................................................................................................................................................................................................................................................17
* 2.5 Personal Protective Equipment (PPE)................................................................................................................................................................................................................................................................................................................................................................................................18
* 2.5.1 Skin Protection................................................................................................................................................................................................................................................................................................................................................................................................18
* 2.5.2 Respiratory Protection................................................................................................................................................................................................................................................................................................................................................................................................18
* 3 Nanotechnology Processes and Engineering Controls................................................................................................................................................................................................................................................................................................................................................................................................21
* 3.1 Primary Nanotechnology Production and Downstream Processes................................................................................................................................................................................................................................................................................................................................................................................................21
* 3.2 Engineering Control Approaches to Reducing Exposures................................................................................................................................................................................................................................................................................................................................................................................................22
* 3.3 Ventilation and General Considerations................................................................................................................................................................................................................................................................................................................................................................................................24
* 3.4 Exposure Control Technologies for Common Processes................................................................................................................................................................................................................................................................................................................................................................................................25
* 3.4.1 Reactor Operation and Cleanout Processes................................................................................................................................................................................................................................................................................................................................................................................................27
* 3.4.2 Small-scale Weighing and Handling of Nanopowders................................................................................................................................................................................................................................................................................................................................................................................................30
* 3.4.2.1 Fume Hood Enclosures................................................................................................................................................................................................................................................................................................................................................................................................31
* 3.4.2.2 Biological Safety Cabinets................................................................................................................................................................................................................................................................................................................................................................................................33
* 3.4.2.3 Glove Box Isolators................................................................................................................................................................................................................................................................................................................................................................................................34
* 3.4.2.4 Air Curtain Fume Hood................................................................................................................................................................................................................................................................................................................................................................................................35
* 3.4.2.5 Summary................................................................................................................................................................................................................................................................................................................................................................................................36
* 3.4.3 Intermediate and Finishing Processes................................................................................................................................................................................................................................................................................................................................................................................................37
* 3.4.3.1 Product Discharge/Bag Filling................................................................................................................................................................................................................................................................................................................................................................................................38
* 3.4.3.2 Bag Dumping/Emptying................................................................................................................................................................................................................................................................................................................................................................................................41
* 3.4.3.3 Large-scale Material Handling/Packaging................................................................................................................................................................................................................................................................................................................................................................................................43
* 3.4.3.4 Nanocomposite Machining................................................................................................................................................................................................................................................................................................................................................................................................44
