Which method of heat transfer is the person in the picture below most worried about? Radiation

Conduction

Convection

Conduction is the transfer of heat when two things come in contact with each other. The energy transfer is from hotter body to the colder body.

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There is a trick behind fire-walking. When the coal burns, after sometime there is a layer of ash on the surface of the coal which blocks the radiation. So the transfer of heat is not possible from radiation. Conduction is the only way possible. The person's feet and coal both are poor conductor of heat so if we walk quickly i.e. there is minimal time of contact with the coal, it will just feel a little warm. As the person start walking on the coal, It has to do it quickly, that way Person will feel its sole warming up but it is not that hot because of the layer of ash and poor conductance, after few steps the ash also sticks on to the sole of the person which makes kind of double layers of ash. So the only way for heat transfer is CONDUCTION.