Centers for Disease Control

and Prevention

National Institute for Occupational 

Safety and Health

Prevention through 

Design (PtD)

Prevention through Design (PtD) 

can be defined as designing out 

or eliminating safety and health 

hazards associated with processes, 

structures, equipment, tools, or 

work organization. The National 

Institute for Occupational Safety 

and Health (NIOSH) launched a 

PtD initiative in 2007. The mission 

is to reduce or prevent occupational injuries, illnesses, and fatalities 

by considering hazard prevention 

in the design, re-design, and retrofit of new and existing workplaces, 

tools, equipment, and work processes [NIOSH 2008a,b]. 

Summary 

Engineered nanomaterials (ENMs) 

are materials that are intentionally 

produced to have at least one primary 

dimension less than 100 nanometers 

(nm). These materials have new or 

unique properties different from 

those of larger forms of the same material, making them desirable for specific product applications. The health 

effects associated with nanomaterials 

are not yet clearly understood, so it is 

important for producers and users of 

ENMs to reduce employee exposure 

and manage risks appropriately. In 

2013, the National Institute for Occupational Safety and Health (NIOSH) 

published a compendium of control 

approaches for nanomaterial production and use processes entitled 

Current Strategies for Engineering Controls in Nanomaterial Production and 

Downstream Handling Processes. This 

Workplace Design Solutions document provides guidance on exposure 

control approaches for protecting 

workers during nanomaterial reactor 

operations.

Background 

The toxicity of many nanomaterials is presently unknown, but initial 

research indicates that there may be 

health concerns related to occupational inhalation exposures. Only a 

few types of ENMs have undergone 

extensive toxicological evaluation 

by NIOSH, e.g., titanium dioxide 

(TiO2) and carbon nanotubes (CNTs). 

Results from animal studies with 

TiO2 and other poorly-soluble, lowtoxicity particles of fine and ultrafine 

(nanoscale) sizes have shown adverse 

pulmonary responses in exposed rats, 

including persistent pulmonary inflammation and lung tumors [NIOSH 

2011; Oberdörster 2002; Donaldson 

2009; Poland et al. 2012]. Similar 

toxicological responses have also been 

observed in rats and mice exposed to 

CNTs and carbon nanofibers (CNFs) 

[NIOSH 2013]. Because of the potential for adverse human health effects, 

it is important to control worker exposure and to manage risks appropriately throughout the lifecycle of ENM 

production.

Protecting Workers during 

Nanomaterial Reactor Operations
Description of Exposure 

ENMs are often produced from aerosolized precursor materials in a variety of enclosed reactors using methods such as 

furnace flow (hot wall), laser, plasma/discharge, and flame reactors [Buesser and Pratsinis 2012]. In these processes, vapor/

aerosol phase synthesis techniques are effective in producing 

a wide range of ENMs with different compositions and 

shapes, including metal and metal oxide nanoparticles, nanotubes and nanowires including CNTs and fibers [Virji 

and Stefaniak 2014]. 

Harvesting nanomaterials from reactors results in potentially 

high exposures [Demou et al. 2008; Lee et al. 2010, 2011; 

Methner 2008; Yeganeh et al. 2008]. In addition, cleanout of 

reactors contributes to increased facility concentrations and 

exposures among operation and maintenance workers. Leakage from pressurized reactors can also contribute to background concentrations and result in exposure to employees 

throughout the facility. Emission sources related to reactor 

operations, harvesting, and maintenance can be categorized as 

fugitive or task–based. The approaches to control both fugitive 

and task-based emissions from the reactor have primarily 

been ventilated enclosures.

NIOSH recommends that manufacturers and downstream users of nanomaterials develop PtD strategies to protect workers 

during the production and handling of engineered nanomaterials. Engineering controls protect workers by removing or 

designing out hazardous conditions or by placing a barrier 

between the worker and the hazard, and along with good 

work practices, they are likely to be the most effective control 

strategy for nanomaterials. The identification and adoption 

of effective control technologies is an important first step in 

reducing the risks associated with worker exposure to ENMs 

and ENM-associated byproducts. 

