Hazards associated with blue light emitted during gas metal arc welding of mild steel using various shielding gases and currents

Blue light emitted during arc welding is known to potentially cause photoretinopathy. To help prevent retinal injury, it is important to identify the hazards associated with various welding conditions. The present work conducted experiments involving gas metal arc welding of mild steel under various conditions, and measured the spectral radiance of the arcs. The effective radiance values, as used by the American Conference of Governmental Industrial Hygienists (ACGIH) to quantify exposure level of blue light, were subsequently calculated from the data. The resulting values were in the range of 5.0-118 W/cm2/sr, corresponding to hazardous levels according to ACGIH guidelines. The effective radiance was increased at higher welding currents and when pulsed currents were used rather than steady currents. The blue light hazard was also affected by the type of shielding gas employed. These data confirm that it is very hazardous to stare at arcs during gas metal arc welding of mild steel. As such, appropriate eye protection is necessary during arc welding, and directly staring at the arc should be avoided.

Application of Multiple Occupational Health Risk Assessment Models for Metal Fumes in Welding Process

Welding fumes have an important role to create the adverse health effects. So, the aim of this study was to use of multiple occupational health risk assessment models for metal fumes in welding process. This cross-sectional study was conducted among welding workers. Sampling of heavy metals such as Sn, Zn, Al, Fe, Cd, Pb, Cu, Mn, Ni, Cr, and As was provided based on the National Institute for Occupational Safety and Health (NIOSH) method 7300 and analyzed by inductively coupled plasma mass spectroscopy (ICP-MS). Risk assessment was managed by four methods including Malaysia's method, Control of Substances Hazardous to Health Essentials (COSHH model), Chinese OHRA standard (GBZ/T 298-2017), and EPA method. Also, Monte Carlo simulation was used to examine the uncertainties by using the Crystal Ball tool. To compare the models, the risk levels of each model were converted into the risk ratio and the SPSS 22.0 software was used to the statistical analysis. The consistency of the two occupational health risk assessment models was examined by Cohen's Kappa. Risk ration was the highest level for Cr (VI) fumes in all models. Also, carcinogenic risk was unacceptable for all examined fumes. Moreover, non-carcinogenic risk was the highest (HI > 1) for As fumes. Mont Carlo simulations suggested that exposure time (ET) had a significant effect on the risk. Also, there was a good consistency between Malaysia method/GBZ/T 298-2017 and COSHH model/GBZ/T 298-2017. Therefore, it is recommended that the engineering and administrative controls should be provided to reduce exposure.

[Bibliometric and visual analysis of neurological damage caused by electrical welding operations]

Objective: To analyze and summarize the trends and hot spots in the field of neurological damage caused by electric welding operations, and to provide ideas for new researches by searching the domestic and international literature. Methods: In December 2022, using Web of Science Citation Index (Web of Science), China Journal Full-Text Database (CNKI) and Wanfang Database as search databases, literature search was conducted on the Chinese and English search terms related to eletrical welding operations and neurological damage. The bibliometric analysis software VOSviewer 1.6.18 and CiteSpace 6.1.6 were used to visualize the publication year, publication quantity, country, research institution and key words of the literature. Results: A total of 309 articles (112 in Chinese and 197 in English) were included in this study. The first domestic and international papers were published in 1976 and 1994 respectively, and the number of papers reached the peak in 2006 and 2018, and then showed a downward trend to varying degrees. In China, Shandong First Medical University (including Shandong Institute of Occupational Health and Occupational Disease Prevention and Shandong Academy of Medical Sciences) and Wuhan University of Science and Technology had the largest number of publications. The 309 articles were from 52 Chinese journals and 86 English journals. The co-occurrence analysis of key words showed that the domestic research mainly focused on eletrical welding operation, welding workers, neurobehavioral function and manganese, and the nervous system damage caused by manganese in welding smoke was the field of international attention. Long term exposure, risk, and performance were key buzzwords in the field. Conclusion: The research focus in the field of nervous system damage caused by electric welding operation has an obvious trend of time evolution, gradually transiting from clinical manifestations to its toxic mechanism and early biomarkers.

