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Assessment and control of nanoparticles exposure in welding operations by use of a Control Banding Tool
Journal of Cleaner Production 89 (2015) 296e300
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Assessment and control of nanoparticles exposure in welding operations by use of a Control Banding Tool P.C. Albuquerque a, J.F. Gomes b, c, *, C.A. Pereira b, R.M. Miranda d ~o II, Lote 4.69.01, 1990-096 Lisboa, Portugal ESTESL, Escola Superior de Tecnologia da Saúde de Lisboa, Av. D. Joa Area Departamental de Engenharia Química, ISEL e Instituto Superior de Engenharia de Lisboa, R. Conselheiro Emídio Navarro, 1959-007 Lisboa, Portugal c IBB e Instituto de Biotecnologia e Bioengenharia / Instituto Superior T ecnico e Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal d ^nica e Industrial, Faculdade de Ci^ UNIDEMI, Departamento de Engenharia Meca encias e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 April 2014 Received in revised form 2 November 2014 Accepted 3 November 2014 Available online 12 November 2014
This paper describes the use of a Control Banding Tool to assess and further control of exposure of nanoparticles emitted during welding operations. The tool was applied to Metal Active Gas (MAG) arc welding of mild and stainless steel, providing semi-quantitative data on the process, so that protection measures could be derived, e.g. exhaust gas ventilation by hoods, local ventilation devices and containment measures. This tool is quite useful to compare and evaluate the characteristics of arc welding procedures so that more eco-friendly processes could be preferred over the more potentially noxious ones. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Eco-friendly welding processes Control Banding Tool Nanoparticles Exposure
1. Introduction The traditional industrial hygiene approach for controlling exposures to harmful particles in the workplace considers measuring air concentrations in the worker's breathing zone and assess those concentrations in view of Threshold Limit Values (TLV) previously determined for those particles (Paik et al., 2008), Further on, protection control measures can be derived in order to reduce concentrations below TLVs. This procedure implies that: i) the sampled concentrations are representative of the atmosphere that the worker is actually breathing, ii) the adequate TLV is known, iii) appropriate analytical methods are available to quantify the exposure level, and iv) the exposure levels at which those particles can produce adverse health effects are also known (Maidment, 1998). If any of these factors is not well defined, measurements performed have limited value in risk assessment. Consequently,
* Corresponding author. Area Departamental de Engenharia Química, ISEL e Instituto Superior de Engenharia de Lisboa, R. Conselheiro Emídio Navarro, 1959007 Lisboa, Portugal. Tel.: þ351 96 3902456. E-mail address: [email protected] (J.F. Gomes). http://dx.doi.org/10.1016/j.jclepro.2014.11.010 0959-6526/© 2014 Elsevier Ltd. All rights reserved.
the derived protection measures can also be questionable as they cannot be ascertained as effective. This situation tends to be rather complicated when addressing exposure to nanomaterials, which can refer to both engineered nanoparticles and/or accidentally emitted nanoparticles (Maynard, 2007). In fact, when worker exposures to nanoparticles are concerned, it is not easy to comply with the previously mentioned requirements. Traditionally, particles concentration in the worker breathing zone are measured by using a sampling pump, which uses forces such as particle inertia and gravity in order to force nanoparticles to follow the sampled air into the sampler line. However, the gravity field is considerably weak for nanoparticles, which are defined as having two or three dimensions lower than 100 nm (ASTM, 2007). So far, the second requirement has not been satisfied for nanoparticles as an appropriate index of exposure has not yet reached scientific international consensus (NIOSH, 2006), although some studies suggest that total surface area concentration may be a better exposure index than traditional mass concentration (Oberdorster et al., 1994; Tran et al., 2000). The inexistence of agreement on an appropriate index of exposure for nanoparticles results in the nonexistence of a standard analytical method of quantification, particularly when methods and commercially available
P.C. Albuquerque et al. / Journal of Cleaner Production 89 (2015) 296e300 Table 1 Main characteristics of emitted nanoparticles during MAG welding of mild steel. Gas shielding mixture
Alveolar deposited surface area (mm2/cm3)
Characteristics of emitted nanoparticles Elements found
Morphology
Size (nm)
Arþ10% CO2 Arþ18% CO2 100% CO2
8325e17,574 22,266e42,896 12,899e18,292
Fe, Mn, Si Fe, Mn, Si Fe, Mn, Si
Amorphous agglomerates Amorphous agglomerates Amorphous agglomerates
10e20 10e20 10e20
Table 2 Main characteristics of emitted nanoparticles during MAG welding of stainless steel. Gas shielding mixture
Alveolar deposited surface area (mm2/cm3)
Arþ5% CO2
23,637e39,376 Fe, Cr, Ni
Characteristics of emitted nanoparticles Elements found
65,829e94,136 Fe, Cr, Ni Arþ18%He þ1%CO2 33,644e80,861 Fe, Cr, Ni Arþ5%He þ2%CO2þ2%N2
Morphology
Size (nm)
Amorphous agglomerates Amorphous agglomerates Amorphous agglomerates
10e20 10e20 10e20
equipment are emerging to quantify some specific characteristics related with nanoparticles in gaseous media (Paik et al., 2008; Gomes et al., 2013). Furthermore, the fourth requirement is possibly the largest barrier to assess the risk of working with nanomaterials (Paik et al., 2008): only very few toxicological data are available for determining exposure limits, as only some limited studies comprise in vitro or in vivo toxicity (Yongbin et al., 2007; Chen et al., 2009), and virtually no human studies have been made, so far (Maynard and Kuempel, 2005). Control Banding (CB) strategies (Zalk and Nelson, 2008) seem to offer a simplified control method of worker exposures in the absence of reliable toxicological and exposure data. Control Banding was developed in the pharmaceutical industry as a
Table 3 Severity and probability factors and maximum points (NM ¼ nanomaterial. PM ¼ parent material) (Paik et al., 2008).
