Karimi Zeverdegani S, Mehrifar Y, Faraji M, Rismanchian M. Occupational exposure to welding gases during three welding processes and risk assessment by SQRCA method. J Occup Health Epidemiol 2017; 6 (3) :144-149
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1- Dept. of Occupational Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran.
2- Dept. of Occupational Health Engineering, Student Research Committe, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran
3- Dept. of Occupational Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran , rismanchian@hlth.mui.ac.ir
Article history
Received: 2017/08/21
Accepted: 2017/09/16
ePublished: 2017/11/21
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Occupational exposure to welding gases during three welding processes and risk assessment by SQRCA method
Karimi Zeverdegani S, PhD1, Mehrifar Y, MSc Student2, Faraji M, MSc Student3, Rismanchian M, PhD4*
1- Assistant Prof, Dept. of Occupational Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran. 2- MSc Student, Dept. of Occupational Health Engineering, Student Research Committe, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran. 3- MSc Student, Dept. of Occupational Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran. 4- Assistant Prof , Dept. of Occupational Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran
Abstract Received: August 2017, Accepted: September 2017
Background: Hazardous chemical agents in the welding operation are a mixture of metal fumes and toxic gases, the inhalation of which causes adverse health effects among welders. The emission of gases in the workplace is a logical cause for concern regarding the potential development of respiratory disease. The aim of the present study was to determine the concentration values of gases discharged during arc welding and perform risk assessment through semi-quantitative chemical risk assessment (SQCRA) method.
Materials and Methods: This cross-sectional study was conducted in an Iranian steel mill on the 3 processes of plasma arc welding (PAW), submerged arc welding (SAW), and gas tungsten arc welding (GTAW). Direct reading instruments were used for sampling of carbon dioxide (CO2), carbon monoxide (CO), nitrogen monoxide (NO), nitrogen dioxide (NO2), and ozone (O3). SQCRA method was used for risk assessment of gases.
Results: The concentrations of O3 (0.356 ppm), CO (41.642 ppm), NO (6.357 ppm), and NO2 (4.871 ppm) were found to exceed their threshold limit values (TLVs), while the concentrations of CO2 (3879.285 ppm) were below its TLV. The maximum exposure concentration of all gases, except CO2, was observed in SAW. SQCRA method showed that among the gases, the highest and least risk rating was related to ozone and nitrogen monoxide, respectively. The risk rating for CO2, CO, and NO2 was low, high, and very high, respectively.
Conclusions: In this study, exposure values were higher than the threshold limit values-time weighted average (TLV-TWA) and the results of risk assessment showed that control engineering should be applied and the use of respiratory protective equipment (RPE) should be made mandatory for welders especially in SAW, PAW, and GTAW processes. |
Keywords: Welding, Exposure, Gases, Steel
Introduction
Welding is an important occupational activity worldwide and includes workers in many industries, especially in the manufacturing, steel, and energy industries. Welding is a common process used to join metals by heating them to welding temperature (1). The US Bureau of Labor Statistics estimated that in excess of 330000 US workers do welding as part of their jobs. About two-thirds of those workers were in manufacturing industries (2). In this sector, there are about 730000 full time welding jobs and 5.5 million welding related jobs in Europe (3). In 2008, About 2.34 million people were killed in work-related accidents, 2.02 cases of which were due to work-related diseases (4). Welding produces multiple hazards during operation, including fumes, gases, and physical agents such as extreme heat and ultraviolet radiation. A review by Antonini et al. detailed a number of occupation related adverse health effects in welders, such as lung disease and possible neurological disease (5). Chemicals have different toxicity, and risk assessment of chemicals determines the risk levels that they present to users (6).
