Pictures, please!
During the shedding, did you in any way "assist" the shedding by pulling a scute off? Is there anything in the tank that he might have caught one of the shedding scutes on and pulled it off prematurely?
If you are 100% positive that you are seeing flesh where there should be shell, you should go to a vet. No, it's not normal, and the exposed flesh can get infected, which will likely kill him. If you cannot afford a vet or there isn't one in your area, you can try to treat him yourself, but it's no substitution for a vet's care.
A link to minor first aid is here:
http://www.redearslider.com/forum/viewtopic.php?t=4519
This sounds more like major first aid ... I would recommend posting pictures as soon as possible so we can help you assess what you are seeing and you can find a vet too.