Introduction

Additive manufacturing (AM), also known as three-dimensional (3D) printing, has significantly transformed the manufacturing industry, enabling the fabrication of complex forms and patterns with unprecedented precision and accuracy (Liu et al. 2022; Qu et al. 2022). This technology as shown in Fig. 1, contributes to global sustainability as it reduces energy and resource used in the manufacturing sector (Qu et al. 2022; Mostafaei et al. 2022).

Fig. 1
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Metal additive manufacturing

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High-entropy alloys (HEAs) are a newer type of advanced material made of many metals in roughly equal or near-equal amounts (Tang et al. 2023; Zhang et al. 2022a). Layer-by-layer construction of intricate structures using high-entropy alloys requires melting metal powders with lasers or other heat sources. They have outstanding features like great strength, durability, and corrosion resistance. These characteristics make them very attractive (Tang et al. 2023). There are several AM techniques used in fabricating HEAs; such as Selective Laser Melting, Electron Beam Melting, Direct Energy Deposition, Binder Jetting, Laser Melting Deposition, ultrasonic additive manufacturing, fused deposition modelling, photopolymerization and 3D printing with powder metallurgy.

However, like with any new technology, AM of high-entropy alloys esepecially the direct energy deposition technique poses unique safety issues, such as exposure to hazardous gases and the possibility of fire or explosion during fabrication.

Alijagic et al. (Alijagic et al. 2022) suggested that there is a possibility of reusing AM powders, which can alter their physicochemical properties and increase their toxic potential during AM operations. As a result, it is vital to put strong safety standards in place to safeguard both employees and the environment. (Ljunggren et al. 2019) explained how gravimetric, chemical, airborne particle, or volatile organic chemical analyzing techniques should be used to measure airborne particles and chemicals in AM. However, these measurements are insufficient for assessing exposure-related health risks due to particle sizes ranging from 10 nm to 65 µm. Particle-counting instruments are suggested to identify hazardous process steps. Recent research shows that micro- and nano-sized particles and volatile organic chemicals are present in AM environments, according to Dobrzynska et al. (Dobrzyńska et al. 2021).

Despite these safety drawbacks, AM adoption can lead to five major environmental advantages: a decrease in raw material requirements, energy-intensive manufacturing processes, reduced weight of transport-related products, improved functional and operational performance, and decentralized part manufacturing closer to the point of consumption, according to Achilles et al. (Achillas et al. 2015). The design of the 3D printer, the characteristics of the raw materials, the factors involved in its construction, and the colour of the filament applicable to FDM, all affect emission levels and particle diameters, which are measured around 30 nm (Zhang et al. 2022b). Materials like Acrylonitrile Butadiene Styrene (ABS), nylon, and polylactic acid (PLA) may emit hazardous volatile organic chemicals. Extruder temperature and printer failure play crucial roles in particle emissions, with ABS filaments emitting significantly more particles than PLA filaments. Nonetheless, there are limited studies on the emission rates of additively manufactured high-entropy alloys (Mahmood et al. 2023; Ron et al. 2023; Arif et al. 2022).

This study investigates the safety procedures and occupational dangers of high-entropy alloy via additive manufacturing, focusing on the complexities of the manufacturing process and the critical relevance of safety standards. It provides a detailed understanding of the issue’s manufacturers face in maintaining employee safety while producing high-quality products efficiently.

Occupational health risks associated with the use of metal powders in the additive manufacturing of high entropy alloys

There are different element combinations of HEAs, categorised into transition, refractory, and lightweight high-entropy alloys. In these categories, some toxic elements may be incorporated into HEAs to achieve a specific property. For instance, lead (Pd) is a heavy metal used to improve the ductility of HEAs but is toxic to the kidney, reproductive, and nervous systems. Arsenic (As) is used to improve wear and hardness resistance, but it is also a carcinogenic element responsible for neurological problems and skin lesions. Hence, the use of HEAs in AM requires specific risk assessments compared with other alloys and manufacturing techniques due to several factors. Since HEAs are a new class of material, their potential hazards and long-term behaviour are still under investigation. Consequently, there are few reports on the health and environmental risks associated with the fabrication of these materials via AM. HEAs also consist of multiple elements, which could make predicting their potential hazards complex. Furthermore, there are currently very limited standardised regulations for the use of HEAs in AM since HEAs are relatively new, and this lack of regulatory guidelines may have potential. There are also HEAs powder recycling challenges, machine learning compatibility, and problems with the reactive elements with oxygen in the composition, which could pose some undesired health hazards.