Several studies, generally performed in large companies and focusing on atmospheric exposure of welders to particulate matter and metals, have characterized the main determinants of external exposure to be the welding process, ventilation, working in confined spaces, and the composition of consumables (7, 8). In contrast, very few risk assessment studies have been performed on gases and conditions of exposure in small and medium-sized enterprises (SMEs) are seldom available (9). Several gases including ozone (O3), nitrogen oxides (NOx), carbon monoxide (CO), and carbon dioxide (CO2) are generated during arc welding operations (10). Ozone (O3) is produced in a photochemical reaction induced by ultraviolet light with atmospheric oxygen gas during the welding process. Ozone is produced within 30 seconds during welding. However, the length of time that O3 remains in the air after welding is completed (post-welding) is unknown (11). Findings have shown that O3 alters pulmonary morphology, physiology, and biochemistry, and it also is a proven cause of asthma in humans (12). O3 is a strong oxidant that generates reactive oxygen species (ROS) in tissues, and even causes DNA damage (13). Welding operations producing comparatively high concentrations of ozone (O3) can cause occlusive impairment of the welders’ bronchioles (14).
Carbon monoxide (Co) is a lethal poison and can overcome the exposed individual without warning because it is colorless, tasteless, odorless, and non-irritating. Overexposure to CO inhibits the body’s red blood cells from carrying sufficient oxygen to other body tissues, which results in asphyxiation. Symptoms of overexposure include pounding of the heart, a dull headache, flashes before the eyes, dizziness, ringing in the ears. High concentrations may become rapidly fatal without producing significant warning symptoms. The effects are also more severe in people who are working hard and in places where the temperature is high (4).
Carbon dioxide (CO2) is primarily a colorless, odorless gas. In the earth’s atmosphere, it acts as a “greenhouse gas” which plays a major role in global warming and anthropogenic climate change. Human activities are altering the carbon cycle and have contributed substantially to climate change by adding CO2 and other heat trapping gases to the atmosphere. With a global radiative forcing of 1.74 W/m2, CO2 is the largest contributor among well-mixed long-lived greenhouse gases, accounting for more than 63% of the total (15). Exposure to high concentrations of oxidant gas, nitrogen dioxide (NO2) and nitrogen monoxide (NO), can induce pulmonary disorders such as acute inflammation and pulmonary edema (16, 17). Welding is an important process in the steel industries and has crucial impact on the economy of countries. Therefore, its welders are exposed to chemical agents.
In general, managing health and safety risks at workplaces involves identifying hazards, risk assessment, risk control, and reviewing control measures (18). The risk assessment process includes many phases including hazard identification, exposure assessment, and risk characterization. Risk assessment is a useful tool to improve occupational health and safety policies and the decision-making process for control approaches (19). The aim of the present study was to determine the concentration values of gases discharged during different processes in arc welding and perform risk assessment through semi-quantitative chemical risk assessment (SQCRA) method for exposer to welding gases in an Iranian steel mill.
Material and Methods
This cross-sectional study was performed on the welders at a steel mill in 2017. Welders were selected through census method from welding stations (n = 21). The 3 welding stations selected were related to welding processes commonly used in the steel industry including plasma arc welding (PAW), submerged arc welding (SAW), and gas tungsten arc welding (GTAW).
The concentrations of ozone (O3), carbon monoxide (CO), carbon dioxide (CO2), nitric oxide (NO), and nitric dioxide (NO2) were measured with direct reading instruments known as real time instruments including detector tubes (GASTEC Corporation, Japan) and piston pump (Gastec GV-100-S-TR, GASTEC Corporation, Japan). The SQCRA method, which was proposed by the Occupational Safety and Health Division of the Ministry of Manpower of Singapore (19), was used to determine chemical exposure risks. This method involves identifying harmful pollutants, hazard rate (HR), and exposure rate (ER), and determining the level of exposure risk. After the identification of the hazardous and common gases in the welding process, the hazard coefficients of and exposure to these gases were determined using the relevant tables and the results of measured values from the work environment were determined. From the square root of the multiplication of risk degree to exposure risk (the following formula), the numerical value of the risk was calculated.
Risk =