Study on the soluble and insoluble fume and hexavalent chromium emitted from a new covered electrode with micro and nano sized-sodium and potassium titanate-based flux

The present study discusses the effect of the addition of nano-sized arc stabilizing materials on fume emissions and its solubility characteristics. Micro and nano-sized sodium/potassium titanates were added to the SMAW electrode flux as a substitute for the conventional sodium and potassium silicate compounds. The total and soluble metal concentration of fumes from the newly developed electrodes were estimated and compared with that of commercially available electrodes. The estimation of fume formation rate and breathing zone concentration of fumes followed the ISO 15011-1 and ISO 10882-1 standard. An average 50% reduction in the soluble fraction of fumes was observed from the electrodes containing micro-sized potassium-titanate compounds, and the reduction was further improved by 60% when nano-sodium titanate was added to the flux. Whereas, the reduction in soluble metal concentration for potassium titanate coated electrodes were 45% and 55%, in that order, for their micro and nano-structured forms. The soluble fraction of hexavalent chromium from the electrodes containing 100% nano sodium/potassium titanates was reduced up to 50% in each impactor stage. The inclusion of nano-sized sodium titanate in the flux resulted in a reduction in fume formation rate up to 55% and breathing zone concentration of fumes by 58% compared to the conventional sodium silicate coated electrodes. The electrode assaying 100% nano-potassium titanate showed a reduction of 59% in fume formation rate and 61% in breathing zone concentration compared to that of conventional potassium silicate-coated electrodes.

Review of welding fume emission factor development

The fumes created from welding activities present a unique occupational hazard. Due to the complex processes which govern fume formation, the characterization of welding fumes is difficult. Emission factors (EFs) are one method to characterize fume formation from different processes and scenarios. This paper reviews the development of EFs and similar metrics both historic research which contributed to the US EPAs AP-42 summary of welding emission factors released in 1995, and more recent research initiatives. Through a critical analysis of what research has been done in this area and the strength of the emission factors developed, this paper proposes a set of recommendations for future research. Research on emission factors for gas metal arc welding (GMAW) is the most complete amongst the different types of electric arc welding. Despite it being generally known that flux core arc welding (FCAW) creates significant fume emissions compared to some of the other processes few studies have looked at FCAW since the AP-42. Shielded metal arc welding is also under-researched particularly in terms of metal-specific emission factors. The influence of different welding activity parameters such as welding location, speed or current is well defined for GMAW but requires more attention for other welding processes. Further effort towards compiling and comparing available emission factor data of quality, evaluating the available data statistically and organizing this data in a practically useful way is required. The availability of reliable emission factors will allow the development or improvement of exposure modelling tools that would be very useful for exposure assessment when monitoring is not practical.s.

Carcinogenic and non-carcinogenic risk of exposure to metal fume in different types of welding processes

The international agency for cancer research (IARC) has classified welding fumes as definitive carcinogens. The aim of the present study was to assess health risk due to exposure to welding fumes in different welding types. In this study, exposure to fumes of iron (Fe), chromium (Cr), and nickel (Ni) in the breathing zone air of 31 welder engaged in arc, argon and CO2 welding was assessed. Carcinogenic and non-carcinogenic risk assessments due to exposure to fumes were performed using the method proposed by the Environmental Protection Agency (EPA) by Monte Carlo simulation. The results showed that in the CO2 welding, concentration of Ni, Cr, and Fe was lower than the 8-h Time-Weighted Average Threshold Limit Value (TWA-TLV), recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). In argon welding, Cr and Fe concentrations were higher than the TWA-TLV. In arc welding, concentrations of Ni and Fe were more than the TWA-TLV. In addition, the risk of non-carcinogenicity due to exposure to Ni and Fe in all three types of welding was more than standard level (HQ>1). The results indicated that the welders are at health risk due to exposure to metal fumes. Preventive exposure control measures such as local ventilation need to be implemented in welding workplaces.

Occupational Exposure to Metal Fumes Among Iranian Welders: Systematic Review and Simulation-Based Health Risk Assessment

There have been numerous reports of welder's worker exposure to metal fumes. Carcinogenic and non-carcinogenic (neurological, dermal, and etc.) effects are the adverse outcomes of exposure to welding fumes. In this review study, data were collected from previous studies conducted in Iran from 1900 to 2020. The risk of carcinogenicity and non-carcinogenicity due to exposure to welding metal fumes was assessed using the United States Environmental Protection Agency (USEPA) method based on the Monte Carlo simulation (MCS). Results showed mean of metal fume concentration in gas welding was in the range of 1.8248 to 1060.6 (µg/m³) and in arc welding was 54.935 to 4882.72 (µg/m³). The mean concentration of fumes in gas welding is below the recommended American Conference of Governmental Industrial Hygienists (ACGIH) standard exposure limit except for manganese, and in the arc welding, all metal fume concentrations are below the standard exposure limit except for manganese and aluminum. The results showed that the risk of carcinogenicity due to exposure to nickel, manganese in both gas and arc welding, and cadmium in gas welding was higher than standard level (hazard quotient (HQ) more than 1). Cancer risk due to exposure to nickel in both gas and arc welding was probable (1 × 10^-6 < cancer risk (CR) < 1 × 10^-4). Health risk assessment showed that welders are exposed to health risks. Preventive measures should be applied in welding workplaces to reduce the concentrations of metal fumes.

