摘要：Two (portable and mobile) local exhaust ventilation (LEV) units were developed in collaboration with the Rural Technology Institute, Gandhinagar, India. Basically, each unit consists of three parts comprising an electric motor, a blower and a fume hood. In both units the motor is fixed in a rectangular iron frame in a foot-mount position and equipped compactly with a blower, which in turn is connected to a fume hood through a flexible hosepipe. The portable unit is light in weight (50 kg) and has a cone shaped metallic fume hood. The mobile unit, on the other hand, differs from the portable model with respect to its weight (150 kg), size, RPM, voltage requirement, hood shape and size, and has a motor enclosure. The efficiency of the portable and mobile units on trial bases was tested by measuring the manganese concentration as a reference metal in welding fumes generated by electric arc welding. The concentration of manganese (mean ± SD) was 0.218 ± 0.06 μg/m3 in the general environment. In the workplace area where joining of metal objects by welding was done, the concentration of manganese was found to be 0.63 ± 0.09 and 3.75 ± 0.56 μg/m3 at a distance of 5 m and 2 m away from the site of operation, respectively. In the breathing zone it was 22.16 ± 20.90 μg/m3 which was reduced to 8.25 ± 4.5 μg /m3 after application of a portable LEV showing about 63% removal of the manganese concentration from the breathing zone of the welder. In another experiment conducted with a mobile LEV unit for heavy-duty work, the concentration of manganese in the breathing zone without operating the mobile LEV was 70.06 ± 37.38 μg /m3 but was lowered to 8.29 ± 1.76 μg /m3 after operating the mobile LEV. This indicated an average removal of manganese content by about 88% from the breathing zone of the welder. In both the experiments locations of sample collection were similar.
