A coal mine explosion that may have been sparked by lightning trapped 13 miners underground Monday, setting off an urgent rescue operation. The condition of the miners was not immediately known. Four co-workers tried to rescue them but were stopped by a wall of debris, and the blast knocked out the mine's communication equipment, preventing authorities from contacting the workers. It was not immediately known how much air they had or how big a space they were trapped in. Hours after the apparent methane blast, rescue teams had not been able to enter the Sago Mine because gases were still being vented and it was too dangerous to enter, said Sam Kitts, vice president of operations for International Coal Group Inc., which owns the mine.