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POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 1 ELECTRICAL SAFETY ELECTRIC SHOCK, TRAUMA & SAFE WORKING 1 OUTLINE OF UNIT.............................................................................................................................3 2 INTRODUCTION.................................................................................................................................3 3 ARCS.......................................................................................................................................................3 4 ELECTRICAL SHOCK AT POWER FREQUENCIES .......................................................................4 5 EDF 10 YEAR STUDY ...........................................................................................................................5 6 RESISTANCE OF THE HUMAN BODY ............................................................................................6 7 CONTACT SITE MARKS......................................................................................................................9 8 VENTRICULAR FIBRILLATION & HEART CURRENT FACTOR................................................9 9 INFLUENCE OF VOLTAGE ON SEVERITY OF SHOCK ............................................................. 11 10 DELAYED DAMAGE DUE TO CURRENT FLOW.......................................................................... 11 11 ELECTRIC FENCES .......................................................................................................................... 12 12 SAFE WORKING PRACTICES........................................................................................................... 13 13 SOME ACTUAL INCIDENTS............................................................................................................ 14 13.1 13.1.1 The Incident ............................................................................................................................................................. 14 13.1.2 Contributing Factors ................................................................................................................................................ 15 13.1.3 Recommendations ..................................................................................................................................................... 16 13.2 ELECTRIC SHOCK WORKING IN CEILING SPACE ................................................................................................. 16 13.2.1 The Incident ............................................................................................................................................................. 16 13.2.2 Analysis of Incident.................................................................................................................................................. 18 13.3 14 PERSON ELECTROCUTED AFTER TOUCHING A LIVE TERMINAL............................................ 14 DEATH BY ELECTRIC SHOCK AND FALLING ......................................................................................................... 19 13.3.1 The Incident ............................................................................................................................................................. 19 13.3.2 Analysis of Incident.................................................................................................................................................. 19 REFERENCE LIST.............................................................................................................................20 Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A Revision List A : original Prepared by Dr K A Walshe email : [email protected] PAGE 0 - 2 POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A 1 PAGE 0 - 3 Outline of Unit Detail Duration Comment Electrical safety – understand what causes electric shock; it’s magnitude and consequences 1 unit In an increasingly litigious industrial environment, it is essential that the engineer / manager is fully aware of how electric shock occurs and how it may be prevented. 2 Introduction Electric shock can range to the barely noticeable tingle to massive burning bone fracture and burning of tissue. In addition surface radiant burns are common as a result of a persons close proximity to an electric arc. It is therefore very necessary that persons exposed to potentially live conductors or likely to be in control of tradesmen who are exposed to potentially live conductors appreciate some of the factors that determine the severity of electric shock and basic precautions to mitigate the consequence of such shock. As an engineer / manager you are responsible for the safety of the people reporting to you and indirectly of anybody else whom may be working in an unsafe manner. 3 Arcs An electric arc is formed when ever an insulated gaps between two electrodes of differing potential breaks down. This can occur as a result of an excessive voltage being applied to a constant gap or as a result of moving current carrying contacts separating and arcing until the dielectric strength of the gap being created causes the arc to extinguish (this is normal AC circuit breaker action). The breakdown strength of air and Standard Temperature and Pressure is approximately 30 kV/cm and there is also a requirement of there being a minimum of 300 volts (absolute value not rms) across an airgap before breakdown can occur. It is very difficult for any airgap to breakdown on 110 ~ 120 V AC systems Once an arc has formed it only requires approximately 20V/cm to maintain itself. Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 4 Arcs can however be initiated at much lower voltages as a result of tracking across insulators. Electric arcs have core temperatures in the range 2,000 degC to 10,000 degC and thus result in severe (2nd 3rd and sometimes 4th order burns) to anybody within a radius of 2 ~ 3 metres away from the arc. Electricians working on live LV switchboards are the most at risk since they will often be close to busbars having a fault current duty of 30 ~ 60 kA. 4 Electrical Shock at Power Frequencies The generally accepted spectrum of power frequency electric shock is :Effect Noticed current for hand - foot shock no perception <1 mA tingle 1 < I < 3 mA mild sensation; no skin damage pain full shock 3 < I < 10 mA pain, some skin marking, onset of No-Let-Go Arm paralysis asphyxiation 10mA < I < 75 mA ventricular fibrillation probability level ventricular fibrillation 75mA < I < 2.5 Amps cardiac arrest I > 2.5 Amps tissue burning I > 4.0 Amps organ burning I > 20. Amps onset 0.5% A major step change in the current that flows occurs in the range 500 V to 700 V at power frequencies due to the outer layer of the skin breaking down by electric stress Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A 5 PAGE 0 - 5 EdF 10 Year study In a study by EdF 1 (Electric de France) (the single overall generation, transmission and retailing authority for electricity in France) over a ten year period a total of 123 electrical accidents sustained by it’s employees were recorded and analysed. EdF employees approximately 120,000 people. High voltage working in power authorities is normally carried out under strict preprogrammed procedures thus high voltage electric shock incidents ought to have a lower incident in this study than in the population as a whole. Type of incident % of incidents Comment Immediate death 2.4 in majority of cases electric current flowed through the body and ventricular fibrillation occurred Not immediately fatal, loss of consciousness apparent death 7.2 inhibition of major body functions; respiration, consciousness but usually not cardiovascular arrest; responds well to immediate intensive care Initial lesions; burns 93 arc burns are most frequently observed 77% of cases. Ocular burns are often associated with low voltage (< 1000V) incidents Electrothermal burns 15% of burns cases this is the type of burn associated with passage of electric current in the body; extensive electrothermal burns (deep tissue burning) seen in 10% of all electrothermal burns cases Mixed burns 6% of burns normally multi-site and associated with HV shock and often have severe, progressive effects with major sequelae. Delayed onset fatalities 1% mainly associated with extensive burns & kidney failure also several cases of death through onset of cardiovascular failure. Neurological & psychological sequelae 7.3% sequelae include headache, dizziness, physical or psychological lassitude, mood and personality disturbances Psychological neurovegatative sequelae 1% some cases of true neurotic disturbance recorded; electric shock need not have involved the head. 3.6% of non- ocular : 8% of arc injuries involved ocular injury Sensory Sequelae 1 or all Industrial Accidents and their complications, Cabanes, J; chapter 2 Electrical Trauma ed Lee, Cravalho & Burke, Cambridge University Press 1992 Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A Permanent disabilities PAGE 0 - 6 fatal accidents (chronic conjunctivitis) Four cases (out of 1231) each of corneal burns and retina burns. cataracts rarely occur Auditory sequelae observed in 1.3% of accidents lesion and vestibular damage. 21% see graph of distribution of degree of permanent disability Distribution of Permantent Disability by % impairment number of cases 1000 100 10 1 0 10 20 30 40 50 60 70 80 90 100 % impairment Figure 1 : % distribution of Permanent disabilities It is seen from this graph that 50% bodily impairment occurred with a frequency of 1% in a population sample where high voltage shock could reasonably be expected to have a far greater occurrence than in the general population. From this it necessarily follows that the percentage of electric shock incidents in the general population leading to a given level of impairment will be significantly lower than the above graph. 6 Resistance of the Human Body For electrical purposes the body can be thought of as a thin insulating shell surrounding a near uniform conducting mass with long rods of poorly conducting material (bone). Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 7 The conducting mass comprises the subcutaneous layers of the skin and all the internal parts of the body. Typical values of conductivity are :Conductivity Siemens/ metre skin 3.8 * 10^- fat 5 * 10^-4 muscle 4 * 10^-4 bone 1 * 10 ^-4 The epidermis layer can exhibit resistance values from a few thousand ohms with young moist and / or cracked skin to many tens of thousands of ohms in older dry skin. In contrast to this insulating shell the inner body tends to exhibit a composite resistance in the range from 500 Ohms to a few thousand ohms depending on the magnitude of the applied voltage and its frequency. At power frequencies (50 ~ 60 Hz) and with sinewave applied voltage, the variation of body resistance with applied voltage is as shown in Figure 2 below. Prepared Dr K A Walshe Figure 2 by : Total Body Impedance email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 8 It is known that the body resistance to DC is between 25% and 50 % higher than that at power frequencies. Furthermore there is a marked difference between sinewave excitation and impulse excitation. This has led to an equivalent circuit for the body where the skin is a parallel Resistance / Capacitance - fig 3. Figure 3 : Model of Body Impedance The impedance of individual sections of the body relative to the Hand to Foot path are distributed as :from to % of total wrist elbow 26.4 elbow arm pit 10.9 arm pit to top of shoulder 6.9 arm-pit arm-pit 6.9 arm-pit centre chest 9.9 centre chest navel 1.3 navel top of leg 5.1 top of leg top of adjacent leg 8.7 top of leg knee 14.1 Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A knee 7 PAGE 0 - 9 sole of foot 32.3 Contact Site Marks The medical literature makes free use of the terms “Entry” and “Exit” sites when talking of the electrode contact points. Some writers describe an exit site as exhibiting an explosive exit of current; almost as if the electrons have had to burst their way out from the body. In more recent times these terms have been recognised as being less than accurate; their use for power frequency wounds is not so prevalent as previously. A contact mark will be observed depending on the current density and duration of exposure. This is very similar to a thermal burn and hence the marks left by the passage of current are similar. current density observation < 10 mA/mm^2 no permanent change in skin; For current flow longer than several seconds skin below electrode may become grey-white with coarse texture 10 ~ 20 mA/mm^2 reddening of skin with a white colour along the edge of the electrode 20 ~ 50 mA/mm^2 brownish colour sinking into the skin below electrode; for exposure of several tens of seconds blisters are observed around the electrode > 50 mA/mm^2 carbonisation of the skin occurs NB for exposure times of less than one second, the above current densities have to nearly double to obtain the effect described for long exposure. 8 Ventricular Fibrillation & Heart Current Factor Ventricular fibrillation is uncoordinated pulsation of the heart which results in little if any blood flow in the body. It is considered the main cause of death from electric shock Some cases of death by asphyxia and cardiac arrest are reported but the frequency is much lower than VF. Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 10 VF occurs when the current in the range 50 mA for 1 sec to about 2.5 amps 0.04 seconds at which level cardiac arrest occurs. If the current does not flow uniformly down the trunk of the body, then the heart will experience a small exposure. A “Heart Current Factor” is thus defined to relate the severity of different electrode contact sites to a full “left hand to both feet”. IEC 479 defines a factor that permits the calculation of the current Ih through paths other than the left hand to (both) feet which presents the same risk of VF Ih = Iref /F where Iref = current left hand to both feet for a given risk of VF F = factor in Table below Current path Heart current Factor left hand to left or right or both feet 1.0 both hands to both feet 1.0 left hand to right hand 0.4 right hand to left foot, right foot or both feet 0.8 back to right hand 0.3 back to left hand 0.7 chest to right hand 1.3 chest to left hand 1.5 seat to left hand, right hand or both hands 0.7 If the electric current flows for 0.2 seconds or less VF will only occur if the passage of current coincides with the vulnerable “T” periods (ventricular recovery from excitation) of the cardiac cycle. A particularly brave Italian engineer researched this aspect of electric shock for many years and ultimately proved that VF could be avoided if power was removed in 30mseconds – he did this by experimentation on himself and was ultimately awarded one of Italy’s highest honours for his work. This is now the basis of the “earth leakage circuit breaker”. Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 11 9 Influence of voltage on severity of shock Electric shocks have been arbitrarily divided into low and high voltage with the boundary between the two set at 1000 V although care must be taken as some authors have located the boundary as low as 380 Vac when differentiating between the two “types” of shock. It has already been seen that the body resistance remains nearly constant above about 700 V. This happens because at 700 V the outer layer of the skin breaks down very quickly and thus the skin starts to have little effect on the overall body impedance. Medical research has also shown2 that high electric field strengths across cells can lead to cell membrane breakdown. Thus in high voltage shock incidents the mechanisms of both thermal damage leading to thrombosis (the Joule heating effect) and cell wall breakdown (voltage stress) contribute to muscle and organ damage. 10 Delayed damage due to current flow There has long been two schools of thought in the medical world regarding the sequela of electric shock. One school believed that the consequential damage to tissue developed over time requiring long hospitalisation and repeated surgical intervention to remove dead tissue whilst the other school held that all the damage was done at the time of the shock and that effects that appeared later where only a manifestation of the difficulty in identifying all nonviable tissue when the first surgical exploration is under taken. The second school of thought advocates large scale removal of nonviable and marginal tissue at the earliest opportunity followed by rapid wound closure to prevent infection and encourage regeneration of muscle tissue3. 2 Lee, R.C. ; Pathophysiology and clinical management of electrical injury, in book “Electrical Trauma” ed Lee, Cravalho & Burke, pub Cambridge Univ Press 1992 Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 12 It certainly appears true that within hours of the injury, the damaged muscles begin to swell as the permeability of the tissues begins to change. Once fluid pressure in excess of 30 mm Hg is observed in muscle compartments surgery is required to prevent compression injuries to tissue and nerves. Irrespective of the rights and wrongs of the two theories, it is clear that time is of the essence in treating electric shock; immediate testing for excessive current ( fluid pressure, discoloured urine etc) must be made to ensure tissue loss in minimised. 11 Electric Fences Electric fences are regulated in Australia by reference to AS 3000 ( the “Wiring Rules”) and AS 3014 ( Electrical installations – Electric Fences). Apart from matters relating to the insulation between the 240V power circuit and the HV fence circuit, the Standard places a limit on the energy per pulse and the pulse mark to space ratio. Based on the various Pulse into 500 Ohms factors already 1 discussed it is held 0.8 that a pulse of less 500 ohm load and lasting for no more than 0.1 seconds with votlage per unit of 10 kV. than 8 Joules into a 0.6 0.4 0.2 0 -0.2 -0.4 a -0.6 repetition rate of not more one per second -0.8 -1 time 0 to 0.075 sec. will cause discomfort but no damage to the vast majority of humans. 3 Gottlieb, Saunders & Krizek; Surgical technique for salvage of electrically damaged tissue, , in book “Electrical Trauma” ed Lee, Cravalho & Burke, pub Cambridge Univ Press 1992 . Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 13 This then allows voltages as high as 10 kV to be applied. The figure above shows the current in a 500 Ohms resistive load occasioned by a 24 volt battery powered electric fence energiser. The recording was made via a high speed 8 bit digital recorder and this produced some in the output waveform. 12 Safe Working Practices • Only qualified persons are permitted by law to carry out installation work defined in AS3000. • Know how to isolate all power to the work area before starting work. • Make sure “Others” know where you are going to be working • Ensure that there are no obstructions to access of work area that might make egress difficult in the event of a fire • Know were the fire fighting gear is before starting work. • Ensure that resuscitation and first-aid facilities are nearby. • Have an assistant trained for electrical accidents close by and able to turn power off quickly if required. • Live working (ie working on live equipment and wiring) is only to be undertaken in the last resort and full Personnel Protective equipment must be available to the electrician and must be used. This includes rubber mats, rubber gloves, rubber soled shoes (boots), goggles and hard hat. • Test before acting and prove the test equipment before relying on it. • Cotton shirt and trousers (both to be full length) must be worn to minimise the area of bare flesh that might be accidentally earthed or made alive. • Remove wrist watch. • Only use handtools with fully insulated handles and use the tool properly. Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A • PAGE 0 - 14 Regularly test the insulation on the handles with a megger; destroy any handtool with substandard insulation. • All power leads to be tested and tagged as required by law. • Safety lock and tag off all circuits before working on them. • Never remove a safety lock or tag other than your own. • Analysis the risks inherent in a job before undertaking it (on large job sites this will require a written risk analysis appraisal before work starts). • Do not let anybody onto a job site without first explaining to them what the risks and safety procedures are. Engineers can find themselves required to undertake testing or fault finding work where it is impossible to predetermine what is to be done. Accidents tend to happen due to the engineer taking short cuts such as 1. Propping an escutcheon plate in a precarious position and having it slide into live terminals, 2. Trying to get access to dead equipment via a compartment with live busbars in it. 3. Dropping spanners down gaps into live busbars 13 Some Actual Incidents 13.1 PERSON ELECTROCUTED AFTER TOUCHING A LIVE TERMINAL The following is an Incident Report prepared by the West Australian WorkSafe office. 13.1.1 The Incident A crewmember on a fishing trawler died after receiving an electric shock from a live brass terminal on an ammeter, which was located on the rear of a switchboard cover. The fingers of his right hand came in contact with the terminal and the electrical current passed from his right hand through his body to both feet. Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 15 His feet were in contact with the metal floor of the vessel. A polycarbonate switchboard housed all of the electrical circuit breakers and overload devices for the distribution of 240/415-volt power throughout the vessel. Because there were only two circuits for general-purpose electrical distribution and because of demand, the circuit breakers, or thermal overload, for the entire system would activate causing the power to shut down. 13.1.2 Contributing Factors Additional electrical appliances had been added to the two circuits for general purpose use, which when all were turned on simultaneously, drew more electrical current than each individual circuit was designed to carry. This therefore created an imbalance that caused the circuits to trip out. The larger appliances (air conditioner, hot water system) were not individually wired back to the switchboard to ensure that a regular imbalance did not occur when all items requiring electricity were switched on at the same time. The thermal overload reset button on the main contactor was located under the polycarbonate switchboard cover and was not accessible from the outside of the cover. The cover had to be removed to reset the button. The screws holding the polycarbonate cover in place had been removed and duct tape was used to hold the cover in place. At the time of the accident the duct tape did not have sufficient adhesive on it to hold the cover in place either temporarily or permanently. No lock out or tag out procedure was in place to ensure the switchboard was isolated from electrical current prior to attempting to reset any overload devices. This would include the shutting down of the gen-set or disconnecting the shore power supply. No-one onboard the vessel was qualified to work on 240/415-volt systems. Removal of the switchboard cover is considered electrical work under the Electricity Act 1945. Silver adhesive tape (duct tape) used to hold the switchboard cover in place. The screws had been removed to obviously allow for Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 16 simple access to (button in centre) the main contactor switch. The cover did not have access from the outside to the main contactor (overload) switch. 13.1.3 Recommendations • Owners and Skippers of vessels to ensure all electrical equipment on vessels is maintained in a condition such that no modification can expose crew to a risk of electrocution. • The control of hazardous energy is the most important step in safe maintenance of equipment. Suitable Lockout - Tagout procedures protect persons in the workplace from unplanned energy sources from moving machinery, chemical energy, thermal energy, pneumatic energy, stored and of course electrical energy. • Compliance with Australian Standard 3000 - 1991 SAA Wiring Rules. Equipment mounted on or behind a switchboard panel shall be of the self-contained type or be installed in a metal or approved enclosure and require the use of a tool or key to expose live parts. Any work to expose live parts must be undertaken by a technically competent and skilled person exercising appropriate safety procedures to avoid contact with live parts. • In accordance with the Regulations for the Electrical and Electronic Equipment of Ships under the Western Australian Marine Act 1982 and Regulations, lighting circuits should be supplied by final sub-circuits separate from those for heating and for power requirements. The Australian Standard 3000 - 1991 Wiring Rules also requires a similar standard to ensure unplanned imbalance of power does not occur. 13.2 Electric Shock working in ceiling space This is a summary of an electric shock case investigated by the author 13.2.1 The Incident An electrician was employed to add a new light switch to an existing installation in a small parade of shops with office suites over the top. Each shop had a light and a power circuit but these were controlled from a remote main-switchboard on the first floor of the office area. Access to the offices was by a doorway fronting the main Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 17 street and a flight of stairs. The front door was locked at weekends. The shops had wooden floors. In order to install the new light and switch, the electrician decided to loop an active conductor from an existing light switch, pull the active wire up the cavity wall using the existing cable as a draw wire and then take the new circuit through a ceiling space to the location of the light fitting. As it was summer time, the electrician was wearing shorts, thongs and a singlet. He elected to do the work on a Sunday when his wife, who ran a small clothing shop in the parade was sorting out her stock. There was no access to the office area and so he was unable to isolate the lighting circuit at the main switchboard. The circuit that he was going to connect into was a two way light circuit. He • removed the switch cover and disconnected the incoming active, • bared the end of a new earth wire and twisted it together with the bare end of the active, • climbed a metal ladder into the ceiling space, • lay across the beams and over a metal air-conditioning duct, Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 18 • started to pull the active wire with earth cable attached into the ceiling space, • received an electric shock as soon as he reached the bare twisted wire ends. It was some time before his wife heard his groans. She had to get her farther, who had training as a linesman with Telecom, to come and remove her husband (this was achieved by putting a rubber mat on the ladder and pulling his legs clear of the airconditioning duct). It was some 40 minutes after the initial shock before he was cleared. During that time he received repeated shocks every time he moved. The electrician lost several fingers, had recurring bouts of dizziness and head-aches. He was subsequently not able to resume his trade and had to take a less skilled job. In a subsequent court action the electrician claimed he had tested the active circuit he was using as a draw wire and had been misled by the instrument – it had indicted the circuit was dead when it was in fact alive. 13.2.2 Analysis of Incident The incident occurred because the electrician broke the following safety rules:1. Improper clothing – full sleeve length cotton shirt and full length trousers are to be worn when working on electrical equipment. 2. Working on potentially live equipment without an assistant – had a trained assistant been present he would have been pulled clear within a few minutes and suffered a lot less trauma. 3. Using an inappropriate test instrument 4. Failure to verify operation of the test instrument on a known live circuit before use 5. Failure to isolate the circuit before working on it. 6. Failure to insulate himself from earth when working on a potentially live circuit. Subsequent testing of the light switch and subject test instrument showed it worked perfectly some 6 months after the event and registered a strong electric field all around the subject switch. Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 19 The claims regarding the test instrument (it was not a Voltmeter but a battery powered neon light device that capacitively couples to an electric field) misleading the electrician where most likely a construct in order to claim damages from the manufacturer because my testing showed quite clearly that the subject instrument would register a strong electric field all round the existing light switch from which the electrician took the active. When he first removed the active and connected one end of a new earth wire to it (to form a draw wire) he would have touched the bare conductor with his hand(s). He received no shock at that time (and it would have been much better if he had – explain why) because he was wearing thongs and standing on a wooden floor both of which insulate the body from the return circuit via earth. However when trying to maneuver in the confined ceiling space he had his bare leg against the metal covering of flexible air-conditioning ductwork. This provided a moderate resistance path to earth. Had it been a sheet metal duct he would most likely have been electrocuted4 . 13.3 Death by electric shock and falling This is a summary of an electric shock case investigated by the author 13.3.1 The Incident A fourth year electrician apprentice was killed by falling off a metal ladder when he received an electric shock whilst cutting a cable. 