CURRENT STRATEGIES FOR ENGINEERING CONTROLS IN

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Nanomaterial Production and 

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

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Suggested Citation

NIOSH [2013]. Current strategies for engineering controls in nanomaterial production and 

downstream handling processes. Cincinnati, OH: U.S. Department of Health and Human 

Services, Centers for Disease Control and Prevention, National Institute for Occupational 

Safety and Health, DHHS (NIOSH) Publication No. 2014–102.

DHHS (NIOSH) Publication No. 2014–102

November 2013
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes iii 

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.

John Howard, M.D.

Director, National Institute for 

 Occupational Safety and Health

Centers for Disease Control and Prevention 
iv Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

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

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.
This page left intentionally blank
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes vii 

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

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

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

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

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

List of Abbreviations

ACGIH American Conference of Governmental Industrial Hygienists

AIHA American Industrial Hygiene Association

ANSI American National Standards Institute

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

LPM liters per minute

MPPS most penetrating particle size

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

PHA preliminary hazard assessment

PM preventive maintenance

PPE personal protective equipment

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

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, MS, 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
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 1 

CHAPTER 1

Introduction

The number of commercial applications of nanomaterials is growing at a tremendous rate. As 

this rapid growth continues, it is essential that producers and users of nanomaterials ensure 

a safe and healthy work environment for employees who may be exposed to these materials. 

Unfortunately, because nanotechnology is so new, we do not know or fully understand how 

occupational exposures to these agents may affect the health and safety of workers or even 

what levels of exposure may be acceptable. Given our current knowledge in this field, it is 

important to take precautions to minimize exposures and protect safety and health. 

This document discusses approaches and strategies to protect workers from potentially 

harmful exposures during nanomaterial manufacturing, use, and handling processes. Its 

purpose is to provide the best available current knowledge of how workers may be exposed 

and provide guidance on exposure control and evaluation. It is intended to be used as a 

reference by plant managers and owners who are responsible for making decisions regarding 

capital allocations, as well as health and safety professionals, engineers, and industrial 

hygienists who are specifically charged with protecting worker health in this new and 

growing field. Because little has been published on exposure controls in the production and 

use of nanomaterials, this document focuses on applications that have relevance to the field 

of nanotechnology and on engineering control technologies currently used, and known to 

be effective, in other industries. This document also addresses other approaches to worker 

protection, such as the use of administrative controls and personal protective equipment. 

1.1 Background

Nanotechnology is the manipulation of matter at the atomic scale to create materials, devices, 

or systems with new properties and/or functions. Around the world, the introduction of 

nanotechnology promises great societal benefits across many economic sectors: energy, healthcare, 

industry, communications, agriculture, consumer products, and others [Sellers et al. 2009]. 

Some nanoparticles are natural, as in sea salt or pine tree pollen, or are incidentally produced, 

as in volcanic explosions or diesel engine emissions. The focus of this document is engineered 

nanomaterials, those materials deliberately engineered and manufactured to have certain 

properties and have at least one primary dimension of less than 100 nanometers (nm). 

Nanomaterials have properties different from those of their bulk components. For example, 

many of these materials have increased strength/weight ratios, enhanced conductivities, 

and improved optical or magnetic properties. These new properties make nanomaterial 

development so exciting and are the reason they hold the promise of great economic potential. 

Nanomaterials are often classified by their physicochemical characteristics or structure. The 

four classes of materials of which nanoparticles are typically composed include elemental 

carbon, carbon compounds, metals or metal oxides, and ceramics. The nanometer form 

of metals, such as gold, and metal oxides, such as titanium dioxide, are the most common 
2 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

engineered nanomaterials being produced and used [Sellers et al. 2009]. Nano-sized silica, 

silver, and natural clays are also common materials in use. The carbon nanotube is a unique 

nanomaterial being investigated for a wide range of applications. These tubes are cylinders 

constructed of rolled-up graphene sheets. Another interesting carbon structure is a fullerene 

(also known as a Bucky Ball). These are spherical particles usually constructed from 60 

carbon atoms arranged as 20 hexagons and 12 pentagons. As shown in Figure 1, the structure 

resembles a geodesic dome (designed by architect Buckminster Fuller, hence the name). 

Nanomaterials are widely used across industries and products, and they may be present in 

many forms. 

Significant international health and safety research and guidance concerning the handling 

of nanomaterials is underway to support risk management of commercial developments. 

Both risks and rewards are inherent in these new materials. Scientists around the world are 

conducting toxicological studies on these nanomaterials, and initial findings are concerning. 

Animals exposed to titanium dioxide (TiO2) and carbon nanotubes (CNTs) have displayed 

pulmonary inflammation [Chou et al. 2008; Rossi et al. 2010; Shvedova et al. 2005]. Other 

studies have shown that nanoparticles can translocate to the circulatory system and to the 

brain and cause oxidative stress [Elder et al. 2006; Wang et al. 2008]. Perhaps the most 

troubling finding is that CNTs can cause asbestos-like pathology in mice [Poland et al. 2008; 

Takagi et al. 2008].

Figure 1. Atomic structure of a spherical fullerene
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 3 

1.2 Industry Overview

In March 2006, the Woodrow Wilson International Center for Scholars created an inventory 

of 212 consumer products or product lines that incorporate nanomaterials (http://www.

nanotechproject.org/inventories /consumer/analysis_draft/). These products were broken 

down into eight categories using a publically available consumer product classification 

system. As of March 2011, the number of consumer products has increased by 521% (212 to 

1,317 nano-enabled products) with products coming from more than 24 nations [WWICS 

2011]. These products include acne lotions, antimicrobial treatment for socks, sunscreens, 

food supplements, components for computer hardware (such as processors and video cards), 

appliance components, coatings, and hockey sticks. Of the current 1,317 nano-enabled 

products, the largest product category with 738 products was health and fitness. The most 

common type of nanomaterial used in these products was silver (313 products), followed by 

carbon (91 products) and titanium dioxide (59 products).

Roco [2005] reports that worldwide, the investment in nanotechnology has increased 

from $432 million in 1997 to about $4.1 billion in 2005. In this same time period, the U.S. 

government investment in nanotechnology has increased to nearly $1.1 billion. Estimates 

made in 2000 suggested that $1 trillion in products will use nanotechnology in some way by 

2015. The National Science Foundation estimates that the number of workers in this industry 

will increase to 2 million worldwide by 2015. 

Currently, most production facilities are relatively small, with lab, bench, or, at most, 

pilot plant operations [Genaidy et al. 2009]. This is also indicative of downstream users 

(applications and product development). As new manufacturing processes and technologies 

are developed and introduced, novel materials with unknown toxicological properties will 

require effective risk management approaches. As more of these products enter the market, 

concern about the health and safety of the workers grows. 

1.3 Occupational Safety and Health Management Systems

Control measures for nanoparticles, dusts, and other hazards should be implemented 

within the context of a comprehensive occupational safety and health management system 

[ANSI/AIHA 2012]. The critical elements of an effective occupational safety and health 

management system include management commitment and employee involvement, worksite 

analysis, hazard prevention and control, and sufficient training for employees, supervisors, 

and managers (www.osha.gov/Publications/safety-health-management-systems.pdf). In 

developing measures to control occupational exposure to nanomaterials, it is important to 

remember that processing and manufacturing involve a wide range of hazards. Conducting 

a preliminary hazard assessment (PHA) encompasses a qualitative life cycle analysis of an 

entire operation, appropriate to the stage of development:

▪ Chemicals/materials being used in the process

▪ Production methods used during each stage of production

▪ Process equipment and engineering controls employed

▪ Worker’s approach to performing job duties
4 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

▪ Exposure potential to the nanomaterials from the task/operations

▪ The facility that houses the operation

The steps taken to perform PHAs for specific operations should be documented to let 

others know what was done and to help others understand what works. PHAs are frequently 

conducted as initial risk assessments to determine whether more sophisticated analytical 

methods are needed and to prepare an inventory of hazards and control measures needed for 

these hazards. One or two individuals with a health and safety background and knowledge of 

the process can perform PHAs. As part of the assessment, the health and safety professional 

should evaluate the magnitude of the emissions (or potential emissions) and the effects of 

exposure to these emissions. PHAs are an important first step toward developing control 

measures that can be considered during the planning stage. Essentially, hazard control 

should be an integral component of facility, process, and equipment design and construction. 

This includes design for inherent process safety. The use of engineering controls should be 

considered as part of a comprehensive control strategy for hazards associated with processes/

tasks that cannot be effectively eliminated, substituted for, or contained through process 

equipment modifications. 

The standards for an occupational health and safety management system, as outlined in 

ANSI/AIHA Z10 [ANSI/AIHA 2012] and BSI 18001 [BSI 2007c], promote a continuous 

improvement cycle (plan, do, check, act), which does not have an exit point and is the basis 

for worksite analysis. Figure 2 illustrates how control measures are incorporated into an 

occupational safety and health management system. The continuous improvement loop is 

applicable to all hazards in a process/facility (e.g., airborne contaminant exposures, ergonomic, 

combustible dusts, fire safety, and physical hazards). The hazard assessment should be 

reviewed during each cycle described by Figure 2 and periodically updated when major 

changes occur. Although the optimal time to undertake a PHA is during the design stage, 

hazard assessments can also be done during the operation of a facility and have the benefit of 

using existing data.

After the PHA is complete, the nanomaterial risk management plan is designed to avoid 

or minimize hazards discovered during the assessment. The following options should be 

considered:

▪ Automated product transfer between operations—a process that allows for continuous 

process flow to avoid exposures caused by workers handling powdered or vaporous 

materials.

▪ Closed-system handling of powdered or vaporous materials, such as screw feeding or 

pneumatic conveying. 

▪ Local exhaust ventilation. Steps should be taken to avoid having positive pressure 

ducts in work spaces because leakage from ducts can cause exposures. Ducts or pipes 

should be connected using flanges with gaskets that prevent leakage. 

▪ Continuous bagging for the intermediate output from various processes and for 

final products. A process discharges material into a continuous bag that is sealed 

to eliminate dust exposures caused by powder handling. Bags are heat sealed after 

loading. 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 5 

Figure 3. Worker reaching into drum 

▪ Minimizing the container size for manual material handling. Minimizing the size of 

the container or using a long-handled tool is recommended so that the worker does 

not place his breathing zone inside the container (as shown in Figure 3). NIOSH 

recommends a maximum container depth of 25 inches [NIOSH 1997]. If large 

containers are required, engineering controls to provide a barrier between the container 

and the breathing zone of the worker are recommended.

Figure 2. How control measures are selected, implemented, and managed into an occupational safety 

and health management system. (adopted from [ANSI 2005])

Photo by NIOSH
6 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Many good resources are available on the occupational safety and health risk management 

of nanomaterials. Comprehensive documents have been produced by a number of 

organizations. Some of these are listed in Appendix A.

1.3.1 Prevention through Design (PtD)

The concept of Prevention through Design (PtD) is to design out or minimize hazards, 

preferably, early in the design process. PtD is also called inherent or intrinsic safety, safety 

by design, design for safety, and safe design. When PtD is implemented, the control 

hierarchy is applied by designers (e.g., engineers, architects, industrial designers) and 

business leaders (e.g., owners, purchasers, managers) who consider the benefits of designing 

safety into things external to the worker to prevent work-related injuries and illnesses. 

PtD strategies, like the hierarchy of controls, can take many forms. Elimination and 

substitution measures are desirable, but these strategies may be difficult to implement 

when working with nanomaterials because these materials are likely being used for their 

unique properties. The pharmaceutical industry has addressed some of these challenges 

since their products must be contained rather than removed or eliminated from the process. 

They have adopted a containment hierarchy of controls that addresses designing inherent 

safety into the process [Brock 2009]. The initial levels of containment include elimination 

and substitution as well as product, process, and equipment modifications. Only after 

efforts have been made to design the process to reduce potential emissions sources should 

engineering controls be considered. 

Other PtD strategies can be considered: 

▪ Limiting process inventories by producing the nanomaterials as they are consumed 

in the process.

▪ Operating a process at a lower energy state (e.g., lower temperature or pressure), 

which typically results in lower fugitive emissions and therefore safer operation.

▪ Using fail-safe devices where possible. Fail-safe devices are designed so that if they 

fail, the system reverts to a safer condition. An example of a fail-safe device is a 

valve controlling a reagent for a reaction. If the safe condition for the system is for 

this valve to be closed, the fail-safe valve would automatically close in the event of a 

failure.

▪ Installing a closed transport system to eliminate worker exposures during transport 

activities.

PtD strategies typically do not include administrative controls and personal protective 

equipment (PPE) as the primary controls. These measures require worker interaction with 

the process or active steps to limit the extent of the hazard. Most effective PtD approaches 

reduce or eliminate hazardous conditions without relying on input from workers. Humans 

are generally recognized as being much less reliable than most machines, particularly in 

emergencies [Kletz 2001]. The use of administrative controls and PPE in PtD strategies is 

generally for redundancy—further safeguards should the primary control fail.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 7 

The ideal time to develop a PtD strategy is during the development phase of a process, material, 

or facility. As the nanotechnology field is still in its relative infancy, there are numerous 

opportunities to implement PtD in the early stages. The manner in which these materials are 

handled and processed can largely affect the overall safety of the process, and the health and 

safety of workers may be significantly improved through the implementation of a PtD strategy.

1.3.2 OELs as Applied to Nanotechnology

Occupational exposure limits (OELs) are useful in reducing work-related health risks by 

providing a quantitative guideline and basis to assess the worker exposure potential and the 

performance of engineering controls and other risk management approaches. Currently, 

no regulatory standards for nanomaterials have been established in the United States. 

However, NIOSH has recently published two current intelligence bulletins (CIBs) regarding 

occupational exposures to nanomaterials. In a CIB on titanium dioxide (TiO2), NIOSH 

recommends exposure limits of 2.4 mg/m3 for fine TiO2 and 0.3 mg/m3 for ultrafine 

(including engineered nanoscale) TiO2, as time-weighted average (TWA) concentrations for 

up to 10 hours per day during a 40-hour work week [NIOSH 2011]. In a CIB on carbon 

nanotubes and nanofibers, NIOSH recommends that worker exposure be limited to no more 

than 1 μg/m3 [NIOSH 2013].

Other countries have established OELs for various nanomaterials. For example, the British 

Standards Institute recommends working exposure limits for nanomaterials based on various 

classifications such as solubility, shape, and potential health concerns as related to larger particles 

of the same substance [BSI 2007b]. Germany’s Institut für Arbeitsschutz der Deutschen 

Gesetzlichen Unfallversicherung, an institute for worker safety, has published similar guidelines 

[IFA 2009]. 

In the absence of governmental or consensus guidance on exposure limits, some manufacturers 

have developed suggested OELs for their products. For example, Bayer has established an 

OEL of 0.05 mg/m3 for Baytubes® (multiwalled CNTs) [Bayer MaterialScience 2010]. For 

Nanocyl CNTs, the no-effect concentration in air was estimated to be 2.5 μg/m3 for an 8-hr/day 

exposure [Nanocyl 2009]. 

Another approach that may be taken when OELs are absent is the ALARA concept, As Low 

As Reasonably Achievable. While ALARA is generally the goal for all occupational exposures, 

this concept is particularly useful when OELs are absent or in the case of contaminants with 

unknown toxicity.

1.3.3 Control Banding

Control banding is a qualitative risk characterization and management strategy, intended to 

protect the safety and health of workers in the absence of chemical and workplace standards. 

Control banding groups workplace risks into hazard bands based on evaluations of hazard 

and exposure information [NIOSH 2009b]. Note that control banding is not intended to be a 

substitute for OELs and does not alleviate the need for environmental monitoring or industrial 

hygiene expertise. 
8 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

To determine the appropriate control scheme, one should consider the characteristics of the 

substance, the potential for exposure, and the hazard associated with the substance. Four main 

control bands, based on an overall risk level, have been developed:

▪ Good industrial hygiene (IH) practice, general ventilation, and good work practices 

▪ Engineering controls including fume hoods or local exhaust ventilation

▪ Containment or process enclosure allowing for limited breaks in containment

▪ Special circumstances requiring expert advice

One basic principle of control banding is the need for a method that will return consistent, 

accurate results even when performed by nonexperts. Other requirements include having a 

user friendly strategy, readily available required information (e.g., material safety data sheet 

[MSDS]), practical guidance on applying the strategy, and worker confidence in the results. 

With the absence of OELs, control banding can be a useful approach in the risk management 

of nanomaterials [Maynard 2007; Schulte et al. 2008; Thomas et al. 2006; Warheit et al. 

2007]. Several control banding tools are available for use with engineered nanomaterials. The 

CB Nanotool, for example, bases the control band for a particular task on the overall risk 

level, which is determined by a matrix that uses severity scores and probability scores [Paik et 

al. 2008]. The severity score is based on the toxicological effects of the nanomaterial, while the 

probability score relates to the potential for employee exposure. The health hazard categories 

for some control banding approaches are based upon the European Union risk phrases, while 

exposure potentials include the volume of the chemical used and the likelihood of airborne 

materials, estimated by the dustiness or volatility of the source compound [Maidment 1998].
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 9 

CHAPTER 2

Exposure Control Strategies and

the Hierarchy of Controls

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 controls. Figure 4 shows one representation of this hierarchy. 

