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High voltage probes: beware the dangers High voltage probes can be lethal if used incorrectly or for servicing equipment other than that for which they were designed. This coronial report of a recent accident in Victoria highlights the dangers. RECORD OF INVESTIGATION INTO DEATH I, Susan Adele Blashki, Coroner, having investigated the death of ...... . with inquest held at the Coronial Services Centre, South Melbourne on the 12th June, 1992, find that the identity of the deceased was ....... and thatthe death occurred on 25th July, 1991 at the premises of HY-DU-EX, 15 Ormond Avenue, Sunshine from the effects of electrocution in the following circumstances. (1). The deceased, on 25thJuly 1991, was repairing a radio frequency welder at the premises of HY-DU-EX, 15 Ormond Avenue, Sunshine. He was a contractor, employed as an "A" Grade Electrical Mechanic by K. T.V.. Electronics, a small electrical -contracting company. He was the holder of an "A" Grade electrical mechanic's licence and had 28 years experience in this capacity. (2). The welder is designed for the purpose of welding PVC. It is between 15 and 20 years old. On the previous day the deceased had replaced the high voltage transformer and on the day of the accident he had tested two rectifier valves and found them faulty. He had then replaced the valves and was in the process of fine tuning the radio frequency welder. At the time of the accident it is probable that the deceased was testing the high voltage transforrner, us64 SILICON CHIP ing a "Leader High Voltage Probe", LHM - 80 Serial No. 5050061. This probe was found under his body after the accident. The deceased had completely overhauled and rebuilt this radio frequency welder some 3 years prior to this accident. The machine had then operated effectively for a number of years before K.T.V. Electronics was again called and Mr ..... .. attended to service the machine. Editorial Comment This coronial report has been published in full for the information of our readers . While the exact circumstances may not be certain, several cautions can be drawn from the report. (1 ). Use the utmost care when measuring high voltages in big power supplies, such as in microwave ovens or RF welders. They are far more dangerous than the EHT supply in a TV set. (2). Wear rubber soled shoes and rubber gloves while making high voltage measurements. (3). If at all possible; do not work alone. Footnote: the name of the deceased has been omitted to prevent further distress to relatives. He was sufficiently familiar with this particular machine to produce a set of technical, electrical drawings on it. (3). It is probable that the accident was caused either by the earth lead of the probe dislodging and coming into contact with high voltage, or the deceased may have been attempting to put the earth clip on the earth centre tap of the 6000 volt secondary connections and inadvertently put the clip on one of the positive terminals. It appears that the electrical current may have passed up the earth/ return lead and exited through the potentiometer adjustment screw access hole to the hand of the deceased, thereby delivering a high voltage shock to him. This shock would have thrown him back when he then struck his head on the cutting ·board of an adjoining click press and fell to the floor. No other person was present at the time this incident occurred, but both the proprietor and another employee . at the building at the time heard a loud bang and discovered the deceased with scorch marks on his right fingers and marks on the back of his head. (4). The deceased, whilst working at these premises the previous day, had complained of being faint and requested a chair. He had also complained to members of his family that he was very cold on the eve·n ing of the · 24th July, 1991 and to the factory manager at HY-DU-EX on 25th July, 1991 that his legs were very cold just prior to th!:) accident. About 6-8 months previously the deceased had collapsed whilst at work and been absent for approximately three months, but was at the time of the accident considered by his doctor to be fit for normal duties. (5). The general area of HY-DU-EX measures 31 metres long by 9.5 metres wide. It was constructed by a steel frame with corrugated iron walls and roof sheets. The area where the deceased was located had a concrete floor, and there was a section of what appeared to be rubber conveyor belting covering the concrete in the form of a floor mat. The temperature on the 25th July, 1991 at approximately 2pm was between 7°C and 10°C, with even lower temperatures being recorded earlier that morning. (6). At the time the deceased was working on this machine there were a number of tools scattered around including screwdrivers, pliers and electrical type tools, but the only one considered to be dangerous was the high voltage probe which was found to have recent burn marks on the handle. It is probable that the electric shock originated· from this piece of equipment as the burn mark