| There is a large amount of respirable dust with aerodynamic equivalent diameter of less than 1μm in the welding fumes.Long-term exposure will have a serious impact on the respiratory system of operators,and may even cause welder pneumoconiosis.Study the deposition characteristics of welding fumes in the respiratory system is essential for quantitative studies of dose-response relationship and more accurate occupational health risk evaluation.In this paper,taking the steel structure workshop of an enterprise in Chongqing as the research object,the CFPD model is used to carry out the numerical simulation of welding smoke from the emission source to the receiving body,so as to analyze its diffusion and deposition characteristics,defines the actual exposure level of welding smoke under different ventilation conditions in the workplace,compares the deposition of welding smoke with different particle sizes in the respiratory system under different concentrations,analyze the influence of ventilation and dust removal system on the deposition dose in employees’respiratory system,and put forward targeted occupational hazard control measures.The research results obtained are as follows:1.On-site investigation results show that welding fume is the key factor to prevent occupational disease hazards in the underframe assembly workshop,and the detection results of the concentration of which at the height of employees’breathing zone are all qualified.Dust source concentration in the range of particle size below 0.1μm,0.1～0.5μm,0.5～1.0μm and above 1.0μm.According to the field survey data,a 3D model of the chassis group workshop with a grid number of 6,680,368 was constructed based on Solid Works,and a 3D model of the respiratory system(nose-G7 level)with a grid number of 34,875,529 was constructed based on Mimics.2.The diffusion of welding fume in the workshop under displacement ventilation is studied under four ventilation conditions of 10.50×10~4m~3/h,7.00×10~4m~3/h,5.00×10~4m~3/h,and2.47×10~4m~3/h.(1)When the ventilation volume is the same,the concentration of dust particles in the same particle size range increases with the increase of the horizontal height,reaches the maximum value at a certain horizontal height,and then decreases with the increase of the horizontal height.(2)When the ventilation volume is the same but the particle size range is different,the height of dust particles reaching the maximum concentration is different.The smaller the particle size,the higher the maximum concentration height.(3)When the ventilation volume is different,the height of the highest concentration of dust particles in the same particle size range is different.The greater the ventilation volume,the higher the height.(4)The larger the ventilation volume,the higher the horizontal position where the total dust reaches the maximum concentration is from the ground,and the maximum value is reached at 3～5m under the four working conditions.(5)Under various working condition,the total dust concentration at the breathing zone level is 1.189mg/m~3,1.910mg/m~3,2.360mg/m~3 and 4.020mg/m~3respectively.(6)The dust concentration of the four working conditions calculated by the formula of ventilation volume in China cannot reach the German MAK standard.3.Compare the deposition of welding fumes in the respiratory system for each particle size range at different concentrations:(1)Overall deposition:under any ventilation volume the larger the particle size of the welding fumes,the higher the deposition rate.There is a certain critical point of particle size from 0.1μm to1.0μm,beyond which the deposition of welding fume in the respiratory system will be accelerated.(2)Regional deposition:under any ventilation volume the deposition rate in the nasal cavity area is the largest,and the welding fume with small particle size was more likely to enter the lower respiratory tract.The deposition rate in the upper lobe of the lung is higher than that in the lower lobe,and the deposition rate in the lower lobe of the right was higher than that in the lower left lobe.(3)The influence of various working condition on the deposition dose:when the ventilation rate is 10.50×10~4m~3/h or 7.00×10~4m~3/h,the deposition dose of welding fumes in the respiratory system is very small,that is,the harm to employees is relatively slight.When the ventilation rate is 5.00×10~4m~3/h,the deposition rate of each particle size in the throat area and bronchus G1 grade(B1 area)changes greatly,indicating that the dust removal effect is poor under this working condition.When the ventilation volume is 2.47×10~4m~3/h,the deposition rate of each particle size of welding fume is the largest,indicating that the ventilation rate calculated according to the empirical formula of displacement ventilation cannot guarantee the health of the workers for a workshop with a large space and certain dust pollution.4.According to the numerical simulation results,the following protective measures against occupational disease hazards are proposed:(1)The horizontal level of the vent of the ventilation and dust removal system should be raised to be parallel to the dust source position of the working platform to prevent the loss of air volume.(2)When designing the ventilation volume of the workshop,it is suggested that the minimum value should be the ventilation volume calculated by the minimum dust generation of the welding equipment,that is,the ventilation volume should be selected as 7.00×10~4m~3/h and above.(3)It is recommended that employees of the workshop still need to take personal protective measures during welding operations.The research results show that the numerical simulation of the workshop and respiratory system based on the CFPD model can clarify the actual exposure level of productive dust and its deposition characteristics in the respiratory system under different ventilation conditions.The research results can accurately evaluate occupational health risks in the workplace,which can provide a reference for the revision of the standards for the occupational exposure limit of welding fumes in China.The research results can also provide a reference for optimizing the parameters of the ventilation and dust removal system in the workplace,so as to ensure the occupational health and safety of employees. |
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