Health and Safety in 3D Printing

*Hector Garcia Gonzalez and Mª Teresa Lopez Pola*

## **Abstract**

Nowadays, it is possible to find 3D printers everywhere, at homes, schools, work offices, etcetera. 3D printing is an additive manufacturing process that is increasingly gaining popularity, and it can create functional parts with a wide variety of shapes and sizes. But on the other hand, there are health risks associated with 3D printers, like nanoparticles and volatile organic compounds (VOCs), which are important to know to improve health and safety and avoid diseases such as asthma, allergic rhinitis and chronic obstructive pulmonary disease, among others. This chapter analyses techniques for sampling the nanoparticles and VOCs exposure during 3D printing and a health effects review, giving tools to evaluate the risks and recommendations to avoid or minimise these risks using engineering controls like extraction systems or good ventilation.

**Keywords:** nanoparticles, VOCs, health, air quality, 3D printing

## **1. Introduction**

Every day 3D printing is more present in our lives. In 2018, 1.42 million units were sold; it is expected that by 2027 more than eight million units will be sold. Their relatively low price (from around 140 euros) means that they are present in many companies, homes and even nursery schools; with them, it is possible to produce prototypes of unique designs at a meagre cost; in addition, there are already models of games, figures or pieces that can be download for free from the Internet and print them with 3D printers.

However, they are not all advantages; with 3D printing, a series of emerging risks are associated, such as exposure to nanoparticles and volatile organic compounds (VOCs) [1–3]. The most investigated materials are poly lactic acid (PLA) and acrylonitrile butadiene styrene (ABS) since they were the most used; however, many compounds and other printing technologies are entering the market strongly, such as 3D resin printers.

In addition, it should be noted that there is no occupational exposure limit value (OELV) for nanoparticles in most countries. However, there are some reference values to help evaluate the exposures of nanoparticles from 3D printers. Regards the VOCs, not all of them are regulated with an OELV.

## **2. Nanomaterials and nanoparticles**

According to the ISO/TS 27687, the nanoscale size ranges from approximately 1 to 100 nm, and the materials in these sizes usually show new or unusual properties. The European Union [4] defined "nanomaterial" as a natural, incidental or manufactured material consisting of solid particles that are present, either on their own or as identifiable constituent particles in aggregates or agglomerates, and where 50% or more of these particles in the number-based size distribution fulfil at least one of the following conditions:


No air quality standards are in place to regulate exposure to airborne nanoparticles because there is still debate over the number of nanoparticles that are acceptable to be exposed. There are no consensus measurement methods or tools [5]. However, it is evident that the harmful effects mainly depend on the nanoparticle's surface. Because nanoparticles have a large surface area to volume ratio compared to the same substance in bulk, they are a better metric for assessing risks than the conventionally (and officially) employed mass-based approach [6, 7].

To explain the importance of measuring nanoparticles, it is better to show an example; if there is a mass of 0.1 g in the air with a density of 2.65 g/cm3 , it can be calculated how many particles could be in the air from different sizes of particles. **Table 1** shows the number of particles and the superficial area of a mass as a function of the particle size.

If all the particles in the mass of 0.1 g had a size of 1 μm, the particle area would be 0.22 m2 , but on the other hand, if all particles had 1 nm, the total area would be 226 m2 . If these particles could irritate or damage the lungs, a person with the exact mass exposure could be exposed to a surface of 0.22 m2 or 226 m2 ; potentially, the health effects will be very different. It is estimated that the lung area is around 70 to 100 m2 (**Figure 1**), but the nanoparticles are not deposited uniformly in the lungs; it is a complex issue, and there are different deposition probabilities according to the particle size [8].


#### **Table 1.**

*Simulation of particle numbers and superficial area in a mass of 0.1 g with different sizes of particles.*

#### **Figure 1.** *Lungs area (left) and 3D printer (right).*

The circle graph in **Figure 2** shows **Table 1**, which represents the area of mass of 0.1 g (density of 2.65 g/cm3 ) in relation to the particle size. It is clear that the area increases with the particle size reduction.

