本研究擬建立雷射金屬沉積作業金屬燻煙微粒之特徵與逸散速率，並評估雷射金屬沉積作業勞工金屬燻煙微粒的暴露情形，且透過可接受之暴露風險的角度，提出LMD作業空間所需最保守估計之通風時間，來控管作業人員之進出，以達保護勞工健康之目的。本研究以一設置一台機械手臂式雷射金屬沉積機台，及一提供100ACH的整體換氣系統之庫房(3.6m× 3.8m × 2.9m)為研究地點，使用SMPS於雷射沉積金屬機械手臂作業前之庫房內測量其背景濃度，再於庫房內使用上述直讀式儀器搭配MOUDI進行作業過程中微粒逸散的三重複採樣，以獲得之樣本再進行粒數、質量、表面積、重金屬濃度與逸散速率之特徵分析，分析後的重金屬濃度推估增量致癌風險作為勞工之健康風險評估，再以逸散速率推估不同LMD時間下微粒的數目、質量、表面積濃度，並以微粒的數目、質量、表面積濃度及增量致癌風險為暴露評估指標並推估所需的通風時間以做為建立通風系統操作指引之基礎。本研究結果顯示該作業產生之金屬燻煙微粒的數目濃度其CMD為0.029 μm與GSD為1.88，MMD為0.069 μm與GSD為1.91，及SMD為0.045 μm與GSD為1.91。該作業之逸散速率為1.20×1010 #/min，且微粒沉積於肺泡區(AL: 58 – 71%)之比例皆遠大於頭區(HA: 11 – 18%)及氣管支氣管區(TB: 18 – 24%)。鎳的平均重金屬濃度為83.62 ± 36.19 μg/ m3，95百分位值為161.07 μg/ m3，超過短時間時量平均容許濃度（PEL-STEL = 50），且其總致癌風險（1.16×10-4）超過可接受標準值（10-6）。進一步利用作業場所之逸散速率推估不同LMD時間下其微粒的數目、質量、表面積總濃度範圍分別為7.77×1011 – 8.56×1011 #/cm3，2.13×109 – 2.29×109 μg/ m3及4.61×107 – 1.37×108 μm2/cm3。由不同LMD操作時間與不同的可接受暴露評估指標進行通風時間之計算，發現由微粒數目、質量、表面積濃度和總致癌風險所需的通風時間分別為13、10、10及7分鐘，從審慎的角度來看，因此建議LMD製程採用13分鐘的通風時間，以降至可接受之暴露濃度。

Introduction
The laser metal deposition (LMD) technology has been widely used in metal mold, aerospace, steel, petrochemical, mechanical hardware and many other industries. It is a method for depositing molten metal by irradiating a laser beam while ejecting metal powder to form a metal protective layer for anti-corrosion and anti-wear, or using the metal powder melt as the material for printing 3D objects. During the LMD process, the laser power is set at 2000 watts (temperature : 1500 ℃ or higher), the metal powder was heated over the melting point and volatilized into the air, then the metal vapor is aggregated at the ambient temperature to form the metal particles in a nanoparticle form. Inhalatory exposures to these oxidized metals might encounter potential health hazards. The question regarding how to reduce the exposure of workers becomes an important issue. The present study was set out first to investigate the emission characteristics of metal fume particles generated from the LMD process, then to determine the suitable ventilation time for workers to enter the LMD chamber to prevent them from being exposed to the emissions from the LMD process.

Materials and Methods
The studied LMD chamber (3.6m × 3.8m × 2.9m) is installed with a robot laser metal deposition machine and equipped with a general exhaust ventilation (GEV) system providing air exchange rate at 100 ACH. Direct-reading instruments of a SMPS and an APS were used to conduct sampling inside and outside the chamber to measure particle concentrations, and a MOUDI was used to conduct sampling inside to measure particle number and mass concentrations. Measurements conducted outside and inside were used to characterize the concentrations of the background and the LMD emissions, respectively. Samples collected by MOUDI were further analyzed for their heavy metal concentrations using ICP-MS. The resultant emission rates of the particle number, mass and surface area were used to determine the required ventilation time for different LMD time based on the acceptable levels of different exposure metrics. Finally, results obtained from the present study were served as a basis to establish safety operating guidelines for the studied LMD process.