There are occupational health issues linked to the use of high-entropy alloy metal powders via additive manufacturing. While additive manufacturing technology has transformed the industrial manufacturing sector, there are certain risks connected with the process (du Plessis et al. 2022; Adamopoulos and Syrou 2022). According to Dugheri et al. (Achillas et al. 2015), the increasing use of automated printing techniques raises concerns about the safety of operators. The AM technology only automates the printing process, but manual or semi-automatic work steps during pre- and post-processes raise concerns about exposure to metal powder. Hence, the use of high-entropy metal powders in additive manufacturing, in particular, has been linked to respiratory and skin illnesses, as well as other health risks (Popov et al. 2021). Cobalt, a neurotoxic metal, may induce cancer and lung complications. Nano-sized particles, such as ultrafine particles (UFPs), have different toxicological properties than larger particles and may have high cellular toxicity. Constant exposure to the alloy powders during manufacture may result in mental disorientation. Furthermore, some high-entropy alloy metal powders containing Titanium, Aluminium, and magnesium are flammable and can cause fires and explosions in certain situations, making it necessary to implement adequate safety precautions. Fume Fever is a condition induced by breathing metal fumes that produces symptoms such as fever, headache, chills, and fatigue. It could also lead to occupational asthma, which is a disorder that develops when employees are exposed to airborne particles, such as high-entropy metal powders, which can induce inflammation in the airways and create breathing difficulties (Mäki et al. 2023). Chronic Obstructive Pulmonary Disease (COPD) is a set of lung disorders that develop as a result of long-term exposure to airborne particles such as high-entropy metal powders, including bronchitis and emphysema. Hence, as the use of high-entropy alloys grows in popularity, it is necessary to address these health concerns and provide complete safety standards to safeguard employees (Mäki et al. 2023). Aside from respiratory ailments, the use of high-entropy alloy metal powders in additive manufacturing without precaution can lead to skin disorders such as contact dermatitis, which can cause skin redness, itching, and irritation. Currently, the European Community has not proposed specific international regulations or occupational exposure limits for nanoparticles. The World Health Organization has guidelines and recommendations for managing exposure to nanoparticles. According to Lyunggren et al. (Kavouras et al. 2022), the American Conference of Governmental Industrial Hygienists reported 56 occupational exposure limits in 2018. The US NIOSH set 0.3 mg/m3 for TiO2 nano-objects and 1.0 µg/m3 for carbon nanotubes, however, there has been nothing set for high entropy oxides or nanoparticles.

Nonetheless, the following precautions can be taken to avoid respiratory and skin infections: Personal Protective Equipment (PPE) should be worn to reduce exposure to metal powders, and workers should use proper PPE such as respirators, gloves, and protective clothes. Adequate ventilation should be available to remove metal dust and pollutants from the workplace; thus, adequate ventilation systems, such as local exhaust ventilation (LEV), should be implemented (Claxton et al. 2022). Metal powders should be handled and stored safely to reduce the danger of exposure. This involves utilizing proper containers, appropriately identifying them, and keeping them in a separate place away from other chemicals. According to Brereton and Alenbach (22), several screening risk assessment methodologies for chemical hazards primarily concentrate on evaluating the potential dangers posed to human health within occupational settings. There are three fundamental modes in which these procedures are categorised: risk ranking, chemical ranking and scoring, and control banding (CB). The use of Control Banding (CB) is employed as a means of effectively managing occupational chemical hazards in the absence of comprehensive toxicological and exposure data. This approach is rooted in the risk paradigm, which aims to mitigate potential dangers associated with chemical substances in the workplace. Risk assessment approaches are characterised by simplicity, since they rely on a binary scale of yes or no, without using complex aggregating procedures.