An arc profile-based approach to evaluate gas pollutants in welding

Welding is widely used to make assembly of structural components and it will trigger serious environmental pollution, especially waste gas, i.e., carbon dioxide (CO₂), ozone (O₃), nitrogen oxide (NO_x), and particulate matter (PM). It is hard to accurately measure gas pollutants because of their fluidity and diffusivity. However, the pollutants could be evaluated by exploring its generation procedure, i.e., how these pollutants are produced and how to quantify these pollutants. In this paper, an arc profile-based approach to evaluate the emissions of gas pollutants in welding was proposed. The emission of gas pollutants in welding can be calculated according to the chemical reaction and corresponding reaction condition, i.e., the intensity of discharge that determines the coverage volume of the welding arc. To obtain the coverage volume, the welding arc was observed using a high-speed camera and the arc edge was extracted and reconstructed by a binarization processing based method. A welding experiment was performed for recording the arc shape and measuring the emission of gas pollutants. Results show that the measured concentrations of NO_x and O₃ are 70% and 79% of the calculated emissions of gas pollutants, respectively. It demonstrates the proposed method is credible and feasible, which can help quantitatively analyze the emission of gas pollutants. Meanwhile, the influence of welding time, welding current, and arc length on the emission of gas pollutants was investigated for lowering emission of gas pollution in welding, in order to support the development of sustainable manufacturing processes.

Incipient Wear Detection of Welding Gun Secondary Circuit by Virtual Resistance Sensor Using Mahalanobis Distance

Wear of the secondary of the welding gun, caused by mechanical fatigue or due to a bad parameterization of the welding points, causes an increase in quality problems such as non-existent welds or a reduced weld nugget size. In addition to quality problems, this defect causes production stoppages that affect the final cost of the manufactured part. Different studies have focused on evaluating the importance of different welding parameters, such as current, in the final quality of the welding nugget. However, few studies have focused on preventing weld command parameters from degrading or changing. This investigation seeks to determine the wear of the secondary circuit to avoid variability in the current supplied to the welding point caused by this defect and the increase in circuit resistance, especially in industrial environments. In this work, a virtual sensor is developed to estimate the resistance of the welding arm based on previous research, which has shown the possibility of detecting secondary wear by analysing the duty cycle of the power circuit. From the data of the virtual sensor, an anomaly detection method based on the Mahalanobis distance is developed. Finally, an integral system for detecting secondary wear of welding guns in real production lines is presented. This system establishes performance thresholds based on the analysis of the Mahalanobis distance distribution, allowing monitoring of the secondary circuit wear condition after each welding cycle. The results obtained show how the system can detect incipient wear in welding guns, regardless of which part of the secondary the wear occurs, improving decision-making and reducing quality problems.

Assessment of welding fume impacts in a confined workplace by two extraction patterns - a case study of small-scale manufacturing industries

Welding fume exposure at work is recognized as a known concern for public health. This study aims to assess the welding fumes produced during welding using two different extraction patterns and to compare their influences. A thorough assessment of domestic arc welders in the erode district of India was done to assess their exposure to welding gases. The survey results chose the gas metal arc welding (GMAW) process for future investigation. The stainless-steel grade SS 316 L was used in this study. To weld 3-mm, 5-mm, and 6-mm-thick stainless-steel specimens, ER316 L filler wire and four shielding gas compositions were used. Two distinct, cost-effective welding hoods with a square duct section and a conical duct section were constructed to examine welding gases. The produced fume was collected on a 240 mm glass fibre filter and re-weighted during welding. Gas flow rates of 5, 10, and 15 LPM were investigated, with current intensities of 150A, 200A, and 275A. A novel attempt has been made to compare fume formation rates (FFR) obtained using two extraction patterns. According to this investigation, weld fume hoods with conical duct sections extract more welding gases than square duct sections. The extraction rate using two extraction patterns was compared. Furthermore, the addition of CO₂ to any shielding gas mixture results in a higher fume formation rate. The experimental FFR values were quite close to the American Welding Society (AWS) specifications. This finding also revealed that welders' socio-demographic characteristics, such as age, marital status, level of education, and work experience, influenced their awareness of occupational hazards and personal protection equipment (PPEs). As a result, there should be a strong emphasis on hazard identification education and strict enforcement of proper PPEs use among small-scale welders in and around the erode district to protect welders from a variety of hazards.

