Any advice? what temperature(f) causes second or third degree burns?

144 degrees: The break point is 144 degrees f, below that for about 10 degrees there can be reddening but no damage. Above 144, depending upon the part of the body (for instance skin on the inner thigh is more vulnerable), and the length of exposure, there will be more damage. There is no breakpoint temperature for 2nd to 3rd, just a matter of time.