The idea behind the hierarchy of controls is that the control methods at the top of the triangle 

are generally more effective in reducing the risk associated with a hazard than those at the 

bottom. Following the hierarchy normally leads to the implementation of inherently safer 

systems, ones where the risk of illness or injury has been substantially reduced. Designing out 

hazards early in the design process is a basic tenet of PtD. When PtD is implemented, the 

control hierarchy is applied by designers and owners/managers to include safety into the process.

The following sections discuss each element of the hierarchy of controls—elimination, 

substitution, engineering controls, administrative controls, and PPE— and how it may relate 

to nanotechnology. 

2.1 Elimination 

Elimination and substitution are generally most cost effective if implemented when a process 

is in the design or development stage. If done early enough, implementation is simple and, in 

the long run, can result in substantial savings (e.g., cost of protective equipment, first cost and 

operational cost for ventilation system). For an existing process, elimination or substitution 

may require major changes in equipment and/or procedures in order to reduce a hazard.

Figure 4. Graphical representation of the hierarchy of controls
10 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Elimination is the most desirable approach in the hierarchy of controls. As its name implies, 

the idea behind elimination is to remove the hazard. Eliminating hazards is generally 

easiest to accomplish at the design stage, while the material, process, and/or facility is being 

developed. An example of elimination in a process step might be the removal of an incoming 

inspection step for nanomaterials. An incoming inspection that requires opening a package 

containing nanomaterials leads to the potential of aerosolization of those materials and 

therefore a potential hazard to the inspector. Eliminating the inspection step removes the 

hazard, thus creating an inherently safer process. 

2.2 Substitution

Within the hierarchy of controls, the purpose of substitution is to replace one set of 

conditions having a high hazard level with a different set of conditions having a lower hazard 

level. Examples of substitution could include replacing a solvent-based (i.e., flammable) 

material with a water-based material, substituting a highly toxic material for one of lower 

toxicity, or changing a process’s operating conditions so they are less severe (e.g., reduced 

pressure). Substitution of a nanomaterial may be difficult since it was likely introduced for its 

particular properties; however, some substitution may be possible. Substituting a nanomaterial 

slurry for a dry powder version will reduce aerosolization and provide a level of protection for 

workers handling the material. The specific nanomaterial should also be assessed because in 

some cases a less hazardous nanomaterial may provide the desired performance.

2.3 Engineering Controls

Engineering controls protect workers by removing hazardous conditions (e.g., local exhaust 

ventilation that captures and removes airborne emissions) or placing a barrier between the 

worker and the hazard (e.g., isolators and machine guards). Well-designed engineering 

controls can be highly effective in protecting workers and will typically be passive, that is, 

independent of worker interactions. It is important to design engineering controls that do 

not interfere with the productivity and ease of processing for the worker. If engineering 

controls make the operation more difficult, there will be a strong motivation by the operator 

to circumvent these controls. Ideally, engineering controls should make the operation easier 

to perform rather than more difficult. A good mantra in designing engineering controls is 

to “make it easier to do it the safe way.” This also applies to administrative controls that are 

discussed later. 

The initial cost of engineering controls can be higher than administrative controls or personal 

protective equipment (PPE); however, over the long term, operating costs are frequently lower 

and, in some instances, can provide a cost savings in other areas of the process. The major 

benefit of engineering controls over administrative controls or PPE is, however, the inherent 

safety of the worker under a variety of conditions and stress levels. The use of engineering 

controls reduces the potential for worker behavior to impact exposure levels.

Thus, when elimination and substitution are not viable options, the most desirable alternative 

for mitigating occupational hazards is to employ engineering controls. Engineering controls 

are likely the most effective and applicable control strategy for most nanomaterial processes. 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 11 

In most cases, they should be more feasible than elimination or substitution and, given 

the potential toxicity of many nanomaterials, should prove to be more protective than 

administrative controls and PPE.

Engineering controls are divided into two broad categories for discussion below: ventilation 

and nonventilation controls. 

2.3.1 Ventilation

The general concept behind ventilation for controlling occupational exposures to air 

contaminants, including nanomaterials, is to remove contaminated air from the work 

environment. The efficiency of the ventilation system can be affected by its configuration and 

flow volumes of both the air supplied to and the air exhausted from the work space. Effective 

ventilation applies to a wide range of applications including office heating, ventilating, and air 

conditioning (HVAC); infection control in healthcare; and control of emissions in industrial 

processes. Ventilation for occupant comfort, HVAC, is a specialized application of dilution 

ventilation and is not within the scope of this document. Filtration is a topic directly affecting 

ventilation; exhaust air laden with nanomaterials may need to be cleaned before being released 

into the environment. 

General ventilation can be used to achieve several goals for workplace contaminant control. 

A properly designed supply air ventilation system can provide plant ventilation, building 

pressurization, and exhaust air replacement. As new local exhaust hoods are installed in the 

production area, it is important to consider the need for replacement air, the location of the 

hood installation, and the need to rebalance the ventilation system. In general, it is necessary 

to balance the amount of exhausted air with a nearly equal amount of supply air. Without this 

replacement air, uncontrolled drafts will occur at doors, windows, and other openings; doors 

will become difficult to open due to the high pressure difference, and exhaust fan performance 

may degrade. In addition, turbulence created through high pressure differentials can defeat 

the design intent of the ventilation. Placement of the air supply registers in relation to other 

exhaust ventilation systems is important so that they do not negatively impact the desired 

performance. The use of general ventilation for dilution of contaminants being generated in 

the space should be restricted in its use depending on several factors discussed below. 

General ventilation used for dilution of contaminants by its nature is inefficient. One of two 

methods, recirculated air or single-pass air, may be used for this purpose. As the terms imply, 

recirculated air involves the treatment of exhaust air prior to its being returned to the area 

from which it was exhausted. Single-pass air is exhausted to the outside and may or may not 

require treatment prior to discharge. Both of these methods are expensive—the treatment of 

the recirculated air involves both first-cost and operating-cost penalties, while makeup-air 

treatment for single-pass air is inherently costly. 

According to the American Conference of Governmental Industrial Hygienists (ACGIH) 

Industrial Ventilation: A Manual of Recommended Practice for Design (hereafter referred to as 

the Industrial Ventilation Manual), dilution ventilation (i.e., air changes) to control exposure 

should be used only under specific conditions. Dilution ventilation for controlling health 

hazards is restricted by four limiting factors: (1) the quantity of contaminant generated must 
12 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

not be too great or the airflow rate necessary for dilution will be impractical, (2) workers must 

be far enough away from the contaminant source or the evolution of contaminant must be 

in sufficiently low concentrations so that workers will not have an exposure in excess of the 

established threshold limit values (TLV®), (3) the toxicity of the contaminant must be low, 

and (4) the evolution of contaminants must be reasonably uniform [ACGIH 2013]. There are 

several issues with using dilution ventilation to control nanomaterial concentrations, including 

(1) there are no occupational exposure limits (TLVs mentioned above) or health effects data 

for many of the nanomaterials, (2) the toxicology data from some nanomaterials indicate 

that they may be associated with adverse health effects, and (3) it is difficult or impossible 

to calculate proper air change rates for contaminant control due to the variability in most 

operations. Therefore, local exhaust ventilation and good work practices should be used for 

controlling exposure, and air change rates should be based on the heat load requirements, 

general air movement, and comfort needs. 

The use of supply air for maintaining proper pressurization between production and 

nonproduction areas is a reasonable approach to reducing the exposure to nanomaterials 

outside of the immediate work zone. The fugitive emissions from nanomaterial production 

and processing may result in high background concentrations in the production area. When 

adjacent plant areas are nonproduction areas (e.g., office, quality assurance/control labs) 

or production areas where nanomaterials are not used, infiltration of nanoparticles may 

occur and result in the exposure of workers in those areas. Therefore, a negative air pressure 

differential should be maintained in the nanomaterial production area with respect to adjacent 

rooms/areas. This will help reduce the potential migration of airborne nanomaterials and 

exposure to other workers in adjacent rooms or areas. To maintain a slight negative pressure, 

the room supply air volume should be slightly less than the exhaust air. A general guide is 

to set a 5% flow difference between supply and exhaust flow rates but no less than 50 cfm 

[ACGIH 2013]. As with any good engineering control, a real-time monitor of differential 

pressure between areas should be employed, preferably with the control capability to modify 

airflows to maintain the required pressure differential.

2.3.1.1 Local Exhaust Ventilation 

Local exhaust ventilation (LEV) is the application of an exhaust system at or near the 

source of contamination. If properly designed, it will be much more efficient at removing 

contaminants than dilution ventilation, requiring lower exhaust volumes, less make-up 

air, and, in many cases, lower costs. By applying exhaust at the source, contaminants are 

removed before they get into the general work environment. When designing a local 

exhaust ventilation system, it is important to understand the transport mechanisms of the 

contaminants that are to be removed. This will allow the design to use optimal flow rates 

and capture locations, maximizing the contaminant capture while minimizing impact on the 

process and reducing operating costs. LEV typically involves five components [Washington 

State L & I, no date]:

▪ Exhaust hood. Examples include an enclosing hood to contain the contaminant, a 

receiving hood to capture or receive a contaminant that is released at a high velocity 

(e.g., grinding swarf ), or simply an open duct.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 13 

▪ Duct. Transports the contaminant through the exhaust ventilation system.

▪ Air cleaner. Reduces the concentration of the contaminant in the exhaust air stream; 

may or may not be required.

▪ Fan. Moves the air through the exhaust system.

▪ Exhaust stack. Installed where the exhaust system discharges the air.

The exhaust hood captures the contaminant released by the process. It should be designed for 

the specific process being controlled, an important consideration for hot processes and those 

processes generating contaminants at high velocities. In either case, induced air flow (from 

high velocity air streams or rising air from a hot process) can overwhelm an insufficiently 

designed hood and allow contaminants to escape into the work environment. An important 

hood design factor is the capture velocity. This is the velocity of air needed to overcome 

contaminant velocity as well as room air currents. ACGIH Industrial Ventilation Manual

contains a large collection of industrial ventilation hood designs for a wide selection of 

industrial processes [ACGIH 2013]. Though many of these designs have not been tested with 

nanomaterials, most are expected to perform effectively with these materials. An important 

consideration in hood design with nanomaterials is to provide the appropriate flow rates to 

prevent fugitive emissions without causing conditions that will remove nanomaterials from 

the process stream. Because of their very low mass, entrainment of nanomaterials in airflow 

streams occurs much more readily than with higher-mass particles.

Duct systems transport air between the various components of the LEV system. Designing 

duct systems requires balancing several factors. Duct losses caused by friction will increase 

with higher duct velocities, resulting in increased fan requirements and higher energy 

consumption; however, using larger ducts (in an effort to reduce duct velocity) results 

in increased duct purchase costs. A detailed method for designing and sizing LEV duct 

systems is provided by ACGIH [ACGIH 2013]. The choice of duct materials and sealing 

methods is particularly important when dealing with nanomaterials. The duct material 

needs to be impervious to the nanomaterials and suitable for use with nanomaterials having 

increased reactivity. The joints in the ducts should be sealed in such a way as to contain the 

nanomaterials. 

Fans move air throughout the LEV system. Fans need to be sized to ensure adequate air 

flow while overcoming the system pressure drop (i.e., resistance to flow). Pressure drop is 

encountered when air is accelerated, such as within a hood; through ductwork due to frictional 

losses, particularly in fittings such as elbows; and through filters and other air-cleaning devices. 

Fan selection affects not only the control effectiveness of the LEV system but also its energy 

consumption. The fan system and the make-up air conditioning are typically the two greatest 

energy-consuming components of an LEV system. Proper fan selection needs to balance both 

control performance and operating efficiency [ACGIH 2013]. The same leakage and reactivity 

factors mentioned in the section on ductwork apply to fan selection.

Air cleaning is an important component of the LEV system, particularly if the exhaust air 

is returned to the building environment. Air cleaning involves the removal of gases and 

vapors, often with scrubbers and sorbent systems; however, in the case of nanomaterials, 

particulate removal systems will be required to eliminate them from the air stream. Cyclones, 
14 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

scrubbers, and other similar systems can be used to remove larger-sized particles, but smaller, 

nanoparticles will most likely be collected by filtration (see next section, Air Filtration).

2.3.1.2 Air Filtration 

Air filtration removes unwanted particulate from an air stream. Particulate air filters are 

classified as either mechanical or electrostatic filters. Although the two types of filters have 

important performance differences between them, both are fibrous media or membranes and 

are used extensively in HVAC and industrial applications. Efficiency is dependent on several 

factors including fiber diameters, packing density, and material used. A fibrous filter is an 

assembly of fibers that are randomly laid perpendicular to the airflow. The fibers may range 

in size from less than 1 μm to greater than 50 μm in diameter. Filter packing density ranges 

from 1%–30%. Fibers are made from cotton, fiberglass, polyester, polypropylene, or a number 

of other materials [Davies 1977].

Fibrous filters of different designs are used for various applications. Three types are used for 

capturing particulate:

▪ Flat-panel filters contain all the media in the same plane. This design keeps the filter 

face velocity and the filter media velocity roughly the same. 

▪ Pleated filters have additional filter media added to reduce the air velocity through 

the filter. This allows for an increased collection efficiency for a given pressure drop. 

Alternatively, pleated filters can be used to reduce the pressure drop for a given airflow 

velocity because of the larger filter area.

▪ Pocket or baghouse filters allow the flow of exhaust air through small pockets or 

bags consisting of filter media. As with pleated filters, the increased surface area of 

the pocket filter reduces the velocity of the airflow through the filter media, allowing 

increased collection efficiency for small particles at a given pressure drop. 

Figure 5 presents four different collection mechanisms that govern particulate air filter 

performance:

▪ Diffusion is the result of the random (Brownian) motion of a particle. The particle 

may contact a fiber on its path through the filter.

▪ Interception occurs when the radius of a particle moving along an air streamline is 

greater than the distance from the streamline to the surface, thus causing the particle 

surface to contact the surface of the fiber. The particle adheres to the fiber due to 

intermolecular forces. 

▪ Inertial impaction occurs when an air stream bends around a fiber, and a particle 

traveling in that air stream continues in a straight path due to particle inertia. The 

particle collides with the fiber and adheres to it due to intermolecular forces.

▪ Electrostatic attraction occurs when the particle and the fiber are oppositely charged. 

As the force of this attraction is governed by the charge-to-mass ratio of the particle, it 

becomes more effective as particle size decreases. 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 15 

Figure 5. Four primary filter collection mechanisms

Figure 6. Collection efficiency curve, i.e., fractional collection efficiency versus particle diameter for a 

typical filter (Used with permission from Lee and Liu [1980].)

These mechanisms apply mainly to mechanical filters and are influenced by particle size. 

Impaction and interception are the dominant collection mechanisms for particles greater than 

0.2 μm, and diffusion and electrostatic attraction are dominant for particles less than 0.2 μm, 

including nanomaterials. The combined effect of these collection mechanisms results in the 

classic collection efficiency curve, shown in Figure 6.
16 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Research on common air filter materials has shown that fractional efficiency for collection of 

particles of different sizes is consistent with the single fiber theory [Heim et al. 2005; Kim et 

al. 2007; Shin et al. 2008]. Kim et al. [2006] found that humidity has little effect on particle 

collection efficiency. Huang et al. [2007b] determined that the use of electrostatic filters 

(commonly used for respirators) improves particle collection in the 0.1–1-μm particle size range. 

Testing of respirator filters showed that the most penetrating particle size (MPPS) shifted 

from 30–60 nm to 200–300 nm following treatment of respirators by liquid isopropanol, which 

removes electrostatic charges on the filter materials [Rengasamy et al. 2009]. This result suggests 

that capture by electrostatic forces is important for particles in the 250–300-μm range. Overall, 

filters appear to behave in a manner consistent with theoretical predictions that common filter 

materials allow for efficient collection through diffusion of nanoparticles less than about 10 nm 

[Heim et al. 2005; Huang et al. 2007b; Kim et al. 2007; Shin et al. 2008].

Some researchers have found evidence of thermal rebound, which increases particle 

penetration through filters for nanoparticles in the size range of 1–10 nm [Bałazy et al. 2004; 

Kim et al. 2006]; however, several other filter testing studies did not reveal this effect, even at 

higher temperatures [Heim et al. 2005; Huang et al. 2007b; Kim et al. 2007; Shin et al. 2008]. 

The thermal rebound effect is a result of the thermal velocity of the particle exceeding the 

critical sticking velocity for a particle on a filter, allowing the particle to move past the filter 

fiber and penetrate the filter. The critical sticking velocity of an incident particle is defined as 

the maximum impact speed at which the particle will stick to a surface; above this velocity, 

the particle will bounce and not stick to the filter. The primary adhesive forces for nanomatersized particles are the London-van der Waals forces. These forces are caused by random 

movement of electrons creating complementary dipoles between particle and filter material 

[Hinds 1999]. As the particle gets smaller, it is more difficult to remove the particle from 

surfaces.

High efficiency particulate air (HEPA) filtration is commonly used for applications 

requiring reliably high filtration. By definition, HEPA filters are 99.97% efficient at the 

most penetrating particle size of 0.3 microns (Figure 6). These filters are disposable and are 

usually replaced when the pressure drop exceeds a predetermined number, typically 100 mm 

water gauge (wg). When properly sized and installed, HEPA filtration is appropriate for 

nanomaterial applications both for ventilation systems and respiratory protection.

