I just read an AR post by Mark Reusch called "Time to Pay Attention" that really struck a chord with me and I thought I would add my own twist on the topic.
Mark brought up the topic of heat injuries while working this summer. I posted on his blog some general advice and warning signs, but I'll go into more details here.
There are 3 types of heat injuries: Heat Cramps, Heat Exhaustion, and Heat Stroke.

In a former career, I was an Army officer and I saw lots of heat injuries here and overseas so I am very familiar with what I am talking about. As a matter of fact, I have had heat cramps dozens of times, and heat exhaustion at least half a dozen times from pushing myself beyond the limit. I know very well what MY limits are, but for those less familiar with their bodies this could be a deadly experience.
Heat Cramps - This is when your body is saying, "Hey, Dummy, its hot. Get me some water." You may experience heat cramps before heat exhaustion, but not always. Some symptoms include headache (I feel mine in my upper neck at the base of the skull), muscle cramps (sometimes in the legs, under the chin, or in the feet). Other abdominal cramps feel a little like severe gas pains that may double you over in pain. I've been told that they feel a little like contractions during childbirth. Get to a cool, shady area as soon as you can, SIP water (if you gulp it you may puke), rest for several minutes, take it easy, continue to drink water, and take frequent breaks. Continue to monitor yourself to make sure you don't go into Heat Exhaustion.
Heat Exhaustion - This is when you body goes into overdrive to try and cool itself off. You will also start to feel more effects of dehydration. You may experience a severe headache, dizzyness, confusion, PROFUSE SWEATING (this is how your body is trying to cool off), pale cool clammy skin (a result of all that sweating), Possible heat cramps, tingling lips or other extremeties, Very dark urine (almost the color of weak coffee). STOP IMMEDIATELY. Move to a cool shady area, elevate your feet, loosen restrictive clothing like boots, unbutton your pants and belt (this is to help cool off and to help keep you from going into shock.) SIP water. You may pour water on you, but drinking is the first priority if you have limited water. An IV may be good now, but you probably won't have access to that. Keep sipping water until your urine is clear. You'll have a massive headache for the rest of the day and will be very tired (hence the name Heat Exhaustion). You probably won't finish the inspection.
Heat Stroke - Your body runs out of water to cool yourself and you are screwed. Headache, dizzyness, confusion, slurred speech, unconscousness, red hot dry skin (no more sweating, probable salt stains on clothing), tingling lips, no urine, shock, and death. Treat the same as for Heat Exhaustion and call 911 immediately or they may die.
Tips to avoid heat injuries: Drink lots of water the night before and during the inspection. By the time you get thirsty, you are already low on fluids. Avoid sodas, coffee, alcohol, and energy drinks (Red Bull) while inspecting. If you drink Gatorade, use it in a 1:2 ratio. For every 1 bottle of Gatorade, drink 2 bottles of water to help keep your electrolytes balanced. Take breaks. Don't over do it. Use a Camelbak hydration system while inspecting (especially the attic) so you always have a drink. I fill mine with water and add a little Gatorade powder so that it is at 1/3 the strength of regular Gatorade. That way I don't have to drink separate water and Gatorade.
There are great sites on the web that tell a lot more information about this then I can list here. Take care of your body and you will be much better off. Trust me. I've pushed myself over the limit many times and have regretted it ever time.