South Korean authorities briefly ordered civilians to evacuate on Tuesday following reports of a white phosphorus leak at the Osan Air Base near Seoul, NBC News reported. While local authorities explicitly identified the issue as a white phosphorus leak, the U.S. 51st Fighter Wing provided a slightly different perspective in their official statement. They did not confirm the presence of white phosphorus, instead describing the event as “a ground mishap.” White phosphorus is a particularly intense substance that is often used in smoke shells and incendiary munitions. Because of these properties, the caution exercised by local officials and base command is understandable.