2.3.2 Nonventilation Engineering Controls 

Nonventilation engineering controls cover a range of control measures (e.g., guards 

and barricades, material treatment, or additives). Nonventilation controls can be used 

in conjunction with ventilation measures to provide an enhanced level of protection for 

nanomaterial workers.

A variety of dust control methods have been used and evaluated in many industries and may 

be applicable to the processes used in the manufacturing and processing of nanomaterials 

[Smandych et al. 1998]. These methods include the enclosure of material-conveying 

equipment, such as belt and screw conveyers, as well as the use of pneumatic conveyance 

systems. Other work practices have been used to reduce the aerosolization of dust during bag 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 17 

filling, including minimizing leak paths by securing the bag to the outlet spout and wetting 

the outside of the bag to prevent surface dust from becoming airborne. Research over the 

years in a variety of industrial settings has shown that water spray application is effective 

in lowering respirable dust levels [Mukherjee et al. 1986]. The use of atomization nozzles 

was shown to be one of the most effective water-spray delivery systems in dust knockdown 

performance tests. Water sprays lower respirable dust concentrations by knocking down the 

dust, fibers, and particles, and they also can induce airflow to direct the remaining dust away 

from the workers.

Other nonventilation engineering controls include many devices developed for the 

pharmaceutical industry, including isolation containment systems [Hirst et al. 2002]. One of 

the most common flexible isolation systems is glove box containment, which can be used as 

an enclosure around small-scale powder processes, such as mixing and drying. Rigid glove 

box isolation units also provide a method for isolating the worker from the process and are 

often used for medium-scale operations involving transfer of powders. Glove bags are similar 

to rigid glove boxes, but they are flexible and disposable. They are used for small operations 

for containment or protection from contamination. Another nonventilation control used in 

this industry is the continuous liner system, which allows the filling of product containers 

while enclosing the material in a polypropylene bag. This system is often used for off-loading 

materials when the powders are to be packed into drums.

2.4 Administrative Controls 

Administrative controls and PPE are frequently used with existing processes where hazards 

are not well controlled. This could occur when engineering control measures are not feasible 

or do not reduce exposures to an acceptable level. Administrative controls (which include 

training, job rotation, work scheduling, and other strategies to reduce exposure) and PPE 

programs may be less expensive to establish but, over the long term, can be very costly to 

sustain. These methods for protecting workers have also proven to be less effective than other 

measures and often require significant effort by the affected workers [ACGIH 2013; DiNardi 

2003]. A valuable application of administrative controls is as a redundancy to engineering 

controls. While the engineering controls provide the primary protection for the worker, the 

administrative controls serve as a valuable back-up should the engineering control fail.

NIOSH recommends that facilities implement the following work practices as part of an 

overall strategy to control worker exposure to nanomaterials: (1) Educate workers on the 

safe handling of engineered nanomaterials to minimize the likelihood of inhalation exposure 

and skin contact. (2) Provide information on the hazardous properties of the materials being 

handled with instructions on how to prevent exposure. (3) Encourage workers to use handwashing facilities before eating, smoking, or leaving the worksite. (4) Provide additional 

control measures (e.g., use of a buffer area, decontamination facilities for workers if warranted 

by the hazard) to ensure that engineered nanomaterials are not transported outside of the 

work area. (5) Where there is the potential for area or personnel contamination, provide 

facilities for showering and changing clothes to prevent the inadvertent contamination 

of other areas (including take-home) caused by the transfer of nanomaterials on clothing 

and skin. (6) Avoid handling nanomaterials in the open air in a “free particle” state. (7) 
18 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Store dispersible nanomaterials, whether suspended in liquids or in a dry particle form, in 

closed (tightly sealed) containers whenever possible. (8) Ensure work areas and designated 

equipment (e.g., balance) are cleaned at the end of each work shift, at a minimum, using 

either a HEPA-filtered vacuum cleaner or wet wiping methods (where the use of liquid 

does not create additional safety hazards). Dry sweeping (i.e., using a broom) or compressed 

air should not be used to clean work areas. Cleanup should be conducted in a manner that 

prevents worker contact with wastes. (9) Dispose of all waste material in compliance with 

all applicable federal, state, and local regulations. (10) Avoid storing and consuming food or 

beverages in workplaces where nanomaterials are handled [NIOSH 2009a].

2.5 Personal Protective Equipment (PPE)

PPE (e.g., respirators, gloves, protective clothing) is the least desired option for 

controlling worker exposures to hazardous substances. PPE is used when engineering and 

administrative controls are not feasible or effective in reducing exposures to acceptable 

levels or while controls are being implemented. It is the last line of defense after 

engineering controls, work practices, and administrative controls. A program that addresses 

the hazards present, employee training, and PPE selection, use, and maintenance should be 

in place when PPE is used.

2.5.1 Skin Protection

Nanomaterials have been shown to accumulate in hair follicles, and quantum dots have 

been shown to penetrate the skin into the dermis [Smijs and Bouwstra 2010]. Flexing the 

skin may enhance skin penetration [Smijs and Bouwstra 2010; Tinkle et al. 2003]. Woskie 

[2010] recommends wearing gloves, gauntlets, and laboratory clothing or coats when 

working with nanoparticles. Other studies of specifically engineered nanomaterials have 

resulted in the material not penetrating beyond the stratum corneum. Of importance is to 

establish a barrier between the potentially hazardous material and the skin.

Air-tight polyethylene was found to be more resistant to nanoparticle penetration by 

diffusion than cotton or polyester; gloves made of latex, neoprene, or nitrile resisted 

nanoparticle penetration “during exposure of a few minutes” [Woskie 2010]. Proper 

selection of gloves should take into account the resistance of the glove to the nanomaterial 

and any other chemicals or liquids with which the hands may come into contact. Gloves 

should be changed whenever they show visible signs of wear or contamination. Gao et al. 

[2011] studied nano- and submicron-size (30–500 nm) iron oxide particle penetration 

through some protective clothing materials. They found that particle penetration increased 

with increasing wind velocity and increasing particle size. Results from the study indicated 

that the MPPS for protective clothing materials tested was found to be about 300 to 500 

nm, compared to an MPPS for N-95 respirators of 50 nm.

2.5.2 Respiratory Protection

Respiratory protection is used to reduce worker exposures to acceptable levels in the absence 

of effective engineering controls, during the installation or maintenance of engineering 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 19 

controls, for short-duration tasks that make engineering controls impractical, and during 

emergencies. The decision to use respiratory protection should be based upon professional 

judgment, hazard assessment, and risk management practices to keep worker inhalation 

exposures below an internal control or an exposure limit. Several types of NIOSH-certified 

respirators (e.g., disposable filtering facepiece, half-mask elastomeric, full facepiece, powered, 

airline, self-contained) can provide different levels of expected protection to airborne 

particulate when used in the context of a complete respirator program [60 Fed. Reg. 30336 

(1995); NIOSH 2004]. In a survey designed to better understand health and safety practices 

in the carbonaceous nanomaterial industry, NIOSH found half-mask elastomeric particulate 

respirators fitted with HEPA filtration media to be the most commonly used respiratory 

protection, followed by disposable filtering facepiece respirators [Dahm et al. 2011].

The 2009 NIOSH Approaches to Safe Nanotechnology document as well as the Current 

Intelligence Bulletins on titanium dioxide and carbon nanotubes contains recommendations 

on respirator use and selection when working with nanoparticles. Recommendations from 

other organizations and a discussion of the scientific rationale for respirator selection have 

been reviewed [Shaffer and Rengasamy 2009]. Current respirator performance research 

suggests that NIOSH’s traditional respirator selection tools apply to nanoparticles. 

NIOSH-certified respirators should provide the expected levels of protection, consistent 

with their assigned protection factor, and should be selected according to the NIOSH 

Respirator Selection Logic [NIOSH 2004] by the person who is in charge of the program 

and knowledgeable about the workplace and the limitations associated with each type of 

respirator. As part of the risk assessment process, respirators with 95-, 99-, or 100-class filters 

can be selected for workplaces with concentrations of nanoparticles near their MPPS (50 to 

100 nm). Furthermore, NIOSH recommends that all elements of the OSHA Respiratory 

Protection Standard [29 CFR 1910.134] for both voluntary and required respirator use 

should be followed [63 Fed. Reg. 1152 (1998)].

Selection of respiratory protection for airborne particulate contaminants is typically done by 

dividing the measured or anticipated time-weighted average concentration of the airborne 

contaminant by the OEL and comparing that quotient to the respirator’s assigned protection 

factor (APF). Alternatively, the respirator’s APF can be multiplied by the OEL to find its 

maximum use concentration (MUC). The MUC is then compared to the TWA to select 

the appropriate respirator. In the absence of an OEL for nanoparticles, Woskie [2010] 

recommends that a health and safety professional “familiar with the workplace” choose the 

appropriate respirator based on goals for nanoparticle control, sampling results, and the 

capabilities of each type of respirator.

The NIOSH respirator selection logic recommends (and it is mandated by OSHA where 

the use of respirators is required) that respirators in the workplace be used as part of a 

comprehensive respiratory protection program. The program should include written standard 

operating procedures; workplace monitoring; hazard-based selection; fit-testing and training 

of the user; procedures for cleaning, disinfection, maintenance, and storage of reusable 

respirators; respirator inspection and program evaluation; medical qualification of the user; 

and the use of NIOSH-certified respirators [NIOSH 2004].
20 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Several studies have been conducted of respirator media filtration performance against 

nanoparticles. Many employers provide filtering facepiece respirators (FFRs) due to their 

common availability and low cost. One study of N95 FFRs showed penetration levels 

by nanoparticles in the size range of ~30 to 70 nm, which exceeded the 5% level allowed 

by NIOSH [Balazy et al. 2006]. A later study used two test methods (challenges using a 

monodisperse aerosol and a polydisperse aerosol similar to the NIOSH certification test) and 

compared particle penetration of N-95 FFRs [Rengasamy et al. 2007]. Those authors found 

that a monodisperse aerosol challenge test using particles from 20 nm to 400 nm in diameter 

resulted in a MPPS near 40 nm. The monodisperse test found that two respirators exceeded 

the NIOSH 5% allowed penetration, but the exceedance was not statistically significant, 

while the polydisperse challenge produced penetration levels from 0.61% to 1.24%. The 

NIOSH-allowed penetration level of < 0.03% was not exceeded by P100 FFRs, but two 

nanoparticle test aerosols did exceed 1% penetration for two N99 FFRs [Eninger et al. 2008; 

Rengasamy et al. 2009]. Five models of N95 and two models of P100 FFRs challenged with 

4–30-nm monodisperse aerosols provided approved levels of protection [Rengasamy et al. 

2008]. Rengasamy et al. [2009] tested two models each of N95 and P100 respirators with 

monodisperse aerosols in the 4–30-nm range and the 20–400-nm range. The penetration 

levels were less than the NIOSH-allowed levels of < 5% and < 0.03% across all test methods 

used. The penetration was < 4.28% for the N95 respirators and < 0.009% for the P100 

respirators at the MPPS range of 30–60 nm.

NIOSH-certified FFRs have been shown to provide “expected levels of filtration efficiency 

against polydisperse and monodisperse aerosols > 20 nm in size” [Rengasamy and Eimer 

2011]. A study showed that eight commercially purchased models of NIOSH-approved N95 

and P100 and CE-marked FFR models “provided expected levels of laboratory performance 

against nanoparticles” [Rengasamy et al. 2009]. 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 21 

CHAPTER 3

Nanotechnology Processes and

Engineering Controls

3.1 Primary Nanotechnology Production and

Downstream Processes

Currently, nanomaterials are produced using a variety of methods that provide conditions for 

the formation of desired shapes, sizes, and chemical composition. These production processes 

can be separated into six categories [HSE 2004; NNI, no date]:

▪ Gas phase processes, including flame pyrolysis, high-temperature evaporation, 

and plasma synthesis. This process involves the growth of nanoparticles by 

homogenous nucleation of supersaturated vapor. Nanoparticles are formed in a 

reactor at high temperatures when source material in solid, liquid, or gaseous form 

is injected into the reactor. These precursors are supersaturated by expansion and 

cooled prior to the initiation of nucleated growth. The size and composition of the 

final materials depend on the materials used and process parameters.

▪ Chemical vapor deposition (CVD). This process has been used to deposit thin films 

of silicon on semiconductor wafers. The chemical vapor is formed in a reactor by 

pyrolysis, reduction, oxidation, and nitridation and deposited as a film with the 

nucleation of a few atoms that coalesce into a continuous film. This process has been 

used to produce many nanomaterials including TiO2, zinc oxide, silicon carbide, 

and, possibly most importantly, CNTs. The use of fluidized bed technology has been 

adopted as a way to prepare CNTs on a large scale at low cost [Wang et al. 2002]. 

This technology fluidizes CNT agglomerates and produces high yields necessary for 

larger-scale operations.

▪ Colloidal or liquid phase methods. Chemical reactions in solvents lead to the 

formation of colloids. Solutions of different ions are mixed to produce insoluble 

precipitates. This method is a fairly simple and inexpensive way to produce 

nanoparticles and is often used for the synthesis of metals (e.g., gold, silver). These 

nanomaterials may remain in liquid suspension or may be processed into dry powder 

materials often by spray drying and collection through filtration. 

▪ Mechanical processes including grinding, milling, and alloying. These processes 

create nanomaterials by a “top-down” method that reduces the size of larger bulk 

materials through the application of energy to break materials into smaller and smaller 

particles. This technique has been referred to as nanosizing or ultrafine grinding.

▪ Atomic and molecular beam epitaxy. Atomic layer epitaxy is the process of 

depositing monolayers (i.e., layers one molecule thick) of alternating materials and 

is commonly used in semiconductor fabrication. Molecular beam epitaxy is another 

process for depositing highly controlled crystalline layers onto a substrate.
22 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

▪ Dip pen lithography. A “bottom-up” method is a production process that involves 

depositing a chemical on the surface of a substrate using the tip of an atomic force 

microscope (AFM). The AFM tips are coated with the chemical, which is directly 

deposited on a substrate in a specific pattern.

Downstream processes use engineered nanomaterials for product application and 

development. Examples of these tasks or operations include weighing, dispersion/sonication, 

mixing, compounding/extrusion, electro-spinning, packaging, and maintenance. These 

activities should be evaluated for potential sources of exposure. 

3.2 Engineering Control Approaches to Reducing Exposures

Engineering controls are used to remove a hazard or place a barrier between the worker 

and the hazard, and though costs of engineering controls may be higher than that of 

administrative controls or PPE initially, over the long term, operating costs are often lower. 

A major advantage of engineering controls is that, when properly designed, they require little 

or no user effort or training to be effective. Many industries have implemented engineering 

controls to reduce exposure and risk of disease among their workers. The pharmaceutical 

industry uses hazardous (i.e., biologically active) liquids and powders that often do not have 

OELs. To address these hazards, the pharmaceutical industry has adopted a performancebased strategy using exposure control limits. This approach is based on establishing qualitative 

or semiquantitative criteria for assessing risk associated with the compounds and matching 

that information with known exposure-control approaches [Naumann et al. 1996].

Many of the processes used in pharmaceutical production are similar to those used in the 

nanoparticle industries discussed above and include blending, mixing, and handling of 

hazardous compounds in liquid and powder form. The general control concepts required 

for working with hazardous materials include specification of general ventilation, LEV, 

maintenance, cleaning and disposal, PPE, IH monitoring, and medical surveillance 

[Naumann et al. 1996]. Particular work practices, such as using HEPA-filtered vacuums 

instead of dry sweeping, are required. In addition, routine IH and medical monitoring ensure 

that work practices and engineering controls are effective.

Source containment is considered the highest level in the containment hierarchy and is used 

by the pharmaceutical industry [Brock 2009]. This category contains many options including 

elimination, substitution, product modifications, process modifications, and equipment 

modifications. These steps could include reworking the process to reduce the number of times 

material is transferred or keeping the product in solution to minimize aerosolization potential. 

The next level of control for capturing process emissions is the use of engineering controls 

such as glove boxes, downflow booths, and local exhaust ventilation. 

Genaidy et al. [2009] conducted a detailed hazard analysis of a CNF manufacturing process 

and suggested the following potential sources of workplace exposure to nanomaterials:

▪ Leakage and spillage from reactors and powder processing equipment 

▪ Manually harvesting product from reactors
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 23 

▪ Discharging product into containers

▪ Transporting containers of intermediate products to the next process

▪ Charging the powders into processing equipment

▪ Weighing out powder for shipment

▪ Packaging material for shipment

▪ Storing material between operations

▪ Cleaning equipment to remove debris stuck to side walls 

▪ Changing filters on dust collection systems and vacuum cleaners

▪ Further processing of products containing nanomaterials (e.g., cutting, grinding, 

drilling) 

This detailed analysis, along with the review of exposure assessment studies in nanomaterial 

production and downstream user facilities described below, identify common processes that 

may lead to worker exposure to nanomaterials. This section provides some information on 

engineering control approaches that may be applicable for these common processes/tasks. 

Table 1 shows a generic process list along with applicable engineering controls and references. 