The effect of mask fit test on the association between the concentration of metals in biological samples and the results of time-weighted average personal exposure: A study on Japanese male welders

OBJECTIVES

The mask fit test confirms whether the wearing condition of the wearer's face and the facepiece of the respirators are used appropriately. This study aimed to examine whether the results of the mask fit test affect the association between the concentration of metals related to welding fumes in biological samples and the results of time-weighted average (TWA) personal exposures.

METHODS

A total of 94 male welders were recruited. Blood and urine samples were obtained from all participants to measure the metal exposure levels. Using personal exposure measurements, the 8-h TWA (8 h-TWA) of respirable dust, TWA of respirable Mn, and 8-h TWA of respirable Mn were calculated. The mask fit test was performed using the quantitative method specified in the Japanese Industrial Standard T8150:2021.

RESULTS

Fifty-four participants (57%) passed the mask fit test. Only in the Fail group of the mask fit test, it was observed that blood Mn concentrations be positively associated with the results of TWA personal exposure after adjusting for multivariate factors (8-h TWA of respirable dust; coefficient, 0.066; standard error (SE), 0.028; P = 0.018, TWA of respirable Mn: coefficient, 0.048; SE, 0.020; P = 0.019, 8 h-TWA of respirable Mn: coefficient, 0.041; SE, 0.020; P = 0.041).

CONCLUSIONS

The results clarify that welders with high concentrations of welding fumes in their breathing air zone are exposed to dust and Mn if there is leaking air owing to the lack of fitness between respirators and the wearer's face when using human samples in Japan.

Human biomonitoring and personal air monitoring. An integrated approach to assess exposure of stainless-steel welders to metal-oxide nanoparticles

In welding, there is a potential risk due to metal-oxide nanoparticles (MONPs) exposure of workers. To investigate this possibility, the diameter and number particles concentration of MONPs were evaluated in different biological matrices and in personal air samples collected from 18 stainless-steel welders and 15 unexposed administrative employees engaged in two Italian mechanical engineering Companies. Exhaled breath condensate (EBC) and urine were sampled at pre-shift on 1st day and post-shift on 5th day of the workweek, while plasma and inhalable particulate matter (IPM) at post-shift on 5th day and analysed using the Single Particle Mass Spectrometry (SP-ICP-MS) technique to assess possible exposure to Cr₂O₃, Mn₃O₄ and NiO nanoparticles (NPs) in welders. The NPs in IPM at both Companies presented a multi-oxide composition consisting of Cr₂O₃ (median, 871,574 particles/m³; 70 nm), Mn₃O₄ (median, 713,481 particles/m³; 92 nm) and NiO (median, 369,324 particles/m³; 55 nm). The EBC of welders at both Companies showed Cr₂O₃ NPs median concentration significantly higher at post-shift (64,645 particles/mL; 55 nm) than at pre-shift (15,836 particles/mL; 58 nm). Significantly lower Cr₂O₃ NPs median concentration and size (7762 particles/mL; 44 nm) were observed in plasma compared to EBC of welders. At one Company, NiO NPs median concentration in EBC (22,000 particles/mL; 65 nm) and plasma (8248 particles/mL; 37 nm) were detected only at post-shift. No particles of Cr₂O_3, Mn₃O₄ and NiO were detected in urine of welders at both Companies. The combined analyses of biological matrices and air samples were a valid approach to investigate both internal and external exposure of welding workers to MONPs. Overall, results may inform suitable risk assessment and management procedures in welding operations.