Once the nanoparticle size's importance is known, it is critical to know reference levels; as previously exposed, it is still debatable because various types of nanoparticles have different or unknown health effects. When sampling nanoparticles, it is common to find different sizes distributions and heterogeneous compositions. In 2011 the Institut für Arbeitsschutz (IFA) proposed a benchmark concentration level based on particle numbers concentrations, **Table 2**.

According to **Table 2**, it is possible to carry out a nanoparticle health and safety assessment considering the material density and the particle number concentration. In materials with low density (most of the 3D printing filaments, poly lactic acid (PLA),

#### **Figure 2.** *Representation, surface in relation to particle size for the same mass.*


#### **Table 2.**

*IFA nanoparticles benchmark level (IFA, 2009) [9].*

acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA), ….), the reference level is 40,000 particles/cm3 , and for heavy materials 20,000 particles/cm3 . It is essential to know the sampling device characteristics because most of them also count water particles, and when sampling, it is crucial to take a sample for the background levels. In some cases, if the intention is to evaluate a process, the nanoparticles could be from the background (nanoparticles from diesel engines or pollen).

There are multiple nanoparticle sampling devices in **Table 3**, **Figure 3** shows two examples of sampling devices, and **Figure 4** shows filaments and a 3D printer.

There are many studies about particles emission during 3d printing. All the international literature agrees that respirable dust measurements are well below the OELV


#### **Table 3.**

*Examples of devices for sampling nanoparticles.*

**Figure 3.** *Nanoparticles sampling devices: CPC 3007 (left) and EEPS3090 (right).*

## *Health and Safety in 3D Printing DOI: http://dx.doi.org/10.5772/intechopen.109439*

**Figure 4.** *Different 3D printing filaments (left) and 3D printer (right).*

(3 mg/m3 ), so 3d printing is not a risk if only the traditional and official assessment of dust mass (concentration in mg/m3 ) is considered.

Chan et al. obtained concentrations of 700 µg/m3 of total dust and 400 µg/m3 of respirable dust well below the occupational limits, with the predominant sizes being between 27 and 115 nanometers [10]. Runström et al. obtained total dust and respirable dust values below the laboratory detection limit (negligible) and a maximum concentration of nanoparticles of 25,000 particles/cm3 [11]. Jensen et al. obtained concentrations of 50.4 µg/m3 in respirable dust [12].

As for nanoparticles, for different filaments in studies carried out in a chamber by Floyd et al. [13], values of up to 1,000,000 particles/cm3 were obtained, which coincides with the studies by Zhang et al. [14] reporting this last author differences between various ABS manufacturers.

In the same way, Kwon et al. [1] detailed a maximum concentration of 54,000 nanoparticles/cm3 in ABS and 1326 nanoparticles/cm3 in PLA filament printing at the temperature recommended by the manufacturer, increasing the emission of nanoparticles at higher temperatures, very similar results than García-González and Lopez-Pola [7].

Azimi studies in a chamber showed concentrations between 108-1011 particles/ cm3 [15].

In metal printers, Jensen et al. measured maximum values of 10,000 particles/cm3 [12], while studies by Yi et al. observed differences in the emission of nanoparticles and their size depending on the material filament colour, both in PLA and ABS filaments, obtaining concentrations in a chamber up to 2.18 x 1011 particles/cm3 [16].

## **3. Volatile organic compounds (VOCs)**

According to the United States Environmental Protection Agency (EPA), VOCs are gases containing various chemicals released from liquids or solids with a high vapour pressure at room temperature [17].

VOCs are classified into four groups:

• Very volatile organic compounds (VVOCs) with Tb: < to 50–100°C (e g. propane, butane and methyl chloride).


VOCs are usually sampled with direct reading devices to obtain the total volatile organic compounds (TVOC), defined as the sum of all VOCs that elute between and include n-hexane and n-hexadecane on a non-polar capillary column. Also, the VOCs can be sampled with a personal pump, a tygon tubing air sampling and a Tenax® TA sorbent tube (**Figure 5**) and analysed in the laboratory with a gas chromatograph; this procedure requires a low flow of 50 ml/min or less, and the sample volume must be around 6 litres, with this technique, it is possible to quantify multiple individual VOCs, this method is based on NIOSH 2549.

