Sansa Fuze battery exploded

Well, it has not exploded yet. Your battery has experienced swelling. Most likely from overheating. DO NOT ATTEMPT TO CHARGE THE BATTERY!!! If the battery pouch vents, it will release toxic gas. Lithium-polymer batteries generally will not burn, but they will get extremely hot and release gas. They may cause other materials near them to burn. This type of battery should only be charged at room temperature with the correct charger. NEVER attempt to charge these batteries in a hot car interior, which may have been what caused your battery to overheat.