What's the maximum bearable thermal limit for hot surfaces for human fingers?

The human body temperature is 37°C. The max bearable temperature depends on the conductivity of the hot body the hand/finger will touch. Under the skin the blood convects heat from the contact zone. If the transmitted heat is withi the convective limits of the blood circulation the skin temperature does not grow too high and the cells will not be "boiled". The higher the conductivity the lower has to be the hot body temperature. For metals it should stay around 40°C. The critical temperature for the cells destruction is over 50°C. Meat is grilled at 60°C.

The above mentionned convective capability connected to the low heat content of coal and its low conductivity as well as to the thicker skin of the foot allows the impressive walk on burning coal.

Hi Nick Name,

It is really appreciated very much, your explanations are logical. Would you please provide some URL/web links to read more about what you have stated?

Is there any standard regional or international that requires that external surfaces of the enclosures of consumer devices be kept below 40° C?

Thanks,

Personnel protection type barriers/insulation are usually specified in industry for surfaces over 70 degC that could be contacted accidentally.

Sorry, those are informations obtained long time ago when I worked on a special project where there was a risk of contact with hot surfaces.

It should be considered that when the contact is very limited in time temperature can be over 40..50°C but the higher it is the higher the probability of tissues destruction.