Results and Discussion
Results show that the particle distributions of metal fume particles emitted from the LMD process were found with CMD and GSD as 0.029 μm and 1.88, MMD and GSD as 0.069 μm and 1.91, and SMD and GSD as 0.045 μm and 1.91, respectively. The emission rate (ER) and emission factor (EF) of the particle number were found as 1.2×1010 #/min and 4.67×108 #/g, respectively. The fractions of the metal fume particles deposited on the alveolar region (AL: 58 – 71%) were much higher than that of other two regions (head airways (HA: 11 – 18%) and tracheobronchial (TB: 18 – 24%)). The mean workplace heavy metal concentrations for nickel was 83.62 ± 36.19 μg/m3 with a 95%-tile level (161.07 μg/m3) exceeding the current exposure limits (PEL-STEL = 50μg/m3). The resultant total cancer risk (CR) (1.16 × 10-4) could not comply with the acceptable value (10-6). The obtained emission rates were further used to estimate the emitted concentrations of metal fume particles for LMD time from 1 min to 5 min. Results show that the resultant particle number concentrations, mass concentrations, and surface area concentrations fell to the range of 7.77×1011 – 8.56×1011 #/cm3, 2.13×109 – 2.29×109 μg/ m3, and 4.61×107 – 1.37×108 μm2/cm3, respectively. Using the above as a basis, if a general exhaust system with 100 ACH was installed in the LMD chamber, the required ventilation times for the exposure metrics of the particle number, mass, surface area concentrations and acceptable excessive cancer risk were found as 13, 10, 10 and 7 minutes, respectively. From the prudent aspect, the longest one (13 minutes) is suggested as the acceptable ventilation time for the LMD process.
Conclusions
Particles emitted from the LMD process were in the form of the bimodal. The emitted metal fumes contain nano- and submicron-particles, and the fraction of particles deposited on the AL region was higher than that of the other two regions. The emitted heavy metal concentrations and the resultant health risks were found to be unacceptable. The present suggest a ventilation time of 13 minutes for the LMD process if a general exhaust system with 100 ACH was installed in the LMD chamber.

AIHA AIHA. 2015. A strategy for assessing and managing occupational exposure. USA.
Antonini JM, Lewis AB, Roberts JR, Whaley DA. 2003. Pulmonary effects of welding fumes: Review of worker and experimental animal studies. American journal of industrial medicine 43:350-360.
Azimi P, Zhao D, Pouzet C, Crain NE, Stephens B. 2016. Emissions of ultrafine particles and volatile organic compounds from commercially available desktop three-dimensional printers with multiple filaments. Environmental science & technology 50:1260-1268.
Barcikowski S, Hahn A, Kabashin A, Chichkov B. 2007. Properties of nanoparticles generated during femtosecond laser machining in air and water. Applied Physics A 87:47-55.
Buonanno G, Morawska L, Stabile L. 2009. Particle emission factors during cooking activities. Atmospheric Environment 43:3235-3242.
Buonanno G, Morawska L, Stabile L. 2011. Exposure to welding particles in automotive plants. Journal of Aerosol Science 42:295-304.
Buzea C, Pacheco II, Robbie K. 2007. Nanomaterials and nanoparticles: Sources and toxicity. Biointerphases 2:MR17-MR71.
Chao CY, Wan M, Cheng EC. 2003. Penetration coefficient and deposition rate as a function of particle size in non-smoking naturally ventilated residences. Atmospheric Environment 37:4233-4241.
Chiung Y-mH, Chun-ming; Liu,Pei-shan. 2011. Cell toxicity and worker health caused by nano-sized metals from laser-cutting process. Institute of Labor, Occupational Safety And Health, Ministry of Labor IOSH99-M324.
Demou E, Peter P, Hellweg S. 2008. Exposure to manufactured nanostructured particles in an industrial pilot plant. Annals of Occupational Hygiene 52:695-706.
Demou E, Stark WJ, Hellweg S. 2009. Particle emission and exposure during nanoparticle synthesis in research laboratories. Annals of occupational hygiene 53:829-838.
Donaldson K, Li X, MacNee W. 1998. Ultrafine (nanometre) particle mediated lung injury. Journal of Aerosol Science 29:553-560.