The engineering control column provides a framework for identifying exposure controls for 

particular processes. The third column shows the industry in which these control approaches 

have been tested. References are listed in the fourth column for studies that apply to each of 

these processes and controls. 
24 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Table 1. Engineering controls and associated tasks for various industries

Process/task Engineering control Industry Reference

Reactor fugitive 

emissions

Enclosure Nanotechnology Tsai et al. 2009b 

Lee et al. 2011

Product harvesting Glovebox Nanotechnology Yeganeh et al. 2008

Reactor cleaning Spot LEV system/fume 

extractor

Nanotechnology Methner 2008

Small-scale weighing Chemical fume hood Nanotechnology Tsai et al. 2009a

Ahn et al. 2008

Tsai et al. 2010

Biological safety cabinet Nanotechnology and 

laboratory

Cena and Peters 2011

Macher and First 1984

Glovebox isolator Pharmaceutical Walker 2002

Hirst et al. 2002

Nano fume hood Pharmaceutical

Air curtain isolation hood Nanotechnology/research Tsai et al. 2010

Product discharge/

bag filling

Discharge/collar hood Silica and pharmaceutical ACGIH 2013

HSE 2003e

Hirst et al. 2002

Continuous liner Pharmaceutical Hirst et al. 2002

Inflatable seal Pharmaceutical Hirst et al. 2002

Bag/container 

emptying

Bag dump station Silica HSE 2003d

Heitbrink and McKinnery 1986

Cecala et al. 1988

Large-scale weighing/

handling

Ventilated booth Pharmaceutical Hirst et al. 2002

Floura and Kremer 2008

HSE 2003b

Nanocomposite 

machining

High velocity-low volume Woodworking

Wet suppression Nanotechnology Bello et al. 2009

Air filter change-out Bag in-bag out Pharmaceutical 

3.3 Ventilation and General Considerations

It is important to confirm that the LEV system is operating as designed by regularly measuring exhaust 

airflows. A standard measurement - hood static pressure - provides important information on the 

hood performance, because any change in airflow results in a change in hood static pressure. For hoods 

designed to prevent exposures to hazardous airborne contaminants, the ACGIH Industrial Ventilation: 

A Manual of Recommended Practice for Operation and Maintenance recommends the installation of a 

fixed hood static pressure gauge [ACGIH 2010]. 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 25 

In addition to routinely monitoring the hood static pressure, additional system checks 

should be completed periodically to ensure adequate system performance, including smoke 

tube testing, hood slot/face velocity measurements, and duct velocity measurements using 

an anemometer. A dry ice test is another method of evaluation designed to qualitatively 

determine the containment performance of fume hoods. These system evaluation tasks should 

become part of a routine preventative maintenance schedule to check system performance. 

It is important to note that the collection and release of air contaminants may be regulated; 

companies should contact agencies responsible for local air pollution control to ensure 

compliance with emissions requirements when implementing new or revised engineering 

controls. To reduce the risk of exposure to nanomaterials, a few standard precautions should 

be followed in areas where exposures may occur:

▪ Isolate rooms where nanomaterials are handled from the rest of the plant with walls, 

doors, or other barriers.

▪ Maintain production areas where nanomaterials are being produced or handled under 

negative air pressure relative to the rest of the plant.

▪ Install hood static pressure gauges (manometers) near hoods to provide a way to verify 

proper hood performance.

▪ When possible, place hoods away from doors, windows, air supply registers, and aisles 

to reduce the impact of cross drafts.

▪ Provide supply air to production rooms to replace most of the exhausted air.

▪ Direct exhaust air discharge stacks away from air intakes, doors, and windows. 

Consider environmental conditions, especially prevailing winds.

3.4 Exposure Control Technologies for Common Processes

In a review of exposure assessments conducted at nanotechnology plants and laboratories, 

Brouwer [2010] determined that activities that resulted in exposures included 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. Particle concentrations during production activities ranged from about 

103–105 particles/cm3. Most studies showed bimodal particle distributions with modes of 

about 200–400 nm and 1,000–20,000 nm, indicating that the emissions are dominated by 

aggregates and agglomerates. With the exception of leakage from reactors when primary 

manufactured nanoparticles may be released, workers are believed to be primarily exposed to 

agglomerates and aggregates. 

Methner et al. [2010] summarized the findings of exposure assessments conducted in 12 

facilities with a variety of operations: seven were R&D labs, one produced CNTs, one 

produced nanoscale TiO2, one produced nanoscale metals and metal oxides, one produced 

silica-iron nanomaterials, and one manufactured nylon nanofibers. The most common 

processes observed at these facilities were weighing, mixing, collecting product, manual 

transfer of product, cleaning operations, drying, spraying, chopping, and sonicating. 
26 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Engineering controls used included portable vacuums with filters, laboratory fume hoods, 

portable LEV systems, ventilated walk-in enclosures, negative pressure rooms, and glove 

boxes. Tasks such as weighing, sonicating, and cleaning reactors showed evidence of 

nanomaterial emissions. The highest nanoparticle exposures measured occurred inside spray 

booth-type enclosures and during a spray dryer collection drum change-out. Other activities 

that resulted in higher exposures include reactor cleanout tasks (e.g., brushing and scraping 

slag material). Incidental (nonprocess) ultrafines were measured from a variety of sources, 

including electric arc welding, operating a propane-powered forklift, and the exhaust of a 

portable vacuum outfitted with filters. 

From a review of published studies, some common sources of nanoparticles and fine particles 

can be identified. As expected, those processes that require material handling resulted in worker 

exposure to nanomaterials. Other activities that require operator interface with the reactor 

can result in nanoparticle exposure, and background concentrations may increase as a result of 

leakage from reactors under positive pressure. In addition, several studies found that evaluation 

of process emissions and exposure should take into account major sources of incidental 

nanoparticles that may be present in the workplace and also sources of natural nanoparticles, 

e.g., tree pollen brought into the work area through the facility HVAC system. Common 

incidental sources include diesel exhausts in outdoor air, welding fumes, forklifts, and gasfired heaters. Several studies showed that the use of engineering controls can reduce operator 

exposure, while one study showed that a poorly designed enclosure actually increased exposure 

[Cena and Peters 2011; Methner et al. 2007; Tsai et al. 2009a, 2010; Yeganeh et al. 2008]. 

The following sections describe applicable engineering controls for common processes used by 

nanotechnology companies described in the literature. For each control, a background is given 

along with a summary of relevant research conducted on their performance. Many of the 

control concepts discussed in this section come from the HSE Control Guidance Sheets in 

COSHH Essentials: Easy Steps to Control Chemicals [HSE 2003a,b,c,d] and the ACGIH 

Industrial Ventilation Manual [ACGIH 2013]. Table 2 lists common processes and tasks, 

along with potential emission points and the section or figure(s) that address those processes.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 27 

3.4.1 Reactor Operation and Cleanout Processes

Harvesting material from reactors has been identified as a potentially high exposure 

activity in several manufacturing plants [Demou et al. 2008; Lee et al. 2010, 2011; Methner 

2008; Yeganeh et al. 2008]. In addition, cleanout of reactors has contributed to increasing 

facility concentrations and exposures to operation and maintenance workers. Leakage from 

pressurized reactors can also contribute to background concentrations and result in exposure 

to employees throughout the facility. When the reactors are small, some facilities have placed 

them inside fume hoods to help control fugitive emissions. Two studies have shown that when 

the reactor is housed in a well-designed and operated fume hood, particle loss to the work 

environment is low [Tsai et al. 2009b; Yeganeh et al. 2008]. When the reactors are larger, 

enclosures can be built that isolate the reactor from the environment and seek to reduce 

fugitive emissions (Figure 7). 

Methner et al. [2010] summarized airborne measurements in 12 facilities that processed 

nanomaterials, including manufacturers and research and development labs. The authors found 

that some of the highest measured exposures occurred during reactor cleanout tasks, which 

included brushing and scraping slag material from the reactor walls and during torch cleaning. 

Demou et al. [2008] evaluated exposure to nanoparticles at a pilot-scale nanomaterial 

production facility. The major emission source was determined to be the production unit as 

the airborne particle concentrations rose when the unit was started and fell when production 

rate was decreased. The other task that resulted in substantial particle release was cleaning of 

the reactor using a vacuum cleaner not fitted with a HEPA filter. Evans et al. [2010] studied 

nanoparticle concentrations in a facility that manufactured and processed carbon nanofibers 

(CNFs). During the thermal treatment of the CNFs in a reactor under positive pressure, 

elevated concentrations of non-CNF ultrafines were released. 

Table 2. Process/tasks and emission

Process/task

Potential emission/

exposure points See section See figures

Production of bulk 

nanomaterials

Reactor fugitive emissions 3.4.1 7, 8

Product harvesting 3.4.1 12

Reactor cleaning 3.4.1

Downstream

processing

Product discharge/bag filling 3.4.3.1 14, 15, 16

Bag/container emptying 3.4.3.2 17

Small-scale weighing 3.4.2 10, 11, 12, 13

Machining of products 3.4.3.4

Product packaging Small-scale weighing/handling 3.4.2 10, 11, 12, 13

Large-scale weighing/handling 3.4.3.3 18

Product packaging 3.4.3 14, 15, 16, 18

Maintenance Facility equipment cleaning 3.4.4

Air filter change-out 3.4.4.1 19

Spill clean-up 3.4.4.2
28 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Lee et al. [2010] conducted personal, area, and real-time sampling in seven CNT plants. 

Results showed that nanoparticles and fine particles were most frequently released upon 

opening the chemical vapor deposition (CVD) furnace. Catalyst preparation and the opening 

of the CVD furnace resulted in the release of nanoparticles in the range of 20–50 nm. 

Lee et al. [2011] also evaluated workplace exposures to nanoscale TiO2 at manufacturing 

plants. In one TiO2 plant, the reactor was small and was placed in a fume hood; the entire 

process was conducted in that hood. Even though the reactor was located in the hood, high 

concentrations of nanoparticles were measured outside the hood. Worker exposure increased 

during product harvesting because the worker put his head into the hood to brush out the 

product powder. A second TiO2 plant isolated the large-scale reactor with a vinyl curtain and 

used a glove box for the harvesting of product from the reactor. Overall, airborne particle 

concentrations were fairly stable during production although increases occurred during both 

the operation of a process vacuum pump and welding conducted in the facility.

Yeganeh et al. [2008] evaluated a small facility producing carbonaceous nanomaterials including 

fullerenes. The process involved the production of materials in an arc furnace that was enclosed 

in a ventilated fume hood. This hood had a plastic front face shield and ports that allowed 

worker access during the process. The process involved placing graphite rods into the furnace, 

volatilizing the graphite in the furnace, producing raw soot, and using a scoop and brush to 

remove raw soot into a jar. At the beginning or end of each day, the reactors were completely 

cleaned by manual sweeping and vacuuming to remove residual soot. Real-time particle 

analyses showed that physical handling of material (sweeping of the reactor) resulted in the 

aerosolization of ultrafine particles. Measurements inside and outside the reactor enclosure (i.e., 

fume hood), however, showed that the hood was effective at containing particulates.

Figure 7. A large-scale ventilated reactor enclosure used to contain production furnaces to mitigate 

particle emissions in the workplace (Used with permission from Flow Sciences, Inc.)
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 29 

Methner [2008] evaluated the use of a portable LEV unit for controlling exposure during 

cleanout of a vapor deposition reactor used for producing nanoscale metal catalytic materials 

comprised of manganese, cobalt, or nickel. Following the automated collection of product 

materials, an operator cleaned out slag and waste product from the reactor using brushes 

and scrapers. Initial measurements had shown this task to be a high-exposure task for the 

operator. A follow-up survey was conducted at the facility using a commercially available 

fume extraction unit with HEPA filtration to pull airborne dusts away from the operator 

during cleanout. Analysis of real-time instrumentation and filter samples analyzed for metals 

showed an average reduction in airborne concentrations of 88%–96% during three cleanout 

procedures. 

Emission sources related to reactor operations, harvesting, and maintenance can be 

categorized as fugitive or task–based. The approaches that have been used for controlling 

fugitive emissions from the reactor have primarily been ventilated enclosures. Laboratory 

fume hoods and glove boxes can be used when the reactor is small, typical of R&D or 

pilot operations. Where the production reactors are larger, custom-fabricated enclosures 

often constructed from a polycarbonate, transparent thermoplastic material, or vinyl 

curtains have been used to reduce emissions (Figure 7). When designing these types of 

enclosures, it is necessary to consider reactor access needs, determination of exhaust airflows 

capable of maintaining a negative pressure (even during the opening of access doors), and 

accommodation of heat loads generated by the process. Failure of containment can result 

from not carefully addressing these key design needs. When looking at pressure differentials, 

it is important to study the airflow to minimize turbulent situations that can actually increase 

particle release rather than containing the particles.

Figure 8. A canopy hood used to control emissions from hot processes 
30 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

When a process is heated, the use of canopy hoods (Figure 8) may be another reasonable 

alternative as long as the design meets the operational and facility exposure control 

requirements [ACGIH 2013; McKernan and Ellenbecker 2007]. Even if the process does not 

involve heat, contaminant capture velocities suitable for gas/vapor contaminants (rather than 

coarse particulates) may be sufficient, as ultrafine and nanoparticles possess negligible inertia 

and follow the flow stream well. 

When controlling exposures during operations such as product harvesting and reactor 

cleanout, solutions such as spot LEV systems (e.g., a fume extractor) or containment may 

be acceptable alternatives. Manual harvesting of product materials may be better suited for 

higher-level enclosure controls such as a glove box or a specially designed enclosure to provide 

good capture while minimizing loss of product materials. The use of a commercially available 

fume extractor has been shown to be effective in reactor cleanout and provides a flexible 

solution that may meet facility needs across a range of operations [Methner 2008]. Selection 

of any control should be evaluated to ensure worker acceptance and use as well as verifying 

that it meets the exposure control objectives. 

3.4.2 Small-scale Weighing and Handling of Nanopowders 

Small-scale weighing and handling of nanopowders are common tasks; examples include 

working with a quality assurance/control sample and processing small quantities in 

downstream industries. During these operations, workers may weigh out a specific amount of 

nanomaterials to be added to a process such as mixing or compounding. The tasks of weighing 

out nanomaterials can lead to worker exposure primarily through the scooping, pouring, 

and dumping of these materials. Many different types of commercially available laboratory 

fume hoods can be employed to reduce exposure during the handling of nanopowders. 

Other controls have also been used in the pharmaceutical and nanotechnology industries 

for containment of powders during small-quantity handling and manipulation. They include 

glove boxes, glove bags, biological safety cabinets or cytotoxic safety cabinets, and homemade 

ventilated enclosures. 

Methner et al. [2007] evaluated a university-based research lab that used CNFs to produce 

high-performance polymer materials. Several processes were evaluated during the survey: 

chopping extruded materials containing CNFs, transferring and mixing CNFs with acetone, 

cutting composite materials, and manually sifting oven-dried CNFs on an open benchtop. 

Real-time monitoring did not identify any process as a substantial source of airborne CNF 

emissions; however, weighing/mixing of CNFs in an unventilated area resulted in elevated 

particle concentrations compared to background. Other studies have shown that benchtop 

activities such as probe sonication of nanomaterials in solution can also result in emission of 

airborne particles [ Johnson et al. 2010; Lee et al. 2010]. Producing dispersions by sonication 

is a primary operational step, and the industrial hygiene assessment should address the 

sound level exposure as well as the potential exposure to aerosols of nanomaterials from the 

sonication. Maintaining the sonicator/dispersion process within an enclosure such as a hood 

can be an effective means for mitigating the noise and aerosol exposure.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 31 

3.4.2.1 Fume Hood Enclosures

In 2006, a survey was conducted of international nanotechnology firms and research 

laboratories that reported manufacturing, handling, researching, or using nanomaterials 

[Conti et al. 2008]. All organizations participating in the survey reported using some type of 

engineering control. The most common exposure control used was the traditional laboratory 

fume hood with two-thirds of firms reporting the use of a fume hood to reduce exposure 

to workers. These devices have been used for many years in research laboratories to protect 

workers from chemical and biological hazards. The design and operation of the fume hood 

is an important factor when considering good exposure control. Traditional designs for 

laboratory fume hoods create airflow patterns that form recirculation regions inside the hood. 

In addition, airflow around the worker, as shown in Figure 9, creates a negative pressure 

region downstream of the worker, which may provide a mechanism for the transport of 

materials out of the hood as well as into the breathing zone of the worker. 

Recent research has shown that the laboratory fume hood may allow the release of 

nanomaterials during their handling and manipulation [Tsai et al. 2009a]. This research 

evaluated exposures related to the handling (i.e., scooping and pouring) of powder 

nanoalumina and nanosilver in a constant air volume (CAV) hood, a bypass hood, and a 

variable air volume (VAV) hood. This study showed that the CAV fume hood, in which 

face velocity varies inversely with sash height, allowed the release of significant amounts 

of nanoparticles during pouring and transferring activities involving nanoalumina. The 

particles that escaped the fume hood were circulated to the general room air and were not 

cleared by the general ventilation system for 1/2–2 hours. Sash heights both above and below 

the recommended height (corresponding to a face velocity of 80–120 ft/min) may lead to 

increased potential exposure for the user. In contrast, more modern hoods such as the VAV 

hood, which is designed to maintain the hood face velocity in a desired range regardless of 

sash height, yielded better containment of nanoparticles than the other hoods tested. 

