ro
R.F. LeBouf , S.B. Martin Jr. , M.G
J.L. du Plessis 2,*
1National Institute for Occupational Safety and Health,
2North-West University, Occupational Hygiene and Hea
3National Institute for Occupational Safety and Health,
4North-West University, Technology and Innovation Sup
a r t i c l e i n f o
articles and organic
cing real-world in-
orea LLC. This is an
nses/by-nc-nd/4.0/).
will continue to grow and gain value in manufacturing [2]. With
this growth, there is also potential for AM machines to emit con-
taminants into occupational environments resulting in worker
that inhalation of
red to as material
and cardiovascular
e of work-related
of acrylonitrile butadiene styrene (ABS) filament. In a survey of AM
workers who primarily used material extrusion machines, 59% re-
ported respiratory symptoms [6]. In an animal toxicology study,
* Corresponding author. North-West University Occupational Hygiene and Health Research Initiative Private Bag X6001 Potchefstroom 2520, South Africa.
E-mail addresses: AStefaniak@cdc.gov (A.B. Stefaniak), AJohnson13@cdc.gov (A.R. Johnson), dupreezsonette@nwu.ac.za (S. du Preez), DHammond@cdc.gov
(D.R. Hammond), RWells@cdc.gov (J.R. Wells), JHam1@cdc.gov (J.E. Ham), RLebouf@cdc.gov (R.F. LeBouf), SMartin1@cdc.gov (S.B. Martin), MDuling@cdc.gov (M.G. Duling),
ac.za (D.J. de Beer), Johan.DuPlessis@nwu.ac.za (J.L. du Plessis).
Contents lists available at ScienceDirect
Safety and Health at Work
ge
Safety and Health at Work xxx (2018) 1e8LBowers@cdc.gov (L.N. Bowers), AKnepp@cdc.gov (A.K. Knepp), Deon.deBeer@nwu.usually layer upon layer [1]. Economic forecasts indicate that AM asthma in a worker exposed to emissions from material extrusion(NIOSH)-recommended exposure levels.
Conclusion: Industrial-scale AM machines using thermoplastics and resins released p
vapors into workplace air. More research is needed to understand factors influen
dustrial-scale AM process emissions and exposures.

 2018 Occupational Safety and Health Research Institute, Published by Elsevier K
open access article under the CC BY-NC-ND license (http://creativecommons.org/lice
1. Introduction
Additive manufacturing (AM) is the process of joining materials
to make physical objects from 3-dimensional (3-D) model data,
exposure [3,4]. Emerging evidence indicates
emissions from one type of AM process, refer
extrusion, is associated with adverse respiratory
health effects. House et al [5] reported a caswere specifically attributed to the AM processes. Personal exposures to metals (aluminum and iron) and
eight volatile organic compounds were all below National Institute for Occupational Safety and HealthArticle history:
Received 23 July 2018
Received in revised form
28 September 2018
Accepted 31 October 2018
Available online xxx
Keywords:
Additive manufacturing
Material extrusion
Material jetting
Ultrafine particles
Volatile organic compounds2093-7911/$ e see front matter 
 2018 Occupational S
ND license (http://creativecommons.org/licenses/by-n
https://doi.org/10.1016/j.shaw.2018.10.003
Please cite this article in press as: Stefan
Manufacturing Machines, Safety and Health. Duling , L.N. Bowers , A.K. Knepp , D.J. de Beer ,
Morgantown, WV, 26505, USA
lth Research Initiative, Private Bag X6001, Potchefstroom, 2520, South Africa
Cincinnati, OH, 45213, USA
port Office, Private Bag X6001, Potchefstroom, 2520, South Africa
a b s t r a c t
Background: Emerging reports suggest the potential for adverse health effects from exposure to emis-
sions from some additive manufacturing (AM) processes. There is a paucity of real-world data on
emissions from AM machines in industrial workplaces and personal exposures among AM operators.
Methods: Airborne particle and organic chemical emissions and personal exposures were characterized
using real-time and time-integrated sampling techniques in four manufacturing facilities using
industrial-scale material extrusion and material jetting AM processes.
Results: Using a condensation nuclei counter, number-based particle emission rates (ERs) (number/min)
frommaterial extrusion AMmachines ranged from 4.1 
 1010 (Ultem filament) to 2.2 
 1011 [acrylonitrile
butadiene styrene and polycarbonate filaments). For these same machines, total volatile organic com-
pound ERs (mg/min) ranged from1.9
 104 (acrylonitrile butadiene styrene and polycarbonate) to 9.4
 104
(Ultem). For the material jetting machines, the number-based particle ER was higher when the lid was
open (2.3 
 1010 number/min) than when the lid was closed (1.5e5.5 
 109 number/min); total volatile
organic compound ERs were similar regardless of the lid position. Low levels of acetone, benzene, toluene,
andm,p-xylene were common to both AM processes. Carbonyl compounds were detected; however, noneA.B. Stefaniak 1, A.R. Johnso
1 1 1 1 1 4n 1, S. du Preez 2, D.R. Hammond 3, J.R. Wells 1, J.E. Ham1,Original Article
Insights Into Emissions and Exposures F
Additive Manufacturing Machines
journal homepaafety and Health Research Institute
c-nd/4.0/).
iak AB, et al., Insights Into
at Work (2018), https://doi.om Use of Industrial-Scale
: www.e-shaw.org, Published by Elsevier Korea LLC. This is an open access article under the CC BY-NC-
Emissions and Exposures From Use of Industrial-Scale Additive
rg/10.1016/j.shaw.2018.10.003
rats who inhaled ABS emissions from a material extrusion machine
developed acute hypertension [7]. It is unclear if these respiratory
and cardiovascular endpoints are associated with inhalation of
airborne particles, organic vapors, or both.
