Table 6.

Advantages and limitations of real-time instruments and time-integrated samplers used to characterize emissions and exposures from additive manufacturing processes.

Approacha	Details	Metric(s)	Useb	Commentc
Real-time particle monitors
PSM	1 to 3 nm	#/cm3, size	A	+ Lowest size cutoff among available instruments; used for ME process category
				− Instrument heavy and delicate which can limit use in workplace studies
F/SMPS	6 to 560 nm	#/cm3, size	A	+ Lower size cutoff sufficient for PBF, MJ, ME, DED, and BJ processes
				− Limited portability for field studies; some particles for ME and BJ outside size range
miniDiSC	7 to 400 nm	#/cm3, size	A, P	+ Lower size cutoff sufficient for PBF, MJ, ME, DED, and BJ processes
				− Slow response time (~ 7 sec) could underestimate exposure for short duration tasks
EDB	7 to 400 nm	#/cm3, size	A	+ Lower size cutoff sufficient for PBF, MJ, ME, DED, and BJ processes; good accuracy
				− Lower size resolution compared with mobility particle sizers
CNC	10 to 1000 nm	#/cm3	A	+ Hand-held; lower size cutoff sufficient for PBF, MJ, ME, DED, and BJ processes
				− Wick has finite sampling duration; cannot count smallest particles
DC	10 to 300 nm	#/cm3, size	A	+ Hand-held; sufficient for PBF, MJ, ME, and DED processes
				− External “envelope” surface area only
LDSA	10 to 487 nm	#/cm3, size, μm2/m2 lung	A, P	+ Hand-held; particle collection onto TEM grid; sufficient for PBF, MJ, ME, and DED processes
				− modeled value and generally only accurate in the 10 to 400 nm size range
AMS	30 to 1000 nm	Size, mass	A	+ Chemically resolved particle size and non-refractory mass distribution; used for ME process
				− Uncertainty with collection efficiency and ionization efficiency for organic aerosols
LSP	0.1 to 15 μm	μg/m3	A	+ Gives PM1, PM2.5, PM10, and total particle mass concentrations; sufficient for BJ processes
				− Small particles emitted from PBF, MJ, ME, and DED processes scatter little light (poor signal)
OPS	0.3 to 10 μm	#/cm3, size, μg/m3	A	+ Multiple metrics; particle collection onto TEM grid permits microscopic characterization
				− Many particles from PBF, MJ, ME, and DED processes smaller than lower size cutoff
Time-integrated particle samplers
Direct-to-substrated	Particles	Shape, size, composition	A	+ Minimizes artifacts from sample handling; chemical information with appropriate detector
				− Time- and cost-intensive; individual particle analysis might not represent bulk sample
NRD	Particles	<300 nm	A, P	+ Selective for nanoscale particles; successfully used for ME and MJ process categories
				− Nanoscale particles have little mass; sampler interferences possible (e.g., Ti in membranes)
PVC, TF	Dust	μg/m3	A, P	+ Simple; inexpensive; multiple sampling heads available for total and size-selective fractions
				− Gravimetric analysis nonspecific; insensitive for ME, VP, and MJ process categories
PVC, CN	Elements	μg/m3	A, P	+ Multiple elements; multiple sampling heads available for total and size-selective fractions
				− Incomplete digestions will underestimate mass; sample interferences possible
QFF	Cr(VI)	μg/m3	A, P	+ Specific to Cr(VI); multiple sampling heads available for total and size-selective fractions
				− Impregnated filter needed to prevent redox reactions of Cr compounds before analysis
TEPC	Particles	Shape, size, composition	A, P	+ Smooth surface for SEM analysis; chemical information with appropriate detector
				− Time- and cost-intensive; individual particle analysis might not represent bulk sample
Real-time gas monitors
PID	10.6 eV lamp	TVOC	A, P	+ High resolution (1 sec interval)
				− nonspecific; only measures organic compounds with ionization potential below eV of lamp
Sensor	Various	CO, CO2, HCN, NH3, NO2	A	+ Multiple gases from one instrument
				− Sample interferences possible from other gases
Sensor	Semiconductor or UV-based	Ozone	A	+ Hand-held; short response time; accurate
				− Need to select appropriate sensor a priori; slow response time at high concentrations
Sensor	Electrochemical	Formaldehyde	A	+ Hand-held; specific
				− Slow response time (8 to 60 sec) could underestimate exposure for short duration tasks
Time-integrated gas samplers
Badge	Individual VOCs	μg/m3	A, P	+ Multiple compounds from one sample; no air sampling pump or tubing
				− Diffusion coefficient must be known for each sampled substance; generally ppm levels
Canister	Individual VOCs	μg/m3	A, P	+ Whole air sample; multiple compounds from one sample; sensitive; no air sampling pump
				− Bulky; humidity effects for some VOCs; not amenable for reactive VOCs (e.g., aldehydes)
DNPH	Carbonyls	μg/m3	A, P	+ Multiple compounds from one sample
				− Requires reaction with derivitizing agent and formation of stable product until analysis
Impinger	Carbonyls	μg/m3	A	+ Multiple compounds from one sample
				− Requires reaction with derivitizing agent and formation of stable product until analysis
TD tube	Individual VOCs	μg/m3	A, P	+ Many sorbents available to collect a wide range of VOCs; multi-compound analysis
				− Humidity and storage effects; adsorbent specific to compound or groups of compounds
OE nose	Individual VOCs	Presence	A	+ Many dyes available for identification of VOCs; potential for personal sampling
				− Time-intensive sample preparation; qualitative results