Research on Trajectory Recognition and Control Technology of Real-Time Tracking Welding

Real-time tracking welding with the assistance of structured light vision enhances the intelligence of robotic welding, which significantly shortens teaching time and guarantees accuracy for user-customized product welding. However, the robustness of most image processing algorithms is deficient during welding practice, and the security regime for tracking welding is not considered in most trajectory recognition and control algorithms. For these two problems, an adaptive feature extraction algorithm was proposed, which can accurately extract the seam center from the continuous, discontinuous or fluctuating laser stripes identified and located by the CNN model, while the prior model can quickly remove a large amount of noise and interference except the stripes, greatly improving the extraction accuracy and processing speed of the algorithm. Additionally, the embedded Pauta criterion was used to segmentally process the center point data stream and to cyclically eliminate outliers and further ensure the accuracy of the welding reference point. Experimental results showed that under the guarantee of the above-mentioned seam center point extraction and correction algorithms, the tracking average error was 0.1 mm, and even if abnormal trajectory points existed, they did not cause welding torch shaking, system interruption or other accidents.

Real-Time Condition Monitoring System for Electrode Alignment in Resistance Welding Electrodes

Electrode misalignment, produced by mechanical fatigue or bad adjustments of the welding gun, leads to an increase in expulsions, deformations and quality problems of the welding joints. Different studies have focused on evaluations of the influence of a misalignment of the electrodes and the final quality of the weld nugget. However, few studies have focused on determining a misalignment of the electrodes to avoid problems caused by this defect, especially in industrial environments. In this paper, a method for performing the condition monitoring of electrode alignment degradation was developed following previous research, which has shown the relationship between the misalignment of short-circuited electrodes and the magnetic field generated by them. This method was carried out by means of a device capable of measuring the magnetic field. Finally, an integral system for the detection of misalignments in real production lines is presented. This system set behavior thresholds based on the experimentation, allowing the condition monitoring of the alignment after each welding cycle.

In vivo and in vitro toxicity of a stainless-steel aerosol generated during thermal spray coating

Thermal spray coating is an industrial process in which molten metal is sprayed at high velocity onto a surface as a protective coating. An automated electric arc wire thermal spray coating aerosol generator and inhalation exposure system was developed to simulate an occupational exposure and, using this system, male Sprague-Dawley rats were exposed to stainless steel PMET720 aerosols at 25 mg/m³ × 4 h/day × 9 day. Lung injury, inflammation, and cytokine alteration were determined. Resolution was assessed by evaluating these parameters at 1, 7, 14 and 28 d after exposure. The aerosols generated were also collected and characterized. Macrophages were exposed in vitro over a wide dose range (0-200 µg/ml) to determine cytotoxicity and to screen for known mechanisms of toxicity. Welding fumes were used as comparative particulate controls. In vivo lung damage, inflammation and alteration in cytokines were observed 1 day post exposure and this response resolved by day 7. Alveolar macrophages retained the particulates even after 28 day post-exposure. In line with the pulmonary toxicity findings, in vitro cytotoxicity and membrane damage in macrophages were observed only at the higher doses. Electron paramagnetic resonance showed in an acellular environment the particulate generated free radicals and a dose-dependent increase in intracellular oxidative stress and NF-kB/AP-1 activity was observed. PMET720 particles were internalized via clathrin and caveolar mediated endocytosis as well as actin-dependent pinocytosis/phagocytosis. The results suggest that compared to stainless steel welding fumes, the PMET 720 aerosols were not as overtly toxic, and the animals recovered from the acute pulmonary injury by 7 days.

[Comparative analysis on occupational hazards of three welding operations]

Objective: To explore the occupational hazards caused by three kinds of welding operations, and to provide data support for individual protection. Methods: In October 2020, the welding fumes, metal elements and welding arc generated by three welding operations of argon gas shielded welding (JS80 welding wire) , manual welding (ZS60A welding rod) and carbon dioxide shielded welding (907A flux cored wire) were collected and measured in the welding laboratory. The samples were analyze and compare in the laboratory, and the differences of the occupational hazard factors of the three welding operations were judged. Results: The concentration of welding fume produced by carbon dioxide shielded welding, manual welding (ZS60A electrode) , and argon gas shielded welding (JS80 welding wires) were 6.80 mg/m(3), 6.17 mg/m(3), and 3.13 mg/m(3), respectively. The effective irradiance of the welding arc outside the welding mask from high to low is manual welding (ZS60A electrode) , carbon dioxide shielded welding (907A flux-cored welding wire) , and argon shielded welding (JS80 welding wire) , respectively 1 010.7, 740.9, 589.5 μW/cm(2). The long-wave ultraviolet UVA intensity generated by argon shielded welding (JS80 welding wire) is the largest, which is 1 500 μW/cm(2). The content of Mn in the three welding operations is the highest, and JS80 welding wire has the highest Mn content of 128493.2 mg/kg. 907A flux cored wire has the highest Ti content, which is 24355.5mg/kg. The electrode ZS60A has the highest Cu content, which is 24422.12 mg/kg. Conclusion: The intensity of occupational hazards is different in the three kinds of welding operations, so the methods of personal protective equipment, field exposure assessment and health monitoring should be more targeted.

