Javad Sajedifar, Amir Hosein Kokabi, Kamal Azam, Somayeh Farhang Dehghan, Ali Karimi, Farideh Golbabaei,
Volume 6, Issue 4 (12-2016)
Abstract
Introduction: Nowadays, Shielded Metal Arc Welding (SMAW) is the most widely used arc welding. During the welding operation, typically, various harmful agents such as fumes, gases, heat, sound and ultraviolet radiation are produced of which fume is the most important component from the viewpoint of occupational health. The present study aims to compare the number and the mass concentration emitted in SMAW to determine the most appropriate index of exposure to fumes in the welding processes.
Material and Method: In this study, the portable laser aerosol spectrometer and dust monitor of GRIMM, model 1.106, was used to measure the number and mass concentration of fumes emitted from SMAW on 304 stainless steel with a thickness of 0.4 mm. Air sampling was performed at a distance of 41 cm representing the welder’s breathing zone. The measurements of number concentration (NC) and mass concentration (MC) were taken under the condition of 25 volt voltage and direct current of the electrode polarity.
Result: The total NC and MC of welding fumes in welder’s breathing zone was 1140451 particles per liter and 1631.11 micrograms per cubic meter, respectively. The highest number concentration was found to correspond to the particles with 0.35 to 0.5 micrometer-sized distribution (NC1; 938976 particles per liter) and the lowest was related to the particles with 5 to 6.5 micrometer-sized distribution (NC7; 288 particles per liter) and the particles larger than 6.5 micrometer (NC8; 463 particles per liter). Moreover, the highest mass concentration was related to the particles with 0.35 to 0.5 micrometer-sized distribution (MC1; 450 micrograms per cubic meter) and the particles larger than 6.5 micrometer (MC8; 355 micrograms per cubic meter).
Conclusion: The findings indicated that there is no agreement between number and mass concentration as two particles assessment index, and as the particles’ size become smaller, the mismatch of them is becoming more apparent. Since the smaller particles penetrate into the lower respiratory tract and have higher potential for adverse health effects, it is necessary to measure and assess particles in various size distributions and especially the smaller fraction of particles. Therefore, it is thought that considering the mass concentration alone and not paying attention to number concentration in the assessment of exposure to particles in the industrial workplaces and specifically in welding stations will not be reflected valid assessment of adverse health effects of welding fumes as a systemic poison on body organs.
Hassan Rajabi-Vardanjani, Hassan Asilian-Mahabadi, Morteza Bayareh, Morteza Sedehi,
Volume 9, Issue 4 (12-2019)
Abstract
Introduction: Usually, in the toxicological studies of airborne particulate pollutants, inhalation exposure chambers are used for providing and distributing the test atmosphere uniformly and stability in the respiratory zone of laboratory animals. The purpose of this study was to design, evaluate and optimize a whole-body exposure chamber, specifically for small laboratory animals exposed to particulate matter.
Material and Methods: In the first, the papers and scientific resources which had provided the technical details and performance of the inhalation exposure chambers were studied, and the advantages, disadvantages and those factors affecting their performance were extracted. Then the assumptions of the initial design of the chamber were prepared with regard to the principles of fluid dynamics and the standard conditions of lab animal housing. To create a uniform distribution of particles inside the chamber, guide plates of flow were used in the upper cone. Numerical simulation and ANSYS Fluent software were used to optimize the initial design. Drawing geometry of the chambers was done using Design modeler software and meshing of the computational field using ANSYS meshing software. The particles used had a mean aerodynamic diameter of 10 μm, spherical, inert, and a density of 1,400 kg. m^-3 and entered the chamber at the carrier gas velocity. Particle concentration was measured in the chambers along the cylindrical radius at 10 cm intervals on the x-axis. Then the percentage of variation coefficient of the particle concentration for each line was calculated. In the final analysis of the results, the geometry design with the lowest coefficient of variation of particle concentration along the selected sampling line was selected as the best chamber design.
Results: The optimized inhalation chamber has a dynamical flow and consists of a cylinder with two upper and lower cones. The flow enters from the upper cone and after passes through the guide plates, distributes in the interior of the chamber and exits from the lower cone. The k-ε turbulence and Discrete Phase Models could have modeled this problem. Design No. 7 was optimal design with the lowest coefficient of variation of the concentration (4.08%).
Conclusion: The numerical simulation method for planning and optimizing of the chambers, at a much lower cost than the empirical methods, was able to provide comprehensive information on the solution field. The analysis of this information led to the selection of the best chamber design to provide uniform concentration of the particles in the respiratory region of the animals.
