Application of the AIHA IH-Decision-Making Framework and Process Model on Review of Particulate Matter Exposures

1211 

Professional Poster 

F Louie¹

¹Insight Exposure & Risk Sciences Group, South San Francisco, CA

Fian Louie  
Insight Exposure & Risk Sciences Group

This research applies the AIHA Industrial Hygiene (IH) Decision-making Framework and Process model, as outlined by Jahn et al. (2015), to additive manufacturing (AM), often generally referred to as 3D-printing, through selective laser sintering (SLS) using polymeric-based powders (e.g., commonly nylon, such as Polyamide 2200 (PA-12)). We summarize the available information and identify knowledge gaps for the four key risk assessment steps: 1) hazard assessment, 2) exposure assessment, 3) risk characterization, and 4) risk management. SLS falls under a broader category of AM called powder bed fusion (PBF), which builds parts layer by layer by fusing powder particles using a heat source, such as a laser. This emerging technology has many advantages compared to traditional manufacturing, including high precision, advanced fabrication, and reduced use of precursor materials. However, the occupational hazards and exposure potential to workers are highly variable and not well understood. Particularly in R&D settings, SLS may pose unique exposure scenarios to workers due to the potential for novel processes, variable selection of feedstock materials that may involve mixtures, reuse of feedstock powders, and relatively increased product handling. While SLS and AM technologies continue to evolve, IH and OEHS practitioners can benefit from going through the risk assessment steps to identify potential knowledge gaps and inform the development of risk management plans.

Research on additive manufacturing (AM) has grown in recent years, particularly in 3D printing applications that are consumer-facing. However, significant data gaps remain regarding selective sintering laser (SLS) operations, particularly in industrial and R&D applications. The available data from the few published studies that have characterized potential exposures associated with SLS and polymeric based powders are not representative of all potential scenarios, nor have the data been aggregated into the AIHA IH Decision-making Framework and Process model to date. Compared to other AM operations, SLS requires relatively increased product handling (e.g., weighing powder, taking product out of powder, sieving and reusing powder). Additionally, given its use in novel R&D applications, there is the potential for mixing of different powders as feedstock material. As such, the hazards and exposure potential associated with SLS operations are highly variable and not well understood. Therefore, walking through this framework would benefit IH and OEHS professionals to 1) characterize hazards, exposure potential, and risks within the risk assessment paradigm, 2) manage risks associated with novel AM technologies, and 3) highlight to researchers where there are specific knowledge gaps to be filled.

A literature search was conducted on PubMed to identify relevant peer-reviewed, published studies to inform the application of the IH Decision-making Framework and Process to SLS/polyamide. Studies were considered for review that included data on emissions during powder bed fusion (PBF) operations, specifically SLS, in the workplace using powdered nylon. Additionally, literature on PubMed and publicly available safety data sheets (SDSs) for a commonly used nylon powder in SLS (trade name: Polyamide 2200, also referred to as PA2200 or PA-12) were reviewed for hazard information, occupational exposure limits (OELs) to establish hazard criteria, and recommendations for risk management actions (e.g., appropriate engineering controls, personal protective equipment).

There is limited knowledge on potential inhalation health effects of polyamide. No data were available on acute oral, dermal, or inhalational toxicity; dermal or ocular irritation; respiratory or skin sensitization; reproductive toxicity; or carcinogenicity (EOS, 2024, 2025). It was found that smaller particles may be produced through reuse of powders which may alter their hazard potential (Alijagic et al. 2022).
No OELs specific to polyamide were identified. There is limited exposure data on particulate matter (PM) emissions from SLS operations using polyamide. The available data included average, median, or single concentrations of respirable dust (RD), inhalable dust (ID), total dust (TD), and submicron and nanosized particles (NP). These data were based on task-based and long-term sample durations; real-time and active monitoring; personal and area sample locations; and pre-process, machine operation, and post-process tasks (Damanhuri et al. 2019a,b; Vaisanen et al. 2019; Zisook et al. 2020; Eden et al. 2021; Kangas et al. 2023). For particulates not otherwise regulated or specified (PNOR or PNOS), ACGIH and OSHA have 8-hr TWA OELs established for both RD and TD or ID (ACGIH – RD: 3 mg/m3; ID: 10 mg/m3; TD: 15 mg/m3; OSHA – RD: 5 mg/m3; TD: 15 mg/m3). Due to the lack of hazard information, the use of PNOR/PNOS standards for polymeric materials may be insufficient. The ACGIH and OSHA 8-hr TWAs were not exceeded during any SLS tasks in the literature reviewed.
No OELs exist for submicron particles or NP from ACGIH or OSHA, but other organizations have proposed OELs for engineered NP. If selected as relevant hazard criteria, the values posed can prompt exposure control measures if exceeded during SLS. Controls to reduce dust and particle concentrations include isolation, increased ventilation, or avoiding prolonged exposure at close proximity in an unventilated room. Respiratory protection is recommended if exposures cannot be controlled through ventilation. Regular confirmation of effective control and risk management measures, via evaluation of the magnitude and daily duration of exposure which must be tailored to specific tasks, is also essential.
This framework and process allow IH/OEHS professionals to better understand the state of the knowledge on hazards, exposures, and risks associated with SLS using nylon powders, from which risk management decisions can be facilitated. Knowledge gaps include the need for hazard information, particle size distribution data on raw vs. spent powder, task-based vs. full-shift concentrations with and without controls, and efficacy of controls for the full range of SLS tasks. Due to the limited data, it was difficult to compare results due to variability in study methods and data reporting limitations. While this exercise focused on inhalation exposure to PM, further data and application of this framework and process are needed for dermal exposure and other constituents emitted during SLS (e.g., VOCs).

Risk Assessment

Risk Management

Work Environments, Occupations, and Industrial Processes