Donaldson K, Tran L, Jimenez LA, Duffin R, Newby DE, Mills N, et al. 2005. Combustion-derived nanoparticles: A review of their toxicology following inhalation exposure. Particle and fibre toxicology 2:10.
Elihn K, Berg P. 2009. Ultrafine particle characteristics in seven industrial plants. Annals of Occupational Hygiene:mep033.
Elsaesser A, Howard CV. 2012. Toxicology of nanoparticles. Advanced drug delivery reviews 64:129-137.
Ferreira-Baptista L, De Miguel E. 2005. Geochemistry and risk assessment of street dust in luanda, angola: A tropical urban environment. Atmospheric Environment 39:4501-4512.
Fuks NA. 1989. The mechanics of aerosols:Dover Publications.
Gatoo MA, Naseem S, Arfat MY, Mahmood Dar A, Qasim K, Zubair S. 2014. Physicochemical properties of nanomaterials: Implication in associated toxic manifestations. BioMed research international 2014.
Gonser M, Hogan T. 2011. Arc welding health effects, fume formation mechanisms, and characterization methods. In: Arc welding:InTech.
Gray C, Hewitt P, Dare P. 1983. New approach would help control weld fumes at source. Part three: Mma fumes.
Grinshpun S, Lipatov G, Sutugin A. 1990. Sampling errors in cylindrical nozzles. Aerosol Science and Technology 12:716-740.
Grinshpun S, Willeke K, Kalatoor S. 1993. A general equation for aerosol aspiration by thin-walled sampling probes in calm and moving air. Atmospheric Environment Part A General Topics 27:1459-1470.
Gu D, Meiners W, Wissenbach K, Poprawe R. 2012. Laser additive manufacturing of metallic components: Materials, processes and mechanisms. International materials reviews 57:133-164.
Han JH, Lee EJ, Lee JH, So KP, Lee YH, Bae GN, et al. 2008. Monitoring multiwalled carbon nanotube exposure in carbon nanotube research facility. Inhalation toxicology 20:741-749.
Hinds WC. 2012. Aerosol technology: Properties, behavior, and measurement of airborne particles:John Wiley & Sons.
Howard-Reed C, Wallace LA, Emmerich SJ. 2003. Effect of ventilation systems and air filters on decay rates of particles produced by indoor sources in an occupied townhouse. Atmospheric Environment 37:5295-5306.
HSE HaSE. 2014. Local exhaust ventilation (lev) guidance. HSE.
ICRP ICoRP. 1994. Human respiratory tract model for radiological protection, publication 66,annals of icrp.
Khlystov A, Stanier C, Pandis S. 2004. An algorithm for combining electrical mobility and aerodynamic size distributions data when measuring ambient aerosol special issue of aerosol science and technology on findings from the fine particulate matter supersites program. Aerosol Science and Technology 38:229-238.
Kim Y, Yoon C, Ham S, Park J, Kim S, Kwon O, et al. 2015. Emissions of nanoparticles and gaseous material from 3d printer operation. Environmental Science & Technology 49:12044-12053.
Kyogoku H. 2014. < レビュー> 金属 3d プリンタの開発動向と今後の展開. 近畿大学次世代基盤技術研究所報告 5:139-143.
Lee M-H, McClellan WJ, Candela J, Andrews D, Biswas P. 2006. Reduction of nanoparticle exposure to welding aerosols by modification of the ventilation system in a workplace. In: Nanotechnology and occupational health:Springer, 127-136.
Marple VA, Rubow KL, Behm SM. 1991. A microorifice uniform deposit impactor (moudi): Description, calibration, and use. Aerosol Science and Technology 14:434-446.
Maynard AD. 2003. Estimating aerosol surface area from number and mass concentration measurements. Annals of Occupational Hygiene 47:123-144.
Maynard AD, Kuempel ED. 2005. Airborne nanostructured particles and occupational health. Journal of nanoparticle research 7:587-614.
McCann B, Hunter R, McCann J. 2002. Cocaine/heroin induced rhabdomyolysis and ventricular fibrillation. Emergency Medicine Journal 19:264-264.
Meeker JD, Susi P, Flynn MR. 2007. Manganese and welding fume exposure and control in construction. Journal of occupational and environmental hygiene 4:943-951.
