 When they heard nothing about an explosion during the next few days, they assumed that their bomb had failed to explode.But they had mistakenly set the bomb on an inactive level, and it did not go off until some time later, when the superintendent and the shift boss got off to inspect the 600-foot level, and set off the dynamite.The union blamed the employers for the Vindicator mine explosion, claiming it was just another devious plot that went wrong.