QUESTION 1
A worker is using a hand-held circular saw to cut extruded aluminium strips in the manufacture of storm windows. He is holding the workpiece firmly in his left hand and holding the saw in his right hand. Aluminium is an excellent conductor of electricity, and the workpiece is making solid electrical contact with ground. In an accident that happens frequently, the worker unintentionally saws the electrical cord in half.
(a) What are the feasible consequences in the following three sets of circumstances? :
Case A: The tool is grounded through the third prong of the electrical plug
Case B: The tool is double insulated
Case C: The tool has a three-prong plug that is connected through an adapter to a two-hole wall socket; the tool is ungrounded
Describe your answers with reference to the current path and assume a circuit breaker is installed in the power supply.
(b) The following protective devices are commonly used in electrical circuits.
Describe their principle of operation and state one advantage and one disadvantage for each.
(i) Fuses,
(ii) Circuit Breakers,
(iii) Residual Current Devices.
(c) Describe how to remove the contact between live conductor and a person undergoing electric shock.
(d) Describe five strategies for establishing an effective electrical safety programme.
QUESTION 2
A power press is protected by an infra-red beam type presence-sensing device. A stop-time measurement system is used to compute the time between breaking of the infrared beam and stoppage of the press ram. This stop time is found to be 0.294 second. The safety distance is the minimum separation distance that must exist between the plane of the infrared sensing and the point of operation of this power press.
(a) Calculate the safety distance in this case. (Assume hand-speed constant =
160 cms/second).
(b) Explain the term "point of operation". What is the point of operation of a power press?
(c) List three different types of safeguarding methods available for the point of operation of a power press. Briefly describe their mode of operation.
(d) What are a Lock out and Tag out systems? List four factors that are essential for effective lock out/tag out systems.
(e) Under what circumstances would you require the use of lock out/tag out systems for a power press? Elaborate on your answer.
QUESTION 3
An air compressor takes the air in a room and forces it into a container (an air receiver) under pressure. Compressed air is used to power a variety of tools and machinery. For example compressed air is used to power pneumatic wrenches and lifts in automobile service stations.
(a) In relation to an air receiver, what do you understand by the following
(i) Design Pressure,
(ii) Maximum Operating Pressure,
(iii) Safe Working Pressure.
(b) What is the relationship between design pressure, maximum operating pressure and safe working pressure?
(c) What is the maximum pressure at which a safety valve can be set to lift?
(d) List and describe the importance of at least four safety components of an air compressor with air receiver.
(e) A registered machinery inspector examines an air receiver as required under section 59 of OSHA 2005. During his examination he notices that the pressure gauge on the air receiver is damaged, however, the pressure relief valve is functional. He mentions same on his report and submits it to the employer. As a safety and health officer would you allow usage of the air receiver? Explain your answer.
QUESTION 4
(a) What are the three simple categories of conventional welding? Which of the three is the cleanest and most healthful? Explain your answer
(b) Why should acetylene cylinders be stored valve end up? Explain the safety measures required for the storage of oxygen and acetylene cylinders.
(c) In what ways are greasy gloves of particular hazard to the oxyacetylene welder?
(d) What is a hot work permit? Describe its importance when doing welding works?
List two components that must be present in a hot work permit for welding works.