per
factor
Severity factor
Maximum points
Maximum severity score
Surface chemistry (NM) Particle shape (NM) Particle diameter (NM) Solubility (NM) Carcinogenicity (NM) Reproductive toxicity (NM) Mutagenicity (NM) Dermal toxicity (NM) Toxicity (PM) Carcinogenicity (PM) Reproductive toxicity (PM) Mutagenicity (PM) Dermal hazard potential (PM)
10 10 10 10 7.5 7.5 7.5 7.5 10 5 5 5 5
100
Probability factor
Maximum points
Maximum severity score
Estimated amount of nanomaterial Dustiness/mistiness Number of employees with similar exposure Frequency of operation Duration of operation
25
100
pragmatic tool to manage risks resulting from exposure to a wide variety of potentially hazardous substances in the absence of the above mentioned data. Basically, it is a risk assessment approach using the generally accepted risk paradigm, where risk can be measured as a function of the severity of impact (also known as hazard) and the anticipated probability of that impact (exposure). Both hazard and exposure are then classified into two to five different levels, usually referred to as bands. The two sets of bands are combined in a matrix, resulting into control or risk bands (Brouwer, 2012). CB principles have been widely used for the last decades to implement a risk management strategy, where R(isk) and S(afety) phrases are allocated to hazard bands (Brooke, 1998), and exposure bands are based on the statistical analysis of exposure data. Brouwer (2012) performed an assessment of existing approaches, comprising the first CB approach for occupational “nano” exposure proposed by Maynard (2007), which was further on published by Zalk et al. (2009) and known as CB Nanotool 2.0 (available at: http://www.controlbanding. net). CB approaches represent a wide panel of methods to indicate, or prioritize, risks related to the use of nanomaterials, and it is expected that some modifications and adjustments on those approaches will arise in the next years as a result of the acquired experience with the application to real case studies (Brouwer, 2012). It is well known that arc welding generates potentially hazardous fumes, which depend on process parameters and shielding gas composition (Pires et al., 2007). The fact that welders are exposed to welding fumes triggered the number of epidemiologic studies (Gomes et al., 2012a) in recent years due to the increasing concern with welding fumes and the existence of more sophisticated equipment for detection and analysis of particles in the nano range scale. More recent studies were made regarding the emission of ultrafine and nanoparticles occurring in several welding processes (Pfefferkorn et al., 2010; Gomes et al., 2012a, 2012b; Guerreiro et al., 2014; Meneses et al., 2014). The ultimate aim of these studies is to define safety measures in order to limit welder's exposure, which is compromised by the fact that, currently, there are no defined TLVs for nanoparticles emitted in welding operations, neither the exposure levels at which those particles can produce adverse health effects are known. As pointed out previously, the lack of information greatly compromises the effectiveness of any derived protection measures, which calls for the use of risk assessment techniques such as the ones based on CB. This work concerns the application of the CB approach to the risk assessment to the most widely used welding
30 15 15 15
297
Fig. 1. RL matrix as a function of severity and probability.
298
P.C. Albuquerque et al. / Journal of Cleaner Production 89 (2015) 296e300
Table 4 Base characteristics for risk assessment on MAG welding of carbon steel using shielding gas 100% CO2. Activity
Description
Name or description of the nanomaterials
CAS#
Activity Classification
Actual control practice
1
Originated from the use of a filler material as a solid continuous wire consumable “Lincoln ER70S-6”
Metallic nanoparticles (C, Mn, S, Si, P, Cu, Ni, Mo, V, Cr),
Nanoparticles generation in gas phase
Exhaust or local ventilation
2
MAG (fusion welding process) with shielding of the welding pool using an active gas mixture Welding base material: mild steel: metallic alloy of Fe and C (1.5%) and small quantities of other elements
Gas (CO2)
Ni: 7440-02-0 Cu: 7440-50-8 Mn: 7439-96-5 Mo: 7439-98-7 Cr: 740-47-3 S: 7404-34-9 Si: 90337-93-2 V: 7440-62-2 P: 7723-14-0 C: 7440-44-0 CO2: 124-38-9
Exhaust or local ventilation
Metallic nanoparticles originated from mild steel fusion
Mn: 7439-96-5 S: 7404-34-9 Si: 90337-93-2 P: 7723-14-0 C: 7440-44-0 Fe: 7439-89-6
Nanoparticles generation in gas phase Mechanical action over materials containing nanoparticles
3
processes in industry (Meneses et al., 2014), which consists in a particularly interesting risk assessment, considering that around 3 million workers can be exposed to those risks (Pires et al., 2006). This risk assessment is performed with the aim of deriving effective exposure control measures. Apart from that this CB tool, by comparing the hazardous character of processes, can help choosing the more eco-friendly ones.
