HEALTH & SAFETY
on muscles, nerves, and the cardiovascular system. Potential consequences range from muscle cramps and respiratory arrest to ‘current marks’—small, point- like burns at the entry and exit points of the current. A current of 30 milliamperes or more pose an acute risk to life. The ‘let-go current’ is between 10 and 15 mA for alternating current and around 50 mA for direct current. If this threshold is exceeded, muscle cramps can be so severe that those affected are no longer able to let go of live parts without assistance— an especially high risk for welding specialists in everyday working life. Alternating current is considered to
be significantly more dangerous than direct current, as it can affect the heart’s natural rhythm and trigger ventricular fibrillation. Another factor that often goes underestimated is that even low amperages of between 1 and 10 mA are sufficient to trigger involuntary reflex movements, which often result in secondary accidents. These uncontrolled reactions could, for example, lead to a fall from a ladder or other injuries. In addition to the amperage, the
duration of exposure to the human body also plays a decisive role in the risk of injury. The longer the flow of current lasts, the more serious the impacts on health. For this reason, it is essential that welding specialists wear suitable protective equipment at all times. In Europe, welding gloves must meet the requirements of the EN 12477 standard, while work shoes should be protection class S3 in accordance with EN ISO 20345.
Determine the danger The amperage (I) is dependent on the applied voltage (U) and the resistance (R) and follows Ohm’s law (U = R x I). If you want to determine the amperage, a human resistance (without protective equipment) of 1,000 Ohms can be assumed from hand-to-hand or hand-to- foot. If the welding machine has an open circuit voltage of 50 V according to the rating plate, a potentially lethal current of 50 mA can pass through the body in accordance with Ohm’s law (I = U / R).
Caution when welding with several welding machines If welding specialists are working on a
workpiece with several welding machines at the same time or on components with a conductive connection, the contact voltage
Drawing 2: Using a voltmeter to measure voltage
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that occurs—especially the open circuit voltage—can reach levels higher than permitted. In many cases, this hazardous situation is not immediately evident. But the situation becomes especially
critical when welding with different polarities at the same time. In this case, the total open circuit voltages of the welding machines can lead to dangerously high voltage levels when welding with direct current (DC). “This happens fairly often, especially
on construction sites,” reports Franz Bichler, a welding trainer at Fronius International. “In the past, we often worked in pairs or threes when welding components several meters long—and even with different polarities, to get the best results on complex components. If the
grounding is faulty in a situation like this, the accumulated voltage can pass through the welder’s body—with life-threatening consequences such as electric shocks, cardiac arrhythmia, or severe burns.” When welding with alternating current
(AC), both the polarity of the circuits and the grid-side connection of the devices influence the resulting open circuit voltage. Under less favorable conditions, the contact voltage can increase to the total of all open circuit voltages of the devices used. Therefore, it is essential to measure the voltage between the welding torches or electrode holders before starting work. The measurement is carried out with a voltmeter by placing both measuring tips directly on the welding torch (electrode holder)—see drawing 2.
Drawing 1: Transverse flow of current through a human body that has accidentally become part of the circuit
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