Harvesting of Product Nanomaterials

The opening of a reactor and collection of nanomaterials has 

been shown to be a source of emissions to the workplace in a 

variety of studies. Methner et al. [2010] reported that opening 

a sealed reactor resulted in elevation of both fine and ultrafine 

particle concentrations above background in two facilities. 

One of these facilities showed a dramatic decrease in emissions 

when using local exhaust ventilation (LEV). Lee et al. [2010] 

reported that the opening of the reactor for harvesting was the 

task most often associated with emission of nano-scale and 

fine particles at seven multi-walled carbon nanotube facilities. Because of the potential for release of primary nanoparticles, manual harvesting of product materials may be better 

controlled by higher-level enclosures such as a glove box or 

a specially designed enclosure to provide good capture while 

minimizing loss of product materials. 

Small Reactors

Laboratory fume hoods, enclosures, and glove boxes can be 

used when the reactor is small (less than approximately 3 feet 

in length and 2–3 feet in width), such as in R&D operations. 

Two studies have shown that when the reactor is housed in a 

well-designed and operating fume hood, particle loss to the 

work environment is low [Tsai et al. 2009; Yeganeh et al. 2008]. 

NIOSH has published information about protecting workers 

during the handling of nanomaterials using chemical fume 

hoods and glove boxes as well as other ventilated enclosures 

[NIOSH 2018]. The figure (small reactor harvest enclosure) 

below provides an example of a glovebox unit fitted to the outlet of a small reactor which could be used to harvest products 

from an enclosure. 

Medium and Large Reactors

Where the production reactors are larger, custom-fabricated 

enclosures (often constructed from a polycarbonate, transparent thermoplastic material) or vinyl curtains can be used to 

reduce fugitive emissions. Since production reactors typically 

house hot processes, the required exhaust flow calculations 

should consider the buoyant thermal plume from the reactor 

[McKernan and Ellenbecker 2007]. A canopy-type hood can 

be used to collect materials emitted when the reactor is opened 

for product harvesting (see large reactor harvest enclosure 

figure below). Side baffles or plastic curtains can be used to 

improve collection efficiency by minimizing the adverse effects 

of drafts. The size of the canopy hood (especially depth) should 

be sufficient to contain reactor emissions while allowing access 

for the operator. 

The bullet points listed with the figure below offer important 

design and operational considerations for these enclosures.
Large Reactor Harvest 

Enclosure

▶ Ventilated enclosure for capturing reactor 

emissions during the harvesting of ENMs.

▶ Exhaust flowrate should be designed to 

maintain an inward air velocity between 80–100 

fpm at the face of the enclosure (curtains).

▶ A hard enclosure made of a suitable plastic such 

as polycarbonate or acrylic or a soft enclosure 

constructed with vinyl curtains can be used to 

enclose the reactor.

▶ Ensure that enclosure materials are compatible 

with the process (i.e. high temperature or 

anti-static).

▶ Check performance using a visual indicator 

such as a smoke tube/source to confirm that 

air flows move away from the worker breathing 

zone and toward the exhaust. 

Small Reactor Harvest 

Enclosure

▶ Ventilated enclosure for capturing emissions 

during the harvesting of ENMs from a reactor.

▶ Enclosure design must account for operator 

access needs and process visibility to be 

effective. 

▶ A low exhaust flowrate should be sufficient to 

maintain negative pressure in the enclosure and 

contain emissions. 

▶ After ENMs are harvested, they should be 

placed in a sealed container to minimize 

contamination during removal from the 

enclosure.

▶ A pass through box allows for the removal 

of nanomaterials from the enclosure with 

minimal potential for release of materials to the 

workplace.
Reactor Cleaning

▶ Local exhaust ventilation (LEV) can be used to 

collect emissions during cleaning. 

▶ Place the exhaust pickup as close to the emission 

source as possible (typically within 6 inches). 

Velocity decreases rapidly moving away from 

the exhaust pickup. 

▶ The air velocity at the point where contaminants 

are emitted should be at least 100 fpm. 

▶ Use baffles and side shields to enclose the 

process as much as possible. Cross currents and 

drafts in the workplace can reduce effectiveness.

▶ Note the direction of the air flow is away from 

the breathing zone of the worker and towards 

the exhaust. 