2. Ways and means This study consisted in the application of the CB Nanotool 2.0 (Zalk et al., 2009) in order to assess the welders' exposure to nanoscale particles emitted in Metal Active Gas (MAG) metallurgical industries: a) in mild steel, using three different shielding gas mixtures (Arþ10% CO2; Arþ18% CO2, and 100% CO2); b) in austenitic stainless steel, using three different shielding gas mixtures (Arþ5% CO2; 81% Arþ18% Heþ1% CO2; 91% Arþ5% Heþ2% CO2þ 2% N2); For these conditions, monitoring tests were made in real welding environments as described elsewhere (Guerreiro et al.,
Fig. 2. Determination of the risk level for MAG welding of carbon steel, using a shielding gas of 100% CO2.
Exhaust or local ventilation
2014). These measurements followed the methodology described by Gomes et al. (2014), and comprised the following: 1. Alveolar deposited surface areas of emitted nanoparticles was monitored on-line using a Nanoparticle Surface Area Monitor (NSAM, TSI, model 3550), which allows the estimation of the quantity of nanoparticles, expressed as mm2/cm3, during the respective release period. As a specific software is used for data acquisition, the emissions can be ascribed to specific process events; 2. The size range distribution of released nanoparticles was measured on-line using a the Scanning Mobility Particle Sizer (SMPS, TSI, model 3034); 3. Simultaneously released nanoparticles were sampled with a Nanometer Aerosol Sampler (NAS, TSI, model 3089) for further observation and characterization. Nanoparticles are collected in a suitable substrate, such as copper grids. It should be noted that sampling is performed during a sufficient time span in order to capture enough nanoparticles for observation and analysis; 4. Finally, the previously collected samples were observed using electron microscopy, which allowed the determination of morphology, dimensions, crystalline structure, and also elemental chemical composition. For this purpose, a Transmission Electronic Microscopy (TEM, Hitachi, model H-8100 II), equipped with an Energy Dispersive X-ray Spectroscopy (EDS) probe, was used. It should be noted that, during tests, ventilation conditions (extracting air at a flow rate of 4 m3/min) were the same for all conditions tested. Table 1 shows the main characteristics of emitted particles, determined in MAG welding of mild steel, and Table 2 shows the main characteristics of emitted particles determined in MAG welding of stainless steel (Pereira, 2013). It should be noted that the observed range of ADSA corresponds to the use of different welding transfer modes (short-circuit, globular and spray), which depend on the shielding gas used, the current intensity and the arc voltage. Then, severity determination comprises the following characteristics: surface chemistry, particle shape, particle diameter, solubility, carcinogenicity, reproductive toxicity, mutagenicity, dermal toxicity, toxicity of parent material, carcinogenicity of parent material, reproductive toxicity of parent material, mutagenicity of parent material, and dermal hazard potential of parent material. The overall severity score is determined based on the sum of all the points from the severity factors, the maximum score being 100, as shown in Table 3. Table 3 also shows the factors considered for probability determination:
P.C. Albuquerque et al. / Journal of Cleaner Production 89 (2015) 296e300
estimated amount of nanomaterial used during task, dustiness/ mistiness, number of employees with similar exposure, frequency of operation, and duration of operation. Again, the maximum score is 100. Based on the severity score and probability score for an operation, the overall RL and corresponding control band is determined by the matrix shown in Fig. 1 (Paik et al., 2008). 3. Results and discussion The obtained results from the application of the CB matrix are presented hereafter. Only some examples are presented, as the obtained matrix was, approximately, the same for all studied cases, which means that there are not enough distinct features among these situations. Therefore, the results are presented for each welding procedure. Risk assessment was mainly based of the following criteria: i) chemical composition of the filler material; ii) chemical composition of the shielding gas; iii) chemical composition of the base material to be welded (mild steel and stainless steel). The characterization of each base material used in each welding procedure was based on its safety data sheets, and is shown on Table 4. This information was used to obtain the inputs to the CB tool as shown in Appendix 1. The output matrix, comprising severity and probability indexes together, with resulting control measures, is depicted in Fig. 2. From this example it can be noticed that the chemical composition of the base material to be welded results in the highest risk level, and thus determines the protection measures to be considered. In fact, the inclusion of other shielding gas mixtures does not have relevant impact on the risk level. Even the consideration of stainless steel, instead of mild steel, does not
299
increases significantly the risk level. In fact, the main difference between these two situations is, obviously, the presence of chromium and nickel which are present in stainless steel but not in mild steel. However, in spite of the carcinogenic character of these two metals, as they are present as alloyed to the steel, the matrix does not distinguishes this particular situation so as to increase the level of risk. Nevertheless, the recommended protection measure is considered as adequate as it comprises the use of fume hoods of local ventilation devices for activities 1 and 2 and containment for activity 3, which is, of the course, the most potentially noxious one. 4. Conclusions The reduction of nanoparticles emissions during metal arc welding is necessary in order to improve working conditions in industry and to reduce the exposure risk level for welders. However, the obtention of such an improvement is a complex problem thus involving the development of newer and more efficient protective measures, as well as welding processes and even the use of only some more eco-friendly materials instead of some potentially toxic ones. Generally, the adoption of good working practices should take into account the feasibility of changes to be considered in what concerns technological aspects, chemical composition of consumable materials and even shielding gases, thus related with an increased use of efficient ventilation systems and effective containment techniques. The use of risk assessment tools, such as the one described in this paper, is an easy method that can be used in order to protect the welder's health, reduce occupational diseases and, at the same time, develop more eco-friendly welding techniques. Apart from that, as the use of this tool results in a semi-quantitative assessment of different welding processes, providing its ranking in terms of hazardous potential, it can also be used to select more eco-friendly processes.