Infrared Visual Sensing Detection of Groove Width for Swing Arc Narrow Gap Welding

To solve the current problem of poor weld formation due to groove width variation in swing arc narrow gap welding, an infrared passive visual sensing detection approach was developed in this work to measure groove width under intense welding interferences. This approach, called global pattern recognition, includes self-adaptive positioning of the ROI window, equal division thresholding and in situ dynamic clustering algorithms. Accordingly, the self-adaptive positioning method filters several of the nearest values of the arc’s highest point of the vertical coordinate and groove’s same-side edge position to determine the origin coordinates of the ROI window; the equal division thresholding algorithm then divides and processes the ROI window image to extract the groove edge and forms a raw data distribution of groove width in the data window. The in situ dynamic clustering algorithm dynamically classifies the preprocessed data in situ and finally detects the value of the groove width from the remaining true data. Experimental results show that the equal division thresholding algorithm can effectively reduce the influences of arc light and welding fume on the extraction of the groove edge. The in situ dynamic clustering algorithm can avoid disturbances from simulated welding spatters with diameters less than 2.19 mm, thus realizing the high-precision detection of the actual groove width and demonstrating stronger environmental adaptability of the proposed global pattern recognition approach.

Exploring a new method for the assessment of metal exposure by analysis of exhaled breath of welders

Purpose

Air monitoring has been the accepted exposure assessment of toxic metals from, e.g., welding, but a method characterizing the actual dose delivered to the lungs would be preferable. Sampling of particles in exhaled breath can be used for the biomonitoring of both endogenous biomarkers and markers of exposure. We have explored a new method for the sampling of metals in exhaled breath from the small airways in a study on welders.

Methods

Our method for particle sampling, Particles in Exhaled Air (PExA®), is based on particle counting and inertial impaction. We applied it on 19 stainless steel welders before and after a workday. In parallel, air monitoring of chromium, manganese and nickel was performed as well as blood sampling after work.

Results

Despite substantial exposure to welding fumes, we were unable to show any significant change in the metal content of exhaled particles after, compared with before, exposure. However, the significance might be obscured by a substantial analytical background noise, due to metal background in the sampling media and possible contamination during sampling, as an increase in the median metal contents were indicated.

Conclusions

If efforts to reduce background and contamination are successful, the PExA® method could be an important tool in the investigations of metals in exhaled breath, as the method collects particles from the small airways in contrast to other methods. In this paper, we discuss the discrepancy between our findings and results from studies, using the exhaled breath condensate (EBC) methodology.

Toxicity of stainless and mild steel particles generated from gas-metal arc welding in primary human small airway epithelial cells

Welding fumes induce lung toxicity and are carcinogenic to humans but the molecular mechanisms have yet to be clarified. The aim of this study was to evaluate the toxicity of stainless and mild steel particles generated via gas-metal arc welding using primary human small airway epithelial cells (hSAEC) and ToxTracker reporter murine stem cells, which track activation of six cancer-related pathways. Metal content (Fe, Mn, Ni, Cr) of the particles was relatively homogenous across particle size. The particles were not cytotoxic in reporter stem cells but stainless steel particles activated the Nrf2-dependent oxidative stress pathway. In hSAEC, both particle types induced time- and dose-dependent cytotoxicity, and stainless steel particles also increased generation of reactive oxygen species. The cellular metal content was higher for hSAEC compared to the reporter stem cells exposed to the same nominal dose. This was, in part, related to differences in particle agglomeration/sedimentation in the different cell media. Overall, our study showed differences in cytotoxicity and activation of cancer-related pathways between stainless and mild steel welding particles. Moreover, our data emphasizes the need for careful assessment of the cellular dose when comparing studies using different in vitro models.