Routine Cleaning of the Reactor

Following the completion of production, unwanted byproducts 

frequently coat the walls of the reactor requiring periodic maintenance/cleaning. The cleanout of reactors may involve manual 

sweeping, brushing, or scraping to remove waste materials. A 

study of exposures linked to reactor cleanout showed that the 

potential for emission of nanoparticles exists during cleaning 

[Zimmermann et al. 2012]. This study looked at a variety of 

different reactor-based production methods (chemical vapor 

deposition, physical vapor deposition, pyrosol) and cleaning 

methods (dry/wet dusting, scraping, scouring pad, sanding, 

heat gun). The researchers concluded that cleanout of reactors 

could lead to emissions of nanoparticles regardless of method. 

Wet methods resulted in generally lower emissions while dry 

and energetic methods (like scraping, sanding, and use of an air 

jet) resulted in higher emissions. Demou et al. [2008] showed 

that the use of a vacuum cleaner, outfitted with a Class M (medium efficiency) filter, was one of the highest particle emission 

sources when cleaning a reactor.

Yeganeh et al. [2008] evaluated a nanotechnology process 

that was enclosed in a ventilated fume hood. The reactor was 

cleaned daily using manual sweeping and vacuuming to remove the waste material. The ventilated fume hood adequately 

contained the particles generated during the cleaning process. 

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

controlling exposure during cleanout of a vapor deposition 

reactor which was used for producing nanoscale metal oxides 

(see reactor cleaning figure below). Following the automated 

collection of product materials, an operator cleaned out slag 

and waste product from the reactor using brushes and scrapers. 

The use of a commercially available portable fume extractor 

with HEPA filtration resulted in an average reduction in airborne concentrations of 88%–96% during cleanout procedures. 
Fugitive Emission Control

Leakage of nanoparticles from reactors to the work environment 

has not been well documented. If the reactor is operated under negative pressure with respect to the environment, emissions are less likely, except when opening the reactor for harvesting or cleaning. However, a study has shown that leakage from 

reactors can result in the increase in workplace nanoparticles 

[Demou et al. 2008]. Demou et al. showed a consistent increase in 

the workplace concentrations over the course of a day as production continued followed by a drop off once production ceased. 

Large Reactor Enclosure

▶ Ventilated enclosure for capturing fugitive 

emissions (leaks) from reactor.

▶ Must account for operator and maintenance 

access needs and heat dissipation from reactor 

to be effective.

— Lack of proper exhaust ventilation for 

heat loss may require that enclosure doors 

remain open to maintain the required 

process temperature.

— Exhaust ventilation for maintaining a 

negative pressure in the enclosure will 

typically not provide adequate capture 

when doors are open. 

▶ The use of transparent doors and walls allow for 

visibility of the reactor by the operator. 

Design and Operational Considerations

The local exhaust ventilation hood or enclosure should be 

designed to effectively capture the contaminants released by a 

process. It should be tailored to the specific process being controlled (especially important for hot processes, processes generating contaminants at high velocities, and processes where 

other chemicals, such as solvents, may co-occur). Information 

about the design, operation, and maintenance of engineering 

controls for industrial processes is available from a variety of 

sources [ACGIH 2007, 2016; Burton 1999; Burgess et al. 2004]. 

When designing these types of controls, it is necessary to follow the design and operational considerations below:

 Consult a qualified industrial ventilation engineer, industrial 

hygienist, or containment specialist to design the new control 

system.

 Consider access requirements when designing the control 

to ensure that the operator and maintenance personnel can 

perform required tasks without reducing control effectiveness 

(e.g. leaving enclosure doors open). 

 Consider heat loads generated by the process when designing 

the enclosure and determining the airflow. A tight enclosure 

with inadequate airflow may affect reactor temperature. 

 Determine exhaust airflows capable of maintaining a negative 

pressure (even during the opening of access doors). Fans that 

move air through the LEV system need to be adequately sized 

to ensure the system works properly.

 Provide an easy way of checking that the control system is 

working, e.g., manometer, pressure gauge or other visual 

indicator. Always confirm that the exhaust is turned on and 

working prior to starting the task.