Appendix. Entries for the Control Banding Tool for MAG welding of mild steel using 100% CO2 as shielding gas.
Activity number
Scenario description
CAS#
1
Filler material wire Lincoln ER70S-6
2
MAG process with 100% CO2 Base material mild steel
Ni Cu Mn Mo Cr S Si V P C CO2
3
Mn S Si P C Fe
Current engineering control
Severity: Parent material Lowest OEL
Carcinogen
Reproductive hazard
Mutagen
Dermal hazard
Asthmagen
Generating nanoparticles in the gas phase
Fume hood or local exhaust ventilation
101 to 1000
No
No
No
No
No
Generating nanoparticles in the gas phase Machining, sanding, drilling or other mechanical disruptions of materials containing nanoparticles
Fume hood or local exhaust ventilation Fume hood or local exhaust ventilation
101 to 1000
No
No
No
No
No
No
No
No
No
No
Activity classification
300
P.C. Albuquerque et al. / Journal of Cleaner Production 89 (2015) 296e300
Activity number
Scenario description
1
Filler material wire Lincoln ER70S-6 MAG process with 100% CO2 Base material mild steel
2 3 Activity number
Scenario description
1
Filler material wire Lincoln ER70S-6 MAG process with 100% CO2 Base material mild steel
2 3
Severity: Nanoscale material Surface reactivity
Particle shape
Particle diameter
Solubility
Carcinogen
Mutagen
Dermal hazard
Asthmagen
Low
Anisotropic
>40 nm
Unknown
Unknown
Unknown
Unknown
Unknown
Low Unknown
Anisotropic Unknown
>40 nm Unknown
Unknown Unknown
Unknown Unknown
Unknown Unknown
Unknown Unknown
No Unknown
Probability
Severity
Probability
Estimated minimum amount of substance
Dustiness
Number of employees with similar exposure
Frequency of operation
Operation duration (per shift)
Score
Band
Score
Band
<1 mg
Low
11e15
Weekly
30-60 min
35
MEDIUM
57.5
LIKELY
<1 mg
Low Unknown
11e15 Unknown
Weekly Weekly
30-60 min 30-60 min
30.5 62.5
MEDIUM HIGH
57.5 55
LIKELY LIKELY
References ASTM International, 2007. Terminology for Nanotechnology (West Conshohocken, PA). Brooke, I., 1998. A UK scheme to help small firms control health risks from chemicals: toxicological considerations. Ann. Occup. Hyg. 42, 377e390. Brouwer, D., 2012. Control banding approaches for nanomaterials. Ann. Occup. Hyg. 56, 506e514. Chen, Y., Hang, Y., Liau, J., Huang, G., 2009. Assessment of the in vivo toxicity of gold nanoparticles. Nanoscale Res. Lett. 4, 858e864. Gomes, J., Albuquerque, P., Miranda, R., Vieira, M., 2012a. Determination of airborne nanoparticles from welding operations. J. Toxicol. Environ. Health, Part A 75, 747e755. Gomes, J., Albuquerque, P., Miranda, R., Santos, T., Vieira, M., 2012b. Comparison of deposited surface area of airborne ultrafine particles generated from two welding processes. Inhal. Toxicol. 24, 774e781. Gomes, J.F.P., Albuquerque, P., Esteves, H., Carvalho, P., 2013. Notice on a methodology for characterizing emissions of ultrafine particles/nanoparticles in microenvironments. Energy Emiss. Control Technol. 1, 15e27. Gomes, J.F.P., Miranda, R., Carvalho, P., Quintino, L., 2014. The effect of metal transfer modes and shielding gas composition on the emission of ultrafine particles in ~o 19 (2), 168e176. MAG steel welding. Soldagem e Inspeça Guerreiro, C., Gomes, J.F.P., Carvalho, P., Santos, T., Miranda, R., Albuquerque, P., 2014. Characterisation of airborne particles generated from MAG welding process. Inhal. Toxicol. 26, 345e352. Maidment, S., 1998. Occupational hygiene considerations in the development of a structured approach to select chemical control strategies. Ann. Occup. Hyg. 42, 391e400. Maynard, A., Kuempel, E., 2005. Airborne nanostructured particles and occupational health. J. Nanoparticle Res. 7, 587e614. Maynard, A., 2007. Nanotechnology: the best next thing of much ado about nothing? Ann. Occup. Hyg. 51, 1e12.