Herein, desktop scale refers to machines with relatively small
build volumes, limited control over applicable build parameters (e.g.,
build chamber or temperature), and/or slower print speed, whereas
industrial scale refers to machines with relatively larger build vol-
umes, defined control over build parameters, and relatively faster
print speeds. With few exceptions, emission assessments of AM
machines to date have mostly focused on material extrusion, a
process by which a solid thermoplastic filament is heated and then
extruded through a nozzle onto a build plate tomake an object.More
specifically, these studies have focused on inexpensive desktop-scale
printers using fused deposition modeling (FDM) technology
(commonly referred to as “3-D printers”) which were placed in a
At Facility A, characterization of material extrusion machine
emissions and personal air sampling were performed on two
consecutive days. This building had several rooms, each containing
a different type of AM machine, but we focused on a 66-m3 room
that contained three industrial-scale material extrusion machines
(all from Stratasys Inc., Eden Prairie, MN, USA). None of the
industrial-scale AMmachines in the other rooms were in operation
on the sampling days. One machine used ABS filament (Part
Number P430) with butyl acrylateemethacrylic acidestyrene
polymer support material (SR30), another used polycarbonate
filament (PC, Part Number PC10) with methyl methacrylatee
methacrylic acid copolymer support material (Part Number SR10),
and the third machine used Ultem filament (Part Number 9085)
with phenol 4,4`-(1-methylethylidene)bis-polymer with 1,10-sul-
fonylbis[4-chlorobenzene] support material (Part Number 9085)
(all from Stratasys Inc.). The door to each industrial-scale machine
r
r
r
r
Saf Health Work 2018;-:1e82chamber or small room to simulate a work environment. Studies of
these desktop-scale FDM machines indicate that ultrafine particles
(UFPs, diameter <100 nm) and volatile organic compounds (VOCs)
are released during printing [8e27]. Emerging evidence indicates
that UFP and VOC emissions could also occur during operation of
industrial-scalematerial extrusionmachines [3]. Another type of AM
process is material jetting, in which an object is built by dispensing
liquid resin onto a build platformvia hundreds of nozzles, curing the
polymer using an ultraviolet laser, and repeating the process layer by
layer. To our knowledge, only industrial-scale material jetting ma-
chines are commercially available, and there are no reports on
whether they emit particles or VOCs during operation.
Based on the reviewed literature and the larger scale and
throughput of industrial machines, it is reasonable to expect that
exposures to particles and vapors may occur in occupational set-
tings where industrial-scale AM processes are used. Despite early
indications of potential for adverse health effects from inhalation of
these emissions, there is little understanding of the magnitude and
characteristics of emissions and exposures from industrial-scale
AM processes in workplaces [3,4]. Such data are crucial, so that
informed decisions can be made with regard to risk management.
Hence, the purpose of this study was to evaluate emissions and
exposures in multiple workplaces using industrial-scale material
extrusion and material jetting AM processes.
2. Methods
Assessments were performed at four facilities designated AeD.
Table 1 summarizes the AM machines, consumables (filament or
resin type and color) in use at the time of sampling, and machine-
operating conditions.
Table 1
Summary of additive manufacturing machines by facility
Facility Machine
Manufacturer Model Type Description
A Stratasys Fortus 250mc ME Sealed doo
Stratasys Fortus 900mc ME Sealed doo
Stratasys Fortus 400mc ME Sealed doo
B Stratasys Objet Connex 350 MJ Hinged lid
C Stratasys Fortus 450mc ME Sealed doo
D Stratasys Objet Connex 350 MJ Hinged lidABS, acrylonitrile butadiene styrene; ME, material extrusion; MJ, material jetting; N/A, p
Please cite this article in press as: Stefaniak AB, et al., Insights Into
Manufacturing Machines, Safety and Health at Work (2018), https://doi.owas closed and remained sealed during printing. An air condi-
tioning unit was present in the room but was not operational
during sampling. No local exhaust ventilation (LEV) designed to
remove emissions directly from the printer source or general
ventilation (openwindows, etc.) existed in the room. This roomwas
staffed intermittently by one employee.
At Facility B, characterization of material jetting machine
emissions and personal air sampling were performed on two
consecutive days. This facility contained several rooms, each
housing a different type of AMmachine, although we only sampled
in a 90-m3 room with an industrial-scale material jetting 3-D ma-
chine that had a hinged lid (Objet 350 Connex 3; Stratasys Inc.). On
the first day, no other AM machines were in operation, but on the
second day, a nylon powder printer was in use in another room.