The figure below shows an example of a ventilated reactor 

enclosure (see large reactor enclosure figure). These enclosures 

should be designed to account for the removal of heat from 

the process so that the reactor can operate properly when 

doors are closed. When a process is heated, the use of canopy 

hoods over the reactor may be another effective alternative 

as long as the design meets operational and facility exposure 

control requirements [ACGIH 2016; McKernan and Ellenbecker 2007].
 Provide clean make up air to the workroom to replace most of 

the exhausted air. 

 Discharge exhaust air to a safe place away from doors, windows, 

supply air intakes, or other points where re-entry of exhausted 

contaminants into the workplace may occur.

 Keep exhaust ducts short and simple—avoid flexible duct 

if possible. The duct material and filters chosen need to be 

compatible with the ENMs and byproducts generated.

 Conduct initial performance tests of the controls installed 

at the facility. These tests should be scheduled as part of a 

regular preventive maintenance program to ensure adequate 

containment.

 If using a vacuum cleaner, consider purchasing an industrial 

system with HEPA filtration.

Preventive Maintenance and System Checks

 Develop a written preventive maintenance (PM) plan to check 

system performance and repair identified deficiencies.

 Keep equipment in effective and efficient working order. 

 Look for signs of damage to the ducting and ventilation control 

system. Repair damage immediately.

 Regularly check that the enclosure system is working properly 

and that the enclosure has no visible dust leaks. 

 Have a qualified industrial ventilation engineer or industrial 

hygienist examine the ventilation control system and check its 

performance at least once every year or if it is modified or 

relocated.

 Conduct routine industrial hygiene monitoring to ensure 

controls are working at design conditions.

 Keep the information obtained from all engineering control 

system tests/checks in a PM logbook.

Administrative Controls 

The use of engineering controls is likely the most effective 

control strategy for nanomaterials. Administrative controls and 

personal protective equipment (PPE) also have a place in PtD 

strategies and are usually identified as additional safeguards. 

Work practices, an administrative control, are procedures followed by employers and workers to control hazards in the workplace. These include housekeeping and cleaning, storage and use 

procedures, labels and postings, hazard training, and procedures 

for the use of engineering controls, many of which are discussed 

below. In addition, respirators may be needed and can be used 

during the implementation of engineering controls and work 

practices as well as during some short-duration maintenance 

procedures, when engineering and administrative controls are 

not feasible, and in emergencies. Therefore, facilities should consider the following administrative and PPE approaches as a part 

of a comprehensive occupational safety and health management 

plan for nanomaterial production and use.

Cleaning and Housekeeping

 Clean the work area and equipment every day. Deal with 

spills immediately according to written procedures and using 

appropriate PPE. Standard approaches for cleaning spills can 

be used for cleaning surfaces contaminated with dry powder 

nanomaterials. These include using HEPA-filtered vacuum 

cleaners, wiping up dry powders with damp cloths, or wetting 

the powder before wiping.

 Dispose of cleaning wipes and other contaminated materials 

in a sealed bag to prevent release of the dried nanomaterial. 

Nanomaterial contaminated waste, including cleaning materials, 

should be kept in a separate waste stream.

 Do not use dry methods such as a brush, broom, or compressed 

air to clean up contaminated work surfaces.

 Care must be taken when using wet methods for housekeeping 

activities to make sure that any other safety hazards (e.g., 

electrical hazards, slips/trips, etc.) are not introduced into the 

workplace. 

 Cover all containers when not in use. Dispose of empty 

containers safely.

Training

 Provide safety and health training to workers, supervisors, 

and managers including information about proper use, 

maintenance, and inspection of the control.

 Provide workers with sufficient information to understand the 

nature of potential workplace exposures, health risks, routes 

of exposure, and instructions for reporting health symptoms 

[OSHA 2012].

 Ensure that training includes how to keep exposures low; how 

to check that the ventilation control system is working; how to 

use and care for PPE, including respirators; and what to do if 

something goes wrong. 

Personal Protective Equipment

Personal Protective Clothing

Because some types of nanoparticles have been found to penetrate 

the skin, appropriate protective clothing should be worn. PPE 

should be worn when engineering and/or administrative controls 

are not feasible or effective in reducing exposures or when controls are not feasible such as maintenance or response to a spill. 

