求翻译：4. Tanker of mopping the floor wrapped in chains allowed on the beam. Oil and other substances, when friction between an object and the other will also generate static electricity. Electrostatic arcing could ignite the fire of fuel. So in the tanks on the ground to the ground with, but also with a tanker grounded on a chain to prevent a static spark generated within the tank, this chain can not be easily wrapped around the beam frame, must be placed on the ground, and dragging lots of not less than 50 cm.是什么意思？

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