Here's a link about heavy water:
Heavy Water - What Is Heavy Water? - Heavy Water Facts

Speaking of dry ice. I saw something so scary on the show Right This Minute, where they showed this video of a pool party. Someone got the bright idea to film people partying in the pool and they put large amounts of dry ice. Within seconds there was a thick fog and you couldn't see the people in the pool. Well dry ice and chlorine mixed together form a noxious gas and people started fainting in the deep pool. Bystanders couldn't see the ones under the water - several had to be taken to the hospital and one was in a coma from near drowning. Never put dry ice in large amounts in a chlorine pool.