Follow job hazard assessment procedures for determining the 

need for and selection of PPE [OSHA 2002; ACS 2015]. 

 If appropriate, use nitrile or other chemically impervious gloves 

during handling and cleanup of nanomaterials. Gloves should 

be selected based on their effectiveness against the nanomaterial 

as well as any other chemicals being used. Gloves should be 
inspected before use and changed at least at the end of each 

shift and whenever they show visible signs of wear. Used gloves 

should be kept in a sealed plastic bag in the work area until they 

can be disposed of properly.

 Never use compressed air or other high energy techniques such 

as brushing or shaking to remove dust from clothing.

Respirators

Employers should consult with an occupational safety and health 

professional to determine the respirator best suited for their 

specific application. Employers should always follow the Occupational Safety and Health Administration (OSHA) Respiratory 

Protection Standard (29 CFR 1910.134) if respiratory protection 

is used (www.osha.gov/SLTC/etools/respiratory/index.html). 

NIOSH guidance for selecting respirators is found at http://www.

cdc.gov/niosh/docs/2005-100/default.html [NIOSH 2004].

Acknowledgments

This document was prepared by Dr. Kevin H. Dunn, Ms. Jennifer Topmiller, and Ms. Trudi McCleery, NIOSH Division of 

Applied Research and Technology, and Mr. John J. Whalen, 

formerly with NIOSH. Mr. Eugene Smith (on contract with 

NIOSH) prepared the illustrations. The authors gratefully acknowledge the contributions of the following NIOSH personnel who assisted with the technical content and review of the 

document, including: Ms. Laura Hodson, Mr. Kevin L. Dunn, 

Dr. Mary Schubauer-Berigan, and Dr. Ziqing Zhuang. Special 

appreciation is expressed to the following who served as external reviewers, including Dr. Thomas Peters, Dr. Matthew Hull, 

and Mr. Donald Ewert.

Suggested Citation

NIOSH [2018]. Protecting workers during nanomaterial 

reactor operations. By Dunn KH, Topmiller JL, McCleery T, 

Whalen J. 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. 2018-120. DOI: https://doi.

org/10.26616/NIOSHPUB2018120.

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NIOSH developed detailed information about comprehensive PtD strategies for nanomaterial use and production 

[NIOSH 2013b] that can be found in the document Current 

Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes (http://www.cdc.

gov/niosh/docs/2014-102/pdfs/2014-102.pdf). 

The information in this document is based on research 

related to Prevention through Design (PtD) initiatives. More 

information about PtD is available on the NIOSH Website at 

http://www.cdc.gov/niosh/topics/PtD/

The Nanotechnology Research Center (NTRC) leads the 

federal government nanotechnology initiative to conduct 

research and provide guidance on the occupational safety 

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NIOSH Website at https://www.cdc.gov/niosh/topics/nanotech/nanotechnology-research-center.html

Engineering controls protect workers by removing hazardous 

conditions or by placing a barrier between the worker and 

the hazard. More information about the Engineering Controls Program is available on the NIOSH Website at https://

www.cdc.gov/niosh/engcontrols/

To obtain information about other occupational safety and 

health topics, contact NIOSH at:

Telephone: 1–800–CDC–INFO (1–800–232–4636)

TTY: 1–888–232–6348 • CDC INFO: www.cdc.gov/info

or visit the NIOSH website at www.cdc.gov/niosh

For a monthly update on news at NIOSH, subscribe to 

NIOSH eNews by visiting www.cdc.gov/niosh/eNews. 

Mention of any company or product does not constitute 

endorsement by NIOSH. In addition, citations to Websites 

external to NIOSH do not constitute NIOSH endorsement of 

the sponsoring organizations or their programs or products. 

Furthermore, NIOSH is not responsible for the content of 

these websites.

This document is in the public domain and may be freely copied or reprinted. NIOSH encourages all readers of the Workplace Design Solutions to make them available to all interested 

employers and workers.

As part of the Centers for Disease Control and Prevention, 

NIOSH is the Federal agency responsible for conducting 

research and making recommendations to prevent workrelated illness and injuries.

For More Information

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http://www.cdc.gov/niosh/docs/2013-145/. 

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