Meneses, V., Gomes, J., Scotti, A., 2014. The effect of metal transfer stability (spattering) on fume generation, morphology and composition in short circuit MAG welding. J. Mater. Process. Technol. 214, 1388e1397. National Institute for Occupational Safety and Health (NIOSH), 2006. Approaches to Safe Nanotechnology: an Information Exchange with NIOSH, Version I.1. Oberdorster, G., Ferin, J., Lehnert, B., 1994. Correlation between particle-size, in-vivo particle persistence and lung injury. Environ. Health Perspect. 102, 173e179. Paik, S., Zalk, D., Swuste, P., 2008. Application of a pilot Control Banding Tool for risk level assessment and control of nanoparticle exposures. Ann. Occup. Hyg. 52, 419e428. ~o para a caracterizaça ~o da emissa ~o de nanopartículas Pereira, C., 2013. Contribuiça em processos de soldadura e avaliaç~ ao de riscos decorrentes do processo. MSc Thesis in Chemical Engineering. ISEL, Portuguese. Pfefferkorn, F., Bello, D., Haddad, G., Park, J., Powell, M., McCarthy, J., Bunker, K., Fehrenbacher, A., Jeon, Y., Virji, M., Gruetzmacher, G., Hoover, M., 2010. Characterization of exposures to airborne nanoscale particles during friction stir welding of aluminum. Ann. Occup. Hyg. 54, 486e503. Pires, I., Quintino, L., Miranda, R., Gomes, J., 2006. Fume emissions during gas metal arc welding. Toxicol. Environ. Chem. 88, 385e394. Pires, I., Quintino, L., Miranda, R., 2007. Analysis of the influence of shielding gas mixtures on the gas metal arc welding metal transfer modes and fume formation rate. Mater. Des. 28, 1623e1631. Tran, C., Buchanan, D., Culen, R., 2000. Inhalation of poorly soluble particles. II. Influence of particle surface area on inflammation and clearance. Inhal. Toxicol. 12, 1113e1126. Yongbin, Z., Chen, W., Zhang, J., Liu, J., Chen, G., Pope, C., 2007. In vitro and in vivo toxicity of CdTe nanoparticles. J. Nanosci. Nanotechnol. 7, 497e503. Zalk, D., Nelson, D., 2008. History and evolution of control banding: a review. J. Occup. Environ. Hyg. 5, 330e346. Zalk, D., Paik, S., Swuste, P., 2009. Evaluating the control banding nanotool: a qualitative risk assessment method for controlling nanoparticle exposures. J. Nanoparticle Res. 11, 1685e1704.
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Assessment and control of nanoparticles exposure in welding operations by use of a Control Banding Tool P.C. Albuquerque a, J.F. Gomes b, c, *, C.A. Pereira b, R.M. Miranda d ~o II, Lote 4.69.01, 1990-096 Lisboa, Portugal ESTESL, Escola Superior de Tecnologia da Saúde de Lisboa, Av. D. Joa Area Departamental de Engenharia Química, ISEL e Instituto Superior de Engenharia de Lisboa, R. Conselheiro Emídio Navarro, 1959-007 Lisboa, Portugal c IBB e Instituto de Biotecnologia e Bioengenharia / Instituto Superior T ecnico e Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal d ^nica e Industrial, Faculdade de Ci^ UNIDEMI, Departamento de Engenharia Meca encias e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 April 2014 Received in revised form 2 November 2014 Accepted 3 November 2014 Available online 12 November 2014
This paper describes the use of a Control Banding Tool to assess and further control of exposure of nanoparticles emitted during welding operations. The tool was applied to Metal Active Gas (MAG) arc welding of mild and stainless steel, providing semi-quantitative data on the process, so that protection measures could be derived, e.g. exhaust gas ventilation by hoods, local ventilation devices and containment measures. This tool is quite useful to compare and evaluate the characteristics of arc welding procedures so that more eco-friendly processes could be preferred over the more potentially noxious ones. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Eco-friendly welding processes Control Banding Tool Nanoparticles Exposure
1. Introduction The traditional industrial hygiene approach for controlling exposures to harmful particles in the workplace considers measuring air concentrations in the worker's breathing zone and assess those concentrations in view of Threshold Limit Values (TLV) previously determined for those particles (Paik et al., 2008), Further on, protection control measures can be derived in order to reduce concentrations below TLVs. This procedure implies that: i) the sampled concentrations are representative of the atmosphere that the worker is actually breathing, ii) the adequate TLV is known, iii) appropriate analytical methods are available to quantify the exposure level, and iv) the exposure levels at which those particles can produce adverse health effects are also known (Maidment, 1998). If any of these factors is not well defined, measurements performed have limited value in risk assessment. Consequently,
* Corresponding author. Area Departamental de Engenharia Química, ISEL e Instituto Superior de Engenharia de Lisboa, R. Conselheiro Emídio Navarro, 1959007 Lisboa, Portugal. Tel.: þ351 96 3902456. E-mail address: [email protected] (J.F. Gomes). http://dx.doi.org/10.1016/j.jclepro.2014.11.010 0959-6526/© 2014 Elsevier Ltd. All rights reserved.