13.3.2 Analysis of Incident The apprentice was supposed to be pulling a cable along an extensive cable tray about 2.5m above a concrete floor on a building site. He and his supervising electrician had been doing similar work earlier that day. The electrician was also acting as site foreman for a small team of electricians. He needed to attend to some paperwork and gave instructions to the apprentice to lay new cables onto an over head ladder tray. 4 electrocution – death by / as a result of electric shock Prepared by Dr K A Walshe email : [email protected] POWER ELECTRONICS 4TH YEAR ELECTIVE. ELECTRICAL SAFETY; REV A PAGE 0 - 20 It appears that the apprentice decided to do more than he had been instructed and proceeded to prepare a cable end to turn into a junction box. He cut a live cable on the same tray instead of the new cable that he had just pulled into position. He was using side cutters with insulated handles but subsequently other electricians gave evidence that the apprentice had a bad habit of keeping his index finger straight resulting in it touching the bare steel close to the cutting head. Because he was working from a ladder he would have been holding the frame of the ladder or the cable tray with one hand. When he cut the live cable he received a hand – to – hand shock and fell from the ladder. He died of the injuries received from the fall. This death was avoidable by:1. Supervisors insisting on and enforcing safe work practices, 2. Using fiberglass or wooden ladders, 3. The apprentice doing exactly as he had been told, and 4. Testing every circuit before working on it 14 Reference List AS3000 - 2000– “The Wiring Rules” this document has the force of Law in all States and Territories of Australia. It is now jointly published with the New Zealand Standards Association. Similar Standards exist in most other parts of the world. For the effect of lightning see the extensive bibliography “ALPHABETICAL BIBLIOGRAPHY ON MEDICAL EFFECTS OF LIGHTNING STRIKES” published on the internet by ;R. Holle National Severe Storms Laboratory, NOAA, 1313 Halley Circle, Norman, Oklahoma. WorkCover NSW – various pamphlets inc. “Stay Alive Work Dead” Prepared by Dr K A Walshe email : [email protected] WORKSAFE WESTERN AUSTRALIA COMMISSION ELECTRICITY: RESIDUAL CURRENT DEVICES Guidance Note Occupational Safety and Health Regulations 1996 Regulation 3.60 Protection against earth leakage current when portable equipment in use March 1998 SUMMARY 1. Regulation 3.60 applies to the use of portable electrical equipment used in all workplaces, other than construction sites. Electrical equipment used on construction sites is covered by regulation 3.61. 2. Regulation 3.60 requires the users of portable electrical equipment at workplaces to be protected against earth leakage current by means of a residual current device (RCD). 3. Persons having control of the workplace are required to install non-portable type RCDs. They have the choice of installing the RCD at the switchboard or in a fixed socket outlet. 4. It must be readily apparent to the users of portable electrical equipment if and where non-portable RCDs have been installed. 5. If it is not readily apparent or the user is uncertain whether an RCD has been installed, a portable RCD must be provided by the employer and must be used by the employee. 6. This guidance note is issued by the WorkSafe Western Australia Commission to provide information and advice on the duties of employers, employees, self-employed persons and persons having control of workplaces under the Occupational Safety and Health Act 1984 in relation to the use of portable electrical equipment and meeting the requirements of regulation 3.60 of the Occupational Safety and Health Regulations 1996. 1. INTRODUCTION Electricity is a common workplace hazard, and is a frequent cause of electric shocks. Some of these shocks have been fatal. Electricity does not have to be high voltage for an electrocution to occur. Electrocutions have resulted from contact with faulty electrical equipment that has become live, or contact with worn and damaged wiring and switches. While there are many different causes of electrocution, all have one thing in common – they could be prevented. In 1992 Worksafe Australia found that of 95 workplace deaths due to electricity recorded in a work-related fatalities study, 36 deaths – or more than half of those not caused by aerial powerlines – would probably have been prevented by the use of RCDs. The Worksafe Australia study recommended, among other strategies, the use of RCDs in homes and workplaces. This approach was endorsed by the WorkSafe Western Australia Commission. Specific requirements for RCDs to protect users or operators of portable electrical equipment were included in the Occupational Safety and Health Regulations 1996. This guidance note was developed within the tripartite WorkSafe Western Australia Commission, with input from representatives of employer organisations, trade unions and Government. It is published by the WorkSafe Western Australia Commission to provide detailed information to assist employers, self-employed persons, persons having control of workplaces and employees, in meeting their duties under the Occupational Safety and Health Act 1984 and the requirements of regulation 3.60 Protection against earth leakage current when portable equipment in use. 2. LEGISLATION REQUIRING RCDs The Occupational Safety and Health Regulations include specific requirements to protect users or operators of portable electrical equipment. Regulation 3.60 Protection against earth leakage current when portable equipment in use is designed to minimise the risk of a person receiving a harmful or fatal electric shock when using portable electrical equipment. Regulation 3.60 does not apply to construction or demolition sites. Regulation 3.61 Electrical installations on construction sites requires electrical installations on construction sites to comply with Australian and New Zealand Standard AS/NZS 3012 Electrical installations – Construction and demolition sites. AS/NZS 3012 covers the provision of RCDs on construction and demolition sites. GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 PAGE: 1 Protection against earth leakage current when portable equipment in use Regulation 3.60 states (1) This regulation applies to a workplace other than one to which AS/NZS 3012 applies but does not apply to a workplace at which the supply of electricity — (a) does not exceed 32 volts alternating current; (b) is direct current; (c) is provided through an isolating transformer complying with AS/NZS 3108; or (d) is provided from the unearthed outlet of a portable generator. (2) In this regulation — “hand-held equipment” means portable equipment — (a) of a kind that is intended to be held in the hand during normal use; and (b) the motor, if any, of which forms an integral part of the equipment; “portable equipment” means equipment that is — (a) connected to an electricity supply; and (b) intended to be moved when it is in use, and includes, but is not limited to, hand-held equipment; “workplace” means a workplace to which this regulation applies. (3) A person having control of a workplace — (a) must ensure that each non-portable residual current device installed at the workplace is kept in a safe working condition and tested on a regular basis to ensure its continued effective operation; (b) must provide, where electricity is supplied to portable equipment through a fixed socket at the workplace after 31 March 1998, protection against earth leakage current by means of — (i) a non-portable residual current device installed at the switchboard; or (ii) by a non-portable residual current device built into a fixed socket which, having regard to the primary use of the socket and its location, is likely to be used by a person operating portable equipment; and (c) must ensure where a non-portable residual current device has been — (i) installed at a switchboard, that a notice is displayed in a prominent place at or near the switchboard indicating that a non-portable residual current device has been installed at the switchboard; or (ii) built into a fixed socket, that the socket can be identified as providing protection against earth leakage current. Penalty: $25 000. (4) A person who is an employer or a self-employed person at a workplace — (a) must ensure that each portable residual current device used at the workplace by the person or an employee of the person is kept in a safe working condition and tested on a regular basis to ensure its continued effective operation; and (b) where the employer or a self-employed person is not satisfied that protection against earth leakage current has been provided by means of a non-portable residual current device — (i) must provide a portable residual current device for use with each item of portable equipment used by the person or an employee of the person at the workplace after 31 March 1998; and (ii) must ensure that a portable residual current device is directly connected to the output side of a fixed socket when an item of portable equipment is being used by the person or an employee of the person at the workplace after 31 March 1998. Penalty: $25 000. PAGE: 2 GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 (5) An employee who is provided with a portable residual current device for use with an item of portable equipment at a workplace must not use the portable equipment unless the portable residual current device is directly connected to the output side of a fixed socket. Penalty: $5 000. 