"Many refueling installations are installing aboveground flammable and combustible storage tanks to avoid complicated and costly environmental regulations. These installations require a number of fire protection and safety specifications to prevent unwanted spills, leaks, explosions, or fires. One requirement specifies the following guard posts for minimum protection from motor vehicle impact."
Coffee Break Training - Fire Protection Series No. FP-2006-21
United States Fire Administration: http://www.usfa.fema.gov/