Metal enriched quasi-ultrafine particles from stainless steel gas metal arc welding induced genetic and epigenetic alterations in BEAS-2B cells

Recent evidence has supported welding fume (WF)-derived ultrafine particles (UFP) could be the driving force of their adverse health effects. However, UFP have not yet been extensively studied and are currently not included in present air quality standards/guidelines. Here, attention was focused on the underlying genetic and epigenetic mechanisms by which the quasi-UFP (Q-UFP, i.e., ≤ 0.25 μm) of the WF emitted by gas metal arc welding-stainless steel (GMAW-SS) exert their toxicity in human bronchial epithelial BEAS-2B cells. The Q-UFP under study showed a monomodal size distribution in number centered on 104.4 ± 52.3 nm and a zeta potential of -13.8 ± 0.3 mV. They were enriched in Fe > Cr > Mn > Si, and displayed a relatively high intrinsic oxidative potential. Dose-dependent activation of nuclear factor erythroid 2-related factor 2 and nuclear factor-kappa B signaling pathway, glutathione alteration, and DNA, protein and lipid oxidative damage were reported in BEAS-2B cells acutely (1.5 and 9 μg/cm², 24 h) or repeatedly (0.25 and 1.5 μg/cm², 3 × 24 h) exposed to Q-UFP (p < 0.05). Alterations of the Histone H3 acetylation were reported for any exposure (p < 0.05). Differentially regulated miRNA and mRNA indicated the activation of some critical cell signaling pathways related to oxidative stress, inflammation, and cell cycle deregulation towards apoptosis. Taken together, these results highlighted the urgent need to better evaluate the respective toxicity of the different metals and to include the Q-UFP fraction of WF in current air quality standards/guidelines relevant to the occupational settings.

Modelling of exposure to respirable and inhalable welding fumes at German workplaces

The International Agency for Research on Cancer classified welding fumes as carcinogenic to humans, and occupational exposure limits should be established to protect welders. The aim of this study is to estimate exposure levels to inhalable and respirable welding fumes by welding process to use them for exposure assessment in epidemiological studies and to derive occupational exposure limits. In total, 15,473 mass concentrations of inhalable and 9,161 concentrations of respirable welding fumes could be analyzed along with welding-related and sampling information, which were compiled in the German database MEGA between 1983 and 2016. In both particle-size fractions, model-based geometric means of the concentrations were estimated by welding process and material for frequently used welding processes adjusted for sampling time and median-centered for calendar years. The inhalable concentrations were approximately twice the respirable concentrations, with medians of 3 mg/m³ (inter-quartile range: 1.2-7.0 mg/m³) and 1.5 mg/m³ (inter-quartile range: < limit of detection -3.8 mg/m³), respectively. The adjusted geometric means of flux-cored arc welding, metal inert and active gas welding, shielded metal arc welding and torch cutting ranged from 0.9 to 2.2 mg/m³ for respirable welding fumes and from 2.3 to 4.7 mg/m³ for inhalable fumes. In both particle-size fractions, geometric means were between 0.1 and 0.9 mg/m³ when performing tungsten inert gas, autogeneous, resistance, laser, and plasma welding or spraying. Results derived from this large dataset are useful for a quantitative exposure assessment to estimate health risks of welders.

Pulmonary toxicity and lung tumorigenic potential of surrogate metal oxides in gas metal arc welding-stainless steel fume: Iron as a primary mediator versus chromium and nickel

In 2017, the International Agency for Research on Cancer classified welding fumes as "carcinogenic to humans" (Group 1). Both mild steel (MS) welding, where fumes lack carcinogenic chromium and nickel, and stainless steel (SS) increase lung cancer risk in welders; therefore, further research to better understand the toxicity of the individual metals is needed. The objectives were to (1) compare the pulmonary toxicity of chromium (as Cr(III) oxide [Cr2O3] and Cr (VI) calcium chromate [CaCrO4]), nickel [II] oxide (NiO), iron [III] oxide (Fe2O3), and gas metal arc welding-SS (GMAW-SS) fume; and (2) determine if these metal oxides can promote lung tumors. Lung tumor susceptible A/J mice (male, 4-5 weeks old) were exposed by oropharyngeal aspiration to vehicle, GMAW-SS fume (1.7 mg), or a low or high dose of surrogate metal oxides based on the respective weight percent of each metal in the fume: Cr2O3 + CaCrO4 (366 + 5 μg and 731 + 11 μg), NiO (141 and 281 μg), or Fe2O3 (1 and 2 mg). Bronchoalveolar lavage, histopathology, and lung/liver qPCR were done at 1, 7, 28, and 84 days post-aspiration. In a two-stage lung carcinogenesis model, mice were initiated with 3-methylcholanthrene (10 μg/g; intraperitoneal; 1x) or corn oil then exposed to metal oxides or vehicle (1 x/week for 5 weeks) by oropharyngeal aspiration. Lung tumors were counted at 30 weeks post-initiation. Results indicate the inflammatory potential of the metal oxides was Fe2O3 > Cr2O3 + CaCrO4 > NiO. Overall, the pneumotoxic effects were negligible for NiO, acute but not persistent for Cr2O3 + CaCrO4, and persistent for the Fe2O3 exposures. Fe2O3, but not Cr2O3 + CaCrO4 or NiO significantly promoted lung tumors. These results provide experimental evidence that Fe2O3 is an important mediator of welding fume toxicity and support epidemiological findings and the IARC classification.