* 3.4.3.5 Summary................................................................................................................................................................................................................................................................................................................................................................................................44
* 3.4.4 Maintenance Tasks................................................................................................................................................................................................................................................................................................................................................................................................45
* 3.4.4.1 Filter Change-out—Bag In/Bag Out Systems................................................................................................................................................................................................................................................................................................................................................................................................46
* 3.4.4.2 Spill Cleanup Procedures................................................................................................................................................................................................................................................................................................................................................................................................46
* 4 Control Evaluations................................................................................................................................................................................................................................................................................................................................................................................................47
* 4.1 Approaches to Evaluation................................................................................................................................................................................................................................................................................................................................................................................................47
* 4.1.1 Identification of Emission Sources................................................................................................................................................................................................................................................................................................................................................................................................47
* 4.1.2 Background and Area Monitoring................................................................................................................................................................................................................................................................................................................................................................................................47
* 4.1.3 Air Monitoring and Filter Sampling................................................................................................................................................................................................................................................................................................................................................................................................48
* 4.1.4 Assessment of Air Velocities and Patterns................................................................................................................................................................................................................................................................................................................................................................................................50
* 4.1.5 Facility Sampling and Evaluation Checklist................................................................................................................................................................................................................................................................................................................................................................................................52
* 4.2 Evaluating Sources of Emissions and Exposures to Nanomaterials................................................................................................................................................................................................................................................................................................................................................................................................57
* 4.2.1 Direct-reading Monitoring................................................................................................................................................................................................................................................................................................................................................................................................57
* 4.2.2 Off-line Analysis................................................................................................................................................................................................................................................................................................................................................................................................58
* 4.2.3 Video Exposure Monitoring................................................................................................................................................................................................................................................................................................................................................................................................58
* 4.3 Evaluating Ventilation Control Systems................................................................................................................................................................................................................................................................................................................................................................................................59
* 4.3.1 Standard Containment Test Methods for Ventilated Enclosures................................................................................................................................................................................................................................................................................................................................................................................................59
* 5 Conclusions and Recommendations................................................................................................................................................................................................................................................................................................................................................................................................61
* 5.1 General................................................................................................................................................................................................................................................................................................................................................................................................61
* 5.2 Control Banding................................................................................................................................................................................................................................................................................................................................................................................................61
* 5.3 Hierarchy of Controls................................................................................................................................................................................................................................................................................................................................................................................................62
* 5.4 Engineering Controls................................................................................................................................................................................................................................................................................................................................................................................................62
