ASU334 Lecture-03 Machine Safety and Electricity PDF

5. Machine Safety No. Key Learning Points 1 A contractor should mark the platform or cage of a material hoist with the safe working load. Carriage of persons by a material hoist is prohibited. The operation of a material hoist is forbidden when any...

5. Machine Safety No. Key Learning Points 1 A contractor should mark the platform or cage of a material hoist with the safe working load. Carriage of persons by a material hoist is prohibited. The operation of a material hoist is forbidden when any hoistway gate is not closed. A competent examiner is responsible for carrying out the testing and thorough examination for a material hoist. 2 A gondola should be operated by a worker who holds a valid gondola operation certificate. A gondola should be checked by a competent person every week and issued with an approved form stating that it is in safe condition. 3 Factors contributing to accidents of lifting appliances (such as jib crane or tower crane):  Overload causing the crane to overturn or the jib to break.  Insufficient training of the crane operator.  Workers working within the lifting operation area.  Misunderstanding between the crane operator and the signaler. 4 A lifting appliance (such as jib crane or tower crane) should undergo a thorough examination by a registered professional engineer once every 12 months. A competent person should be responsible for the weekly inspection of a lifting appliance. 5 A crane operator shall attain 18 years old and hold a valid relevant certificate. Also, an excavator operator shall attain 18 years old and hold a valid relevant certificate. 6 If a crane is equipped with outriggers, they should be fully extended and supported on rigid timber blocks. When operating a telescopic jib crane near an overhead cable, one should use “goal posts” to restrict the working zone of the jib. 12 No. Key Learning Points 7 Every piece of lifting gear (e.g. wire sling) shall be marked with its safe working load. 8 Lifting gear (e.g. a sling) should undergo a test and thorough examination by a registered professional engineer. 9 Accidents in operating machinery are commonly caused by failure of the machine guarding. 10 Safety precautions for repairing the revolving parts of a machine:  Prevent personnel not responsible for the repairing work from coming near.  Shut off (isolate) the power supply before starting the repairing work.  Post notices regarding the repairing at the switches of the machine and also lock up the switches.  Keep the machine guarding in place for testing and cleaning the machine.  Install back the removed protective guards before re-starting the machine. 11 Safety precautions for using an abrasive wheel:  The safety guard shall be provided and kept in position while the abrasive wheel is in motion.  Affix a notice which specifies the highest permissible speed and the safety rules of using the abrasive wheel.  Replacement of the abrasive wheel can be conducted only by a person authorized by the proprietor in writing.  Select an appropriate abrasive wheel for use. 13 6. Electricity Safety No. Key Learning Points 1 Electrocution is mainly due to serious injury of the heart. 2 Before using an electrical appliance, one should check if the tool is functioning properly. An portable electrical tool should be earthed unless it is of double-insulated construction. Earthing of an electrical tool can reduce the risk of electric shock. The marking of “回” on a portable electrical tool means it is of double-insulated construction. Double-insulation of electrical tools can avoid current leakage. 3 An electrical appliance should be repaired after the power supply has been completely isolated. A failed electrical appliance should be repaired by a competent electrician. Improper repairing of an electrical appliance may cause explosion, burnt or electric shock. 4 Practices/situations leading to electrical accidents:  Repair electrical tools by an unqualified person.  Unauthorized modification of electrical tools.  Allow live parts of electric wires to expose.  Directly connect wires to power supply without using an electric plug.  Conduct arc welding in a humid environment. 5 Practices/situations to avoid electrical accidents:  Repair electrical tools by a competent electrician.  Regularly inspect electrical tools.  Adopt “permit-to-work” for repairing electrical appliances.  Use an appropriate plug to connect power supply.  Stand on an insulated mat. 14 No. Key Learning Points  Adopt water-proof facilities for outdoor electric wires connection.  Use water-proof electrical appliances in a humid environment. 15