Resins used were a support material (Part Number SUP 705),
TangoBlackþ (Part Number FLX980), and VeroClear (Part Number
RGD810) all from Stratasys Inc. On both the days, the machine was
operated with its lid open. Filtered and conditioned fresh air was
supplied to the room via one 32 
 32 cm supply vent (equipment
was not available to measure flow rate at the time of the survey);
there was no return air vent, but there was a louvre in a wall shared
with the building hallway. There was no LEV for the printer. This
room was intermittently staffed by one employee.
At Facility C, emissions from an industrial-scale material
extrusion machine (Stratasys Inc.) located in a high bay were
monitored for one day. This machine was printing PC filament with
support material (Part Number PC-S, Stratasys Inc.). Several metal
working machines (some of which were operating during sample
collection) were also present in the high bay. The AM machine
doors remained sealed during operation. This room did not have
LEV for the AM machine or the metal working machines; however,
Feedstock Color Operating conditions (C)
Extruder Build plate Chamber
ABS Ivory 265 95 70
Support N/A 265 95 70
PC White 270 145 140
Support N/A 270 145 140
Ultem Black 300 Unknown 195
Support N/A 300 Unknown 195
TangoBlackþ Black N/A N/A N/A
VeroClear Clear N/A N/A N/A
Support N/A N/A N/A N/A
PC White 300 180 180
Support N/A 300 180 180
TangoBlackþ Black N/A N/A N/A
VeroWhiteþ Opaque N/A N/A N/A
VeroClear Clear N/A N/A N/A
Support N/A N/A N/A N/Aarameter not applicable; PC, polycarbonate.
Emissions and Exposures From Use of Industrial-Scale Additive
rg/10.1016/j.shaw.2018.10.003
ssessthe bay doors were open to the outdoors during printing which
provided natural air movement in the room. One employee staffed
the high bay, although only intermittently.
At Facility D, emissions from a material jetting machine were
monitored on two different days. This research facility contained a
466-m3 engineering laboratory that housed the same model of
material jetting machine (Objet 350 Connex 3; Stratasys Inc.) and
used the same support material and resins as Facility B, plus
VeroWhite þ resin (Part Number RGD835, Stratasys Inc.). This
machine had a tight-sealing hinged lid that sealed to enclose the
build platform. There was no LEV for the printer. The air exchange
rate in the laboratory was 2/hr during sampling.
2.1. Emissions characterization
The availability of real-time particle sampling instruments was
limited, and not all devices were used on all surveys. At Facilities A
and C, an isopropanol-based condensation particle counter (CPC,
Model 3007; TSI Inc., Shoreview, MN, USA) with a size ranging from
10 to >1000 nm was used to determine particle number concen-
tration. At Facilities B and D, an isopropanol-based condensation
nuclei counter (P-Trak, Model 8525; TSI Inc.) with a size ranging
from 20 to 1000 nm was used to determine particle number con-
centration. An optical particle counter (OPC) (Model 1.108; GRIMM
Aerosol Technik GmbH & Co. Ainring, Germany) was used to
determine particle size distribution from 0.3 to >20 mm. At Facility
D only, a real-time fast mobility particle sizer (FMPS) (Model 3091;
TSI Inc.) was used to measure particle size distribution from 5.6 to
560 nm. All real-time instruments were factory-calibrated before
use. Measurements were data-logged at a frequency of 1 second for
the nuclei counters and FMPS and 6 seconds for the OPC.
Conductive silicone tubing (Part No. 3001788; TSI Inc.) having a
length between 0.1 and 0.5 m was connected to the particle-sam-
pling instrument inlets. According to Jankovic et al [28], losses of
nanoscale particle in nonconductive tubing having a length of 0.7m
can be up to 10%. Hence, the use of 0.1- to 0.5-m-long conductive
tubing in our studies is expected to minimize particle losses in the
sample tubing to <10%, so no correction was made to the mea-
surements. In addition, particles were collected onto 0.8-mm track-
etched polycarbonate filters (SKC Inc., Eighty Four, PA, USA)
mounted in close-faced 37-mm cassettes by drawing air through
the membrane at 4.0 L/min using calibrated sampling pumps. Fil-
ters were analyzed using a field emissionescanning electron mi-
croscope (FE-SEM, S-4800; Hitachi, Tokyo, Japan) to evaluate size
and morphology and by energy-dispersive X-ray analysis (Quantax,
Bruker Scientific Instruments, Berlin, Germany) to identify
elemental constituents.