Figure 9. Schematic illustration of how 

wakes caused by the human body can cause 

transport of air contaminants into the 

worker’s breathing zone 
32 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

A meta-analysis of fume hood containment studies was conducted to identify the important 

factors that affect the performance of a laboratory fume hood [Ahn et al. 2008]. An analysis 

of factors affecting the containment performance of the hoods showed that worker exposures 

to air contaminants can be greatly impacted by a variety of operational issues. Increasing the 

distance between the contaminant source and the breathing zone leads to reduced exposure. 

Exposures can also be reduced by limiting the height/area of the sash opening; increasing the 

height of the sash opening increased the risk of hood containment failure. The presence of a 

manikin/human subject in front of the hood caused the greatest risk of hood failure among 

factors studied. This indicates that containment testing should include an operator or manikin 

to adequately assess hood performance. Face velocity did not make a significant difference in 

hood performance unless it was extremely high or low (> 150 ft/min or < 60 ft/min). Several 

hood operating factors showed an effect but were not statistically significant, including sash 

movement, hand and arm movement, pouring/weighing, and thermal load.

New fume hoods specifically designed for nanotechnology are being developed primarily 

based on low-turbulence balance enclosures, which were initially developed for the weighing 

of pharmaceutical powders. The use of bench-mounted weighing enclosures, as seen in Figure 

10, is common for the manipulation of small amounts of material. These fume hood-like 

LEV devices typically operate at airflow rates lower than those in traditional fume hoods and 

use airfoils at enclosure sills to reduce turbulence and potential for leakage. They also have 

face velocity alarms to alert the user to potentially unsafe operating conditions. Based on the 

hazards assessment, these fume hood-like LEV devices can be outfitted with HEPA filtration 

or connected to the ventilation exhaust system.

Figure 10. Nano containment hood adapted from a pharmaceutical balance enclosure 

Photo by NIOSH
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 33 

3.4.2.2 Biological Safety Cabinets

The Centers for Disease Control and Prevention (CDC) divides biological safety cabinets 

(BSCs) into three classes: Class I, Class II, and Class III. The Class II BSCs are further 

divided into four subcategories (A1, A2, B1, B2) [DHHS 2009]. These hoods are used for 

processes that require operator and product protection. The BSC pulls air into the hood to 

protect the operator while providing a downward flow of HEPA-filtered air inside the cabinet 

to minimize cross-contamination along the work surface (see Figure 11). The most common 

BSC (Type II/A2) uses a fan to provide a curtain of HEPA-filtered air over the work surface. 

The downward moving air curtain splits as it approaches the work surface; some of the air is 

drawn to the front exhaust grille and the remainder to the rear grille. The air is then drawn 

back up to the top of the cabinet where it is recirculated or exhausted from the cabinet. In 

general, 70% of the air is HEPA-filtered and recirculated while 30% is filtered and then 

exhausted from the cabinet. The make-up air is drawn through the front of the cabinet. The 

air being drawn in acts as a barrier to protect the workers from contaminated air leaking out 

of the hood. 

Figure 11. A tabletop model of a Class II, Type A2 biological safety cabinet (BSC) (Used with 

permission from ASHRAE [2011].)
34 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Cena and Peters [2011] evaluated the effectiveness of ventilated enclosures including a Class 

II, Type A2 BSC and a custom fume hood during the manual sanding of epoxy test samples 

reinforced with CNTs. Sanding of CNT-epoxy materials released respirable-sized (micronsized) particles but generally no nano-sized particles. The respirable mass concentration in the 

operator’s breathing zone while using the BSC was approximately two orders of magnitude 

lower than the concentration when using the custom fume hood. The use of the custom 

fume hood resulted in an increase of breathing zone concentrations of about one order of 

magnitude compared to the use of no controls. The custom fume hood had a low average face 

velocity of about 45 ft/min with high variability across the hood face. The authors suggested 

that the poor performance of the custom fume hood may have been due to its rudimentary 

design, which did not include a front sash or rear baffles. The lack of these common fume 

hood features along with the low average face velocity may have resulted in poor airflow 

distribution across the face and increased leakage. 

Macher and First [1984] evaluated the effect of airflow rates and operator activity on 

containment effectiveness for a Class II, Type B1 biological safety cabinet using bacterial 

spores released by two 6-jet collison nebulizers. The hood sash height correlated negatively 

with the containment effectiveness; that is, the higher of two sash heights provided better 

containment of the aerosol. In addition, working in the front half of the cabinet provided 

better protection than working in the rear half of the cabinet. The authors postulated that 

working in the rear of the hood caused the operator to move closer to the hood opening, 

blocking the opening and causing more turbulence and leakage around the sides of the hood. 

The operator withdrawing his arms from the hood caused significantly more leakage than 

moving arms side to side within the hood. The authors concluded that testing BSCs with 

persons working at them provides more information than static testing alone and that even 

well-designed cabinets lose a small fraction of aerosols. 

3.4.2.3 Glove Box Isolators

A glove box isolator fully isolates (contains) a small-scale process and is sometimes referred to 

as a primary protection device (Figure 12) [HSE 2003a]. The design can be either the more 

typical hard unit or a soft, flexible containment unit (often referred to as a glove bag). Glove 

boxes provide a high degree of operator protection but at a cost of limited mobility and size 

of operation. In addition, cleaning the glove box may be difficult, and, to prevent exposures, 

operators should use caution when transferring materials and equipment into and out of the 

glove box. In general, glove boxes include a pass-through port, which allows the user to move 

equipment or supplies into and out of the enclosure. 

The performance of a glove box containment system was evaluated during weighing activities 

of fine lactose powder (a common pharmaceutical surrogate test material). Air samples were 

collected at four locations: inside the glove box, in the pass-through, in front of the glove 

box, and at the exit of the recirculating HEPA filter [Walker 2002]. The results of sampling a 

10-minute task showed the average concentration measured inside the glove box was 298 μg/

m3, the average concentration in the integral pass-through was 35 μg/m3, and concentrations 

measured in the room, including downstream of the glove box exhaust, were below the 

analytical limit of detection of 1 μg/m3. Sample swabs of interior surfaces showed dust 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 35 

contamination within both the main glove box and pass-through. These results indicated that, 

although internal surfaces were contaminated with the materials, no leakage from the glove 

box was detected. 

Figure 12. A glove box isolator for handling substances that require a high level of containment 

(Contains public sector information published by the Health and Safety Executive and licensed under 

the Open Government License v1.0.)

3.4.2.4 Air Curtain Fume Hood

A recent fume hood design addresses the known issues surrounding the recirculating flow 

patterns both inside the fume hood and around the operator (Figure 9). The air curtainisolated fume hood, as shown in Figure 13, uses a push-pull ventilation configuration created 

by a narrow planar jet from the sash to an exhaust slot along the base of the hood opening. 

Tsai et al. [2010] evaluated the performance of this hood during handling and manipulation 

of nanoparticles. In this test, measurements in the worker’s breathing zone were taken while 

nanoalumina powders were manually transferred or poured between several 400-ml beakers. 

The air-curtain hood had very low particle release during all tested conditions (i.e., varying 

sash heights) with low but measurable release occurring at the lowest sash position. This 

same study showed that the particle leakage from two traditional fume hoods (both a CAV 

and VAV hood) exhibited substantial particle release during similar nanomaterial handling 

operations. This study suggested that the air curtain isolated hood may provide better 

containment performance during typical handling procedures. 
36 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Figure 13. Air curtain safety cabinet hood that uses push-pull ventilation (Used with permission from 

Huang et al. [2007a].)

3.4.2.5 Summary

Overall, the published studies suggest that the selection of a fume hood with improved 

operating characteristics such as a VAV hood provides better operator protection than 

conventional fume hoods when handling dry nanomaterials. When using any hood, the 

worker should strive to maintain the face velocity in the recommended range of 80–120 ft/

min [ACGIH 2013]. Additionally, proper use of the engineering control by the operator and 

validation of the performance of the control equipment are essential for risk mitigation. Newer 

nano hoods based on pharmaceutical weigh-out enclosures may be a reasonable alternative 

to larger fume hoods when only small-scale, benchtop manipulation of powders is needed. 

These hoods have proven effective in the pharmaceutical industry but need more thorough 

evaluation to assess the impact of lower airflow rates on containment performance, especially 

in the industrial environment. BSC-type hoods are commonly used for containing hazardous 

powders in hospitals for hazardous drug formulation and may have features designed to improve 

containment performance over traditional fume hoods. However, there are few published studies 

on their effectiveness for containing nanomaterials. The selection of a BSC appropriate for use 

with nanomaterials is essential. Considerations including how to clean the cabinet after use, 

how to maintain the BSC during required maintenance such as filter change-outs, and proper 

exhaust configuration (sending exhaust out of the production area versus recirculating exhaust 

air) should be considered prior to use. Glove box isolators typically provide a greater level of 

worker protection but at a cost of reduced access and limited operational scale. Newer hood 

designs, such as the air curtain fume hood, have shown excellent containment performance in 

initial studies and may be potential control options in the future. 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 37 

Many options are available to facilities that require worker protection during small-scale 

material handling operations. The best option for a given process depends on several factors 

including scale of handling operations, physical properties of materials being handled (size, 

density, wet or dry formulation), work environment (lab versus plant, cross drafts, nearby 

activity), equipment requirements (size of equipment/operation being enclosed), and level 

of protection required. Independent of the control selected, users should also adopt good 

work practices, such as using the smallest possible quantities of materials. Other procedures, 

such as wiping down and sealing containers before they are removed from the enclosure, are 

recommended. In addition, using care when working with powders, such as refraining from 

dropping dust from height, helps to prevent dust generation and to reduce operator exposure. 

The proper positioning of these workstations away from doors, windows, air supply registers, 

and aisleways will help to reduce the impact of cross drafts.

3.4.3 Intermediate and Finishing Processes

Exposures resulting from the manual handling of powdered materials are common in 

industry. Reduction in worker exposure through implementation of careful work practices and 

appropriate engineering controls would benefit these operations. Dumping bags of powdered 

materials has been commonly reported in the literature for production and processing. 

Typically, a worker dumps the ingredients for one process into a hopper and then compacts 

or disposes of the empty bags. Ventilated bag-dumping stations have been used successfully 

in a variety of industries and applications. The transfer of large quantities of nanomaterials 

requires different solutions adapted to the particular process. However, a few controls that 

are applicable to these common processes are available and have been evaluated for similar 

industrial operations. 

After the completion of production, many nanomaterials are sent for further processing. The 

powder product may be refined through a common process such as spray drying [Lindeløv and 

Wahlberg 2009]. Other studies have documented collection of fugitive emissions of nanomaterials 

from the process reactors using devices such as baghouse air filters [Evans et al. 2010]. In both of 

these operations, the nanomaterials are collected in a barrel or drum following the completion of 

these production steps. Several examples of engineered drum or bag filling solutions have been 

described elsewhere and could be implemented to reduce such releases [ACGIH 2013; Hirst 

et al. 2002]. These engineering controls consist of enclosing the product off-loading process 

by temporarily sealing the drum/bag to the filling vessel above and/or overbagging through a 

continuous liner type bagging system. The addition of a local exhaust ventilation hood near the 

drum/bag opening could also be used to capture airborne nanomaterials. 

Evans et al. [2010] studied nanoparticle concentrations in a facility that manufactured and 

processed carbon nanofibers (CNFs). The authors discussed four discrete events that resulted 

in elevations in airborne particle concentrations. The largest increases in particle concentration 

measured within the plant were related to manual handling processes, such as dumping 

product into lined drums and manual change-out and closing bags of final treated CNF 

product. Increases in particle concentrations were the result of the change-out and closing 

of the collection bag containing approximately 15 lbs of CNFs. Emissions from this event 

were almost entirely due to aerosolized CNFs. Tamping of the bag to settle contents (so 
38 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

that it could be adequately closed) and subsequent closing appeared to efficiently aerosolize 

CNF material through the bag opening into the workplace environment. This resulted in an 

increase in respirable mass concentration and a dark visible airborne CNF plume.

A few studies have been conducted to look at the emission of nanoparticles from 

downstream products during machining of nanocomposites. Methner et al. [2007] 

reported increases in total carbon (a marker for nanoparticles), particle number, and 

mass concentration during the wet sawing of a CNF-impregnated composite. However, 

the increase in particle concentration was primarily of particles greater than 400 nm in 

diameter. Vorbau et. al. [2009] evaluated nanoparticle release from oak and steel panels 

coated with polyurethane mixed with zinc oxide nanoparticles. A standard abrasive test rig 

was used to provide uniform conditions for testing the release of particles from the surface 

of the panels. During the abrasion tests, no significant release of particles below 100 nm 

was observed. However, the nanoscale zinc oxide particles were embedded in the aerosols 

with larger surface area. Bello et al. [2009] evaluated the release of nanoscale particles 

during dry and wet cutting of nanocomposite materials. Two composites were used for 

evaluation: a CNT-enhanced graphite prepreg laminate sheet and a woven alumina fiber 

cloth with CNTs grown on the surface of the fibers. Significant exposures to nanoscale 

particles were generated during dry cutting of all composites with emission levels being 

related to composite material and thickness; wet cutting reduced exposures to background 

levels. 

For all processes/tasks discussed, engineering controls should be adapted for the specific 

process. Acceptable exhaust volumes and capture velocities may differ from currently 

available guidance due to differences in materials being handled. Pilot testing of any 

controls should be conducted to evaluate proper control operation and verify that exposures 

are controlled to desired levels.

3.4.3.1 Product Discharge/Bag Filling

The process of filling bags with nanomaterials is commonly done following large-scale 

production or refining processes. The off-loading of product after spray drying, for 

example, may be a significant source of exposure when post-processing nanomaterials. In 

the spray-drying process, a mixture of liquid and powder ingredients (slurry) is sprayed 

within a large sealed tank. Heat within the tank dries the slurry droplets, leaving a 

powder as the finished product. When the process is completed, the powder product is 

commonly discharged into a bulk tote or drum before packaging. Methner et al. [2010] 

reported exposure measurements at 12 facilities and noted that the highest backgroundadjusted concentration was observed during spray dryer drum changeout. Evans et al. 

[2010] reported exposures related to changing out a drum that collected fugitive CNF 

materials from a process reactor using a baghouse filtration system. Even though the 

processes differ, the tasks for each of these steps are similar and include the removal of 

the drum from the process outlet. These drums are often sealed to the process outlet 

minimizing exposure during production but potentially expose workers when removing 

the drums or liners.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 39 

A ventilated, collar-type hood around the discharge point can help minimize worker 

exposure to dust. Figure 14 presents a control approach for filling bags with solid powder 

materials [HSE 2003c]. The control includes the specification of a ventilated enclosure around 

the powder discharge outlet and applies to filling smaller product bags as well as intermediate 

bulk containers. This design guidance recommends an inward air velocity of 200 ft/min (1.0 

m/s) into the enclosure. The ACGIH Industrial Ventilation Manual [ACGIH 2013], Design 

plate VS-15-02, Bag Filling, is similar in design to the HSE exhaust hood (Figure 14) but 

specifies an overall hood flow rate of 400–500 ft3/min for nontoxic dust or 1,000–1,500 ft3/

min for toxic dust with a maximum inward air velocity of 500 ft/min. These flow rates have 

been specified for common industrial powders and may need to be adjusted based on the 

process and properties of the nanoscale materials being addressed to prevent excessive loss of 

product.

Figure 14. Ventilated collar-type exhaust hoods for containing dust during product discharge or manual 

bag filling (Contains public sector information published by the Health and Safety Executive and 

licensed under the Open Government License v1.0.)
40 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

In addition to ventilation solutions, other dust control approaches have been used in a variety 

of industries and should be applicable for nanomaterial production. For example, an inflatable 

seal can be used to create a dust-tight seal on the discharge outlet of a spray dryer during the 

product discharge/bag filling process (Figure 15). The seal inflates during the product transfer 

from the process to the packaging bag (providing the seal) and deflates once the transfer is 

completed to allow removal of the bags. These systems are available on many commercially 

available bulk bag filling systems [Hirst et al. 2002]. 

Another system that can be used to contain powders during process off-loading/emptying is 

the continuous liner system (Figure 16). Polypropylene liners are often used when products 

are discharged from the industrial processes into the intermediate or final product containers. 

In this operation, a sleeve of polypropylene liners is stowed around the circumference of 

the discharge outlet. The first liner, the bottom having been sealed, is pulled down into 

the overpack (usually a drum or a cardboard box). Product is discharged into the liner 

through a butterfly valve on the process outlet. Once full, the top of the first liner sleeve 

is closed using tape or a fastener, or it is heat sealed and cut. The product is sealed within 

the poly-lined container, and a new sealed poly liner is pulled down to start discharge into 

the next container. This continuous process seals off the primary leak paths for dust during 

unloading of an industrial blender or other equipment. These systems are commonly used in 

the pharmaceutical industry and may provide cost-effective alternatives to traditional local 

exhaust ventilation control systems for nanotechnology facilities.

Figure 15. An inflatable seal used to contain nanopowders/dusts as they are discharged from a process 

such as spray drying 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 41 

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 (Used with permission 

from ILC Dover.)