Evaluation of operational parameters role on the emission of fumes

Electric arc welding is a routine operation in the construction of metallic structures, but the fumes generated during the welding process can threaten the health of welders. Fumes are undesirable products of the majority of welding operations and may have various detrimental effects on health. The purpose of this study was to investigate the effect of operational parameters of the shielded metal arc welding (SMAW) process on the emission of fumes. A dust monitor was used to measure the number and mass concentration of fumes generated by SMAW. Measurements were made at the distances of 23 cm (hood inlet) and 41 cm (welder's breathing zone) from the weld point, with different values assigned to three operational parameters, namely current intensity, travel speed, and heat input (HI). Number concentration (NC) decreased with the increase in particle size. The highest mass concentrations (MC) were observed for MC1 (0.35-0.5 μm) and MC8 (Larger than 6.5 μm). For reducing exposures to fumes, welders are recommended to use the lowest voltage and amperage and the highest travel speed to the extent that does not compromise in the quality of welds. For assessment of exposure to airborne particles in industrial workplaces and specially in welding operations, it is thought that taking, solely, mass concentration in to consideration and lack of attention to number concentration would not be able to reflect accurate assessment of the adverse effects of particles on the body organs.

Instant loading with intraoral welding technique and PRAMA implants: a new prosthetic approach

When splinting multiple implants passive fit of the framework should be achieved to avoid excessive force distribution on the implants. Recently, a protocol was suggested for immediate loading of multiple implants by welding a titanium bar to implant abutments directly in the oral cavity so as to create a customized, precise and passive metal-reinforced provisional restoration. The intraoral welding technique subsequently proves to be a successful option in the full-arch immediate restorations of the mandible and maxilla. The aim of this article is to present a case report in which a new prosthetic approach, using trans-mucosal implants, is described. Dental implants are instantly loaded with a provisional prosthesis supported by an intraoral welded titanium framework to obtain a precise passive fit of the immediate loaded prosthesis.

Pneumococcal infection of respiratory cells exposed to welding fumes; Role of oxidative stress and HIF-1 alpha

Welders are more susceptible to pneumococcal pneumonia. The mechanisms are yet unclear. Pneumococci co-opt the platelet activating factor receptor (PAFR) to infect respiratory epithelial cells. We previously reported that exposure of respiratory cells to welding fumes (WF), upregulates PAFR-dependent pneumococcal infection. The signaling pathway for this response is unknown, however, in intestinal cells, hypoxia-inducible factor-1 α (HIF 1α) is reported to mediate PAFR-dependent infection. We sought to assess whether oxidative stress plays a role in susceptibility to pneumococcal infection via the platelet activating factor receptor. We also sought to evaluate the suitability of nasal epithelial PAFR expression in welders as a biomarker of susceptibility to infection. Finally, we investigated the generalisability of the effect of welding fumes on pneumococcal infection and growth using a variety of different welding fume samples. Nasal epithelial PAFR expression in welders and controls was analysed by flow cytometry. WF were collected using standard methodology. The effect of WF on respiratory cell reactive oxygen species production, HIF-1α expression, and pneumococcal infection was determined using flow cytometry, HIF-1α knockdown and overexpression, and pneumococcal infection assays. We found that nasal PAFR expression is significantly increased in welders compared with controls and that WF significantly increased reactive oxygen species production, HIF-1α and PAFR expression, and pneumococcal infection of respiratory cells. In unstimulated cells, HIF-1α knockdown decreased PAFR expression and HIF-1α overexpression increased PAFR expression. However, in knockdown cells pneumococcal infection was paradoxically increased and in overexpressing cells infection was unaffected. Nasal epithelial PAFR expression may be used as a biomarker of susceptibility to pneumococcal infection in order to target individuals, particularly those at high risk such as welders, for the pneumococcal vaccine. Expression of HIF-1α in unexposed respiratory cells inhibits basal pneumococcal infection via PAFR-independent mechanisms.