There are multiple VOCs, and not of them are well studied. **Table 4** shows the OELV recommended by the Instituto Nacional de Seguridad y Salud en el Trabajo (INSST) for some VOCs.

The International Agency for Research on Cancer (IARC) has classified some volatile organic compounds as carcinogenic, such as acrylonitrile, 1–3 butadiene, benzene and formaldehyde.

In the same way, the legislation says that exposure to any carcinogen substance must be as low as technically possible. In non-occupational uses, for example homes, the reference levels are usually 200 μg/m**3** of TVOC [20], and the benchmark levels are proposed in the public health England guide for indoor air quality (**Table 5**).

Volatile organic compounds are emitted mainly in FDM (fused deposition modelling) printing processes [26], although concentrations are generally below occupational limits. In this type of printing, styrene is emitted with ABS material, and methyl methacrylate is more frequent when printing with PLA material [27].

#### **Figure 5.** *Tenax sorbent tube (left), sampling VOCs during 3D printing (right).*

## *Health and Safety in 3D Printing DOI: http://dx.doi.org/10.5772/intechopen.109439*


#### **Table 4.**

*The occupational limit for VOCs (INSST) [19].*


#### **Table 5.**

*Indoor air quality guidelines for selected VOCs [21].*

Runström et al. observed maximum peaks of TVOC (total volatile organic compounds) of 3200 μg/m3 , indicating in their study that levels potentially harmful to health were not detected, which also coincides with the studies carried out on camera by Floyd [13] and García-González [7].

Zhang et al. state that the levels of VOCs in 3D printing are lower than in laser printers [14], coinciding with Stefaniak et al., who assesses the TVOC levels printing ABS at values of 3500 μg/h, 131 μg/h for PLA and around 6000 μg/h for toner printers [28]. Azimi concludes that the levels of VOCs emitted vary between 2 and 180 μg/min [15]. Stefaniak also states that the VOC levels in both PLA and ABS filaments vary according to colour [28].

## **4. Other pollutants in 3D printers**

It is normal to find monomers of the individual materials used in filaments of resins like, for example, styrene [29]. Other contaminants detected in 3D printing are bisphenol A (BPA), bisphenol S (BPS) (endocrine disruptors), aldehydes, CO2, CO, SO2, H2S and CS2 [30].

Ozone levels of 9 μg/m3 were detected in closed 3D printers. The dyes for coloured filament can contain chromium, nickel, aluminium and other chemicals that could be emitted during printing, generating reactive oxygen species.

Ozone's interaction with unsaturated VOCs can change the chemistry of indoor air by creating reactive products such as carbonyl compounds and secondary organic aerosols (e.g., aldehydes and ketones) [28].

Printing with nylon material, concentrations of CO2 have been determined, higher than the established limit, in addition to other compounds such as carbon monoxide, hydrocarbon, ammonia, caprolactam and hydrogen cyanide [27].

In powder metal printers, metals such as aluminium, chromium, nickel, cobalt, etc., have been detected [27] in concentrations that can become harmful.

Another critical issue is observed in the resin printer when the cleaning alcohol is mixed with the resin, generating nano plastics with server impact on the environment if they are not disposed of adequately [31].

Other ancillary chemicals are used in 3D printing; for example, a thin layer of hairspray usually is applied to the bed surface to provide a tacky structure and increase the filament adhesion in the bed. Add the hairspray pollutants (VOCs, resins, bisphenol, etc.) for a correct risk assessment.

Filaments are evolving very quickly; new additives such as inorganic colourants, metal particles, nanomaterials, metal-containing flame retardants, antioxidants, heat stabilisers and catalysts, among others, are putting in the environment metals and other associated pollutants [32].

## **5. Health effects**

The health effects of 3D printing are still not well studied because it is a quite recent technology, some of the effects could appear with decades of exposure, and there is not enough information about the 3D printer emissions and the worker's exposure; nevertheless, even with few years or days of exposure, there is some bibliography with health effects [33].