3.4.3.2 Bag Dumping/Emptying

Technology used to control dusts during bag dumping has been in place for many years. The 

standard control—a ventilated bag dump station—consists of a hopper outfitted with an 

exhaust ventilation system to pull dusts away from workers as they open and dump bags of 

powdered materials. 

This equipment eradicates the dust problems caused by manually emptying bags and the need 

to dispose of empty bags. This ensures a healthy environment is maintained in the process 

area as well as reduces maintenance and repair problems caused by powder contamination to 

surrounding areas. The basic equipment consists of a bag dump cabinet with a dust extraction 

outlet for connection to a separate dust collector or existing plant exhaust. A bag is placed on 

the mesh support shelf and manually slit, with the contents falling directly into the inlet of a 

flexible conveyor or mixing tank. A side-mounted empty bag compactor may also be included. 

Design examples for these devices are available from several manufacturers of industrial 

materials. The British HSE has developed a control approach for a ventilated station for 

emptying bags of solid materials [HSE 2003d]. The control includes the specification of a face 

velocity of 200 fpm (1.0 m/s) and includes a waste bag collection chute (Figure 17).
42 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Research into the effectiveness of these types of devices has shown that worker exposure to 

dust and vapors can be reduced. A review of commercially available units showed that their 

use with a variety of materials—including limestone, carbon black, and asbestos—controlled 

particle concentrations to acceptable levels [Heitbrink and McKinnery 1986]. However, 

particle contamination on the surface of the bag and handling/disposal of bags caused 

increased worker exposure. An integral pass through to a bag disposal chute/compactor 

can help reduce dust exposure resulting from bag handling. Further studies in mineral 

processing plants showed that the use of an overhead air supply also significantly decreased 

worker exposure [Cecala et al. 1988]. The ACGIH Industrial Ventilation Manual also has 

two designs that are applicable to the control of powder materials during bag dumping 

[ACGIH 2013]. Design plate VS-15-20, Toxic Material Bag Opening, is similar in design 

to the HSE station described above but recommends a slightly higher control velocity of 

250 fpm at the face of the station opening. In addition, Design plate VS-50-10, Bin and 

Hopper Ventilation, requires a hood face velocity of 150 fpm. In general, higher velocities are 

specified to adequately capture dusts in a plant environment. While the materials used in the 

studies discussed above were not nanoscale, the application of the dust control concept is still 

relevant. However, the capture velocities specified in the Industrial Ventilation Manual may 

be excessive when attempting to contain nanomaterials; lower velocities may be warranted.

Figure 17. A ventilated bag-dumping station that reduces dust emissions when emptying product from 

bags into a process hopper (Contains public sector information published by the Health and Safety 

Executive and licensed under the Open Government License v1.0.)
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 43 

3.4.3.3 Large-scale Material Handling/Packaging

Unidirectional flow booths, or downflow booths, as seen in Figure 18, are used in 

pharmaceutical applications for large-scale powder packing, process loading, and tray dryer 

loading [Hirst et al. 2002]. Similar applications have been proposed for handling hazardous 

dye powders. In general, these booths supply air from overhead (commonly at 100 fpm) over 

the full depth of the booth. Particles generated by processes carried out in the booths are 

captured and carried to the exhaust registers, which are located along the back wall of the 

booth. For the nanotechnology industry, these booths may provide a flexible solution for 

several common processes, including packaging of materials, transferring materials between 

process containers, or loading materials into containers for post processing. 

Floura and Kremer [2008] evaluated a downflow booth used for transferring 25 kg of 

lactose (a surrogate pharmaceutical material) from drum to drum inside a downdraft booth. 

Air samples were collected in the operator’s breathing zone and around the perimeter of 

the process during the transfer operation. The operator scooped the lactose powder from 

the initial drum into the final product drum until it was nearly empty and then carefully 

inverted the bag to pour the remainder of the contents into the final container. With no 

active ventilation controls, the concentration within the operator breathing zone averaged 

2,250 μg/m3. When the ventilation inside the booth was turned on, the breathing zone 

concentration was substantially reduced to an average of 1.01 μg/m3. Finally, the authors 

Figure 18. A unidirectional downflow booth for handling larger quantities of powders (Used with 

permission from Esco Technologies, Inc. [2012].)
44 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

evaluated the downflow booth with a ventilated collar added. The ventilated collar surrounded 

the interface between the drums and exhausted air at a rate of 425 ft3/min. During this test, 

the initial drum was inverted and the powder materials were emptied by gravity with the 

operator massaging the materials into the final product drum. The operator’s breathing zone 

concentration averaged 0.03 μg/m3 during this process. This study showed that the use of a 

downflow booth significantly reduced operator exposure during powder transfer processes and 

that adding a second level of LEV, the ventilated collar, further reduced the exposure by two 

orders of magnitude. 

HSE Control Guidance Sheet 202, Laminar Flow Booth, presents a design for powderhandling processes called a horizontal- or cross-flow design [HSE 2003b]. The concept 

behind the design is similar to the downflow booth except that air enters the booth from 

the booth face. Air moves across the back of the worker toward the back of the booth. An 

issue with the cross-flow design is the secondary airflow patterns caused by the presence of 

the operator in the booth. Additionally, if purity or cleanliness of the product is important, 

sweeping of the air across the operator could be problematic. These patterns may cause 

turbulent dispersion of dust in the booth and result in higher operator exposure or potential 

leakage, compared to the downflow booth, but may provide a reasonable control for some 

processes.

3.4.3.4 Nanocomposite Machining

Initial studies have shown that machining some nanocomposite materials can result in the 

release of nanoscale particles to the work environment. Engineering controls when machining 

materials are available for most common processes. They range from ventilation of handheld 

tools using a high velocity-low volume (HVLV) system to the use of wet cutting techniques 

commonly adopted for silica control during construction activities. The use of standard dust 

controls such as those described by the HSE for woodworking as well as those identified 

in the ACGIH Industrial Ventilation Manual for machining processes provide a source of 

guidance that can be used to identify controls for machining processes. Bello et al. [2009] 

showed that the use of wet suppression techniques during sawing of nanocomposites reduced 

exposures down to background levels.

3.4.3.5 Summary

Processing nanomaterials involves a variety of steps. Following the production process, 

bulk unrefined materials may be packaged and shipped for use or may be subject to further 

processing. These processes require handling and manipulation of nanomaterials and have 

been shown to be a point of exposure for workers. These processes typically are composed 

of a limited number of tasks that may result in exposure of workers to nanoparticles or their 

agglomerates.

Product discharge. When processes empty into a large container, there is a potential for 

exposure especially when removing the full drum. Several engineering controls are available 

for this process/task. Nonventilation controls, such as inflatable seals and continuous liner 

systems, reduce the possibility of exposure. Ventilation-based options include the ventilated 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 45 

collar or enclosure around the discharge point. These solutions have been used and evaluated 

in a variety of industrial settings and have been shown to effectively capture dusts when 

properly designed and implemented in the process. 

Bag dumping/emptying. When raw, bulk nanomaterials receive further processing/refining, 

those materials are often dumped from containers such as drums or bags into hoppers that 

feed the downstream processing equipment. Ventilated bag dump stations have been in use 

in industry for many years and have been proven to be effective in controlling dusts. Several 

commercial vendors and sources of design guidance exist for these devices. 

Large-scale handling/packaging. When nanomaterials are handled in quantities larger 

than those that can easily fit in a fume-type hood, a unidirectional flow booth can provide a 

suitable control to reduce worker exposure and mitigate a potential emission source. These 

booths are commonly used in the pharmaceutical industry and have also been employed 

for handling hazardous dye powders in industrial settings. They provide the flexibility for a 

variety of operations that require handling of nanomaterials from larger containers, such as 

drums. They can also be designed to provide local exhaust for specific operations that may 

occur inside the booths. These booths are available for a variety of commercial vendors or can 

be designed from sources of readily available guidance.

Machining of nanocomposites. When machining composite materials coated or 

impregnated with nanomaterials, good dust suppression techniques should be used. Guidance 

on dust suppression techniques from ventilation-based (woodworking-type) or mist/

water-based (silica/construction-type) controls may be adopted to reduce worker exposures. 

Exposures during machining should be carefully monitored and controlled. Standard 

engineering controls may need modification to properly control emissions. In addition to 

engineering controls, workers may need to wear appropriate respiratory protection.

3.4.4 Maintenance Tasks

Maintenance of the production facility and equipment can lead to exposures that are often 

overlooked. Demou et al. [2008] noted that maintenance procedures were a source of 

considerable particle emissions, specifically during the vacuuming of a reactor using a vacuum 

cleaner with a high-efficiency filter. However, other researchers have observed that cleaning 

the process area after CNT preparation reduced airborne particle concentrations [Lee et al. 

2010]. Another typical activity not reported in the literature is the changeout of facility air 

filters. When local exhaust ventilation is used to contain nanomaterials and dusts, facilities 

will typically use air filtration prior to exhausting air from the building or recirculating into 

the work zone. When filters require change-out, the use of integral containment equipment 

and procedures can reduce maintenance worker exposure. Other general maintenance 

procedures, such as modifying ductwork or performing fan maintenance, will also require 

appropriate precautions to avoid exposing workers to nanomaterials settled in the equipment. 

In addition, general good housekeeping processes and written spill response procedures can 

help reduce the potential for worker exposure.
46 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

3.4.4.1 Filter Change–out–Bag In/Bag Out Systems

Bag in/bag out procedures are typically designed to protect workers performing maintenance 

on air filter change out. Bag in/bag out housings are specifically designed to allow for removal 

of a dirty air filter while minimizing worker exposure [Filtration Group Inc. 2012]. In 

these systems, a plastic liner is attached to a service port on the filter unit, as shown on the 

following page in Figure 19. When the filter is ready for replacement, the facility maintenance 

worker, wearing appropriate PPE, removes the filter into a liner. This process contains 

the filter with its contaminants so the worker is not exposed and the particulates are not 

resuspended in the workplace environment.

3.4.4.2 Spill Cleanup Procedures

An organized, clean workplace enables faster and easier production, improves quality control, 

and reduces the potential for exposure. It is important to maintain good general housekeeping 

practices so that leaks, spills, and other process integrity problems are readily detected and 

corrected. Proper practices regarding spills include

▪ Allowing only individuals wearing appropriate protective clothing and equipment and 

who are properly trained, equipped, and authorized for response to enter the affected 

area until the cleanup has been completed and the area properly ventilated.

▪ Using HEPA-filtered vacuums, wet sweeping, or a properly enclosed wet vacuum 

system for cleaning up dust that contains nanomaterials.

▪ Cleaning work areas regularly with HEPA-filtered vacuums or with wet sweeping 

methods to minimize the accumulation of dust.

▪ Cleaning up spills promptly.

▪ Limiting accumulations of liquid or solid materials on work surfaces, walls, and floors, 

to reduce contamination of products and the work environment.

Figure 19. 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 

(Used with permission from Filtration 

Group Inc. [2012])
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 47 

CHAPTER 4

Control Evaluations

The effectiveness of engineering controls for reducing exposures to nanomaterials during 

manufacturing and handling has not been widely investigated. To evaluate control measures 

in nanomanufacturing facilities, investigators need to collect both quantitative and 

qualitative data to describe nanoparticle emissions. Accurate direct-reading instruments 

allow investigators to identify the source of contamination in real time for various task 

scenarios. More detailed information about the materials, such as morphology and chemical 

characteristics, can be obtained by collecting air filter samples for off-line analysis. 

4.1 Approaches to Evaluation

Strategies for measuring nanomaterial exposures and emissions in the workplace are being 

developed and evaluated by a range of researchers [Brouwer et al. 2009; NIOSH 2009a; 

OECD 2009; Ramachandran et al. 2011]. Because there are currently no exposure limits 

for engineered nanomaterials in the United States, a multifaceted approach combining 

qualitative analysis with quantitative means should be used to determine nanoparticle 

emissions and control effectiveness [Oberdörster et al. 2005]. However, some researchers 

have suggested using non-mass-based metrics such as surface area or particle number as 

a reasonable approach to assessing health effects [Wittmaach 2007; Rushton et al. 2010; 

Oberdörster et al. 2005]. The evaluation procedures include (1) identification of emission 

sources, (2) background and area monitoring, (3) air concentration measurement by directreading instruments and filter-based sampling, and (4) measurement of air velocity and 

patterns. 

4.1.1 Identification of Emission Sources 

The main purpose of the initial assessment or walk-through survey is to identify potential 

sources of emissions and to help researchers prepare a sampling plan for the in-depth 

evaluation of processes and control measures. Portable direct-reading devices (e.g., handheld CPCs and photometers) are recommended for quick identification. The initial 

assessment should involve looking at the processes and equipment as well as the general 

plant environment. To optimize and improve engineering controls, a control checklist is 

recommended for collecting basic information on methods, manufacturing processes, and 

existing controls. 

4.1.2 Background and Area Monitoring

A plan to assess control effectiveness requires that measurements are first taken of 

background concentrations in adjacent work areas. This allows the contribution of 
48 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

individual processes to be assessed by removing the background component [Brouwer et 

al. 2004; Demou et al. 2008; Peters et al. 2009]. The background measurement should be 

repeated after process or task evaluations. High background concentrations need to be 

addressed before control evaluation. The following factors can affect background data:

▪ Monitoring period. In a nanomanufacturing facility, the day of the week or the 

time of day during the monitoring period will affect background levels since worker 

movement and frequency of worker operations are variable. 

▪ Other activities or operations around the monitored activity. Any operation, such 

as product harvesting or equipment maintenance, in areas outside the monitoring 

location could potentially influence background concentrations at the monitoring 

location.

▪ General ventilation conditions. The layout and operation of the general ventilation 

system in the workplace should be considered while monitoring background 

concentrations. Basic ventilation data (e.g., volume of air flow, location of supply and 

exhaust, general air movement in the facility), including air supply source, should be 

collected. Additionally, variations in environmental conditions (especially humidity) 

need to be measured.

▪ Other sources. Some equipment can produce incidental (nonprocess) nanoparticles. 

Examples include diesel engines, welders, gas-fired heaters, and air compressors for 

pulse-jet baghouses or dust collectors. 

Area (or static) monitoring can also be conducted to evaluate the general air quality of 

workplaces. Instruments such as the CPC and impactors are suitable for this type of 

monitoring. Ideally, filter samples can be taken at the same location as area monitoring with 

direct-reading instruments to make a side-by-side comparison. 

4.1.3 Air Monitoring and Filter Sampling

The selection of direct-reading instruments (Table 3) for field evaluation must cover a wide 

range of particle sizes. Particle diffusion occurs rapidly when nanoparticles are released in 

the workplace. It results in nanomaterial agglomerates because of particle collisions. For 

example, the average particle size (or size distribution) is larger during product transfer 

than right after product harvesting. Based on the data collected during initial assessment, 

characterization of nanomaterial emissions can be conducted with direct-reading 

instruments to provide higher resolutions of spatial and time variation. To evaluate control 

efficiency for specific processes or tasks, the sampling ports should be located as close as 

possible to the suspected emission sources but outside of control measures (or at a worker’s 

breathing zone). Filter sampling for off-line qualitative analysis must occur in parallel 

with real-time monitoring. Sampling duration may not be an issue for most direct-reading 

instruments but should be considered for filter sampling to avoid overloading. The data 

collected from an initial assessment can be used to determine sampling time and flow rate 

for filter samples.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 49 

Table 3. Summary of instruments and techniques for monitoring nanoparticle 

emissions in nanomanufacturing workplaces

Metric Instrument Remarks

Aerosol 

concentration 

CPC Real-time measurement

Typical concentration range of up to 400,000 

particles/cm3 for stand-alone models with coincidence 

correction; 100,000 particles/cm3 for hand-held 

models

DMPS SMPS often uses a radioactive source.

FMPS uses electrometer-based sensors. Concentration 

range from 100−107 particles/cm3 at 5.6 nm and 

1−105 particles/cm3 at 560 nm

Surface area Diffusion charger Need appropriate inlet pre-separator for nanoparticle 

measurement. Total active surface area concentration 

up to 1,000 μm2/cm3

ELPI Real-time size-selective detection of active surface 

area concentration.

2×104–6.9×107 particles/cm3 depending on size 

range/stage.

Mass Size selective

static sampler

Low pressure cascade impactors.

Micro-orifice impactors.

TEOM EPA standard reference equivalent method.

Aerosol 

concentration 

by calculation

ELPI

Surface area by 

calculation

DMPS

DMPS and ELPI

used in parallel

Surface area is estimated by difference in measured 

aerodynamic and mobility diameters.

Mass by 

calculation

ELPI Calculated by assumed or known particle charge

and density.

DMPS Calculated by assumed or known particle charge

and density.

Abbreviations: CPC=condensation particle counter; DMPS=differential mobility particle sizer; SMPS=scanning 

mobility particle sizer; FMPS=fast mobility particle sizer; ELPI= electric low pressure impactor; TEOM=tapered 

element oscillating microbalance
50 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

4.1.4 Assessment of Air Velocities and Patterns

The measurement of air velocity and pattern is important to establish sampling locations, 

evaluate outdoor contaminant penetration, and assess the performance of existing 

control measures. Two widely used air fluid velocity measuring devices are the Pitot tube 

and the hot-wire anemometer. The Pitot tube is useful to measure flow in ducts with 

high temperatures and/or high particle concentrations, which could damage the thermal 

anemometer probe. Shown in Figure 20, a Pitot tube is a primary standard that measures 

total and static pressures, and air velocity is calculated by using the pressure difference (i.e., 

velocity pressure) based on the Bernoulli equation. The method for conducting a Pitot traverse 

is described in the ACGIH Industrial Ventilation Manual [ACGIH 2013]. The Pitot traverse 

is typically used to measure duct air velocity to estimate overall system exhaust flow rate. 

