>> when gas workers arrive on the scene, officer su learns the cause of the explosions. >> i spoke to the edison supervisor and he said there's a type of short that had happened down in the vault. so what was going on was the main power was sending surges, test surges, to the lines and that was causing the explosions. >> the vault is an underground box that houses electrical equipment. captain wolf and firefighter boyle are transported to the hospital and treated for first and second-degree burns to their heads and hands. within a few weeks, they are back to work. >> if we weren't using protective gear we would have injured a lot more. the burns probably would have a lot worse to the rest of our body. >> a lot of edison guys have even said, we don't know how you're alive right now. >> you have to expect the unexpected. this was definitely the unexpected for us.