This type of stressor is unforeseen and unpredictable and, as such, is completely out of the control of the individual. Examples of crises and catastrophes include: devastating natural disasters, such as major floods or earthquakes, wars, etc. Though rare in occurrence, this type of stressor typically causes a great deal of stress in a person’s life. A study conducted by Stanford University found that after natural disasters, those affected experienced a significant increase in stress level. Combat stress is a widespread acute and chronic problem. With the rapid pace and the urgency of firing first, tragic episodes of accidentally killing friendly forces (“brother” killing “brother” or fratricide) may happen. Prevention requires stress reduction, emphasis on vehicle and other identification training, awareness of the tactical situation, and continual risk analysis by leaders at all echelons.