* 5.5 Administrative Controls................................................................................................................................................................................................................................................................................................................................................................................................62
* 5.6 Personal Protective Equipment................................................................................................................................................................................................................................................................................................................................................................................................63
* References................................................................................................................................................................................................................................................................................................................................................................................................65
* Appendix A: Sources for Risk Management Guidance................................................................................................................................................................................................................................................................................................................................................................................................75
* Appendix B: Sources of Guidance for Control Design................................................................................................................................................................................................................................................................................................................................................................................................77
​List of Figures
Figure 1. Atomic structure of a spherical fullerene
Figure 2. How control measures are incorporated into an occupational safety and health management system
Figure 3. Worker reaching into drum
Figure 4. Graphical representation of the hierarchy of controls
Figure 5. Four primary filter collection mechanisms
Figure 6. Collection efficiency curve: fractional collection efficiency versus particle diameter for a typical filter
Figure 7. A large-scale ventilated reactor enclosure used to contain production furnaces to mitigate particle emissions in the workplace
Figure 8. A canopy hood used to control emissions from hot processes
Figure 9. Schematic illustration of how wakes caused by the human body can transport air contaminants into the worker's breathing zone
Figure 10. Nano containment hood adapted from a pharmaceutical balance enclosure
Figure 11. A tabletop model of a Class II, Type A2 biological safety cabinet (BSC)
Figure 12. A glove box isolator for handling substances that require a high level of containment
Figure 13. Air curtain safety cabinet hood that uses push-pull ventilation
Figure 14. Ventilated collar-type exhaust hoods for containing dust during product discharge or manual bag filling
Figure 15. An inflatable seal is used to contain nanopowders/dusts as they are discharged from a process such as spray drying
Figure 16. A continuous liner product off-loading system that uses a continuous feed of bag liners fitted to the process outlet to isolate and contain process emissions and product
Figure 17. A ventilated bag-dumping station that reduces dust emissions during the emptying of product from bags into a process hopper
Figure 18. A laminar downflow booth for handling large quantities of powders
Figure 19. Bag in/bag out procedures. This photo shows the removal of a dirty air filter from a ventilation unit into a plastic bag to minimize worker exposure to particles captured by the filter unit
Figure 20. Operating principle of a Pitot tube (left) and different types of Pitot tubes (right)
Figure 21. Smoke generator to visualize airflow
​List of Tables
Table 1. Potential sources of emission from production and downstream processes
Table 2. Process/tasks and emission
Table 3. Summary of instruments and techniques for monitoring nanoparticle emissions in nanomanufacturing workplaces
Table 4. Checklist of controls for nanomaterial manufacturing and handling
Table 5. Comparison of the fume hood performance test methods
​List of Abbreviations
| ACGIH | American Conference of Governmental Industrial Hygienists |
| ANSI | American National Standards Institute |
| AIHA | American Industrial Hygiene Association |
| APF | assigned protection factor |
| ASHRAE | American Society of Heating, Refrigerating, and Air Conditioning Engineers |
| BSC | biological safety cabinet |
| BSI | British Standards Institute |
| CAV | constant air volume |
| CDC | Centers for Disease Control and Prevention |
| CFM | cubic feet per minute |
| CNF | carbon nanofiber |
| CNT | carbon nanotube |
| CPC | condensation particle counter |
| CVD | chemical vapor deposition |
| DMPS | differential mobility particle sizer |
| ELPI | electrical low pressure impactor |
| EPA | Environmental Protection Agency |
| FFR | filtering facepiece respirator |
| FMPS | fast mobility particle sizer |
| FPM | feet per minute |
| HEPA | high efficiency particulate air |
| HSE | Health and Safety Executive |
| IH | industrial hygiene |
| kg | kilogram |
| lbs | pounds |
| LEV | local exhaust ventilation |
| MPPS | most penetrating particle size |
| LPM | liters per minute |
| MSDS | Material safety data sheet |
| MUC | Maximum use concentration |
| NIOSH | National Institute for Occupational Safety and Health |
| nm | nanometer |
| OEL | occupational exposure limit |
| PEL | permissible exposure limit ​ |
| PHA | preliminary hazard assessment |
| PPE | personal protective equipment |
| PM | preventive maintenance |
| PtD | prevention through design |
| R&D | research and development |
| REL | recommended exposure limit |
| SMACNA | Sheet Metal and Air Conditioning Contractors’ National Association |
| SMPS | scanning mobility particle sizer |
| SOP | standard operating procedures |
| TEM | transmission electron microscopy |
| TEOM | tapered element oscillating microbalance |
| TLV® | threshold limit value |
| TWA | time-weighted average |
| VAV | variable air volume |
| VEM | video exposure monitoring |
| wg | water gauge |
| µg | microgram |
| µm | micrometer |
​Acknowledgments
This document was developed by the NIOSH Division of Applied Research and Technology (DART), Gregory Lotz, PhD, Director. Jennifer L. Topmiller, MS, was the project officer for this document, assisted in great part by Kevin H. Dunn, ScD, CIH. Other members of DART instrumental in the production of this document include Scott Earnest, PhD, PE, CSP; Liming Lo, PhD; Ron Hall, MS, CIH, CSP; Mike Gressel, PhD, CSP; Alan Echt, DrPh, CIH; and William Heitbrink, PhD, CIH (contractor). Elizabeth Fryer also provided writing and editing support in the initial stages.
The authors gratefully acknowledge the contributions of the following NIOSH personnel who assisted with the technical content and review of the document.
Division of Respiratory Disease Studies
Stephen B. Martin, Jr., MS, PE
Education and Information Division Charles Geraci, PhD, CIH
Laura Hodson, MSPH, CIH
Health Effects Laboratory Division
Bean T. Chen, PhD
National Personal Protective Technology Laboratory
Pengfei Gao, PhD, CIH
Office of the Director
Paul Middendorf, PhD, CIH
The authors also wish to thank Cathy Rotunda, EdD, Brenda J. Jones, and Vanessa Williams for their assistance with editing and layout for this report. Cover photographs are courtesy of Quantum Sphere, Inc. and Bon-ki Ku, PhD, of NIOSH.
Special appreciation is expressed to the following who served as independent, external reviewers. Their input contributed greatly to the improvement of this document. Keith Swain, DuPont, Wilmington, Delaware
Richard Prodans, CIH, CSP, Abbott, Abbott Park, Illinois
John Weaver, Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana
Gurumurthy Ramachandran, PhD, CIH, University of Minnesota, Minneapolis, Minnesota
Phil Demokritou, PhD, Harvard University, Boston, Massachusetts
This work is a work of the National Institute for Occupational Safety and Health, part of the Centers for Disease Control and Prevention in the United States Department of Health and Human Services, taken or made as part of an employee's official duties. As a work of the U.S. federal government, it is in the public domain.
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