Kat that is the best question. Reptiles are odd with heat there is a lot of debate as to why and what causes burns. There are no hard studies been done (I think I am thankful they are not intentionally burning snakes...) so conjecture here.

Snake burns can be divided into two groups contact burns and duration burns.

Contact burns need high temps. Much like touching a halogen bulb after being on you would get a burn reptiles get a burn typically 160+ for a fast burn about the temp of coffee if you stick your finger in hot coffee you get a scald almost instantly. So that to me is the lowest point of a contact burn. A animal brushing against something that is 160 or higher will cause a burn almost immediately. This is why many claim RHP to be safe they run below the point a short contact will burn, properly mounted an animal cannot touch it for long periods. General rule of thumb if you find it uncomfortable to hold your hand on for more than 5 seconds it is in the danger zone for a contact burn.

The strange one is the duration burn. Snakes get burned all the time, deep penetrating burns. Why has been a debate in the vet community for some time. There is no proven theory. The issue is a snake will lay on an overly hot surface for some time and become burned, severely burned. Similar to the boiled frog water myth (maybe a myth maybe not that one is sketchy) The temp where this has occurred to my knowledge is over 120º maybe it is hard to get straight info from someone whom has burned a snake. I figure 105ºF is the safe limit likely low but that is what I feel.

The next big question is why don't snakes (reptiles) move? I believe and some of the current theory stands behind it. It comes to ambient temps. The core temp of a snake is greatly effected by the air in the lung. The lung (breathing lung not the other lung) runs past heart, liver, and major circulatory system. Cold air = cold blood. I believe in an attempt to regulate the core temp a snake will lay on a surface and allow the external layers to burn and not move. This is why I constantly harp on ambient temps. Raised awareness of corrected ambient temps may save some burns. Ever notice it is usually larger snakes with burns not babes? I think this helps support this idea, small snakes would warm through the muscle tissues faster before a duration burn.

This is rare in humans but disabled people have been burned by human heating pads because they cannot move off of them. This is why many now have auto off settings and such to protect the people placed upon them who cannot move off on their own.

Glo,
I have emaied Bob on two occasions and never got any response. I guess it is an involved answer and the canadian email precluded an message, don't know, but I never got one.