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Tham khảo tài liệu 'health safety and environment_2', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 302 7 Health Safety and Environment Fig. 7.5 Critical exposure times for different preparation tools solid line according to BGV B3 Larm points from different sources the material to be subjected and the preparation tool. The evaluation parameters of the vibration are its amplitude and velocity frequency . No measurements are available from dry blast cleaning operations. However there are some measurements available from concrete facades treated with other surface preparation tools. Amplitudes and vibration velocities generated by the tools are plotted in Fig. 7.6. The two mechanical methods generated rather high values for vibration velocities whereas the application of water jets led to low vibration velocities. 7.4 Emission of Dust A mist of paint debris and broken abrasive particles is generated during dry blast cleaning in the immediate environment of the operator. An example is shown in Fig. 7.7. A simple model for the evaluation of dust during the blast cleaning of mould casings was introduced by Engelberg 1967 . Unfortunately the dust is difficult to control. The only way to prevent it is the use of shrouded tools. Another way to protect the operator is the application of mechanically guided tools or robotic machinery. Anyway both methods fail as it comes to the cleaning of complex structures. A reduction in dust exposure is possible by adding water to the air particle flow wet blast cleaning and slurry blast 7.4 Emission of Dust 303 preparation method Fig. 7.6 Measurements of body sound emitted from different surface treatment tools Werner and Kauw 1991 neff - effective vibration velocity s - vibration amplitude. Preparation methods 1 - water jetting 2 - hammer and chisel 3 - jack hammering 4 - pneumatic hammer 5 - angle grinder Fig. 7.7 Dust formation during dry blast cleaning Photograph Muehlhan AG Hamburg 304 7 Health Safety and Environment Fig. 7.8 Additional working time in a shipyard due to dust formation Navy cargo ship in a drydock cleaning . .