For gas-phase emissions, a real-time total organic vapor (TVOC)
photoionization detector (RAE Systems, San Jose, CA, USA)was used
to monitor organic vapor concentrations, and a real-time gas-sen-
sitive semiconductor sensor (Model S500; Ozone Solutions, Hull,
IA, USA) was used to monitor ozone concentrations. The TVOC
monitor was factory-calibrated using isobutylene and span-
checked with isobutylene before use. Soil vapor intrusion thermal
desorption (TD) tubes (Perkin Elmer, Waltham, MA, USA) con-
nected to low-flow sampling pumps (calibrated to 0.050 L/min for
2-hour sample collection or 0.030 L/min for 6-hour sample
collection) were used to measure specific VOC concentrations. All
sampler inlets were positioned at breathing zone height and
collocatedwith the aerosol monitors. TD tubes were analyzed using
a thermal desorption unit (ATD650; Perkin Elmer, Waltham, MA,
USA) connected to a gas chromatographemass spectrometer (GC-
MS) as described in the Supplemental File. In addition, 450 mL of
Silonite-coated evacuated canister samples (Model 29-MC450SQT;
A.B. Stefaniak et al / Workplace aEntech Instruments Inc., Simi Valley, CA, USA) were collected at
Please cite this article in press as: Stefaniak AB, et al., Insights Into
Manufacturing Machines, Safety and Health at Work (2018), https://doi.oFacility D only [29]. Details of the canister analytical method are
provided in the Supplemental File. Both TD tubes and canister
samplers were analyzed for 15 different VOCs that have been
observed previously in chamber emissions studies of desktop-scale
3-D printers. Background-corrected concentrations for individual
VOCs were reported only if the measured level exceeded back-
ground. Sampling for gas-phase carbonyl compounds was per-
formed by drawing air using a calibrated sampling pump at 4.0 L/
min into either 25 mL of deionized water in a 60-mL Teflon bubbler
(Savillex; Eden Prairie, MN, USA) or into 40 mL of deionized water
in a 375-mL bubbler depending on sampling duration. After
collection, samples were derivatized and analyzed using GC-MS
(see Supplemental File).
All real-time and time-integrated sampler inlets were posi-
tioned at breathing zone height within 1 m of the AM machines
(i.e., at locations representative of where the AM operator normally
occupied). Samples to establish background levels of particles and
VOCs were collected for up to 30 minutes before the start of
printing. Then, samples were collected to capture emissions from
the start of printing through the postprinting phase to capture
particle and VOC levels in a room. Sampling durations varied
depending on the type of sample collected, facility, type of AM
process, and size of the object that was built.
2.2. Personal sampling
Personal breathing zone samples for metals and VOCs were
collected at Facilities A and B only. Prior laboratory studies have
reported iron, nickel, chromium, and zinc in particulate emissions
from desktop-scale material extrusion printers using ABS and
PL filaments [7,21,27]. As such, we used nanoparticle respiratory
deposition (NRD, Zefon International, Inc., Ocala, FL, USA) samplers
to collect metal-containing particles with diameters from about 15
to 300 nm [30]. NRD samplers were operated using a personal
sampling pump calibrated to 2.5 liters/min, and collection sub-
strates were analyzed for metals using inductively coupled
plasmaemass spectrometry (ICP-MS) in accordance with National
Institute for Occupational Safety and Health (NIOSH) Method 7303.
VOCs were sampled using passive diffusion badges (TraceAir 521;
Assay Technology, Livermore, CA, USA). Badges were analyzed by
gas chromatography-mass spectrometry (GC-MS) by NIOSH
Methods 1500, 1501, and 2500. Personal sampling was approved by
the Health Research Ethics Committee of the North-West Univer-
sity (Ethics clearance number: NWU-00004-16-A1).
2.3. Data analysis
Emission rates (ERs) were calculated using amodel developed to
describe emission from sources in indoor residential and occupa-
tional environments, including AM machine emissions in a room
[19,31]:
Equation 1: ER ¼ V,


Cpeak  Cout
Dt
þ AER þ k,Cin  AER,Cout

(1)
In this equation, V ¼ the room volume, Cpeak ¼ peak concen-
tration of the contaminant during printing, Cout ¼ the outdoor
concentration of the contaminant during printing (assumed to be
equal to the background concentration measured in each printer
room), Dt ¼ the time difference between Cpeak and Cout,
AER þ k ¼ average total removal rate of the contaminant
(AER ¼ air exchange rate in the room, k ¼ rate of contaminant loss
due to deposition onto surfaces), and C ¼ the average concen-
ments of additive manufacturing 3in
tration of the contaminant during printing. This model accounts for
Emissions and Exposures From Use of Industrial-Scale Additive
rg/10.1016/j.shaw.2018.10.003
background particle concentrations in a room, the average rate of
removal of particles by air exchange in the room, and loss due to
deposition onto surfaces. It is assumed that the average concen-
tration measured during background remains constant during
printing, which was reasonable given the characteristics of all
rooms (described previously). Details of the model are provided in
the Supplemental File.
For the material jetting machines at Facilities B and D, the
masses of resin used to printing objects was known to us, which
permitted normalization of emissions to mass printed. To deter-
mine particle emission yield (particle number or mg TVOC/g prin-
ted), the ER (particle number or mg TVOC/min) determined using
Eq. 1 was multiplied by print time (min) to calculate the total
number of particles or mass of TVOC emitted during printing,
which was normalized by the mass of printed resin (g printed).
Given the limited number of print jobs sampled and the explor-
atory nature of these surveys, only descriptive comparisons of ERs
and yields are given, and no attempt was made to analyze the re-
sults statistically.
3. Results
Fig. 1 is a representative example of the influence of material
extrusion AM machine operation on room particle number and
opening of the high bay door during printing was a common
practice. Hence, consideration should be given to the impact of this
type of practice on monitoring efforts in future workplace assess-
ments. In addition, none of these facilities used LEV systems to
control emissions, which precluded our ability to assess the efficacy
of these systems.