When metal particles are heated and fused during the additive manufacturing process of high-entropy alloys, metal vapours are created. The high-entropy alloy powder is melted using a laser or electron beam, allowing it to fuse and form a solid component (Karwasz et al. 2022). As the metal powder melts, metal vapours are emitted into the atmosphere. Metal vapours can contain a variety of dangerous chemicals, including metal oxides and other compounds that can be deadly if breathed in. The particular composition of metal vapours is determined by the metal employed in the additive manufacturing process (Khaki et al. 2020). When iron-based, high-entropy alloy compositions are fabricated, iron oxide emissions are produced.

When titanium-based high-entropy alloys are heated, titanium dioxide fumes are produced, and these gases are especially dangerous since they have been linked to lung cancer. When aluminium-based high-entropy alloys are heated, aluminium oxide fumes are produced, which are pollutants that can induce respiratory discomfort and lung damage. When chromium-based alloys are melted, chromium fumes are produced. These vapours are carcinogenic and have the potential to cause lung cancer (Roth et al. 2019). Finally, when nickel-based high-entropy alloys are melted, nickel fumes are produced, and these fumes can irritate and sensitize the lungs, leading to asthma or other respiratory problems. Hence, to manage and reduce exposure to metal vapours during the additive manufacturing process, proper ventilation, nose masks and other safety precautions are required.

Developing a comprehensive safety protocol for additive manufacturing of high entropy alloys

To ensure the safety and well-being of workers in the industry, it is critical to develop a comprehensive safety protocol during the additive manufacturing of high-entropy alloy metal powders that incorporates best practices for handling and storing the metal powders, implementing ventilation systems, and using personal protective equipment (Barnes et al. 2003). The first stage is to identify possible dangers before fabrication, such as exposure to metal dust and gases, electrical hazards, and fire hazards. A hazard analysis or risk assessment can be used to do this. Investigate and comprehend the regulatory prerequisites and standards governing the handling and storage of metal powders, chemicals, and waste products (Brereton and Alenbach 1998). Education and training on the safety protocols for the handling, storage, use, and disposal of metal powders and other chemicals used in additive manufacturing are based on the recognized dangers and regulatory requirements of Personal Protective Equipment such as respirators, gloves, protective gear, and eye and facial protection that should be worn before fabrication using high-entropy alloy metal powders. Develop suitable ventilation systems to decrease pollution (Pernetti et al. 2023). Mazingi et al. (Mazingi et al. 2020) recommended reducing reliance on global supply chains for personal protective equipment by providing inexpensive choices locally, while Chhabra et al. (Hegab et al. 2023) emphasized the need for current professionals to learn about 3D printing, unmanned robotic devices, and PPE innovation. Finally, there should be an establish standards for frequent maintenance of additive manufacturing equipment to minimize leaks, and create methods following local and federal requirements for the safe disposal of high-entropy alloy metal powders and other waste materials. Emergency preparedness should be a top priority, as established emergency response methods in the event of an accident or spill should be plastered around the environment where the AM equipment is situated, and staff should be trained on the safety procedures. (Chhabra et al. 2020; Van Der Walt et al. 2022).

