http://www.news.navy.mil/search/display.asp?story_id=2387
OCS follows this somewhat. Their flag system differs slightly, unfortunatly I didn't think to write down how that system worked. I was there from DEC to MAY, so it never got hot enough for us to have our training stopped due to heat.
THEY DO check the wet bulb temperature every half hour (actually H class does, so you can thank them for either getting you out of PT for the day, or getting beat in the gym/battalion hallways) to make sure the right flags are put up, and the safety officer and XO both know when the conditions change so what they have is a pretty decent system. I never saw anyone pass out from heat. They encourage you to stop (not without harassment) if you are feeling dizzy or whatnot, especially if you are an Aviator or NFO, as passing out isn't helpful if you want to keep your designator.
Haha, Headcall.... He's right about the water. You drink tons of water. Get used to doing that before you go. It took me by suprise.