Fig. 2 is an FE-SEM image of particles collected in Facility Dwhile
operating a material jetting machine. Particles were clusters of
UFPs composed of carbon. As shown in Table 2, the number-based
particle ER values were in an order of magnitude higher when the
material jetting machinewas operated with the lid open (Facility B)
thanwhen it was closed (Facility D), whereas the TVOC yield values
were similar regardless of the lid position. The FMPS instrument
was only available while sampling in Facility D, and the calculated
particle number ER values were higher than calculated using the P-
Trak data. The higher rates are attributed to the fact that the FMPS
can measure particle sizes down to 5.6 nm, but the P-Trak has a
minimum size cutoff of 20 nm and hence cannot count these
smaller particles measured by the FMPS. The mass of resin
consumed during printing was known, and total particle and TVOC
emissions were normalized to mass to determine yields values
(Table 2). Number-based particle yield values for the P-Trak and
OPC were higher when the printer lid was open than when it was
closed; TVOC yield values were similar regardless of the lid
(e.g., acetone ranged from 5.7 to 33.1 mg/m ), and decreased in the
Fac
Saf Health Work 2018;-:1e84Fig. 1. Real-time particle and total volatile organic compound (TVOC) concentrations inTVOC concentrations. After background, both particle and organic
vapor concentrations increased as printing commenced and
decayed after printing was complete. At Facility A, the ERs during
material extrusion printing with ABS and PC (Day 1) exceeded that
for Ultem (Day 2) based on the number of particles measured using
the CPC (2.2 
 1011 number/min vs. 4.1 
 1010 number/min) and
with a diameter >0.3 mm measured using the OPC (2.7 
 105
number/min vs. 9.6 
 104 number/min). The TVOC ER value for
printingwith ABS and PCwas a factor of five lower thanwhen using
Ultem filament (1.9 
 104 mg/min vs. 9.4 
 104 mg/min). In Facility
C, the high bay door was open during operation of the AMmachine,
which created natural ventilation and diluted any emissions (i.e.,
none of the real-time data had a pattern consistent with emissions
shown in Fig. 1). Discussions with facility staff revealed thatfilament, and after about 120 minutes, a second machine began printing using polycarbonat
t ¼ 5 min and continued for 650 min (plot truncated at t ¼ 300 min for brevity, but decay tre
Please cite this article in press as: Stefaniak AB, et al., Insights Into
Manufacturing Machines, Safety and Health at Work (2018), https://doi.oafternoon after the print jobs were complete (e.g., acetone ranged
ility A. Initially, one machine was printing using acrylonitrile butadiene styrene (ABS)position.
3.1. Quantification of individual VOCs
Six different VOCs (acetone, benzene, styrene, toluene, m,p-
xylene, and o-xylene) were measured on TD tube area samples
during operation of the industrial-scale material extrusion ma-
chines at Facilities A and C. Concentrations of any individual VOC
were at most 6% of their applicable NIOSH Recommended Exposure
Limit (REL). At Facility A, during printing with ABS and PC (Day 1),
the concentrations of individual VOCs were higher in the morning,
reflecting a build-up of contaminants in the room during printing
3e (PC) filament. Background monitoring was from t ¼ 0 to 5 min. ABS printing began at
nd continued for the remainder of sampling). PC printing was from t ¼ 120 to 260 min.
Emissions and Exposures From Use of Industrial-Scale Additive
rg/10.1016/j.shaw.2018.10.003
material jetting machines, room ozone concentrations rapidly
anal
A.B. Stefaniak et al / Workplace assessfrom 2.5 to 15.7 mg/m3). On the second day, just Ultem filament
was extruded, and only acetone (0.4 mg/m3) was quantified above
background.
Results of TD tube area samples revealed that five different VOCs
(acetaldehyde, acetone, benzene, ethanol, toluene and m,p-xylene)
were common to room air during operation of the material jetting
machines in Facility B (lid open) and Facility D (lid closed). In
general, concentrations of these VOCs were similar between facil-
ities regardless of the position of the machine lid and were at most
1.4% of their applicable NIOSH REL. The one exception was acetal-
dehyde (range, 14e214 mg/m3), which NIOSH considers a potential
occupational carcinogen and does not have an REL [32]. Ethanol
was used to clean the build platform on the material jetting ma-
chine in Facility B before operation, and the measured concentra-
tionwas 10.6 mg/m3 on that day, indicating that tasks in addition to
printing could influence AM operator exposure.