The effectiveness of ventilation systems in reducing exposure to harmful fumes during additive manufacturing of high entropy alloys

The effectiveness of ventilation systems in reducing exposure to harmful fumes during the additive manufacturing of high-entropy alloys should be evaluated. Including but not limited to local exhaust ventilation, dilution ventilation, and general ventilation. The effectiveness of each type of system should be evaluated, along with the best practices for their implementation (Rehman et al. 2022). A local exhaust ventilation (LEV) system eliminates airborne pollutants at or near their source before they disseminate into the surrounding environment. A hood is often used to trap the contamination, ductwork is used to carry it, and a fan or blower is used to produce the necessary airflow. The polluted air is filtered or expelled outdoors. On the other hand, dilution ventilation (DV) is a type of ventilation system that dilutes and removes airborne pollutants from an interior environment by using a high volume of fresh air (Jose et al. 2021). This is accomplished by admitting outside air into the area via supply vents, diluting the concentration of pollutants, and lowering their total level. The air is then expelled from the space via exhaust vents. Dilution ventilation is frequently utilized in environments with low quantities of airborne pollutants. However, it may not be successful in decreasing worker exposure to high levels of hazardous chemicals, so it should not be used as the primary technique of control during the fabrication of high-entropy alloys via additive manufacturing. While general ventilation (GV) is a type of ventilation system that circulates air throughout an indoor area by utilizing a building's heating, ventilation, and air conditioning (HVAC) system (Centea et al. 2020), to maintain a comfortable and healthy interior atmosphere, the air is routinely filtered and conditioned. The importance of general ventilation in preserving indoor air quality and minimizing the concentration of airborne pollutants cannot be overstated during fabrication. However, it may not be enough to regulate occupational exposure to high quantities of hazardous high-entropy alloy compounds and should be reinforced by additional technical and administrative controls as needed (Dugheri et al. 2022). The study conducted by Dobrzynska et al. (Dobrzyńska et al. 2022) examined the possible health hazards associated with the use of additive manufacturing technology in enclosed spaces without mechanical ventilation. The researchers employed a fused deposition modelling printer equipped with nine filaments for their investigation. The researchers performed measurements and detected several chemical compounds, which included styrene monomers and breakdown products. The process of 3D printing resulted in the emission of particles with modal sizes spanning from 22.1 to 106.7 nm, hence leading to an elevated concentration of particles in the ambient air of the workplace. The findings of the study suggest that the existence of particles and chemical compounds might potentially have adverse effects on human health, particularly when they are breathed, leading to potential irritation of the eyes and skin. Saliakas et al. (Pinheiro et al. 2022) conducted a study on the exposure to nano- and micro-sized particles emitted from nanocomposites during filament production for 3D printing. The study involved near- and far-field measurements, portable measuring devices, and a Failure Modes and Effects Analysis (FMEA) study for the extrusion process line. The results showed that emissions were not dispersed in far-field areas due to the installed ventilation system and mobile arm hood. The study also observed concentration upsurges during the use of a vacuum cleaner, mainly for particles larger than 0.3 μm. These upsurges were more pronounced for particle number concentrations and mass concentrations. To mitigate the risk, the researchers recommend using ergonomic heat-resistant gloves, lab coats with knit cuffs, and visible warning signs to alert operators to avoid contact with hot equipment surfaces. This could also lower the risk of operator error.

Indoor air pollution, primarily caused by volatile and semi-volatile organic compounds (VOCs and SVOCs) from indoor structures and furniture, leads to health and socioeconomic issues, including reproductive problems, respiratory complications, immune suppression, cancer, and dementia. They are neurotoxic and cause behavioral changes, learning disabilities, and locomotor impairment. To combat this issue, solutions include reducing material sources and increasing removal methods, such as phytoremediation and metal–organic frameworks (Saliakas et al. 2023). Thermoplastic ABS (ABS) filaments emit significantly more Ultra-Fine Particle (UFP) emissions than raw PLA filaments, with emission levels influenced by factors such as printer design, raw material properties, construction factors, and filament color (Sonne et al. 2022). The temperature of the nozzle affects the number of particles ejected, while consumables, filament types, color, printer type, and component design also affect emissions. ABS and PLA filaments have the lowest and highest UFP emission rates for 3D printing using filaments, respectively (Frizziero et al. 2018). A study by Saliakas et al. (Bockstedte et al. 2022) found that 3D printer operators are exposed to low concentrations of airborne exposure agents, with average VOCs between 41 and 87 µg/m3. UFPs are mostly in the 10–45 nm size range, and outgassed products contain similar compounds. The study recommends that resin printer operators store their products for 4 weeks to reduce emissions and potential consumer VOC hazards (Saliakas et al. 2023).