Occasionally it is difficult to find a suitable location for Pitot tube traverses. Accurate duct 

velocity can be obtained using this method; however, poor measuring locations will cause 

inaccurate estimates of exhaust air flow. Sometimes the airflow through a hood can only be 

determined by measuring the air velocity at the hood face. 

The measurement of fume hood face velocity is an important method to assess proper 

operation and containment. The average hood face velocity can be measured by dividing the 

opening of the hood into equal area grids of approximately one square foot and logging the 

velocity at the center of each grid with the thermal anemometer. To measure the velocities at 

each grid point, the anemometer should be held perpendicular to the direction of air flow. An 

average face velocity can be calculated while the variation in hood velocity from grid to grid 

should be assessed and noted [ACGIH 2013; ASHRAE 1995]. 

Figure 20. Operating principle of a Pitot tube (left) and different types of Pitot tubes (right)
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 51 

In addition to Pitot tubes and anemometers for measuring air velocity, smoke generators 

provide a low-cost method to visualize airflow patterns around control measures. Figure 21 

shows an example of a smoke generator. Airflow visualization techniques can be used 

to help understand the patterns of airflow in and around exhaust hoods and pressure 

differences between adjacent areas/rooms. Smoke can be released around the edge 

of, or inside of, a local exhaust hood to visualize the airflow patterns. This will help 

determine whether airborne particles are being effectively captured and removed by 

the ventilation system. Recorded observations should concentrate on (1) how much of 

the smoke is entrained into the LEV, (2) how quickly the exhaust captures the smoke, 

(3) the direction of air flow, and (4) whether or not any of the smoke visibly enters the 

worker’s breathing zone. In addition, multiple replications of smoke-release observations 

should be made at locations where LEV performance is marginal or poor as indicated 

by reverse airflow, lack of air movement, slow clearance time, and escape of smoke from 

the hood. Special attention should be paid in subsequent tracer gas testing and air 

velocity measurements to locations where smoke release observations indicate poor or 

marginal capture efficiency. In addition, video may be taken of airflow visualization tests 

to provide feedback information to the company on system performance and factors that 

negatively affect hood performance. 

Another use for airflow visualization is the evaluation of room pressurization status. It 

is recommended that rooms where nanomaterials are used be kept at an atmospheric 

pressure that is lower than adjacent areas. This condition helps contain the materials 

and reduce exposures to workers in other areas of the plant. Smoke should be released at 

the interfaces (doors or other openings) between any nanomaterial production areas and 

attached spaces. By releasing smoke at these interfaces, it can be easily observed whether 

air is moving into or out of the production area and proper remediation approaches may 

be implemented where necessary. 

Photo by NIOSH Figure 21. Smoke generator to visualize airflow
52 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

To qualitatively assess whether exhaust re-entrainment may be an issue, smoke can 

be released within each hood in the production room while a researcher observes 

the emission of the smoke through the exhaust stack. This qualitative test will help 

to evaluate the potential for re-entrainment of exhaust into any air intakes or roof 

openings. The behavior of the exhaust plume is dependent on varying environmental 

conditions such as wind speed and direction; therefore, this test should be repeated to 

capture the potential for re-entrainment under a variety of conditions. In addition, air 

velocity measurements should be taken at the center of the exhaust duct opening to 

evaluate the discharge velocity of the hood exhaust. These readings should be evaluated, 

along with the physical design and installation of the exhaust stack, against guidance 

from consensus standards organizations such as ASHRAE, ACGIH, or AIHA.

4.1.5 Facility Sampling and Evaluation Checklist 

When evaluating a facility that manufactures or uses nanomaterials, it is important to first 

assess what engineering controls are in place in the facility. The initial assessment should 

involve looking at the processes and equipment as well as the general plant environment, the 

effective use of the engineering control by the operator(s), and the overall performance of the 

control equipment. Checklists are useful tools for helping to identify the process and facility 

factors related to nanomaterial production, use, emissions, and exposure. A checklist as shown 

in Table 4 may help for collecting basic process information (e.g., capacity, location, and 

usage) and control operation and maintenance parameters to ensure effectiveness of exposure 

control.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 53 

Table 4. Checklist of controls for nanomaterial manufacturing and handling

(Continued)

Item Category Data

Process/task (select all applicable) 

 Weighing

 Mixing

 Transferring

 Drying

 Cleaning

 Cutting/sanding

 Harvesting

 Unpacking ENMs

 Maintenance/repair

 Finishing (drilling, sawing, grinding)

 Packaging/shipping

 Others: ________________________

Workspace

Duration (min)

Frequency (times per day)

Number of workers involved

PPE type

Background Concentration

Size distribution: ___________________

Number: __________________________

Mass: _____________________________

Nanomaterial  SWCNT

 MWCNT

 Other carbon-based

 Metals

 Oxides

 Quantum dots

 Composite: ____________________

 Others: ________________________

Processing rate/volume

Primary particle size

Concentration at source

Number: __________________________

Mass: _____________________________

Concentration at worker breathing zone 

or area (designate)

Number: __________________________

Mass: _____________________________

Breathing zone: ____________________

Area: _____________________________
54 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Item Category Data

Control type  NONE

 Local exhaust 

 General exhaust/dilution 

 Ventilated enclosure

 Fume hood

 Dust collector

 Laminar room

 Glove box

 Booth

 Other:_________________________

Dimensions

Location

Operation

 Hood type

 Face velocity: ___________________

 Flow rate: _______________________

 Temp: __________________________

 Enclosure integrity

 Airflow patterns

 Recirculation

Fan/filtration information

Filter type: _________________________

Manufacturer: ______________________

Resistance (pressure drop): __________

Nominal design flow rate: ___________

Fan type: __________________________

Flow rate: __________________________

Stack position/design:

Visual observation Workspace

Surface contamination

Housekeeping

Layout

Table 4 (Continued). Checklist of controls for nanomaterial manufacturing and handling

(Continued)
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 55 

Industrial Exhaust Ventilation Deficiency Report Worksheet

 Building:  Room:  Hood number:

 Date:  Investigator/reporter:  Fan number:

Notes and sketch

Management Ductwork

 No local cognizant person

 Lack of records

 Lack of up-to-date plans and specifications

 Lack of emergency plan

 Insufficient employee training

 No hood testing mechanism

 No hood-use approval mechanism

 Holes, air leaking

 Dents

 Poor construction

 Plugged

 Corroded

 Leaking

 Dampers improperly set

 Fire dampers

 Doesn’t meet SMACNA qualifications

Hood Fan/Motor

 Improper type for operation/chemicals used

 Air leaking from hood (smoke noncontainment)

 Surfaces corroded

 Surfaces dirty

 Hood mechanisms inoperable

 Lack of real-time airflow monitor

 Flammable construction materials

 Slots not open to appropriate size

 Slots blocked by equipment, chemicals

 Worn out or corroded

 Insufficient rpm

 Belts slipping or broken

 Motor burned out

 Undersized fan

Hood operations Stack

 Use of hood when hood exhaust off

 Hood not being used

 Inappropriate materials/equipment in hood

 Noisy

 Not attached

 Inappropriate location

 Inadequate height

 Stack exit velocity insufficient

 Aesthetic enclosure hinders dispersion

Work practices Exhaust hood

 Untrained personnel

 Rapid movements at hood face

 Placing upper body in hood

 Operating outside hood

 Inadequate exhaust volume

 Inadequate face velocity

 Inadequate face velocity range

 Turbulence in hood face

Table 4 (Continued). Checklist of controls for nanomaterial manufacturing and handling

(Continued)
56 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Make-up air System maintenance

 No replacement air

 Insufficient air for dilution of fugitive emissions

 Contaminated by exhaust air

 Supply diffuser blows on hood face

 Supply diffuser blocked

 Temperature inadequate

 Employee complaints (noise, draft)

 Does not meet ASHRAE 62 provisions

 Supply not balanced with exhaust

 Inadequate maintenance (equipment broken)

 Lack of ongoing PM program

Worksite Manifold exhaust systems

 Cluttered, housekeeping poor, dirty

 Hood positioned near door, window, walkway, 

other turbulence

 Fire escape routes blocked

 Aisles blocked

 Likelihood of fire/explosion; mixed chemicals

 Corrosion in manifold

 Condensation in manifold

 One hood goes positive

 Part of system under positive pressure

Notes

SMACNA: Sheet Metal and Air Conditioning Contractors’ National Association

Industrial Exhaust Ventilation Deficiency Report Worksheet (Continued)

Table 4 (Continued). Checklist of controls for nanomaterial manufacturing and handling
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 57 

4.2 Evaluating Sources of Emissions and Exposures to Nanomaterials

4.2.1 Direct-reading Monitoring 

Currently, it is unclear which metrics associated with exposures to engineered nanomaterials are 

most important from a health and safety perspective. The mass-based metric is traditionally used to 

characterize toxicological effects of exposure to air contaminants. Animal in vivo exposure studies and 

cell-culture-based in vitro experiments show that size and shape are the two major factors influencing 

toxicological effects of engineered nanomaterials. Some of the instruments developed to characterize 

nanoparticles are capable of real-time measurement [Brouwer et al. 2004; Pui 1996; Ramachandran 

2005]. Real-time measurement of aerosolized particles, including primary nanoparticles and 

agglomerates, play an important role in identifying nanomaterial emissions and evaluating control 

systems during field surveys. The measuring devices used to evaluate controls in the workplace 

should be portable and robust. Information about readily available instruments and techniques for 

nanoparticle monitoring (Table 3) has been summarized and discussed in technical reports [BSI 

2007a; EU-OSHA 2009; HSE 2004; ISO 2007, 2008; Mark 2007; Park et al. 2010a, b, 2011]. 

It is noted that some of the instruments on the list in Table 3 are not suited for monitoring 

nanomaterial emissions in the workplace. For instance, the tapered element oscillating microbalance 

(TEOM) is used by the Environmental Protection Agency as a standard reference equivalent method 

to monitor environmental air quality, but the cut-off particle sizes of 10, 2.5, or 1 μm and dimensions 

of this instrument limit its use for workplace sampling. Another example is the scanning monitoring 

particle sizer (SMPS), which uses a radioactive source to bring the sampling aerosol to charge 

equilibrium. This can make shipping difficult. Sometimes it can be difficult to obtain quantifiable mass 

concentrations of nanomaterials in the workplace using impactor sampling. Newly developed devices, 

such as photometers, can detect nanoparticles as small as 50−100 nm with resolution around 1 μg/m3. 

These instruments can provide continuous monitoring for real-time mass concentrations. 

Data from direct-reading instruments only provide a semiquantitative indication of potential 

nanoparticle emissions. Fluctuating background concentrations may make determination of control 

efficiency difficult; changes in background concentration may lead the evaluator to think that the 

controls are performing either better or worse than they are actually performing. In addition, directreading instruments cannot distinguish particle source and composition; these can only be determined 

through off-line microscopic and chemical analysis.

Sampling quality is always an issue for field evaluation. High-quality sampling results can be obtained 

by following certain steps. The sampling data can only be trusted by using instruments that have 

been calibrated for nanoparticle sampling before use. Factory calibration for particle counters and 

sizers typically uses reference materials having a range of particle sizes. If possible, the instruments 

should be calibrated with the target nanomaterials in the laboratory before using them for field study. 

The comparison calibration should also be done on identical instruments if they will be used in a 

field survey. To maintain consistent sampling performance, a zero check for instruments should be 

performed before daily use and after sampling high-particle emissions. Sampling loss due to particles 

deposited in sampling tubes can be lowered by using conductive tubing and minimizing tubing length 

and bends in the tubing. The sampling location should be considered carefully, because nanoparticles 

diffuse rapidly through the workplace air. The choice of sampling location could have a large influence 

on the sampling results. The sampling ports must be kept as close as possible to the emission source.
58 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

4.2.2 Off-line Analysis 

In addition to direct-reading instrument measurements, nanoparticle emissions can also be 

characterized using off-line analysis techniques. Off-line analysis methods can determine the physical 

and chemical properties of airborne nanomaterials, such as particle size, shape, surface area, composition, 

and agglomeration state. These properties are useful to evaluate exposure and toxicology of nanomaterials 

in the workplace. Off-line analysis can also be useful in separating background nanomaterials from 

engineered nanomaterials, based on size, shape, morphology, etc.

NIOSH has developed techniques for off-line analysis using filter samples. NIOSH Method 7402 

(Asbestos by TEM) was developed to collect filter samples of materials with large aspect ratios 

for analysis using transmission electron microscopy (TEM) and can be used to determine particle 

morphology and geometry. NIOSH Method 5040 (Diesel particulate matter as elemental carbon) can be 

used to measure elemental carbon (e.g., CNT, CNF). Other nanomaterials (e.g., metals) can be collected 

on filters and analyzed using NIOSH Method 7300 (Elements by ICP). Using the mass determined 

by chemical analysis and dividing by the total air flow volume will provide a mass concentration of the 

nanomaterial of interest. As with real-time instrumentation, background samples are collected to help 

distinguish nanomaterials from incidental ultrafine aerosols. The optical diameters of single particles and 

agglomerates can be compared to data from direct-reading instruments discussed above.

Filters overloaded with particles cannot be analyzed by direct-transfer TEM analysis. Therefore, filter 

sample volume needs to be balanced against the particle emission rate to avoid filter overload. The results 

of the initial walk-through survey with portable particle counters should provide basic information to 

help determine appropriate filter sampling volume and collection time.

4.2.3 Video Exposure Monitoring 

Video exposure monitoring (VEM) is an exposure assessment technique in which real-time monitoring 

devices (e.g., nanoparticle and dust monitors) are synchronized with video of the work activity 

[Beurskens-Comuth et al. 2011]. The product of VEM is a video of the work activity with a graphical 

presentation of exposure concentrations that corresponds to the job task displayed on the video. VEM 

aides in the identification of work practices that can contribute significantly to overall exposure patterns 

by giving a visual display of work activities and the corresponding real-time monitoring values. With 

this exposure assessment tool, both management and employees can be shown which activities have the 

highest exposure concentrations and can therefore benefit from a change in work practice, installation of 

engineering controls to mitigate the exposure, or the use of PPE. 

The VEM method was initially developed by NIOSH engineers in the late 1980s to bring together work 

activity data (video recordings) with direct-reading exposure data. By identifying the critical activities 

that contribute most to a worker’s exposure, sampling resources can be directed to controlling those 

job activities that affect exposures. Work activity variables can also be keyed into the exposure database 

to statistically assess the impact of work activities on exposures. The method permits researchers and 

safety and health professionals to capitalize on the time element of the direct-reading data by uniting 

the exposure measurement with the corresponding work activities. The VEM method allows directreading monitors to be used as more than simple detectors and have a significant impact on occupational 

exposures.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 59 

4.3 Evaluating Ventilation Control Systems

Several methodologies are available to evaluate local exhaust systems and other exposure controls. These 

techniques include indirect approaches, such as the measurement of capture velocity, slot velocities, hood 

static pressure, and other system performance parameters [Goodfellow and Tahti 2001]. Often these 

measures are compared with design guidance or standards from organizations such as ASHRAE, ANSI, 

AIHA, and ACGIH. In general, these tests provide a method of checking system performance without 

the requirement for expensive instrumentation or a high level of operator experience. 

Because these measures do not directly assess system performance, it is often a good idea to use methods 

that are more specialized than these indirect methods. One method commonly used to evaluate the 

capture efficiency of the LEV system is the quantitative capture test. Tracer gas release and measurement 

is a method used to quantitatively estimate the efficiency of industrial exhaust ventilation hoods [Hampl 

1984; Hampl et al. 1986; Marzal et al. 2003b]. This method typically involves using a surrogate for the 

process-generated contaminant and requires the use of special measurement and dispersion equipment to 

conduct the test. A variety of tracers have been used, including oil mist aerosols, polystyrene latex spheres, 

and gases [Beamer et al. 2004; Ellenbecker et al. 1983; Hampl 1984]. 

In addition to the quantitative capture method, qualitative methods, such as smoke release or dry ice 

tests, are often used to evaluate air movement. Smoke generation and capture is a method often used 

to qualitatively evaluate the performance of ventilation controls [Marzal et al. 2003a; Woods and 

Mckarns 1995]. With this method, a source is used to introduce smoke in and around the hood. This 

allows the researcher to better understand the performance of the hood and evaluate the effect of cross 

currents on the capture of contaminants. These tests not only give the experimenter a sense of the system 

performance but provide invaluable information on where other measurements, such as air velocities and 

tracer gas experiments, should be concentrated. This testing is often conducted while workers are not in 

the production area, either after the work shift or while workers are on break.