Chronic obstructive pulmonary disease (COPD) is a progressive disease that may start after exposure to vapours, gases, fumes and dust, produced by 3D printers, which, with continued exposure, can lead to decreased lung function [27].

A case of asthma was detected in a 28-year-old patient after only 10 days of exposure to pollutants emitted by the ABS filament with 10 printers in operation, *Health and Safety in 3D Printing DOI: http://dx.doi.org/10.5772/intechopen.109439*

observing an improvement after the change to PLA filament, reduction in the number of printers and the use of air purifiers. However, it still required the use of an inhaler [34]. Aldehydes and ketones, among other carbonyl substances, are linked to the emergence of asthma [28].

Caprolactam emitted during nylon printing can irritate the eyes and mucous membranes and cause nervous system alterations [27].

The nanoparticles can penetrate the bronchial tubes producing ROS (reactive oxygen species), being able to cause inflammation and DNA damage and even the ability to pass directly into the bloodstream, penetrating biological barriers. Aluminium nanoparticles can cause fibrosis and microcytic hypochromic anaemia. A study of 46 workers in 17 3D printing companies showed that 59% reported respiratory symptoms, 20% reported skin symptoms and 17% reported headaches at least once a week in the past year [35].

Clinical studies by Ljunggren et al. compared welders with metal 3D printing workers, obtaining very similar parameters [36].

Studies in rats exposed to 3D printing nanoparticles for 3 hours report increased blood pressure [37]; the pollutants emitted can cause cardiovascular disease and stroke [38].

Some metals emitted in 3D printing are irritants (aluminium, arsenic, copper, tin and zinc), asthmagens (chromium, manganese, nickel and vanadium) and potentially carcinogenic to humans (arsenic, nickel and vanadium) [30].

Lastly, cases of sarcomas have been reported in teachers using 3D printers for at least 2 years in poorly ventilated rooms, even though the relationship has not been proven yet [39].

## **6. Conclusions**

There are several studies on pollutants emitted during 3D printing; however, different criteria and strategies are adopted, so an international standardised method must be defined so that the results of further studies will be comparable [40, 41].

3D printing can emit contaminants that are potentially dangerous to health, such as volatile organic compounds, nanoparticles and metals, so precautions must be taken before working with this technology.

The current legislation on the particulate matter is based on mass concentration (μg/m3 ), establishing limit values for PM10, PM4 and PM2.5, the levels emitted by 3D printing are generally much lower than these values. However, despite not being legislated, the nanoparticle concentration levels can harm health.

Runström et al. did not find dangerous concentrations of contaminants during 3D printing; however, the 3D printing centres studied had preventive measures such as extractions and confined printers [11].

In order to minimise the health effects of 3D printing, it is recommended (among other measures) that it be confined with an extraction system, using high-efficiency HEPA filters in the printing room and a good ventilation system in place [42], and whenever possible, select the lowest possible print temperature.

Because some 3D printer models have a relatively low cost (less than 200 euros), it is recommended that before buying this equipment, consider places carefully to instal it. The selected locations should have good ventilation and engineering controls like localised extraction, avoiding, as far as possible, placing them in closed rooms with people present.

Use materials from trusted manufacturers. In recent years, PLA and other filaments with unique colours have been reported made (elsewhere) with chemicals prohibited in the European Union.

Lastly, it is strongly recommended to carry out VOCs and nanoparticle measurements and air quality surveys.

## **Acknowledgements**

The Fundación PREVENT financed this research in the Fundacion Prevent 2021 R&D awards.

We thank the Instituto Nacional de Silicosis (INS) and Fundación Prevent for supporting the research and the HUCA library for all the reference material and information provided.

## **Conflict of interest**

The authors declare no conflict of interest.

## **Author details**

Hector Garcia Gonzalez\* and Mª Teresa Lopez Pola Instituto Nacional de Silicosis, Oviedo, Spain

\*Address all correspondence to: hectorg@ins.es

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Section 5
