Element 6: Hazards & Risks Associated with Electricity in the Workplace Flashcards
What is voltage of a circuit?
• Measure of difference in electrical potential between the two terminals of a circuit.
What determines the current in a circuit?
• The current in a circuit is determined by the voltage.
What is short circuit?
• A short circuit is formed where another conductor touches the circuit & provides electricity with alternative path to terminal with a larger potential difference than neutral terminal, usually the earth.
What does earthing do?
• Earthing provides safe path for faulty current to be dissipated to earth through a designated conductor.
What is main effect of electric shock on body?
A convulsive response by nervous system to the passage of electricity through that part of body, causing muscles to contract, often violently.
What are effects of electric shock on body in relation to current (mA)
• 0.5-2mA Threshold of sensation
• 2-10mA Tingling sensation, muscle tremor, painful sensations.
• 10-60mA Muscle contractions, inability to let go, inability to breath.
• 60 + Ventricular fibrillation, cardiac arrest, extreme muscle contractions, burns at contact points and deep tissues.
What is arcing & what risks does it pose?
Arcing is electrical bridging, through air, of one conductor with a very high potential to another nearby, earthed conductor. If the arc is connected to a person, victim may be subject to both flame burn from the arc & electric shock from current which passes through body. There is also danger of burns from ultraviolet radiation & radiated heat, even where arc does not actually touch person. Arcing can provide source of ignition for fire.
Identify risks associated with electricity.
• Electric shock (electrocution)
• Electrical burns (direct & indirect)
• Ventricular fibrillation (VF)
• Asphyxiation
• Cardiac arrest
• Secondary Injuries resulting from falling from access platforms or ladders
What five factors should be used to assess suitability of construction of electrical system?
1) Manufacturers recommendations
2) Likely load & fault conditions
3) probable use of system
4) Need for suitable electrical protection devices eg. Overload protection
5) Environmental conditions which may affect the mechanical strength & protection required.
What is difference between fuse & circuit breaker?
• A fuse forms weak link by melting if current exceeds safe limit.
• A circuit breaker is a mechanical device in form of switch which automatically opens if overloaded.
What is difference between switching off & isolation?
• Switching off deprives equipment of power but still connected.
• isolation- physically separating from any source of electric power, additionally ensuring it cannot inadvertently be reenergised.
What protection is offered by reduced voltage transformer in circuit?
Reduced voltage circuits reduce effect of any shock received from contact with part of circuit as voltage is lower.
What safety device should be used on hand held electrical devices outside?
Residual Current Device (RCD) should be used on all portable electrical appliances used outdoors.
What user checks should be carried out before an item of electrical equipment is used?
• Body of plug is secure
• Outer sheath of flex covers inner cores from body of plug to body of appliance
• Plug cable clamp appears tight
• Flex appears fully insulated- no cracks, splits, severe kinks / pinches.
• Body of appliance is intact
• Appliance cable clamp appears tight.
• Plug & body of appliance have no obvious scorch marks.
What is first step in treating victim for electric shock.
Break any continuing contact between victim & current.
What 3 types of work can be carried out at or near overhead power lines?
• Working in vicinity of overhead power lines.
• Plant / equipment will pass under lines.
• Work carried out beneath lines.
What precautions required for working in vicinity of overhead power lines?
• Ground level barriers are used to prevent close approach. (Min distance 6m unless changed/altered by owner; it will depend on voltage)
• Barriers conspicuously marked. (Red/white stripes; plastic flags or hazard bunting)
• Barriers may be stout poles, fences, tension wire fences earthed at both ends, oil drums filled with rubble/concrete, an earth bank (less than 1m) , solid timber baulks or concrete blocks.
• Lines of plastic flags or hazard bunting (3-6m above ground level) care being taken when erecting to avoid contact or approach near live conductors.
• Where mobile plant/equipment used length of overhanging part plant or jib taken into account.
• Barriers will be required on either one or two sides depending on worksite.
• No storage permitted between or under overhead lines or barriers.
What precautions required when plant/equipment will pass under lines?
• A minimum number of defined, fenced, level & well maintained passageways of restricted width should be used.
• Goal posts made of timber or plastic pipe:
- erected at each end of passageway (parallel to power lines)
- conspicuously marked eg. Red/white stripes.
• Warning notices in place on approaches to crossings to:
- show height of crossbar.
- Instruct drivers to lower jobs & keep below this height.
• Electricity proximity warning devices may be fitted on crane jibs but other safety precautions need to be in place.
• Work after dark requires any notices/ crossbars to be adequately & suitably illuminated. Lighting should be at ground level directing light upwards towards conductors.
What precautions should be in place when work carried out beneath lines?
• Extra barriers, goal posts & warning notices/signs may be required to prevent upward movement of scaffold poles, crane jibs, excavators & buckets.
• If risk of contact when carrying scaffold tubes, ladders or other conducting objects, then they should be excluded, or shorter tubes, ladders or metal sheeting should be used.
• Mobile plant & equipment should be modified by physical restraints to limit their operations. Eg. Mechanical stops, limit switches.
• A roof could be constructed over work area to prevent contact with live lines.
•The use of proximity warning devices & insulating guards without other safety precautions is unacceptable.
Care taken not to reduce distances/height clearances during any type of construction work eg. Dumping, tipping waste, landscaping, scaffolding etc.
• For work where there is buried services (elec/gas/water) extra precautions required.
