*3.3. IN Nanotool—Design*

### 3.3.1. Framework

As previously mentioned, one of the main goals of this study was to design a more accurate control banding based method to manage the risk of exposure to incidental nano-scale matter in metal AM workplaces. This was only possible after studying and understanding the limitations and potential of the currently used methods.

The IN Nanotool redefined inputs by adapting them to incidental nanomaterials originating from metal powders. Additionally, this tool added quantitative data as a potential input, given the possibility to include information on shape and size of nanomaterials, taking into consideration that many authors consider this information fundamental to classify hazards [16].

The IN Nanotool defines four hazard bands, considering metal powder properties and airborne nanomaterials properties, and four exposure bands, considering materials and operation conditions and existing control measures. Then, it allows for the determination of the risk level associated with the exposure to nanomaterials during metal AM, according to previously determined hazard and exposure bands, using a four-by-four matrix. Finally, this method recommends additional control measures depending on the risk level, as an increment to the existing ones.


**Table 6.** Results of the application of Stoffenmanager Nano 1.0.

<sup>1</sup> Defined in Annex III of European Union Directive 67/548/EEC, no longer in force; replaced by CLP Regulation No 1272/2008.

IN Nanotool was thought to be used by occupational safety and health (OSH) professionals, including non-experts. Therefore, it aims to be an intuitive and user-friendly tool, maintaining the necessary accuracy for an assertive risk management, guaranteeing the safety and health conditions of exposed workers. The assessment steps are described in detail on the following subsubsections.

3.3.2. Hazard Band Determination

The hazard band is determined by the sum of all points from 11 different factors related to the metal powder characteristics (50 possible points out of 100) and the airborne nanomaterials characteristics (50 possible point out of 100), as summarized in Table 7.

**Table 7.** Hazard factors and points per factor.


Regarding the properties of the metal powder, the first six factors are related with the hazard classification of the powder: Carcinogenicity, reproductive toxicity, mutagenicity, dermal toxicity, inhalation toxicity and/or other significant health hazards. These properties can be verified, for example, on the second section of the material safety data sheet (MSDS) of the product (hazard identification), confirming if any of the related hazard statements are included. Other CB methods for ENM also include some of this information [14,16,18]. Regardless, IN Nanotool attempts to better catalog these hazards in different factors and also to simplify the process of classification by using as guideline the related hazard statements, according to European Classification, Labelling and Packaging (CLP) Regulation. Many authors considerer that standardized communication, such as MSDS, should be the source of hazard information, including Stoffenmanager authors [19].

There are three more factors for the characteristics of the metal powder: Lowest Occupational Exposure Limit (OEL) applicable, solubility, and average particle size. The first one is based on the CB Nanotool factor Parent Material OEL, considering that it is important to take into account the known and already established occupational exposure limits. These limits may originate from bibliography, legislation, standardization or other reliable source. Next factor, solubility, is a physicochemical property considered in most CB approaches to study exposure to ENM [20]. A material is not considered water-soluble unless the solubility limit exceeds 1 g/L or is listed as soluble or highly water-soluble. Points are given considering that even if the material is soluble does not mean there is no hazard; thus nano-specific properties are expected to be lost when particles are in solution [16]. Finally, the average particle size factor is taken into account, since the size of the primary particles is an important input for a precautionary approach [21]. The particle size can sometimes be found in the material safety data sheet of the product or in its technical sheet. Alternatively, it is possible to obtain this information by performing a SEM or TEM analysis. The points are given depending on a range of sizes, that goes from smaller than 50 μm to higher that 100 μm. Even though, in SLM technology it is very common to use metal powders with a typical particle size of 40 μm [7], there are other technologies that use different size ranges. For instance, several AM technologies use metal powder between 15 to 100 μm [22].

To complete the hazard band determination, there are two significant factors related to the properties of airborne nanomaterials: Shape and size. Shape is also an input in CB Nanotool 2.0 for the severity band of ENM [14] and it was also considered in IN Nanotool given its relevance. It can be scored considering, for example, results of a SEM or TEM analysis. Regarding size, despite the definition of nanomaterial, cells and organisms are also affected by particles whose external dimensions are bigger than 100 nm, since cells are capable of absorbing particles of up to approximately 500 nm [21]. Therefore, it is possible to assign different scores in this last factor, depending on the main size range: Lower than 100 nm, between 100 and 500 nm or higher than 500 nm. This factor can be scored considering, for example, results of a SEM or TEM analysis. If it is not possible to obtain accurate information on the shape and size of airborne matter, the IN Nanotool allows the user to assign 18.75 points to each factor, assuming it is unknown. In fact, for all 11 factors it is possible to classify the factor as unknown, giving the uncertainty in these studies.

After assigning scores to all 11 factors, the hazard band is determined depending on the sum of these points. There are four different hazard bands: low (0–25), medium (26–50), high (51–75) or very high (76–100).

## 3.3.3. Exposure Band Determination

The exposure band is determined by the sum of all points from five distinct factors related to material operation conditions (60 possible points out of 100) and four factors associated with existing control measures (40 possible points out of 100), as presented in Table 8.



The first five factors are related with the material and operation conditions: Dustiness, frequency of operation, duration of operation per day, task characterization and estimated amount of powder used in that task. When handling a powdered material, the main factor for intrinsic emission potential is dustiness [23], therefore this is factor number one in the exposure band factors of the IN Nanotool. Points are given based on a judgment of whether the material's dustiness is high, medium, or low. Most of these five factors are also considered in the other nano CB approaches, since they are essential to study exposure to nanomaterials [24]. In IN Nanotool, the number of employees exposure was not considered, since 3D printers usually are operated by only one or two workers, which means this is not a very relevant input to determine exposure in these workplaces.

The last four factors are related to existing control actions. Considering the already implemented control measures, it is possible to assess the actual exposure of the worker. Therefore, IN Nanotool follows a similar approach to Stoffenmanger Nano [16], which does not compromise the subsequent proposal for additional control measures that can be implemented and effectively reduce the risk.

After summing the scores of the nine factors, the exposure band is defined according to the following criteria: low if the score is under 25, medium if the score is between 26 and 50, high if between 51 and 75 or very high if the sum is 76 or higher.