Evaluating the effectiveness of personal protective equipment in reducing occupational hazards during additive manufacturing of high entropy alloys

Personal protection equipment (PPE) which includes but not limited to face shields/respiratory mask (Powered air-purifying respirators, particulate respirators, self-contained breathing apparatus, supplied air respirators), medical facemasks (N95 respirators, surgical masks, and P100 respirators), and goggles that are impact resistance, UV protected, ventilated, chemical splash resistance, fit and comfortable are essential for limiting occupational health hazards connected with the additive manufacturing (AM) procedures of high entropy alloys (Zhang et al. 2022a). However, various obstacles and constraints must be overcome for PPE to be effective (Cook 2020). One of the most difficult difficulties in choosing proper PPE is the unique risks prevalent in the AM process. AM employs a variety of metal powders, each with distinct physical and chemical qualities that require the use of different forms of PPE. The improper PPE may not effectively protect users from the specific threats to which they are exposed (Dobrzyńska et al. 2022). Another problem is the correct use and maintenance of personal protective equipment (PPE). To guarantee the efficiency of PPE, users must be instructed on how to correctly wear and utilize it. Furthermore, PPE must be examined and maintained regularly to ensure that it is in excellent working order. When choosing PPE, comfort and ergonomics are also important elements to consider. Users may reject wearing PPE if it is unpleasant, cumbersome, or hinders their motions, reducing its efficacy in protecting them from occupational dangers (Akbar-Khanzadeh et al. 1995). Furthermore, personal protective equipment (PPE) may not provide total protection against all threats. Respirators, for example, may not provide appropriate protection against some metal fumes, and gloves may not provide adequate protection against cuts and punctures from sharp items. Finally, PPE might provide users with a false sense of security, causing them to assume they are completely safe from threats. Because of this false sense of security, users may take needless risks and fail to follow adequate safety practices (Singh et al. 2020). Overall, while personal protective equipment (PPE) is an important component in safeguarding users of additive manufacturing equipment from occupational dangers, these problems and limitations must be addressed to maintain its efficacy.

A comparative study of safety practices and occupational hazards of additive manufacturing of high entropy alloys and traditional manufacturing methods

There are also safety risks associated with traditional manufacturing methods for fabricating high-entropy alloys, such as exposure to heavy machinery, repetitive motion injuries, and noise pollution. Arc melting is a popular conventional method of producing high-entropy alloys in which metals are melted using an electric arc (Nagarajan et al. 2020). The metal samples are heated in a furnace in an inert environment, commonly argon or helium, until they reach their melting points. The arc is used to mix the metals after they have been melted, resulting in a homogenous alloy. For decades, this approach has been frequently utilized, and it is especially effective for alloys that are difficult to manufacture using advanced methods. However, arc melting can produce hazardous gases and pose substantial work dangers if not carried out with sufficient safety precautions (Kellens et al. 2017). Despite being a conventional method of producing high-entropy alloys that includes melting and fusing metal samples at high temperatures and electrical currents, Arc melting, like any high-temperature process, has various safety issues that must be considered (Burgess 1995). Electrical shock, burns from contact with hot equipment or molten metal, and exposure to harmful chemicals and vapours created during the melting process are among the dangers.

The process of melting and refining high-entropy alloys in a vacuum atmosphere is known as vacuum induction melting (VIM). This method is extensively employed in the manufacturing of high-performance alloys. The alloy is melted inside a vacuum chamber using electromagnetic induction during the VIM process (Colace et al. 2020). This aids in the removal of contaminants and improves the final product's quality. VIM provides various benefits over traditional smelting and refining processes, including the ability to accurately regulate the chemical composition of the alloy, minimize porosity, and increase overall material performance. However, like every industrial process, VIM has its own set of safety issues that must be appropriately controlled.