4.3.1 Standard Containment Test Methods for Ventilated Enclosures 

Some standard test methods (Table 5) to evaluate fume hoods have been developed: Invent-UK method, 

DIN 12924, BS 7258, EN 14175:2003, and ANSI/ASHRAE 110-1995. One major difference between 

ANSI/ASHRAE 110-1995 and other standard test methods is that only one sampling probe is used to 

detect the test gas concentration near the worker’s breathing zone. Other test methods adopt multiple 

sampling probes connected to a manifold to obtain the area concentration near the fume hood opening. 

The test methods of DIN 12924 and AN-SI/ASHRAE 110-1995 use a manikin to test the containment 

effectiveness of fume hoods. Dynamic test conditions are specified in the test methods of EN 

14175:2003 and ANSI/ASHRAE 110-1995. The purpose of the dynamic test is to evaluate the hood 

during typical maneuvers such as raising or lowering the sash and simulating the airflow disturbance 

related to a person walking in front of the hood.

During field evaluations, ventilated enclosures should also be tested during normal-use conditions. 

Collecting samples both inside and outside the containment opening and in the worker’s breathing zone 

is recommended to assess control effectiveness when workers are performing standard tasks. 
60 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

Table 5. Comparison of the fume hood performance test methods

Test 

method Invent-UK DIN 12924 BS 7258

EN 

14175:2003

ANSI/

ASHRAE 

110-1995

Country United Kingdom Germany Great Britain European 

Union United States

Test 

parameters

Face velocity Tracer gas test Tracer gas 

test

Face velocity Face velocity 

and cross 

draft

Tracer gas test Tracer gas test Smoke 

visualization

Robustness 

test (dynamic 

test by walkbys and traffic)

Tracer gas 

test

Tracer gas 10% SF6

 *+ 90% 

N2 @ 3.0 LPM

10% SF6 + 

90% N2 @ 

3.33 LPM

10% SF6 + 

90% N2 @ 2.0 

LPM

10% SF6 + 90% 

N2 @ 2–4 LPM

100% SF6 @ 

4.0 LPM

Tracer gas 

sampling 

probes

9 20 Multi-probes 

depending 

on opening 

size

Multi-probes 

(inner and 

outer grids)

1 in breathing 

zone

Use of 

manikin

No Yes No No Yes

* Sulfur hexafluoride
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 61 

CHAPTER 5

Conclusions and Recommendations

Engineered nanomaterials are materials that are intentionally produced and have at least 

one primary dimension less than 100 nanometers (nm). Nanomaterials have properties 

different from those of the bulk material, making them unique and desirable for specific 

processes. These same properties may also cause adverse health effects in workers. Currently, 

the toxicity of many nanomaterials is unknown, but initial research indicates that there 

may be health concerns related to occupational exposures. Due to the potential for health 

effects, it is important to control worker exposures to the extent possible. The following are 

conclusions and recommendations for reducing the potential for employee exposures during 

nanomanufacturing processes based on current knowledge.

5.1 General

▪ Hazards involved in processing and manufacturing nanomaterials should be managed as 

part of a comprehensive occupational safety and health management plan. Preliminary 

hazard assessments (PHAs) should be conducted to determine the need for control 

measures during the planning stage. Hazard assessments should be done during the 

operation of a facility and regularly updated when any processes change.

▪ The concept of Prevention through Design (PtD) is to design out or minimize hazards 

early in the design process. When PtD is implemented, the control hierarchy is applied 

by designing safety into the work environment to prevent work-related injuries and 

illnesses. 

5.2 Control Banding

▪ With the absence of OELs, control banding is a potentially useful concept in the risk 

management of nanomaterials. Control banding is not intended to be a substitute 

for OELs and does not alleviate the need for environmental monitoring or industrial 

hygiene expertise.

5.3 Hierarchy of Controls

▪ The hierarchy of controls should be followed when controlling potential occupational 

hazards from nanoparticles. Elimination and substitution are at the top of the hierarchy. 

However, eliminating nanomaterials may not be possible as the nanomaterials were 

likely chosen because of their unique properties. The manner in which these materials 

are handled and processed can largely affect the overall safety of the process. 

▪ The substitution of less hazardous materials for those that are a higher hazard should 

be considered to reduce the risk to workers. Substitution also applies to the form of the 

product used; for example, a slurry with less exposure potential could be used to replace 

a dry powder. 
62 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

5.4 Engineering Controls

▪ If elimination and substitution are not feasible to reduce hazards, engineering controls 

should be implemented. These could include local exhaust ventilation, isolation 

measures, and application of water or other material for dust suppression.

▪ Engineering controls are likely the most effective control strategy for nanomaterials. 

Common controls used in the nanotechnology industry include fume hoods, biological 

safety cabinets, glove box isolators, glove bags, bag dump stations, and directional 

laminar flow booths. Each of these controls should be carefully designed and operated 

properly to be effective.

▪ Preventative maintenance schedules should be developed to ensure that engineering 

controls are operating at design conditions.

▪ Non-ventilation engineering controls cover a range of controls (e.g., guards and 

barricades, material treatment, or additives). These controls should be used in 

conjunction with ventilation measures to provide an enhanced level of protection for 

workers. Many devices developed for the pharmaceutical industry, including isolation 

containment systems, may be suitable for the nanotechnology industry. 

a. The continuous liner system allows filling product containers while enclosing the 

material in a polypropylene bag. This system should be considered for off-loading 

materials when the powders are to be packed into drums.

b. Water sprays may reduce respirable dust concentrations generated from processes 

such as machining (e.g., cutting, grinding). Machines and tooling, as well as the 

material being cut or formed, must be compatible with water. If a fluid other than 

water is used, attention should be given to the fluid being applied to avoid creating 

a health hazard to workers.

▪ A variety of controls are currently commercially available for use.

▪ A checklist that collects basic process information (e.g., capacity, location, and usage) 

and control operation and maintenance parameters can optimize and improve existing 

exposure control. An example checklist is provided in Table 4.

5.5 Administrative Controls

Administrative controls and PPE are frequently used with existing processes where 

hazards cannot be effectively controlled solely with engineering controls. This could occur 

when control measures are not feasible or do not reduce exposures to an acceptable level. 

Administrative controls and PPE programs may be less expensive to establish but, over the 

long term, can be very costly to sustain. These methods for protecting workers have proven to 

be less effective than other measures and require significant efforts by the affected workers. A 

program that addresses the hazards present, employee training, and PPE selection, use, and 

maintenance should be in place when PPE is used.

Administrative controls and PPE can also be useful for redundancy, especially in high-hazard 

situations. While engineering controls serve as primary controls, the administrative and PPE 

controls provide backup. 
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 63 

Employers should implement the following work practices to control worker exposure to 

nanomaterials:

▪ Educate workers on the safe handling of engineered nanomaterials to minimize the 

likelihood of inhalation exposure and skin contact. 

▪ Provide information to workers on the hazardous properties of the nanomaterials 

being produced or handled with instruction on how to prevent exposure.

▪ Obtain the material safety data sheets (MSDS) when using nanomaterials from 

an outside source and review the information with employees who may come in 

contact with the materials. Given the lack of complete health information of many 

nanomaterials, the MSDS may not provide adequate guidance and should be assessed 

by the health and safety office. 

▪ To reduce the potential for release of nanomaterials, consider transferring powdered 

materials to a slurry, where possible. 

▪ Clean up spills of nanomaterials immediately and in accordance with written 

procedures. Appropriate PPE should be donned while performing clean-up tasks.

▪ Provide additional control measures (e.g., a buffer area, decontamination facilities 

located by the hazard) to ensure that engineered nanomaterials are not transported 

outside the work area. Place a sticky mat at the exits of production areas to reduce the 

likelihood of spreading nanomaterials.

▪ Encourage workers to use hand-washing facilities before eating, smoking, or leaving 

the worksite.

▪ Provide facilities for showering and changing clothes to prevent the inadvertent 

contamination of other areas (including take-home) caused by the transfer of 

nanomaterials on clothing and skin. 

▪ Prohibit the consumption of food or beverages in work areas where nanomaterials are 

handled.

▪ Ensure work areas and equipment, e.g., balance, are cleaned at the end of each work 

shift, at a minimum, using either a HEPA-filtered vacuum cleaner or wet wiping 

methods. Dry sweeping or compressed air should not be used to clean work areas. 

Cleanup should be conducted in a manner that prevents worker contact with wastes. 

Disposal of all waste material should comply with all applicable federal, state, and local 

regulations. 

▪ Store nanomaterials, whether suspended in liquids or in a dry particle form, in closed 

(tightly sealed) containers whenever possible.

▪ Conduct routine industrial hygiene and medical monitoring to ensure that work 

practices and engineering controls are effective. 

5.6 Personal Protective Equipment

▪ Because nanoparticles have been found to penetrate the skin, items such as gloves, 

gauntlets, and laboratory clothing or coats should be worn when working with 
64 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

nanoparticles. Good hygiene practices for wearing the protective equipment should 

be followed. 

▪ Gloves made of neoprene, nitrile, or other chemical-resistant gloves should be used 

and changed frequently or whenever they are visibly worn, torn, or contaminated. 

▪ Respiratory protection should be used to reduce worker exposures to acceptable 

levels in the absence of effective engineering controls, during the installation or 

maintenance of engineering controls, for short-duration tasks that make engineering 

controls impractical, and during emergencies. 

▪ Respirators in the workplace should be used as part of a comprehensive respiratory 

protection program. The program should include written standard operating 

procedures; workplace monitoring; hazard-based selection; fit-testing and training of 

the user; procedures for cleaning, disinfection, maintenance, and storage of reusable 

respirators; respirator inspection and program evaluation; medical qualification of 

the user; and the use of NIOSH-certified respirators.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 65 

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APPENDIX A

Sources for Risk Management Guidance

ASSE [2009]. Prevention through design: guidelines for addressing occupational risks in 

design and redesign processes. ASSE TR-Z790.001. Des Plaines, IL: American Society of 

Safety Engineers.

Center for Chemical Process Safety [1992]. Guidelines for hazard evaluation procedures: 

with worked samples. 2nd ed. New York: Wiley-American Institute of Chemical Engineers.

NIOSH [2009]. Approaches to safe nanotechnology: managing the health and safety 

concerns with engineered nanomaterials. Cincinnati, OH: U.S. Department of Health 

and Human Services, Centers for Disease Control and Prevention, National Institute for 

Occupational Safety and Health, DHHS (NIOSH) Publication No. 2009–125 [http://www.

cdc.gov/niosh/docs/2009-125/pdfs/2009-125.pdf ]. 

NIOSH [2009]. Qualitative risk characterization and management of occupational hazards: 

control banding (CB)—a literature review and critical analysis. Cincinnati, Ohio: Department 

of Health and Human Services, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health, DHHS (NIOSH) Pub No. 2009–152.

Schulte PA, Geraci CL, Zumwalde RD, Hoover MD, Kuempel ED [2008]. Occupational 

risk management of engineered nanoparticles. J Occup Environ Hyg 5(4):239–249 .

Schulte PA, Geraci CL, Zumwalde R, Hoover MD, Castranova VA, Kuempel E, Murashov 

V, Vainio H, Savolainen K [2008]. Sharpening the focus on occupational safety and health in 

nanotechnology. Scand J Work Environ Health 34(6):471–478.
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Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 77 

APPENDIX B

Sources of Guidance for Control Design

The American National Standards Institute (ANSI) and 

American Industrial Hygiene Association (AIHA)

ANSI/AIHA Z9.2-2007—Fundamentals Governing the Design and Operation of Local 

Exhaust Systems. This standard establishes minimum requirements for the commissioning, 

design, specification, construction, and installation of fixed industrial LEV systems used for 

the reduction and prevention of employee exposure to air contaminants [ANSI/AIHA 2007]. 

ANSI/AIHA Z9.5-2003—Laboratory Ventilation. This expanded standard, first published in 

1992, includes new chapters on performance tests, air cleaning, preventive maintenance, and 

work practices, as well as five appendices, such as “Selecting Laboratory Stack Designs,” and 

an audit form [ANSI/AIHA 2003].

ANSI/AIHA Z9.7-2007—Recirculation of Air from Industrial Process Exhaust Systems.

This standard established minimum criteria for the design and operation of a recirculating 

industrial process exhaust ventilation system [ANSI/AIHA 2007].

ANSI/AIHA Z9.9-2010—Portable Ventilation Systems. This standard discusses portable 

ventilation equipment and systems used for the reduction, control, or prevention of exposure 

to hazardous atmospheres or airborne substances, and for comfort to employees [ANSI/

AIHA 2010].

BSR/AIHA Z9.13—Design, Operation, Testing, and Maintenance of Laminar Flow Fume 

Hoods. This standard applies to laminar flow fume hoods (LFFH) that use filtered supply 

air and ducted exhaust to protect products inside the hood from external contamination and 

exhaust hazardous effluents from the building. This standard provides guidelines for design, 

operation, testing, and maintenance of laminar flow fume hoods [BSR/AIHA 2010].

The American Society of Heating, Refrigerating, and

Air-conditioning Engineers (ASHRAE)

2009 ASHRAE Handbook—Fundamentals. This handbook covers basic principles and data 

used in the HVAC industry. The ASHRAE technical committees that prepare these chapters 

strive to provide new information, clarify existing information, delete obsolete materials, 

and reorganize chapters to make the Handbook more understandable and easier to use 

[ASHRAE 2005]. 

2007 ASHRAE Handbook—HVAC Applications. This handbook covers a broad range of 

facilities and topics and is written to help engineers design and use equipment and systems 

described in other Handbook volumes [ASHRAE 2007].
78 Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

ANSI/ASHRAE Standard 110-1995—Method of Testing Performance of Laboratory 

Fume Hoods). The purpose of this standard is to specify a quantitative and qualitative test 

method for evaluating the containment of a laboratory fume hood.

The American Conference of Governmental

Industrial Hygienists 

Industrial Ventilation. A Manual of Recommended Practice. This IH standard reference of 

ventilation system design and evaluation is made up of two volumes. The first is related to the 

design of ventilation systems including templates for specific operations. The second provides 

guidance on the operation and maintenance of ventilation systems and includes information 

on system performance evaluation.

British Health and Safety Executive (HSE)

COSHH Essentials Control Guidance Sheets. The Generic COSHH Essentials model 

assigns intervention approaches (i.e., control bands) to workplace tasks after the completion 

of a semi-quantitative risk assessment. A combination of a substance’s toxicity and its 

inhalation exposure potential determine the desired level of control. After completing this 

assessment online, users are directed to the appropriate fact sheet. To download the Control 

Guidance Sheets related to Generic COSHH Essentials go to http://oehc.uchc.edu/news/

Control_Guidance_Factsheets.pdf and insert the sheet number in the space indicated. An 

index to these sheets is shown at that Web site. 

The International Organization for Standardization (ISO)

ISO 14644-7:2004—Cleanrooms and associated controlled environments—Part 7: 

Separative devices (clean air hoods, glove boxes, isolators and mini-environments). ISO 

14644-7:2004 specifies the minimum requirements for the design, construction, installation, 

test, and approval of separative devices, in those respects where they differ from cleanrooms as 

described in ISO 14644-4 and 14644-5.

The International Society for Pharmaceutical Engineering (ISPE)

ISPE is the world’s largest not-for-profit association dedicated to educating and advancing 

pharmaceutical manufacturing professionals and their industry.

ISPE Good Practice Guide: Assessing the Particulate Containment Performance of 

Pharmaceutical Equipment. This guide provides a standard methodology for use in testing 

the containment efficiency of solids handling systems used in the pharmaceutical industry 

under closely defined conditions. It covers the main factors that affect the test results for 

specific contained solids-handling systems, including material handling, room environment, 

air quality, ventilation, and operator technique.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 79 

Knowledge Brief: Containment Hierarchy of Controls. This brief explains the basics of 

the Containment Hierarchy of Controls, as described in ISPE’s Baseline® Guide: Volume 

1—Active Pharmaceutical Ingredients. Information beyond the hierarchy described in the 

Baseline Guide has been added to illustrate alternative considerations typically contained 

in other versions of hierarchies, such as those used in industrial hygiene or risk-based 

manufacture of pharmaceutical products (Risk-MaPP) [Brock 2010].

The National Institute for Occupational Safety and Health 

NIOSH is the leading federal agency conducting research and providing guidance on the 

occupational safety and health implications and applications of nanotechnology. This research 

focuses NIOSH’s scientific expertise and its efforts on answering the following central 

questions:

▪ How might workers be exposed to nanoparticles in the manufacturing or industrial use 

of nanomaterials? 

▪ How do nanoparticles interact with the body’s systems?

▪ What effects might nanoparticles have on the body’s systems? 

NIOSH has created a field research team to assess workplace processes, materials, and 

control technologies associated with nanotechnology. Research laboratories, producers, and 

manufacturers working with engineered nanomaterials have the opportunity to participate 

in a cost-free, on-site assessment that will give information about the potential for employee 

exposure, sources of emissions, as well as applicable engineering controls. The NIOSH control 

technology research program conducts engineering control studies. The field-study portion of 

this research is documented in workplace survey reports.
To receive NIOSH documents or more information about 

occupational safety and health topics, contact NIOSH:

1–800–CDC–INFO (1–800–232–4636)

TTY: 1–888–232–6348

E-mail: cdcinfo@cdc.gov

or visit the NIOSH Web site at http://www.cdc.gov/niosh.

For a monthly update on news at NIOSH, subscribe to 

NIOSH eNews by visiting www.cdc.gov/niosh/eNews.

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