Apple iPad iOS 5.1 - Manual (Page 143)

iPad operating temperature
If the interior temperature of iPad exceeds normal operating temperatures, you may experience
the following as it attempts to regulate its temperature:
iPad stops charging. Â
The screen dims. Â
A temperature warning screen appears. Â
Important: You can’t use iPad while the temperature warning screen is displayed. If iPad can’t
regulate its internal temperature, it goes into deep sleep mode until it cools. Move iPad to a cooler
location and wait a few minutes before trying to use iPad again.
143 Appendix C Support and Other Information