the derived protection measures can also be questionable as they cannot be ascertained as effective. This situation tends to be rather complicated when addressing exposure to nanomaterials, which can refer to both engineered nanoparticles and/or accidentally emitted nanoparticles (Maynard, 2007). In fact, when worker exposures to nanoparticles are concerned, it is not easy to comply with the previously mentioned requirements. Traditionally, particles concentration in the worker breathing zone are measured by using a sampling pump, which uses forces such as particle inertia and gravity in order to force nanoparticles to follow the sampled air into the sampler line. However, the gravity field is considerably weak for nanoparticles, which are defined as having two or three dimensions lower than 100 nm (ASTM, 2007). So far, the second requirement has not been satisfied for nanoparticles as an appropriate index of exposure has not yet reached scientific international consensus (NIOSH, 2006), although some studies suggest that total surface area concentration may be a better exposure index than traditional mass concentration (Oberdorster et al., 1994; Tran et al., 2000). The inexistence of agreement on an appropriate index of exposure for nanoparticles results in the nonexistence of a standard analytical method of quantification, particularly when methods and commercially available
P.C. Albuquerque et al. / Journal of Cleaner Production 89 (2015) 296e300 Table 1 Main characteristics of emitted nanoparticles during MAG welding of mild steel. Gas shielding mixture
Alveolar deposited surface area (mm2/cm3)
Characteristics of emitted nanoparticles Elements found
Morphology
Size (nm)
Arþ10% CO2 Arþ18% CO2 100% CO2
8325e17,574 22,266e42,896 12,899e18,292
Fe, Mn, Si Fe, Mn, Si Fe, Mn, Si
Amorphous agglomerates Amorphous agglomerates Amorphous agglomerates
10e20 10e20 10e20
Table 2 Main characteristics of emitted nanoparticles during MAG welding of stainless steel. Gas shielding mixture
Alveolar deposited surface area (mm2/cm3)
Arþ5% CO2
23,637e39,376 Fe, Cr, Ni
Characteristics of emitted nanoparticles Elements found
65,829e94,136 Fe, Cr, Ni Arþ18%He þ1%CO2 33,644e80,861 Fe, Cr, Ni Arþ5%He þ2%CO2þ2%N2
Morphology
Size (nm)
Amorphous agglomerates Amorphous agglomerates Amorphous agglomerates
10e20 10e20 10e20
equipment are emerging to quantify some specific characteristics related with nanoparticles in gaseous media (Paik et al., 2008; Gomes et al., 2013). Furthermore, the fourth requirement is possibly the largest barrier to assess the risk of working with nanomaterials (Paik et al., 2008): only very few toxicological data are available for determining exposure limits, as only some limited studies comprise in vitro or in vivo toxicity (Yongbin et al., 2007; Chen et al., 2009), and virtually no human studies have been made, so far (Maynard and Kuempel, 2005). Control Banding (CB) strategies (Zalk and Nelson, 2008) seem to offer a simplified control method of worker exposures in the absence of reliable toxicological and exposure data. Control Banding was developed in the pharmaceutical industry as a
Table 3 Severity and probability factors and maximum points (NM ¼ nanomaterial. PM ¼ parent material) (Paik et al., 2008).
per
factor
Severity factor
Maximum points
Maximum severity score
Surface chemistry (NM) Particle shape (NM) Particle diameter (NM) Solubility (NM) Carcinogenicity (NM) Reproductive toxicity (NM) Mutagenicity (NM) Dermal toxicity (NM) Toxicity (PM) Carcinogenicity (PM) Reproductive toxicity (PM) Mutagenicity (PM) Dermal hazard potential (PM)
10 10 10 10 7.5 7.5 7.5 7.5 10 5 5 5 5
100
Probability factor
Maximum points
Maximum severity score
Estimated amount of nanomaterial Dustiness/mistiness Number of employees with similar exposure Frequency of operation Duration of operation
25
100
pragmatic tool to manage risks resulting from exposure to a wide variety of potentially hazardous substances in the absence of the above mentioned data. Basically, it is a risk assessment approach using the generally accepted risk paradigm, where risk can be measured as a function of the severity of impact (also known as hazard) and the anticipated probability of that impact (exposure). Both hazard and exposure are then classified into two to five different levels, usually referred to as bands. The two sets of bands are combined in a matrix, resulting into control or risk bands (Brouwer, 2012). CB principles have been widely used for the last decades to implement a risk management strategy, where R(isk) and S(afety) phrases are allocated to hazard bands (Brooke, 1998), and exposure bands are based on the statistical analysis of exposure data. Brouwer (2012) performed an assessment of existing approaches, comprising the first CB approach for occupational “nano” exposure proposed by Maynard (2007), which was further on published by Zalk et al. (2009) and known as CB Nanotool 2.0 (available at: http://www.controlbanding. net). CB approaches represent a wide panel of methods to indicate, or prioritize, risks related to the use of nanomaterials, and it is expected that some modifications and adjustments on those approaches will arise in the next years as a result of the acquired experience with the application to real case studies (Brouwer, 2012). It is well known that arc welding generates potentially hazardous fumes, which depend on process parameters and shielding gas composition (Pires et al., 2007). The fact that welders are exposed to welding fumes triggered the number of epidemiologic studies (Gomes et al., 2012a) in recent years due to the increasing concern with welding fumes and the existence of more sophisticated equipment for detection and analysis of particles in the nano range scale. More recent studies were made regarding the emission of ultrafine and nanoparticles occurring in several welding processes (Pfefferkorn et al., 2010; Gomes et al., 2012a, 2012b; Guerreiro et al., 2014; Meneses et al., 2014). The ultimate aim of these studies is to define safety measures in order to limit welder's exposure, which is compromised by the fact that, currently, there are no defined TLVs for nanoparticles emitted in welding operations, neither the exposure levels at which those particles can produce adverse health effects are known. As pointed out previously, the lack of information greatly compromises the effectiveness of any derived protection measures, which calls for the use of risk assessment techniques such as the ones based on CB. This work concerns the application of the CB approach to the risk assessment to the most widely used welding
30 15 15 15
297
Fig. 1. RL matrix as a function of severity and probability.