VIM poses significant risks, including exposure to toxic fumes and vapours, explosions, fires, burns, electrical shocks, and chemical spills. One of the most serious concerns associated with VIM is the possibility of being exposed to toxic fumes and vapours produced during the melting process.

These fumes and vapours are very poisonous and, if breathed in, can cause major respiratory and other health issues. Furthermore, the high temperatures and pressures involved in VIM can lead to explosions and fires if sufficient safety precautions are not implemented. Burns, electrical shocks, and chemical spills are some of the other possible hazards linked with VIM. As a result, it is critical to design thorough safety measures and to give sufficient training to operators and personnel involved in the process.

A powder processing procedure that involves repeatedly welding, fracturing, and rewelding high-entropy metallic powders in a high-energy ball mill is known as Mechanical alloying (MA). The method generates a fine, uniform powder combination of several components, which may then be consolidated into bulk materials with improved characteristics (Oosthuizen et al. 2004). Mechanical alloying is a potential approach for producing homogeneous, nanocrystalline high-entropy alloy powders that contribute to increased mechanical characteristics in high-entropy alloys (HEAs). However, due to the high-energy impact and milling of metal particles, the technique poses significant safety issues. One of the biggest dangers connected with MA is the formation of tiny particulate matter, which, if breathed in, can cause respiratory problems. Furthermore, the process's large energy inputs might result in increased temperatures, which can pose a burn risk. Milling media, such as balls or rods, can potentially cause bodily harm if not handled appropriately. To limit these hazards and protect the safety of all participants in the process, proper safety procedures and protocols must be applied.

Casting is a process of manufacturing that entails pouring molten, high-entropy alloy into a mould and letting it solidify. The hardened material, known as a cast, is then removed from the mould and treated to form a finished product. Casting is one of the most ancient and commonly used ways of producing metal parts and products (Kumar 2014). Pattern design, mould manufacturing, melting and pouring, solidification, and finishing are all processes in the casting process. To maintain the quality and uniformity of the finished product, each stage must be meticulously monitored. Casting can be done in a variety of ways, such as sand casting, investment casting, die casting, and continuous casting. While casting has numerous advantages, like the capacity to make complicated forms and patterns, it also has certain potential safety issues. These dangers include being exposed to high temperatures, molten metal, and dangerous chemicals, as well as the possibility of mould and equipment failure (Suryanarayana 2001). Finally, powder metallurgy is a manufacturing method that uses finely powdered, high-entropy alloys to create metallic components. The HEA powders are combined with a binder ingredient to make a slurry that is then pressed into a die. The compressed mixture is then heated to a high temperature to remove the binder and sinter the metal particles together, resulting in the formation of a solid metal component. Because of its capacity to make parts with high accuracy and complicated geometries, powder metallurgy is frequently employed in the automotive, aerospace, and medical sectors (Güner and Ekmekci 2019). While powder metallurgy provides many benefits, it also poses considerable safety dangers to personnel involved in the process. These dangers include inhaling metal dust, being exposed to dangerous chemicals used in the process, and fire outburst (Sivakumar et al. 2012).

Conclusion

Finally, the rising popularity of additive manufacturing of high-entropy alloys has heightened awareness of the process's safety measures and occupational concerns. Exposure to metal vapours, fire and explosion threats, and ergonomic stresses are all possible concerns. To reduce these dangers, thorough safety measures, including the use of personal protective equipment and suitable ventilation systems, must be devised and implemented. However, there are certain difficulties and restrictions associated with using PPE in additive manufacturing. To protect the safety and well-being of users of the equipment, organizations must remain up-to-date on regulatory standards and safety best practices. The additive manufacturing sector may continue to develop and innovate by prioritizing safety measures and tackling workplace dangers. By prioritizing safety measures and addressing workplace hazards, additive manufacturing of high-entropy alloys may continue to thrive and innovate.