3. DUTIES OF A PERSON HAVING CONTROL OF A WORKPLACE Section 22 of the Occupational Safety and Health Act requires a person who has, to any extent, control of a workplace to ensure, so far as is practicable, that people who are at the workplace are not exposed to hazards. In many cases employers will have control over their premises thus having duties under sections 19, 21 and 22 of the Act. Persons having control of a workplace include owners, lessors, etc. of premises, who may have no involvement with the work activity at the premises, but who have retained some control over the premises. For more information on the general duties of persons at the workplace see the WorkSafe Western Australia Commission Guidance Note General Duty of Care in Western Australian Workplaces. Regulation 3.60 requires a person having control of a workplace to provide protection for the users or operators of portable electrical equipment against earth leakage current by means of a non-portable RCD. The owner or the person managing a building on behalf of the owner, has the choice of installing non-portable RCDs at the switchboard to protect all or selected circuits only, or at fixed socket outlets. If the installation is at the switchboard, all the wiring and appliances plugged into the circuit will be protected. The size of the building, its use or any plans to refurbish, refit or rewire the building will influence whether to install RCDs at the switchboard for complete or selected circuit protection or at fixed socket outlets. If an owner or manager chooses to have inbuilt RCDs in fixed sockets, not every fixed socket has to be RCD protected. In deciding which fixed sockets are to have inbuilt RCD protection, the likely use of the fixed socket has to be taken into consideration. For example, conveniently located fixed sockets are the most likely to be used by cleaners or maintenance personnel and should be protected with nonportable RCDs. Cleaners and maintenance personnel may use up to 30 metres of extension cord or flexible supply cord between an RCD protected fixed socket and portable equipment. This distance of 30 metres may be used to assist in determining the number and location of RCD protected fixed socket outlets to provide coverage for cleaners. RCD protection at the switchboard must be identified by a notice displayed near the switchboard. Where this protection is for selected circuits only, the socket outlets so protected must each be identified by a notice displayed at the socket outlet. Where RCD protection has been built into a fixed socket, the fixed socket must be identified as providing RCD protection. GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 PAGE: 3 4. DUTIES OF AN EMPLOYER Section 19 of the Occupational Safety and Health Act requires an employer to provide, so far as is practicable, a workplace where employees are not exposed to hazards and to provide a safe system of work. In the case of using portable electrical equipment the employer should establish whether the fixed socket outlets to be used by his or her employees are protected by RCDs and whether they are identified as being protected. The employer must inform the employees if and where protection is provided. If the employer is not satisfied that non-portable RCDs have been installed, the employer should provide a portable RCD and consult with the employee on when and where the portable RCD is to be used. If there is any doubt regarding the installation of RCDs at the workplace, portable RCDs must be provided and used. The use of a portable RCD in a circuit already protected by a non-portable (or portable) RCD has no detrimental effect on the operation of either RCD. 5. DUTIES OF EMPLOYEES Under section 20 of the Occupational Safety and Health Act, employees have a duty to take reasonable care of their own safety and avoid harming the safety or health of other people. Before connecting portable electrical equipment to an electrical power source, an employee should seek the advice of the employer as to whether the outlets are protected by non-portable RCDs. Where neither the employer nor an employee is satisfied that non-portable RCDs have been installed, the employer must provide a portable RCD. The employer and the employee should consult on when and where the portable RCD is to be used. 6. WHAT IS A RESIDUAL CURRENT DEVICE [RCD] RCDs are often known by other names, eg., earth leakage circuit breakers (ELCB) or safety switches. An RCD is an electrical safety device specially designed to immediately switch the electricity off when electricity “leaking” to earth is detected at a level harmful to a person using electrical equipment. An RCD offers a high level of personal protection from electric shock. Fuses or overcurrent circuit breakers do not offer the same level of personal protection against faults involving current flow to earth. Circuit breakers and fuses provide equipment and installation protection and operate only in response to an electrical overload or short circuit. Short circuit current flow to earth via an installation’s earthing system causes the circuit breaker to trip, or fuse to blow, disconnecting the electricity from the faulty circuit. PAGE: 4 GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 However, if the electrical resistance in the earth fault current path is too high to allow a circuit breaker to trip (or fuse to blow), electricity can continue to flow to earth for an extended time. RCDs (with or without an overcurrent device) detect a very much lower level of electricity flowing to earth and immediately switch the electricity off. RCDs have another important advantage - they reduce the risk of fire by detecting electrical leakage to earth in electrical wiring and accessories. This is particularly significant in older installations. Residual Current Device (RCD) Fuses Circuit Breakers RCDs work on the principle “What goes in must come out”. They operate by continuously comparing the current flow in both the Active (supply) and Neutral (return) conductors of an electrical circuit. If the current flow becomes sufficiently unbalanced, some of the current in the Active conductor is not returning through the Neutral conductor and is leaking to earth. RCDs are designed to operate within 10 to 50 milliseconds and to disconnect the electricity supply when they sense harmful leakage, typically 30 milliamps. The sensitivity and speed of disconnection are such that any earth leakage will be detected and automatically switched off before it can cause injury or damage. Analyses of electrical accidents show the greatest risk of electric shock results from contact between live parts and earth. Contact with live parts may occur by touching: * * * bare conductors; internal parts of an appliance; or external parts of an appliance that have become “live” because of an internal fault. Contact with earth occurs through normal body contact with the ground or earthed metal parts. An RCD will significantly reduce the risk of electric shock, however, an RCD will not protect against all instances of electric shock. If a person comes into contact with both the Active and Neutral conductors while handling faulty plugs or appliances causing electric current to flow through the person’s body, this contact will not be detected by the RCD unless there is also a current flow to earth. GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 PAGE: 5 On a circuit protected by an RCD, if a fault causes electricity to flow from the Active conductor to earth through a person’s body, the RCD will automatically disconnect the electricity supply, avoiding the risk of a potentially fatal shock. Fault current path/s to earth 7. TYPES OF RCDs There are three types of RCDs – switchboard mounted, powerpoint (GPO) type and plug in (portable). Switchboard mounted and powerpoint types are referred to as non-portable RCDs. Portable RCDs are plugged into a fixed socket. A non-portable RCD installed at the switchboard is the best option in most situations as it protects all the wiring and appliances plugged into the circuit, however, the regulation provides the option of providing non-portable RCDs built into fixed sockets. Switchboard Units These are non-portable units installed at the switchboard to provide protection of the complete installation, or protection of a selected circuit. Switchboard RCD units. These may be installed at the main switchboard to provide complete installation protection or selected circuit protection PAGE: 6 RCD installed at the switchboard GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 Fixed Socket Units These are non-portable units consisting of RCD protection inbuilt into a fixed socket outlet to provide protection to equipment plugged into the outlet. RCDs incorporated in fixed sockets provide single outlet or single circuit protection. This type of unit may be installed at selected locations instead of providing protection at the switchboard RCD incorporated in fixed socket Portable Units These are to be used where doubt exists that non-portable RCD protection has been provided. Various models are available from simple plug adaptors to units designed for specific equipment such as the portable unit shown below or wired, by a licensed electrical worker, to an extension cord. Portable RCD unit suitable for use with extension cords and portable power tools Portable RCD plug adaptor Plug adaptor wired to an extension cord Portable RCD plugged into external power point GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 PAGE: 7 8. SUPPLY OF ELECTRICITY WHERE REGULATION 3.60 DOES NOT APPLY Regulation 3.60 states that the requirements of the regulation do not apply in the following situations: q Workplaces where AS/NZS 3012 applies AS/NZS 3012 Electrical installations – Construction and demolition sites, specifies requirements for electrical installations which supply electricity to appliances and equipment on construction and demolition sites, and for the in-service testing of portable, transportable and fixed electrical equipment used on construction and demolition sites. Regulation 3.61 Electrical installation on construction sites mandates AS/NZS 3012. The requirements for RCD protection on construction sites has been carried forward from the repealed Occupational Health, Safety and Welfare Regulations 1988. q Where the supply of electricity does not exceed 32 volts alternating current (AC) or is direct current (DC) The severity of an electric shock depends upon the following factors: - the magnitude and path of the current through the body; - the duration of the shock; and - the type of voltage supply, AC or DC. Alternating currents are much more likely to cause serious shocks than direct currents of similar voltages. Alternating currents of even low value exercise a paralysing effect upon the muscles causing the victims grip to tighten, making self release difficult or impossible. Most people will not be adversely affected at 32 volts AC. Alternating current of such low voltage is usually sourced