Lightning is a discharge of atmospheric electricity triggered by differing charges within a cloud. It is dangerous because it can start forest fires and kills over 200 people in the US each year. Facts about lightning include that each second there are 50-100 strikes worldwide and most strikes are 2-3 miles long carrying 100 million volts. In January 2006, lightning struck the Sago Coal Mine in West Virginia, igniting an explosion that trapped 13 miners underground for over 36 hours. Only one miner survived due to a lack of oxygen and delays in the rescue efforts. The disaster could have been prevented if safety standards in the mine had been improved.