^aAMS = aerosol mass spectrometer, CN = cellulose nitrate filters, CNC = condensation nuclei counter (e.g., CPC, P-Trak), DC = diffusion charger (e.g., NanoTracer), DNPH = 2,4-Dinitrophenylhydrazine-coated silica gel sorbent tube, EDB = electrometer-based diffusion battery, F/SMPS = fast/scanning mobility particle sizer, LDSA = lung deposited surface area (e.g., NSAM), LSP = laser scattering photometer (e.g., DustTrak^™, EPAM), NRD = nanoparticle respiratory deposition sampler, OE nose = optoelectronic nose, OPS = optical particle sizer (e.g., Lighthouse, GRIMM, TSI 3300), PID = photoionization detector, PSM = particle size magnifier, PVC = polyvinyl chloride filter, QFF = quartz fiber filter, TEPC = track-etched polycarbonate filter, TD = thermal desorption tube, TF = Teflon^® filter

^bA = area sampling, P = personal breathing zone sampler

^cBJ = binder jetting process category, Cr = chromium, Cr(VI) = hexavalent chromium, DED = directed energy deposition process category, eV = electron volt, ME = material extrusion process category, MJ = material jetting process category, PBF = powder bed fusion process category, PM_x = particulate matter with aerodynamic diameter less than 1 μm, 2.5 μm, or 10 μm, SEM = scanning electron microscopy, TEM = transmission electron microscopy, Ti = titanium, VOC = volatile organic compound

^dDirect to substrate = sampling techniques that deposit particles directly onto a substrate for off-line analysis using scanning or transmission microscopy (can include energy dispersive x-ray detector, electron energy loss spectrometry detector, or other detector), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), or other characterization technique. Examples include critical orifice with TEM grid (Katz et al. 2020), electrostatic precipitator (ESP) with TEM grid (Mendes et al. 2017; Steinle 2016), mini particle sampler (MPS) with TEM grid (Bau et al. 2020; Jensen et al. 2020; Oberbek et al. 2019; Youn et al. 2019), thermophoretic sampler (TPS) with TEM grid (Dunn, Dunn, et al. 2020a; Gu et al. 2019; Zisook et al. 2020; Zontek et al. 2017), nanometer aerosol sampler (NAS) with TEM grid (Gomes et al. 2019), and single-stage impactors with glass substrate (Zontek et al. 2017)