Mueller EJ, Seger DL. 1985. Metal fume fever—a review. The Journal of emergency medicine 2:271-274.
Nemery B. 1990. Metal toxicity and the respiratory tract. European Respiratory Journal 3:202-219.
Nielsen E, Dybdahl M, Larsen PB, Miljøstyrelsen D, Risikovurdering FAfTo. 2008. Health effects assessment of exposure to particles from wood smoke:Danish Environmental Protection Agency.
NIOSH NIfOSaH. 2014. Current strategies for engineering controls in nanomaterial production and downstream handling processes Department of health and human services 2014-102.
NIOSH TNIfOSaH. 2016. Hierarchy of controls. Workplace Safety & Health Topics.
Oberdörster G, Oberdörster E, Oberdörster J. 2005. Nanotoxicology: An emerging discipline evolving from studies of ultrafine particles. Environmental health perspectives:823-839.
OSHA OSaHA. 2009. Assigned protection factors for the revised respiratory protection standard. OSHA OSHA 3352-02.
Pagels J, Wierzbicka A, Nilsson E, Isaxon C, Dahl A, Gudmundsson A, et al. 2009. Chemical composition and mass emission factors of candle smoke particles. Journal of Aerosol Science 40:193-208.
Palmer KT, Poole J, Ayres JG, Mann J, Burge PS, Coggon D. 2003. Exposure to metal fume and infectious pneumonia. American Journal of Epidemiology 157:227-233.
Peters TM, Leith D. 2003. Concentration measurement and counting efficiency of the aerodynamic particle sizer 3321. Journal of Aerosol Science 34:627-634.
Schulte P, Geraci C, Zumwalde R, Hoover M, Kuempel E. 2008. Occupational risk management of engineered nanoparticles. Journal of occupational and environmental hygiene 5:239-249.
Sreekanthan P. 1997. Study of chromium in welding fume.
Stabile L, Fuoco F, Buonanno G. 2012. Characteristics of particles and black carbon emitted by combustion of incenses, candles and anti-mosquito products. Building and Environment 56:184-191.
Stephens B, Azimi P, El Orch Z, Ramos T. 2013. Ultrafine particle emissions from desktop 3d printers. Atmospheric Environment 79:334-339.
Tsai S-JC, Huang RF, Ellenbecker MJ. 2010. Airborne nanoparticle exposures while using constant-flow, constant-velocity, and air-curtain-isolated fume hoods. Annals of occupational hygiene 54:78-87.
USEPA USEPA. 1990. National oil and hazardous substances pollution contingency plan; final rule. 40 CFR part 300.
USEPA USEPA. 2009. Risk assessment guidance for superfund, volume i: Human health evaluation manual (part f, supplemental guidance for inhalation risk assessment), final. Environmental Protection Agency EPA-540-R-070-002, OSWER 9285.7-82.
USEPA USEPA. 2014. Chapter three of the sw-846 compendium: Inorganic analytes. Environmental Protection Agency SW846 Revision 5.
Wehner B, Uhrner U, Von Löwis S, Zallinger M, Wiedensohler A. 2009. Aerosol number size distributions within the exhaust plume of a diesel and a gasoline passenger car under on-road conditions and determination of emission factors. Atmospheric Environment 43:1235-1245.
Xu M, Nematollahi M, Sextro RG, Gadgil AJ, Nazaroff WW. 1994. Deposition of tobacco smoke particles in a low ventilation room. Aerosol Science and Technology 20:194-206.
Zai S, Zhen H, Jia-song W. 2006. Studies on the size distribution, number and mass emission factors of candle particles characterized by modes of burning. Journal of aerosol science 37:1484-1496.
Zhang Q-l, Yao J-h, Mazumder J. 2011. Laser direct metal deposition technology and microstructure and composition segregation of inconel 718 superalloy. Journal of Iron and Steel Research, International 18:73-78.
Zhong C, Chen J, Linnenbrink S, Gasser A, Sui S, Poprawe R. 2016a. A comparative study of inconel 718 formed by high deposition rate laser metal deposition with ga powder and prep powder. Materials & Design.
Zhong C, Gasser A, Kittel J, Wissenbach K, Poprawe R. 2016b. Improvement of material performance of inconel 718 formed by high deposition-rate laser metal deposition. Materials & Design 98:128-134.