Systems of the plant, which is where the radioactive -- most of the radioactive material is kept. pressure was building up in that. most likely to be some hydrogen in that mixture, and they released that. and when the hydrogen and oxygen combined in that building, there was the possibility it could explo explode. it didn't cause damage to the important parts of the plant. and the same would apply if there is explosion at number three part of the plant it has little affect over the course of the action. the most important thing, getting cooling water into the middle of the reactor itself. no ci...