independent of supply mains, or from the supply mains through an isolating transformer. Electrocution from DC current is far less likely than with AC current because with DC current it is easier to remove the grip on live parts and because DC current has a lesser effect on the cardiac system. Direct current, however, should always be treated with care. q Where supply of electricity is provided through an isolating transformer complying with AS/NZS 3108 or from the unearthed outlet of a portable generator An isolating transformer is a transformer designed to supply extra low voltage and low voltage circuits, the input windings being double insulated (or equivalent insulation) from the output windings. Advice from a person competent in electrical installations should be sought regarding the need, or otherwise, for RCD protection of portable equipment supplied from portable generators or through transformers. PAGE: 8 GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 9. INSTALLING AND PROVIDING RCDs The person having control of the workplace, eg., the owner of the property, or the person managing the property on behalf of the owner has a responsibility to provide non-portable RCD protection at the switchboard to protect all or selected circuits only, or in a reasonable number of fixed socket outlets in each section or area of the workplace where portable electrical equipment is in regular use. These outlets must be clearly identified. If it is not readily apparent that non-portable RCDs have been installed at a fixed socket or at the switchboard, the employer of persons using portable electrical equipment must ensure the portable electrical equipment used by their employees is protected by a portable RCD unit which is directly connected to the output side of a fixed socket. The various types of portable RCDs are shown at Section 7. Directly connected means there is no extension cord connecting the portable RCD to the output side of the socket or in the case of a portable RCD with a flexible supply cord, no extension cord is used to connect the RCD to the socket. As the flexible supply cord is not RCD protected, its length should be as short as possible and must not be increased beyond that supplied or specified by the manufacturer. No additional extension cord is to be used to connect the RCD to the socket as this would increase the length of unprotected cord. Non-portable RCDs must be installed by a licensed electrician or licensed electrical in-house worker. Only a correctly installed RCD will provide the required level of personal protection. It is a requirement of the Electricity Act 1945 and Regulations that the installation must comply with AS 3000 Electrical installations – Buildings, structures and premises (known as the SAA Wiring Rules). Portable electrical equipment that is known to be damaged or faulty must not be used until repaired by a licensed electrical worker. 10. EQUIPMENT REQUIRING RCD PROTECTION IN ACCORDANCE WITH REGULATION 3.60 “Portable equipment” is defined as equipment that is — (a) (b) connected to an electricity supply; and intended to be moved when it is in use, and includes, but is not limited to, hand-held equipment. “Hand-held equipment” is defined as portable equipment — (a) (b) of a kind that is intended to be held in the hand during normal use; and the motor, if any, of which forms an integral part of the equipment. GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 PAGE: 9 Portable electrical equipment that requires protection includes, but is not limited to, the following items which are intended to be moved whilst in use: * * * * * hand-held power tools such as drills, saws, planers, grinders and chainsaws; power equipment such as jack-hammers and lawn mowers; cleaning equipment such as vacuum cleaners and industrial polishers; hand-held appliances such as hair dryers and curling wands; and cord extension leads connected to any of the above items (ie., portable RCDs must also protect the cord extension lead). The above items of portable equipment may be single phase or three phase. RCD protection to some types of portable equipment will depend on the situation in which the equipment is used. For example, in the entertainment industry, if any part of a sound system such as a microphone, is intended to be held in the hand or moved when in use, that part of the system should be protected by an RCD if it is powered by alternating current exceeding 32 volts. Similarly, portable or stage lighting exceeding 32 volts which is hand held or intended to be moved when in use should be RCD protected. RCD protection is not required if power is supplied through an isolating transformer complying with AS/NZS 3108. Appliances which are “double insulated” (clearly marked with the words “Double Insulated”, or with the double square symbol o ) provide additional protection against electrocution because of their construction. They protect the user from receiving an electric shock from the casing of the equipment. However, the flexible supply cord attached to the appliance or a cord extension lead used is a potential source of electrocution and requires RCD protection. 11. EQUIPMENT TO WHICH REGULATION 3.60 DOES NOT APPLY Electrical equipment that presents a very low risk includes, but is not limited to: * * * * * * desk top computers, computer printers and monitors; photocopiers; refrigerators; television sets and VCRs; equipment connected by fixed wiring; and large stationary equipment connected by a flexible cord which is not flexed during normal use, for example, a window-mounted air conditioner. RCDs are not suitable for providing protection from electric shock from the handpiece of welding equipment. It is not feasible to provide RCD protection to the welding handpiece since current leaking to earth in the circuit between the electrode conductor and the return conductor will continually trip out an RCD. PAGE: 10 GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 However, the primary winding of the power source of the welding plant will require RCD protection if the welding plant is portable equipment intended to be moved while in use. Portable RCD protection must be provided to any portable or hand held electrical equipment which is supplied with electricity from a power outlet on welding equipment, unless the power outlet has inbuilt RCD protection. AS 1674 Safety in welding and allied processes Part 2: Electrical provides information on preventing electric shock in welding operations through sensible preventative measures involving inspection and maintenance of equipment, safe operating procedures and safety precautions. Medical equipment, where a “trip out” could be detrimental to a patient, should not be RCD protected. All portable electrical equipment should be regularly checked and tested in the workplace by a competent person. 12. RISK ASSESSMENT OF OTHER EQUIPMENT Electrical equipment that is not moved or carried while being operated presents a very low risk of electric shock and while it is not required to be protected by RCDs under the provisions of regulation 3.60, the equipment should be assessed in accordance with regulation 3.1. Identification of hazards, and assessing and addressing risks, at workplaces Regulation 3.1 states A person who, at a workplace, is an employer, the main contractor, a self-employed person, a person having control of the workplace or a person having control of access to the workplace must, as far as practicable — (a) identify each hazard to which a person at the workplace is likely to be exposed; (b) assess the risk of injury or harm to a person resulting from each hazard, if any, identified under paragraph (a); and (c) consider the means by which the risk may be reduced. Penalty:$25 000. Where an assessment under regulation 3.1 indicates a person using electrical equipment is at risk of receiving an electric shock, the use of an RCD should be considered, and if appropriate, used as a means of reducing the risk. It is highly probable the assessment will indicate electrical appliances and equipment likely to be used in a wet or hazardous environment may need to be protected. In some situations these could include washing machines, kettles, frypans, jugs and ice making machines. The presence of moisture will increase the risk associated with the use of electrical equipment. GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 PAGE: 11 13. INSPECTION AND TESTING Guidelines for inspection and testing of portable RCDs are provided in AS 3760 In-service safety inspection and testing of electrical equipment. AS 3760 sets out, in table 1, the intervals between push button testing (by user) and inspection testing for operation by an electrician for various types of environments in which portable RCDs are used. The information in AS 3760, table 1, is set out below. Type of environment in which equipment is used Interval between inspection and tests for portable RCDs Test for operation Push-button test (by (by licensed electrical user) worker) Factories, workshops and places of work of manufacturing, repair, assembly, maintenance or fabrication Daily, or before every use, whichever is the longer Other commercial environments with no special protection, eg., laboratories, tea rooms, office kitchens, and health care establishments 3 months, or before 2 years every use, whichever is the longer 12 months Office environment where 3 months equipment is not subject to constant flexing of the supply cord 2 years Hire equipment Before each hire Before each hire Testing of non-portable RCDs at switchboards or inbuilt into socket outlets must be carried out on a regular basis. This includes both push button testing by the user and inspection testing for operation by a licensed electrical worker. Unless operated from time to time, an RCD may “mechanically freeze” and not trip when required. Push-button testing by the user only confirms satisfactory mechanical performance of the tripping mechanism of the RCD. It does not replace inspection testing for operation by a licensed electrical worker. PAGE: 12 GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 