on the handle matched the burn marks on the hand of the deceased. The Leader high voltage meter probe, model LHM 80 would have been used to check voltage within the machine when it was operating. It was manufactured by Leader Electronics Corporation, Japan, in approximately May, 1975. It is designed not for checking voltage on an RF welder, but for checking DC voltage of television sets. This model did not have any insulating cover fitted over the potentiometer adjustment screw, although since August 1985 this model has been modified to include an insulating cover. Production of the modified unit was discontinued in April, 1991. (7). It is probable that a person holding the lead of a high voltage probe while kneeling or sitting on the concrete floor and the flexible lead or alligator clip coming into contact with a high voltage within the machine could receive an electric shock sufficient to cause death. (8). I find that based on a reasonable belief, for reasons unexplained, the deceased has incorrectly used the EHT probe thereby receiving an electric shock of sufficient intensity to cause death. (9). I further find that whilst the external temperatures were cold, and that the factory may also have been cold, that there is no evidence to suggest that this was a factor contributing to the cause of death, and that no other person has contributed to the cause of death. Care required with high voltage probes I am writing to ask for your assistance in alerting your readers to the potential danger associated with high voltage probes as used in testing television receivers, transmitters and other equipment requiring high voltage measurements. The result of a recent coronial inquest in this State has highlighted the dangers associated with the use of such test equipment. The victim in this incident was a qualified "A Grade" licensed electrical mechanic who was testing a radio frequency welding machine. He had extensive experience in testing and repairing this type of equipment. This incident has highlighted the need to ensure that: tools and equipment are kept in good working condition; equipment is used within the manufacturers' guidelines; the earth connection is intact and operative; COMMENTS AND RECOMMENDATIONS The Leader High Voltage Probe LHM 80 is designed and manufactured by Leader Electronics Corporation, Japan and is marketed in Australia by AWA Distribution. It i.s designed for measuring high voltage (+25,000 volts) in colour TV receivers by qualified TV technicians and is safe to do so. Whilst the probe can be used for other purposes, such as measuring other high voltage sources, qualified and experienced technicians using this equipment should be aware of the possible dangers involving the measurement of dangerous high voltages · as these high voltages can result in the death of the operator if used incorrectly. The dangers to the operator could be measuring a negative supply exceeding 1,000 volts whereby electrocution could occur through the trimpot hole, or where the "earth" clip falls off, where a minor electric shock could occur but which could result in a secondary injury occurring as a result of the operator withdrawing their hand. This EHT probe and other similar types are widely used throughout the TV serving industry for the checking of EHT in TV receivers for being ei- extra care is taken when working in the vicinity of live electrical equipment. There has been an increase in the occurrence of electrical fatalities and serious electrical accidents involving electrical workers including engineers, technicians and mechanics in the past year. We must all take greater care when working with any electrical equipment. I request your assistance in warning your readers, many of whom are involved with the testing, repair, manufacture and design of electrical equipment, that caution should always be exercised when working on live equipment. R.N. Clark, Chief Electrical Inspector, State Electricity Commission, Victoria. ther under or over voltage. They are quite safe to use, and the Leader probe falls into this category when used correctly. It is recommended that all industries which use an EHT probe to measure high voltage be. advised of the dangers of using an EHT probe. In particular, attention is drawn to a new service industry developing in microwave ovens. The high voltage in a microwave oven is several thousand volts, and. is negative. Its existence can be measured with an EHT probe used inversely which may prove fatal if the insulation on the probe breaks down, either through the probe handle if dirty or cracked, or through trimpot holes, or the negative connecting lead if its insulation is damaged. It is noted that a document has already been prepared by ·the Occupational Health and Safety Authority alerting persons who use high voltage meter probes of the dangers associated with their use. It is hoped that distribution of this information to po- · tential users will reduce the likelihood of a further tragedy such as this in the future. S.A. Blashki, Coroner DECEMBER 1992 65