298
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Table 4 Base characteristics for risk assessment on MAG welding of carbon steel using shielding gas 100% CO2. Activity
Description
Name or description of the nanomaterials
CAS#
Activity Classification
Actual control practice
1
Originated from the use of a filler material as a solid continuous wire consumable “Lincoln ER70S-6”
Metallic nanoparticles (C, Mn, S, Si, P, Cu, Ni, Mo, V, Cr),
Nanoparticles generation in gas phase
Exhaust or local ventilation
2
MAG (fusion welding process) with shielding of the welding pool using an active gas mixture Welding base material: mild steel: metallic alloy of Fe and C (1.5%) and small quantities of other elements
Gas (CO2)
Ni: 7440-02-0 Cu: 7440-50-8 Mn: 7439-96-5 Mo: 7439-98-7 Cr: 740-47-3 S: 7404-34-9 Si: 90337-93-2 V: 7440-62-2 P: 7723-14-0 C: 7440-44-0 CO2: 124-38-9
Exhaust or local ventilation
Metallic nanoparticles originated from mild steel fusion
Mn: 7439-96-5 S: 7404-34-9 Si: 90337-93-2 P: 7723-14-0 C: 7440-44-0 Fe: 7439-89-6
Nanoparticles generation in gas phase Mechanical action over materials containing nanoparticles
3
processes in industry (Meneses et al., 2014), which consists in a particularly interesting risk assessment, considering that around 3 million workers can be exposed to those risks (Pires et al., 2006). This risk assessment is performed with the aim of deriving effective exposure control measures. Apart from that this CB tool, by comparing the hazardous character of processes, can help choosing the more eco-friendly ones.
2. Ways and means This study consisted in the application of the CB Nanotool 2.0 (Zalk et al., 2009) in order to assess the welders' exposure to nanoscale particles emitted in Metal Active Gas (MAG) metallurgical industries: a) in mild steel, using three different shielding gas mixtures (Arþ10% CO2; Arþ18% CO2, and 100% CO2); b) in austenitic stainless steel, using three different shielding gas mixtures (Arþ5% CO2; 81% Arþ18% Heþ1% CO2; 91% Arþ5% Heþ2% CO2þ 2% N2); For these conditions, monitoring tests were made in real welding environments as described elsewhere (Guerreiro et al.,
Fig. 2. Determination of the risk level for MAG welding of carbon steel, using a shielding gas of 100% CO2.
Exhaust or local ventilation
2014). These measurements followed the methodology described by Gomes et al. (2014), and comprised the following: 1. Alveolar deposited surface areas of emitted nanoparticles was monitored on-line using a Nanoparticle Surface Area Monitor (NSAM, TSI, model 3550), which allows the estimation of the quantity of nanoparticles, expressed as mm2/cm3, during the respective release period. As a specific software is used for data acquisition, the emissions can be ascribed to specific process events; 2. The size range distribution of released nanoparticles was measured on-line using a the Scanning Mobility Particle Sizer (SMPS, TSI, model 3034); 3. Simultaneously released nanoparticles were sampled with a Nanometer Aerosol Sampler (NAS, TSI, model 3089) for further observation and characterization. Nanoparticles are collected in a suitable substrate, such as copper grids. It should be noted that sampling is performed during a sufficient time span in order to capture enough nanoparticles for observation and analysis; 4. Finally, the previously collected samples were observed using electron microscopy, which allowed the determination of morphology, dimensions, crystalline structure, and also elemental chemical composition. For this purpose, a Transmission Electronic Microscopy (TEM, Hitachi, model H-8100 II), equipped with an Energy Dispersive X-ray Spectroscopy (EDS) probe, was used. It should be noted that, during tests, ventilation conditions (extracting air at a flow rate of 4 m3/min) were the same for all conditions tested. Table 1 shows the main characteristics of emitted particles, determined in MAG welding of mild steel, and Table 2 shows the main characteristics of emitted particles determined in MAG welding of stainless steel (Pereira, 2013). It should be noted that the observed range of ADSA corresponds to the use of different welding transfer modes (short-circuit, globular and spray), which depend on the shielding gas used, the current intensity and the arc voltage. Then, severity determination comprises the following characteristics: surface chemistry, particle shape, particle diameter, solubility, carcinogenicity, reproductive toxicity, mutagenicity, dermal toxicity, toxicity of parent material, carcinogenicity of parent material, reproductive toxicity of parent material, mutagenicity of parent material, and dermal hazard potential of parent material. The overall severity score is determined based on the sum of all the points from the severity factors, the maximum score being 100, as shown in Table 3. Table 3 also shows the factors considered for probability determination:
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estimated amount of nanomaterial used during task, dustiness/ mistiness, number of employees with similar exposure, frequency of operation, and duration of operation. Again, the maximum score is 100. Based on the severity score and probability score for an operation, the overall RL and corresponding control band is determined by the matrix shown in Fig. 1 (Paik et al., 2008). 3. Results and discussion The obtained results from the application of the CB matrix are presented hereafter. Only some examples are presented, as the obtained matrix was, approximately, the same for all studied cases, which means that there are not enough distinct features among these situations. Therefore, the results are presented for each welding procedure. Risk assessment was mainly based of the following criteria: i) chemical composition of the filler material; ii) chemical composition of the shielding gas; iii) chemical composition of the base material to be welded (mild steel and stainless steel). The characterization of each base material used in each welding procedure was based on its safety data sheets, and is shown on Table 4. This information was used to obtain the inputs to the CB tool as shown in Appendix 1. The output matrix, comprising severity and probability indexes together, with resulting control measures, is depicted in Fig. 2. From this example it can be noticed that the chemical composition of the base material to be welded results in the highest risk level, and thus determines the protection measures to be considered. In fact, the inclusion of other shielding gas mixtures does not have relevant impact on the risk level. Even the consideration of stainless steel, instead of mild steel, does not
299
increases significantly the risk level. In fact, the main difference between these two situations is, obviously, the presence of chromium and nickel which are present in stainless steel but not in mild steel. However, in spite of the carcinogenic character of these two metals, as they are present as alloyed to the steel, the matrix does not distinguishes this particular situation so as to increase the level of risk. Nevertheless, the recommended protection measure is considered as adequate as it comprises the use of fume hoods of local ventilation devices for activities 1 and 2 and containment for activity 3, which is, of the course, the most potentially noxious one. 4. Conclusions The reduction of nanoparticles emissions during metal arc welding is necessary in order to improve working conditions in industry and to reduce the exposure risk level for welders. However, the obtention of such an improvement is a complex problem thus involving the development of newer and more efficient protective measures, as well as welding processes and even the use of only some more eco-friendly materials instead of some potentially toxic ones. Generally, the adoption of good working practices should take into account the feasibility of changes to be considered in what concerns technological aspects, chemical composition of consumable materials and even shielding gases, thus related with an increased use of efficient ventilation systems and effective containment techniques. The use of risk assessment tools, such as the one described in this paper, is an easy method that can be used in order to protect the welder's health, reduce occupational diseases and, at the same time, develop more eco-friendly welding techniques. Apart from that, as the use of this tool results in a semi-quantitative assessment of different welding processes, providing its ranking in terms of hazardous potential, it can also be used to select more eco-friendly processes.
Appendix. Entries for the Control Banding Tool for MAG welding of mild steel using 100% CO2 as shielding gas.
Activity number
Scenario description
CAS#
1
Filler material wire Lincoln ER70S-6
2
MAG process with 100% CO2 Base material mild steel
Ni Cu Mn Mo Cr S Si V P C CO2
3
Mn S Si P C Fe
Current engineering control
Severity: Parent material Lowest OEL
Carcinogen
Reproductive hazard
Mutagen
Dermal hazard
Asthmagen
Generating nanoparticles in the gas phase
Fume hood or local exhaust ventilation
101 to 1000
No
No
No
No
No
Generating nanoparticles in the gas phase Machining, sanding, drilling or other mechanical disruptions of materials containing nanoparticles
Fume hood or local exhaust ventilation Fume hood or local exhaust ventilation
101 to 1000
No
No
No
No
No
No
No
No
No
No
Activity classification
300
P.C. Albuquerque et al. / Journal of Cleaner Production 89 (2015) 296e300
Activity number
Scenario description
1
Filler material wire Lincoln ER70S-6 MAG process with 100% CO2 Base material mild steel
2 3 Activity number
Scenario description
1
Filler material wire Lincoln ER70S-6 MAG process with 100% CO2 Base material mild steel
2 3
Severity: Nanoscale material Surface reactivity
Particle shape
Particle diameter
Solubility
Carcinogen
Mutagen
Dermal hazard
Asthmagen
Low
Anisotropic
>40 nm
Unknown
Unknown
Unknown
Unknown
Unknown
Low Unknown
Anisotropic Unknown
>40 nm Unknown
Unknown Unknown
Unknown Unknown
Unknown Unknown
Unknown Unknown
No Unknown
Probability
Severity
Probability
Estimated minimum amount of substance
Dustiness
Number of employees with similar exposure
Frequency of operation
Operation duration (per shift)
Score
Band
Score
Band
<1 mg
Low
11e15
Weekly
30-60 min
35
MEDIUM
57.5
LIKELY
<1 mg
Low Unknown
11e15 Unknown
Weekly Weekly
30-60 min 30-60 min
30.5 62.5
MEDIUM HIGH
57.5 55
LIKELY LIKELY
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