my buddy found a washing machine tub and used it for a fire pit..after about 15 minutes of fire time there was an explosion from the pit . there was shiney shit all over the yard that looked like sand. it seemes to have come from the inside of the tub.my question is what is it ? do they use it to ballance the tub? luckely they were gathering wood when it happened or they could've been hurt. any ideas?