Metal workers have observed that they can dip a hand very briefly into hot molten metal without ill effects. Explain.

Heat energy will transfer by using three modes; conduction, convection, and radiation. Conduction is defined as that mode of transmission of heat, by which heat travels, through an unequally heated body, from the hot end to cold end, from particle to particle, the particles themselves remaining at their position.
The rate of heat transfer will depend upon the time of contact. Larger the time of contact greater will be the chance of heat transfer by conduction from one body to another body. Since the time of contact between the hands and hot molten is very less, thus the energy transfer from one part to another will be less. That is why; metal workers have observed that they can dip a hand very briefly into hot molten metal without ill effects.