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Safe School Design

Stand-Off Distance

The most cost-effective solution for mitigating explosive effects on school buildings is to keep explosives as far away from them as possible. The distance between an asset and a threat is referred to as the stand-off distance. There is no ideal stand-off distance; it is determined by the type of threat, the type of construction, and desired level of protection. The easiest and least costly opportunity for achieving appropriate levels of protection against terrorist threats is to incorporate sufficient stand-off distance into school designs. Maximizing stand-off distance also ensures that there is opportunity in the future to upgrade school buildings to meet increased threats or to accommodate higher levels of protection. Stand-off distance must be coupled with appropriate building hardening, to provide the necessary level of protection to the school.

For schools located in high-risk areas, additional considerations follow:

• The first mode of site protection is to create "keep out zones" that can ensure a minimum guaranteed distance between an explosion (i.e., from a vehicle) and the school structure.
• The perimeter line is the outermost line that can be protected by the security measures incorporated during the school design process. It is recommended that the perimeter line be located as far as is practical from the building exterior. Many vulnerable school buildings are located in urban areas where only the exterior wall of the building stands between the outside world and the building occupants. In this case, the options are obviously limited. Often, the perimeter line can be pushed out to the edge of the sidewalk by means of bollards, planters, and other obstacles. To push this line even further outward, restricting or eliminating parking along the curb often can be arranged with local authorities. In some extreme cases, elimination of loading zones and the closure of streets are an option.
• "Keep out zones" can be achieved with perimeter barriers cannot be compromised by vehicular ramming. A continuous line of security should be installed along the perimeter of the site to protect it from unscreened vehicles and to keep vehicles as far away from the school as possible.
• The following critical building components should be located away from main entrances, vehicle circulation, parking, and maintenance areas. If this is not possible, harden as appropriate:
  • Emergency generator, including fuel systems, day tank, sprinkler, and water supply
  • Normal fuel storage
  • Telephone distribution and main switchgear
  • Fire pumps
  • Building control centers
  • Uninterrupted power supply (UPS) systems controlling critical functions
  • Main refrigeration systems if critical to building operation
  • Elevator machinery and controls
  • Shafts for stairs, elevators, and utilities
  • Critical distribution feeders for emergency power