Fig. 2. Field emissionescanning electron micrograph and energy-dispersive X-ray
manufacturing printing (Facility D).3.2. Ozone and carbonyl formation
Among all facilities, the background-corrected ozone concen-
trations were highest in Facility A during operation of the
industrial-scale material extrusion machines using ABS and PC
(37 mg/m3) and Ultem (43 mg/m3) filaments. Ozone concentration
when running PC at Facility C was 10 mg/m3. During operation of the
Table 2
Emission rates and yields for industrial-scale material jetting additive
manufacturing machines at Facilities B and D
Facility Lid Day Metricy Particle number* TVOC
P-trak FMPS OPC
B Open 1 Rate 2.3 
 1010 n.s. 1.1 
 105 2.8 
 104
Yield 2.1 
 1010 n.s. 9.8 
 104 2.5 
 104
D Closed 1 Rate 1.5 
 109 2.1 
 1012 8.5 
 103 4.5 
 104
Yield 4.1 
 108 6.0 
 1011 2.4 
 103 1.3 
 104
Closed 2 Rate 5.5 
 109 1.8 
 1011 1.1 
 104 2.5 
 104
Yield 7.7 
 109 2.6 
 1011 1.5 
 104 3.5 
 104
FMPS, fast mobility particle sizer; n.s., not sampled (instrument was not available for
use at this facility); OPC, optical particle counter; TVOC, total volatile organic
compound.
* P-Trak range, 20e1000 nm; FMPS range, 5.6e560 nm; OPC range, 0.3e>20 mm.
y Rate units: number (number/min), TVOC (mg/min); yield units: number (num-
ber/g printed), TVOC (mg/g printed).
Please cite this article in press as: Stefaniak AB, et al., Insights Into
Manufacturing Machines, Safety and Health at Work (2018), https://doi.oincreased from about 15 mg/m3 to 30 mg/m3 at the start of printing
in Facility B (lid open), remained elevated during operation
(average¼ 26.3 mg/m3), and decayed rapidly when printing ceased.
When the material jetting machine was operated with the lid
closed, ozone emissions followed the same pattern as when the lid
was open; however, average concentrations were 9e11 mg/m3. The
NIOSH REL for ozone is 200 mg/m3 and is a ceiling value.
Ozone may react with unsaturated VOCs to form new com-
pounds, including carbonyls [33]. While carbonyl compounds were
observed (e.g., glyoxal, methylglyoxal, and 4-oxopentanal) from the
collected air samples in the parts per billion range, no concentra-
tions were observed to be greater than background levels, indi-
cating that they were not emitted or formed during these printing
processes.ysis spectra of particles collected during industrial-scale material jetting additive
ments of additive manufacturing 53.3. Personal exposures to metals and VOCs
Tasks besides operation of AM machines occurred in Facilities A
and B (e.g., cleaning build plates with alcohol), and employees
sometimes left the machine rooms to work in other areas. As such,
measured personal exposures to metals and VOCs are not solely
from AM machine emissions. Personal 8-hour time-weighted
average (TWA) exposures to metals measured using NRD sam-
plers did not exceed 0.01 mg/m3 for aluminum (REL ¼ 5 mg/m3 as
respirable size particles) or 0.01 mg/m3 for iron (REL ¼ 5 mg/m3) at
any facility.
At Facility A, personal exposures to organic vapors during ma-
terial extrusion with ABS, PC, and Ultem included acetone (0.04e
1.88 mg/m3), pentane (0.04e0.11 mg/m3), cyclohexane (0.01e
0.04 mg/m3), ethanol (0.03e0.08 mg/m3), and naphtha (2.06e
2.31 mg/m3); however, concentrations were well below their RELs
of 590, 350, 1050, 1900, and 400 mg/m3, respectively. In addition,
low levels of hexane (0.15e0.19 mg/m3) and benzene (0.03e
0.02 mg/m3) were measured in the breathing zone when printing
with ABS and Ultem, but not PC filament. At Facility B, personal
exposures during material jetting machine operation also included
low levels of these same chemicals, i.e., acetone (0.02e0.08 mg/3),
pentane (0.01e0.06 mg/m3), ethanol (0.52e2.02 mg/m3), and
naphtha (1.53e1.71 mg/m3), as well as isopropyl alcohol (0.07e
0.52 mg/m3; REL ¼ 980 mg/m3).
Emissions and Exposures From Use of Industrial-Scale Additive
rg/10.1016/j.shaw.2018.10.003
ork4. Discussion
In general, particle ERs, regardless of the type of AM process,
were five to six orders of magnitude higher for particle number
measured using condensation nuclei counters (P-Trak or CPC) than
using the OPC instrument, indicating that the dominant particle
size was below 300 nm in these workplaces. Industrial-scale ma-
terial extrusion machines can extrude filaments such as Ultem
which need higher build temperatures than possible in most
desktop-scale machines. In Facility A, particle numberebased ER
values were lower, but TVOC ER values were higher when Ultem
filament was printed relative to ABS and PC filaments (Table 2). To
our knowledge, this was the first evaluation of Ultem filament, and
these data provide important insights into the emissions profile of
this material. In a previous study of material extrusion machines, a
CPC was used to evaluate printer door seals and cooling fan outlets
during printing but did not identify these locations as emission
points [3]. As such, additional evaluations of industrial-scale AM
machines are needed to understand emission points.