As non-portable RCDs are far less susceptible to damage than portable RCDs, they are not subjected to the same testing and inspection procedures. In the case of non-portable RCDs, push button testing is recommended at three monthly intervals. After tripping out, an RCD must be re-activated in accordance with a "re-establishment of supply" procedure which requires the cause of the trip to be established and remedial action taken before re-establishing the supply. These procedures should be drawn up by the employer after consultation with employees and safety and health representatives, if any. GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 PAGE: 13 OTHER PUBLICATIONS The following publications can be purchased from WorkSafe Western Australia, Westcentre, 1260 Hay Street, West Perth [Tel. (08) 9327 8777]: q Occupational Safety and Health Act 1984; q Occupational Safety and Health Regulations 1996; q Codes of Practice published by the WorkSafe Western Australia Commission: * * * * * * * Excavation; First Aid, Workplace Amenities and Personal Protective Equipment; Legionnaires Disease; Manual Handling; Management of HIV/AIDS, Hepatitis B & C at Workplaces; Prevention of Falls at Workplaces; and Styrene. q Guidance Notes published by the WorkSafe Western Australia Commission: * The General Duty of Care in Western Australian Workplaces; and * Election of Safety and Health Representatives, Representatives and Committees and Resolution of Issues. These documents are also available via the Internet Service on Safetyline [http://www.safetyline.wa.gov.au]. The following publications are under development or are expected to commence development during 1997/98 and when available will be listed in “What’s New” on the Internet Service: q Codes of Practice: * * * * * * * * Abrasive Blasting; Control of Noise in the Music Entertainment Industry (Review); Demolition; Isocyanates; Legionnaires Disease (Review) Spraypainting; Steelwork; Young Workers; q Guidance Notes: * * * * * PAGE: 14 Competent Persons; Powered mobile plant; Communication with isolated employees; Registration of plant design; Registration of individual items of plant. GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES 30 MARCH 1998 S E L E C T I O N O F U S N AV Y E L E C T R I C A L AC C I D E N T R E P O RTS The following pages are accident report sheets from the US Navy Naval Facilities Engineering Command Abstract of an Accident FY95-5 MISHAP TYPE: INJURY: DAMAGE: TYPE OF WORK: EQUIPMENT: Explosion (Electrical) None Est. 50K - 100K Drilling (Environmental Site) Drilling Rig DESCRIPTION OF MISHAP An electrical explosion occurred on a BRAC Closure Site during the course of the Phase II Environmental Baseline Survey field effort being conducted by a drilling subcontractor. The subcontractor had obtained site plans showing utility locations, and conducted a site walk-through before selecting soil boring locations. Six days later the drilling rig was set up to begin taking soil samples. Drilling proceeded with caution, as the subcontractor was aware of underground utilities in the area. A hand auger was advanced to 3.5 ft at which point hand auguring was not possible due to the coarse gravel. At this point the 4.25 inch ID hollow stem auger was advanced to a depth of approximately 5 ft. The drillers were about to add another flight of augers. As the auger was slowing to a stop the workers heard a “hissing sound” coming from the hole. Within seconds flames erupted and the workers fled the area. Smoke was subsequently observed coming from two adjacent buildings and from a manhole near the site. The drilling rig was engulfed in flames. DIRECT CAUSE Subcontractor drilled through an electrical high voltage cable supplying power to a building from transformer station. INDIRECT CAUSE - Inadequate identification of underground utility lines. - Use of the 4.25 inch ID hollow stem auger. LESSONS LEARNED Contractors must ensure they identify all existing utilities prior to beginning work. They must not only acquire utility maps but also use the maps and site plans and carefully survey the area to identify problem areas before selecting drilling sites. If there are underground utilities in the immediate area then hand auguring or excavation must be accomplished to avoid mishaps. YOUR SAFETY CONTACT IS.... Naval Facilities Engineering Command Abstract of an Accident FY95-7 MISHAP TYPE: INJURY: TYPE OF WORK: EQUIPMENT: Electrocution Fatality Splicing High Voltage Overhead Line Bucket Truck DESCRIPTION OF MISHAP A High Voltage Electrician was electrocuted by 4160 Volts when he contacted an energized overhead power line with his bare hands. The fatality occurred when a two-man crew, consisting of the electrician and a helper (also an electrician), attempted to permanently repair a temporarily spliced overhead power line. The electrician and his assistant had cut the power to the line from a nearby transformer; however, the lines were being fed from a different location. Thinking the power to the line was off; they began repairing the line. Working from an elevated bucket, the electrician initially worked while wearing his insulated gloves, but later removed them to rejoin the line into a crimp sleeve for the final phase of the repair. With his bare hands, he grasped the two ends of the energized 4160 volt line and was immediately electrocuted. The assistant, working in the bucket next to him, lowered the bucket and summoned emergency personnel, but the electrician died within minutes. DIRECT CAUSE Failure to follow standard Lockout/Tagout/Tryout/Groundout procedures INDIRECT CAUSES No SOP for operation, inadequate supervision, inadequate LO/TO program oversight, inadequate employee development/certification. LESSONS LEARNED Jobs involving lethal voltages should not be considered routine. No SOPs based on JHAs were completed on this job because it was considered a routine, low-risk job. Larger jobs received full written guidance. Supervision must treat all jobs involving electricity with the respect it warrants not just large jobs. The supervisor rarely visited jobs in progress or small-scale jobs like this one, but routinely visited larger jobs. Evaluation and enforcement of LO/TO program requirements is critical to implementing this program throughout an activity. The evaluation of the activity’s program did not involve reviewing employee’s performance applying the program in the field. Supervisors did not routinely enforce the requirements. Employees did not receive specialized training critical to their trade sufficient to work in a safe manner. Generally, employees are hired in at a skill level, there is no system to improve/certify employee skills. YOUR SAFETY CONTACT IS.... Naval Facilities Engineering Command Abstract of an Accident 96-3 ACCIDENT TYPE: INJURY: TYPE OF WORK: EQUIPMENT: Electrocution Fatality Electrical Substation 34.5 KV Overhead Switch DESCRIPTION OF THE ACCIDENT: A contractor worker was installing a high voltage cable support bracket onto the main switch support column of an electrical substation. His supervisor held the bracket in place while the worker stood on a fiberglass ladder next to an energized 34.5KV buss and bolted the bracket in place. During this operation, the worker reached out with his right hand and touched an insulator of the 34.5KV buss and was shocked. High voltage electricity entered his right hand, traveled through his body and exited from multiple locations causing burns to his face, hands, waist, upper back, and internal organs. He collapsed and fell from the ladder, later dying from his injuries. DIRECT CAUSE: Work was performed adjacent to a 34.5KV electrical circuit without the required safe clearance, without securing the electrical circuit and not using high voltage electrical PPE. The injured worker was a laborer and not qualified to work on or near high voltage electricity. CONTRIBUTING CAUSES: • • • Activity Hazard Analysis was not being applied by the contractor's site superintendent Weekly on-site safety training was not conducted Site specific safety training was not conducted prior to this phase of work LESSONS LEARNED: • • • • Always request an electrical outage when work is required to be accomplished on or near high voltage circuits. Contractor safety plan implementation to be site specific is critically important. Phase hazardous analysis could have prevented this mishap by not allowing work to be performed by unqualified workers and properly identifying the hazards associated with this work area. Worker safety awareness is essential in preventing accidents by using only qualified workers and preventing unsafe conditions. Naval Facilities Engineering Command Naval Facilities Engineering Command Abstract of an Accident 97-3 ACCIDENT TYPE: INJURY: TYPE OF WORK: EQUIPMENT: Near - Electrocution Potential Fatality Excavation (Digging Foundation with Jack Hammer) 12 KV Concrete Ductbank DESCRIPTION OF THE ACCIDENT: A Navy civilian worker was chipping concrete with a jack hammer from what he mistakenly thought was a building foundation, but was actually a high voltage ductbank, when the tip penetrated the concrete and contacted a 12,000 Volt (12KV) conductor inside. Although the resulting significant electrical short and arc-blast did not injure the employee, the jack hammer was damaged and power to a large area of the facility was lost for approximately 12 hours. DIRECT CAUSE: Underground utility locator marks, identifying the ductbank before excavating, were removed during the first stages of the excavation work. No site drawings identifying the underground utilities were available for reference after locator marks were removed. CONTRIBUTING CAUSES: • • Although locating and marking of underground utilities is universally required, there is no requirement that site sketches of the identified utilities be made and maintained for reference during excavation. No site specific safety training was conducted prior to digging to acquaint employees with local utilities and to prepare them for the hazards of digging into live utilities. LESSONS LEARNED: • • • • Establish requirement for site sketches which