Dermal exposure and surface contamination associated with the use of a cobalt-chrome alloy during additive manufacturing

Abstract

Introduction: Additive Manufacturing (AM) is a layered-based technology that is used to manufacture three-dimensional products from computer-aided design. AM offers many advantages over traditional methods of manufacturing which have led to an increase in the application of the technology in many industries, homes, and schools. Metal powders such as cobalt-chrome (CoCr) alloys can be used as feedstock materials for the powder bed fusion (PBF) AM processes. During the activities that form part of the three processing phases of AM (pre-processing, processing, and post-processing), dermal exposure may occur when the AM operators come into direct contact with the feedstock powders, or when the powder particles become airborne and settle onto their skin or onto surfaces within the workplace with which they have contact. Dermal exposure is often overlooked due to the perception that respiratory exposure is the main route of concern. To date, only one study has assessed dermal exposure during AM. This study found detectable concentrations of nickel (Ni), Co, and Cr on the index fingers of AM operators. Metals such as Ni, Co, and Cr are known dermal sensitisers that may lead to adverse health effects following dermal exposure. Due to the limited amount of information available, and the adverse health effects associated with dermal exposure to metals such as Co and Cr, there is a need for further investigation into dermal exposure during metal AM. This study, therefore, aimed to expand on the information available by characterising virgin and used samples of a CoCr alloy feedstock powder (CO-538) in terms of its particle size, shape, and elemental composition, and by assessing dermal exposure and workplace surface contamination when the CoCr alloy feedstock powder was used during PBF. Method: To establish the particle size distribution (PSD) and shape of the virgin (new) and used CO-538 feedstock powder, static image analysis (Malvern Morphologi G3) and scanning electron microscopy (SEM) analysis were used. Inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis was used to establish the elemental composition of the virgin and used CO-538 feedstock powder samples. A removal wipe sampling method using GhostwipesTM was used to assess dermal exposure and surface contamination when the CO-538 feedstock powder was used during PBF. All AM operators at the facility (n=2) volunteered to participate in this study which was conducted over a period of eleven days during which six of the same products were manufactured. Anatomical areas such as the index finger, palm, wrist, back of the hand, and neck were sampled before and after each AM processing phase (7 pre-processing, 5 processing, and

7 post-processing phases). Operating (AM) and non-operating (non-AM) workplace surfaces were sampled before and after each shift to quantify surface contamination (35 samples). All dermal and surface wipe samples were analysed using ICP-mass spectrometry (ICP-MS). Results: The PSD analysis indicated a statistically significant difference (p ≤ 0.05) at d(0.1) between virgin and used powder with the used powder particles generally smaller in size than those of virgin powder particles based on the mean. Statistically significant differences (p ≤ 0.05) were also observed in the mean circularity and convexity of virgin and used powders, indicating that the used powders consisted of more particles that were irregularly shaped and less smooth-surfaced than the virgin powder particles. Co, Cr, molybdenum, aluminium, iron, and Ni were detected in the new and used CO-538 feedstock powder. Dermal exposure to CO-538 constituents occurred during all three processing phases, on all the sampled anatomical areas, with the highest total metal concentration detected on the index finger during the post-processing phase of AM with a geometric mean (GM) and 95% lower and upper confidence intervals (CI) of 3.160 μg/cm2 (CI: 0.703-14.210 μg/cm2). The metal with the highest detected concentration was Co, with a GM of 1.224 μg/cm2 (CI: 0.280-5.336 μg/cm2) on the finger during the pre-processing phase. The highest full shift GM concentration of each metal was detected on the finger and followed a trend of Co > Cr > Fe > Al > Mo > Ni. Surface contamination was detected on all AM and non-AM operating sampling areas with concentrations ranging from 0.106 μg/cm2 on operator 2’s office desk to 19.695 μg/cm2 on workbench 1. Conclusion: When CO-538 feedstock powder are used during AM, dermal exposure to metals such as Co, Cr and Ni, which are known dermal sensitisers, does occur. Therefore, a risk of developing adverse dermal health effects following exposure during AM does exist. Furthermore, it is shown that cross-contamination between AM and non-AM areas occurs, and, therefore, all sampled surfaces may act as a secondary source of exposure. There is thus a need for control measures to be implemented in AM facilities to eliminate or reduce dermal exposure and to limit the spread of contaminants within the facility. Comprehensive standard operating procedures regarding housekeeping and personal protective equipment should be developed and implemented in AM facilities. Furthermore, controls such as local extraction ventilation should be used during manual handling activities, and high-risk activities such as using compressed air should be prohibited.