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1、IGC2ELEMENT 5最好的沉淀,ELECTRICAL SAFETY,LEARNING OUTCOMES,Hazards and risks associated with use of electricity at site Controls to combat the electrical risks,Electrical Terms (1),Volts (Pressure difference): The unit of measurement of electrical pressure Ampere (Current): The unit of measurement of fl
2、ow Ohms (Resistance): The unit of measurement of resistance,PRINCIPLES OF ELECTRICITY,Electrical Terms (2),Direct Current (DC): The current flows in one direction between positive and negative terminals Alternating Current (AC): The electric current is constantly reversing its direction of flow at a
3、 given frequency Frequency: Measured in cycles per second is expressed in Hertz,PRINCIPLES OF ELECTRICITY,Electrical Terms (3),Conductors: A material that allows electricity to flow easily :- e.g. copper, steel, water Insulators: Materials that have a high resistance to electrical current:- e.g. pla
4、stic, rubber, wood,PRINCIPLES OF ELECTRICITY,Nature of Electricity,Ohms Law The higher the electrical pressure (V) or the lower the circuit resistance (R), the higher is the current (Ampere) that flows (I), in an electrical circuit: V = I x R Iis measured in amps, which is the electron flow or curre
5、nt Vis measured in volts (V), potential difference or pressure Rthe resistance is measured in ohms (),PRINCIPLES OF ELECTRICITY,Electrical Circuit,Volts (V) Pressure,Amps (I) Current Flow,Ohms (R) Resistance,V = I x R,I = V / R,R = V / I,PRINCIPLES OF ELECTRICITY,OHMS LAW,Electrical Power,Another us
6、eful expression enables the electrical power (P), represented by the flow of electrical current in a circuit, to be determined. Power(P)/Watts = Voltage (V) x Current (I) When: Vis measured in volts (V) I is measured in amperes (A) P is given in watts (W),PRINCIPLES OF ELECTRICITY,Electric Power Exa
7、mple,If current taken by an electric heater is 5 amperes when plugged into a 240 volt supply, then its power load will be 240 x 5 = 1200 watts,W = V x I,PRINCIPLES OF ELECTRICITY,Main Dangers of Electricity,Electric Shock: When any part of the body comes into contact with electricity and at the same
8、 time is earthed (i.e. the body completes the electrical circuit)! Direct Contact: Coming in to contact with a conductor that is supposed to be live Indirect Contact: Coming into contact with a conductor that is not live in normal conditions but has become live due to a fault,PRINCIPLES OF ELECTRICI
9、TY,Severity of Electric Shock,Current in amperes (above 25mA can be lethal) Length of contact time Path through the body Conductivity/resistance of the body The voltage Conductivity of the environment Nature/extent of the contact Age and health status of victim,PRINCIPLES OF ELECTRICITY,If a Person
10、has received an electric shock,Do not touch injured person until the current is switched off. If the current cannot be switched off, stand on some dry insulating material and use a wooden or plastic implement to remove the injured person from the electrical source. Administer first aid if qualified
11、Call professional help,PRINCIPLES OF ELECTRICITY,Causes of Electrical Fire,Inadequate circuits for the current Overloaded circuits Incorrect fuses (e.g. nails) Damaged wiring and insulation Loose connections Overheating of cables Overheating due to thermal insulation Overheating due to lack of venti
12、lation Flammable materials too close to electrical equipment,PRINCIPLES OF ELECTRICITY,Main Dangers of Electricity,Arcing: Electricity can jump an air gap causing shock effects to persons not in contact with conductor Fire: Flow of electricity generates heat. If large flow passes through unsuitable
13、conductor heat can lead to fire Burns: Heat of arcing or excessive flow through body causes tissue damage,PRINCIPLES OF ELECTRICITY,Main Dangers of Electricity,PRINCIPLES OF ELECTRICITY,Secondary hazards Fall from height Falling / dropped objects Impact when thrown Third party injuries,Effects of El
14、ectricity on Human Body,PRINCIPLES OF ELECTRICITY,Note: some smaller microwave ovens use 10.0 Amps (10,000 milliamps) and common florescent lights use 1 Amp (1,000 milliamps),Effects of Electricity on Body,Damage to the nervous system Irregular heartbeat Tissue burns at entry and exit Damage to inte
15、rnal organs Muscular contractions Physical trauma Stopping breathing (respiratory paralysis) Stopping the heart (cardiac arrest),PRINCIPLES OF ELECTRICITY,Video Electrical safety,Electricity Protection Devices,Fuses (over current protection) Circuit breaker Earthing Isolation Reduced voltage Battery
16、 operated tools RCD Double insulation,CONTROL MEASURES,Fuse,A specially designed weak link which is designed to melt at a predetermined value of current,CONTROL MEASURES,Circuit Breakers,Electromagnetic devices which perform the same function as fuses but operate faster,CONTROL MEASURES,Earthing,Ear
17、th lead and spike,Electricity will always try to reach earth and earthing means providing a low resistance path to earth,CONTROL MEASURES,Isolation,Shutting off the electricity supply to an item of equipment and preventing system being mistakenly reconnected,CONTROL MEASURES,Reduced Voltage Systems,
18、Reducing the mains voltage by means of a transformer to a lower safer voltage e.g. 110 volts or 55 volts,CONTROL MEASURES,Residual Current Devices (RCD),Compares the electricity flow to the equipment with the return flow and if a difference is detected the equipment is isolated,CONTROL MEASURES,Doub
19、le Insulation,Two separate layers of insulation are provided which allows for fault detection where one layer has failed the other still provides protection,CONTROL MEASURES,Battery Operated Tools,CONTROL MEASURES,Precautions for Working Live,Permit to work Trained and Competent Staff Accompanied by
20、 another person Adequate Information about the risks Suitable insulated tools Insulated barriers or screens Suitable instruments and test probes Personal protective equipment/rubber mats Restricted access,SAFE SYSTEM OF WORK,Areas to look at for hazards,PORTABLE ELECTRICAL EQUIPMENT,Precautions,Redu
21、ced voltage operation Use of residual current circuit breakers Protected against overload Cables insulated and protected against mechanical damage Correct sheathing (protective covering) Sufficient socket outlets to minimize trailing cables Use of cable drums Correct maintenance and repair Regular i
22、nspections and checks Properly trained staff,PORTABLE ELECTRICAL EQUIPMENT,User checks Formal visual inspection Combined inspection and test (Portable Appliance Testing),TYPES OF INSPECTION,Manufacturers recommendations Age of equipment Robustness of equipment Double insulated or earthed Type of cab
23、le (e.g. armoured) Extent of use Users of equipment Environment Abuse or misuse History of equipment (results of previous inspections),FREQUENCY OF INSPECTION AND TEST,Reason to keep records of inspection and testing of electrical equipment,Inspection by authorised person (enforcement authority) To
24、prove that test frequencies are maintained Record actions if faults rectified,RECORD KEEPING,Emergency Procedures,Do not touch the electrocuted person Call for help Turn off power supply Call for an ambulance If power cannot be disconnected, push or pull the person from the live source using a non-conducting material Check breathing If breathing, place in recovery position If not breathing start CPR Treat for obvious burns Treat for physiological shock Make sure the person gets professional medical treatment,EMERGENCY,