gumbii, If you have a rotten one and you know it and are afraid of it going POW, get a ziploc bag and turn it inside out to pick up the egg and zip it inside to get it out and in the trash or wherever you put them rotten ones. If it explodes, then it is contained.
Lacrystol, you can, and I have heard that you should, open the incubator at least once a day to let it cool a bit. I do while I turn or candled and add water. Some people even recommend misting the eggs at this time too to help keep the moisture up after opening. When a hen goes broody, up until the last couple of days (what us pseudo-hens call 'lock down'), she may get off the next to eat and drink, so even she is letting the nest air out and cool a bit. You don't want to go leaving it open for a half an hour, but 5-10 minutes isn't going to destroy your hatch.
Also, some of those little embryos that you see the veining but not the little feathered seahorse may have them right in the middle of the egg and you can't see it well because it is also being masked by the air sac. I would smell them, and leave them as long as they are not stinky. If they don't darken up by day 15 or so, pitch them or leave them to help as heat sinks. Just my two cents.
Good luck.
By the way, I did have one explode in a big batch I did for our county fair last year. I didn't think about sniffing them before taking them down and I ended up ruining about 30-40 eggs because I didn't take the time to smell the ova
My Hovabator still smells a bit funky even though I scrubbed it and disinfected it.