Results from the other observations of the same model of ma-
terial jetting AM machine using the same consumables Facilities B
and D suggested a decrease in particle numberebased emissions
when the machine was operated with its lid closed, but no impact
on TVOC emissions. One potential explanation for this observation
is that particles may deposit on the interior surfaces of the machine
lid by electrostatic or thermophoretic mechanisms when it is in the
down position, but organic vapors do not adhere to the lid. Addi-
tional sampling is necessary to confirm this explanation. At Facility
B, operation of a nylon powder printer in a different room on the
second day resulted in entrainment of particles into the room
containing the material jetting machine, which precluded mea-
surement of its emissions that day. Despite the absence of a thermal
process, and even with the machine lid closed, particle and TVOC
ER values for thematerial jettingmachines were similar to those for
the material extrusionmachines. Investigation of aerosol formation
mechanisms were beyond the scope of the current investigation,
although one possible explanation for the observed UFP emissions
is that liquid resin droplets were broken apart during jetting from
the printer nozzles (approximate diameter of 50 mm) onto the build
surface. Hence, an important finding of this study is that feedstock
materials in liquid form can emit aerosols and vapors, and closure
of the machine lid may not fully contain emissions.
It is somewhat difficult to compare the ER and yield results from
our study with existing reports in the literature for other AM pro-
cesses because most prior studies were performed in controlled
laboratory chambers, and different measurement methods and
equations have been used among investigators to express these
metrics for particles and chemicals. For example, chamber studies of
desktop-scale “3-D” printers using ABS filament report ERs that
range from 2 
 108 number/min [21] to 2 
 1011 number/min [14].
ERsmeasured for PC in chamber studies range from 3
 109 number/
min [34] tow4 
 1010 number/min [9]. The upper end of the rates
for ABS are on the same order of magnitude, but the rates for PC are
an order of magnitude lower than we observed at Facility A during
simultaneous printing with these filaments (2.2 
 1011 number/
min). A few studies have reported ER data for desktop-scale 3-D
printers using ABS filament in different types of nonindustrial
rooms (classrooms, laboratories, and offices) and estimates range
from 1 to 2 
 1011 number/min [16,22] which is consistent with our
observations. Data on TVOC ERs for ABS and PC are limited to
chamber studies of desktop 3-D printers. Reported ER values for ABS
range from 10 mg TVOC/min [21] to 64 mg TVOC/min [12], and for PC,
only Azimi et al [9] have reported an ER (3 mg TVOC/min); these
values are three orders of magnitude lower than that we measured
Saf Health W6in Facility A (1.9 
 104 mg TVOC/min) during industrial-scale AM.
Please cite this article in press as: Stefaniak AB, et al., Insights Into
Manufacturing Machines, Safety and Health at Work (2018), https://doi.o4.1. Chemical concentrations in workplace air
At Facilities A and C, benzene, styrene, toluene,m,p-xylene, and o-
xyleneweremeasured during operation of thematerial extrusion AM
machines with ABS and PC filaments. Acetone was measured when
printingwith ABS, PC, andUltem filaments at Facility A (but notwhen
printing with PC filament at Facility C). Wojtyla et al [35] used ther-
mogravimetric analysis to evaluate decomposition products of ABS
filament and reported that acetone was a component of emissions.
Azimi et al [9] evaluated emissions fromABS and PC filaments using a
desktop-scale FDM machine in a chamber but did not report the
release of acetone. Other chamber/room studies of desktop-scale
FDM machines have reported release of benzene, styrene, toluene,
m,p-xylene, and o-xylene [9,12,14,20,21]. These reports indicate that
desktop-scale FDM machines can be somewhat informative for un-
derstanding VOC emissions from industrial-scale material extrusion
machines printing with ABS and PC filaments (although high-tem-
perature filaments, such as Ultem, can currently be printed using
industrial-scale machines only). Quantification of styrene, albeit at
low levels, during operation of the industrial-scale material extrusion
machines using ABS and PC filaments is of interest because it may be
an asthmagen [36]. At Facilities B and D, six different VOCs were
quantified in room air during operation of material jetting machines.
Among these vapors, acetaldehyde is of interest as this chemical is
categorized as a potential occupational carcinogen by NIOSH [32].
Given these results for material extrusion filaments and mate-
rial jetting resins evaluated in this study and the ever-expanding
options for feedstock materials on the commercial market, there
is a need for more research to understand VOC emissions from AM
machines using these materials. A standard laboratory method to
quantify or categorize filament emissions (particle and chemical)
could be useful for manufacturers for product stewardship and
informative to consumers when making decisions on consumable
purchases. Such considerations are components of a broader life
cycle assessment strategy for AM [37].
4.2. Ozone and carbonyl reaction product formation
Regardless of machine type, elevated levels of ozone were
measureable in all printer rooms. The exact mechanism by which
ozone was formed by the AM machines is not known. For the
material jetting machines, the ultraviolet laser wavelength used to
cure resin is above 200 nm and would not be capable of forming
ozone. Given that elevated levels of ozone were measured in all
printer rooms, one plausible source is the electrical components of
the AM machines. Carbonyl compounds observed were present in
both the background and during the printing process, suggesting
that the printing process did not emit new carbonyl compounds
into the indoor environment. This trend was observed in all sam-
ples collected from the varying locations and was in contrast to a
previous laboratory chamber experiment, which indicated the
formation of carbonyls during printing [20]. Given an average
ozone concentration of 20 mg/m3 and an average ozone rate con-
stant of 1
1016 cm3molecules1 s1 for alkenes containing one to
two carbonecarbon double bonds, the pseudo-first-order rate
constant is 0.090/hr. We assumed an average air exchange rate of
0.22/hr for Facilities AeC, and the rate was 2/hr for Facility D.