identify location of underground utilities. Ensure sketches are retained for reference during excavation work. Ensure underground utilities, including concrete structures, are not dug/drilled/broken until tested safe to do so. Ensure employees are trained on safe digging practices and dangers of digging without identifying underground utilities. YOUR SAFETY CONTACT IS.... Naval Facilities Engineering Command Abstract of an Accident 98-10 ACCIDENT TYPE: INJURY: TYPE OF WORK: EQUIPMENT: Near Miss Electrocution N/A High Voltage Electrical Hand Operated Cable Cutter DESCRIPTION OF THE ACCIDENT: A certified high voltage cable splicer mistakenly cut an energized high voltage cable in preparation of cable splice work causing an arc which fortunately did not result in property damage or personnel injury. An electrical system outage procedure was followed which included an advanced outage coordination meeting with station utilities to review the work, outage procedures, and contractor hazardous energy control methods. When the cable splicer entered the underground manhole to perform the work he found that the cables were not identified. He then contacted the station utility electrician to assist in assuring the proper cable was deenergized. After performing visual tracing of the cable to be worked on from a nearby manhole, and using two separate electrical test instruments, both showing that the circuit was not energized, the cable splicer cut the cable. The cable was hot. The cable arced for 30 minutes until arrival of the utility electrician who isolated the hot circuit. DIRECT CAUSE: • The cable splicer failed to adequately identify that the circuit was still hot. CONTRIBUTING CAUSES: • There are limits to the ability of electrical test equipment to adequately identify the presence of electrical energy. This is largely based on the amount of cable insulation (%) for the cable type. The tests were performed without identifying the energy because the instrument could not test through 133% cable insulation. • The cable was not cut using a remote non-conductive hydraulic cutter as required in the new 01525-guide specification. The contract was written prior to the existence of the new guide specification. • The outage should have been cancelled when it was found that the cables were not identified. Although the utility electrician came to the site and looked into the manhole he did not perform cable identification for the contractor. LESSONS LEARNED: • Certified high voltage cable splicers must review manufactures instructions of electrical energy detection equipment to correctly understand equipment limitations. A Process Action Team (PAT) has been organized and tasked with providing recommendations for test equipment types and procedures. The PAT team is a cooperation of station utility, safety, and construction professionals. Recommendations will follow. • Cable identification procedures are being formulated by the PAT, which will be incorporated into 01525-guide specification. These procedures will include requiring contractor investigation of cable identification prior to acceptance of any outage request. Additionally, unlabeled cables are to be identified by station utility personnel prior to the requested outage. • Cutting of high voltage cable is to be performed remotely. This requirement has been incorporated into the 1997 01525-guide specification. The guide specification requirement should be incorporated into existing contracts and included in the next version of USACE EM 385-1-1. YOUR SAFETY CONTACT IS.... Naval Facilities Engineering Command Abstract of an Accident 98-8 ACCIDENT TYPE: INJURY: TYPE OF WORK: EQUIPMENT: Electrical Shock Permanent Partial Disability High Voltage Electrical Electrical Distribution Panel DESCRIPTION OF MISHAP Employee was shocked by 7,200 Volts AC when electrical power unexpectedly routed through a transformer he was working on. Employee was part of a crew working on a transformer located in a substation. The transformer had been de-energized, isolated, and grounded on all legs except one that consisted of a fused cutout, which was opened, and the fuses left exposed. After making the transformer “safe”, fellow workers began trouble-shooting auxiliary circuits to turn on power for heaters and lights within the transformer while other workers did unrelated work. When a circuit on the panel labeled “auxiliary power” was turned on, the distribution system back-fed electricity to the transformers’ exposed fuses. The employee, standing directly in front of the fuses, was shocked immediately after actuation of the 120 Volts AC auxiliary circuit. Activating the auxiliary circuit directed power through an uncharted section of the distribution system to the transformer, which amplified it to 7200 Volts AC and energized the fuses where the employee was standing unprotected. The electricity entered the employees’ back and exited through his right hand. DIRECT CAUSE • Failure to follow requirements of lockout/tagout/tryout procedures (1910.147 or .269) – Authorized person did not ensure all personnel were clear of equipment that might be affected before introducing a change in the (lockout/tagout/tryout) process. INDIRECT CAUSES • • System owners did not ensure all circuits were indicated on distribution system drawings/one-line diagrams when the system was built or modified. No procedures for ensuring all circuits are identified and verified before treating as safe. LESSONS LEARNED • • • Supervisors and employees must fully understand and implement Energy Control Program requirements, including lockout/tagout/tryout procedures. Personnel must be protected during all operational phases, including trouble-shooting and experimental evolutions. System drawings, including one-line diagrams, must accurately identify all circuits to reflect system operation and function. YOUR SAFETY CONTACT IS.... Naval Facilities Engineering Command Abstract of an Accident 98-9 ACCIDENT TYPE: INJURY: TYPE OF WORK: EQUIPMENT: Electrical Shock Permanent Disability Construct REBAR Cages for Concrete Forms Hardhat, Steel Toe Boots DESCRIPTION OF ACCIDENT An employee was shocked by 38,000 Volts AC when a REBAR tie wire he was holding contacted an overhead high-voltage powerline. Two employees were tasked with constructing REBAR cages for concrete forms. This required making tie wires for tying and securing REBAR cages in the forms from continuous lengths of wire on coils. The process of making the tie wires involved pulling out two strands of tie wire from a coil, straightening and then manually twisting the two strands together, then cutting the lengths into nine-inch sections. The injured employee was standing on the ground below, and approximately fourteen feet forward of a 38,000 Volt AC overhead powerline located thirty-six feet above. The employees were stretching approximately sixty feet of double strand tie wire when it snapped, recoiled upwards, and contacted the powerline. Electricity traveled down the tie wire, in through the injured man’s hand, and out his leg. DIRECT CAUSE • Lack of situational awareness and deviating from established procedures. CONTRIBUTING CAUSES • • The Project Safety Plan did not include electrical shock hazard for tying REBAR. Job Hazard Risk Analysis for tying REBAR was accomplished for impalement but not for electrical shock hazard. LESSONS LEARNED • • • Standard Operating Procedure (SOP) for tie wire and similar operations should include a check for electrical hazards. Each process change should be evaluated - Significant hazards may exist from process changes although no historical data indicates it (a change in the tie wire preparation process resulted in serious electrical shock from whipping hazard). Ensure Operational Risk Management (ORM) is used for any process. Applying ORM will: identify all potential hazards, assess the hazards to determine severity and probability, develop and implement risk control options, monitor for change in the process. YOUR SAFETY CONTACT IS.…. Naval Facilities Engineering Command Abstract of an Accident 99-03 ACCIDENT TYPE: INJURY: TYPE OF WORK: Electrical Mishap Shock Relocating Outdoor Condenser Unit DESCRIPTION OF ACCIDENT: While relocating an outdoor condenser unit for a 2-ton split A/C a contractor electrician received an electric shock when he attempted to cut a live electrical wire. The injured electrician suffered cardiac and respiratory arrest as a result of the shock. CPR was performed by co-workers, Navy personnel from nearby spaces and by the base medical department. He was revived and transported to a local hospital where he spent a week recovering before returning to work. DIRECT CAUSE: ♦ ♦ Lock-out tag-out procedures were not followed properly. The circuit breaker and double pole switch for the A/C unit is located inside a secure space not readily accessible for contractor access. The contractor requested that a Navy security escort go inside the secure space and switch off the double pole isolator switch for the A/C unit. No attempt was made to secure the breaker (lock-out) or tag either the double-pole switch or the breaker to prevent accidental energizing of the circuit (tag-out). The injured electrician was standing on an aluminum stepladder and working in close proximity to a steel ISO shipping container, both good conductors that may have increased the severity of the shock he received. No insulating material such as rubber matting was used. INDIRECT CAUSE: ♦ ♦ ♦ Inadequate contractor hazardous energy control plan. Failure to consider restricted access to energy control devices. Failure to “lock-out” the system and “tag-out” LESSONS LEARNED: ♦ ♦ ♦ ♦ Contractor’s hazardous energy control procedures must be submitted and accepted by the ROICC prior to start of work. Current lock-out tag-out procedures need to be strictly followed by contractors. ROICC offices should ensure that lock-out tag-out is emphasized in contractor safety meetings and enforced at the site. Contractors need to strictly observe the requirement to coordinate power outages with appropriate base personnel and the ROICC. YOUR SAFETY CONTACT IS....