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Aside from the direct effects of static and extremely low frequencyelectric fields (Static fields (0 Hz), Low frequency (0.1 Hz–1 kHz)), indirect effects can occur in electroconductive objects (e.g. vehicles, large work machines, metal fences) due to the created surface charges. The electrical charge increases with the increasing strength of the external electric field and the increasing isolation of the object against the ground. Charging effects can also occur without an external electric field via a static charge caused by friction between different materials (e.g. when taking off a pullover or while walking over floor carpets; at moving parts of machines, vehicles or technical plants in the work area). Perceptible electrical discharges (spark discharges) can occur when approaching charged objects (or grounded objects in the case of humans being charged themselves – example: touching a door handle). When touching charged objects, a current can flow through the body into the ground (contact current or touch current, see Figure). The potency of these effects depends, among others, on the electric field strength, the position of the chargeable object within the field, the size of the object, the strength and duration of the contact current and the grounding of the human body (corresponding to the shunt resistance to the ground).