Hence, one possible explanation for why new carbonyls did not
form during printing could be that the precursors to carbonyl for-
mation were removed by air currents before reactions occurred.
4.3. Personal exposures to metals and VOCs
Measured personal exposures to metals and individual VOCs
2018;-:1e8were well below their corresponding NIOSH RELs. For metals, NRD
Emissions and Exposures From Use of Industrial-Scale Additive
rg/10.1016/j.shaw.2018.10.003
ssesssamplers were used to measure personal exposure to metal-
containing particles with diameters <300 nm because these par-
ticle sizes have high probability of depositing in the alveolar region
of the lung [38]; however, the mass per particle decreases as size
decreases. Hence, mass exposures to thesemetals could be higher if
they were measured using a sampler that collects larger size par-
ticles which may be useful in future studies. In addition, it is
important to note that the surface-to-volume ratio rapidly in-
creases as particle size decreases, meaning that more atoms are on
the surface of nanoscale particles and available to react with bio-
logical systems, making surface area an important metric for pul-
monary inflammation for exposure to insoluble and poorly soluble
particles [13]. Seven different VOCs were quantified on personal
samples collected from employees at Facility A (acetone, pentane,
hexane, benzene, cyclohexane, ethanol, and naphtha) during ma-
terial extrusion AM processes. He et al [39] measured exposures of
workers during an extrusion process at an ABS plastics recycling
facility and also identified benzene and cyclohexane. At this time, it
is unknown whether the source of naphtha exposure is the AM
machines. Facility A also contains a sand binder jetting machine
(not in use at the time of our survey), and naphtha is often used as a
carrier or reducer in sand-casting processes to improve the drying
and removal process of the metal from the sand cast [40,41].
At Facilities A and B, ethanol was used as a cleaning solvent and
was measured on all personal samples. du Preez et al [3] reported
that postprocessing of ABS- and PL-printed objects using vapor
polishing resulted in personal exposures to acetone and chloro-
form, respectively. Graff et al [4] evaluated preprinting and post-
printing tasks associated with laser sintering printing of metal
powders and reported that these tasks resulted in elevated con-
centrations of particles. Hence, exposures to emissions during
operation of AM machines is just one contributor to total exposure
among AM operators, and consideration should be given to un-
derstanding all contributing sources in these workplaces. Personal
exposures to VOCs were all well below their applicable RELs. It is
important to note that themeasured exposures reflect conditions at
the time of sampling and that any changes to work processes,
including building-related factors (changes to ventilation, etc.),
machine-related factors (number, type, etc.), and feedstock-related
factors (thermoplastic, resin, etc.), could change VOC
concentrations.
5. Conclusions
Overall, particle numberebased ERs in these industrial work-
places were on the order of 109e1010 number/min for material
jetting machines (P-Trak data) and 1010e1011 number/min for
material extrusion machines (CPC data). ERs calculated from OPC
data were several orders of magnitude lower, suggesting that
emitted particles had sizes predominantly below 300 nm regard-
less of the AM process in use. Low levels of metals and organic
chemicals were measurable in all workplaces. Notably, material
jetting machine resin feedstock released particles and VOCs at
levels similar to or greater than some material extrusion machines
that use heat to melt feedstock material. The health significance of
these exposures is currently unknown, although available literature
indicates that inhalation of ABS filament emissions during opera-
tion of a material extrusion AM machine may be associated with
work-related asthma inworkers and acute hypertension in rodents.
At this time, it is unknown if potential adverse effects are attrib-
utable to VOCs, UFP, or both VOCs and UFP. Hence, further work-
place evaluations could help to understand factors that influence
emissions from these and other types of AM processes and to
quantify exposures in larger populations of AM operators. Such
A.B. Stefaniak et al / Workplace ainformation is necessary to understand risk potential and identify
Please cite this article in press as: Stefaniak AB, et al., Insights Into
Manufacturing Machines, Safety and Health at Work (2018), https://doi.oeffective control technologies, if deemed to be necessary. The real-
time monitoring instruments and sampling techniques used in this
study provided useful information on emissions and exposures in
diverse workplaces and could serve as a model to standardize ap-
proaches for future workplace assessments.
Acknowledgments
Funding for this project was provided by NIOSH intramural
funds (ABS, ARJ, DH, JRW, JEH, RFL, SBM, MGD, LNB, AKK) and the
South African Department of Science and Technology (SDP, DJDB,
JDP). The funding sources had no involvement in the study design;
collection, analysis and interpretation of the data; writing of the
report; or the decision to submit the article for publication. The
authors thank C. Qi, K.L. Dunn, and G. Roth at NIOSH for critical
review of this manuscript before submission to the journal.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.shaw.2018.10.003.
Disclaimer
The findings and conclusions in this report are those of the
authors and do not necessarily represent the official position of the
National Institute for Occupational Safety and Health, Centers for
Disease Control and Prevention.
Conflict of interest
The authors declare no conflict of interest.
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rg/10.1016/j.shaw.2018.10.003