There is an article that came out earlier from DRJ (Thomas L. Weems) based on a study that provides guidelines on the required geographical distance for alternate site locations. This is good news for those performing risk assessments where this is considered vulnerability, because as far as I know FEMA has provided no specific guidelines.
http://www.drj.com/articles/spr03/1602-02.html (registration required to view)
Ideally 105 miles point to point is the key number for all the threats listed below. For those who don’t have access to the article below is a breakdown of the recommended geographical distances based on the threat.
NOTE: The article provides a graph so the numbers below is based on my interpretation of the graph.
Alternate Site Distance Recommendations
Military Installation: 45
Forest Fire: 42
Power Grid: 36
Central Office: 29
Civilian Airport: 28
None of the Above: 21
Off Site Storage Facility Distance Recommendations
Military Installation: 41
Forest Fire: 38
Power Grid: 36
Central Office: 25
None of the Above: 24
Civilian Airport: 22
Also the key here is to remember that the off site storage facility should accessible from the alternate site facility, which is a mistake many organizations make.
Problems and Revisions
Based on some quick research there are a few problems with the current distances above. For example, I took three common disasters and did a quick analysis and here are the results along with some suggested changes.
Hurricane – Katrina spanned a much larger distance then 105 files proving that this distance is not adequate in a very large hurricane storm. The article below explains that Katrina expanded over 780 miles whereas the outer regions were probably only affected by rain. However, from my research severe damage was over about a 200 mile radius. Therefore, I would suggest doubling the current metric to 210 miles.
Volcanoes – Although the current figure will probably be fine in most cases there is information to support that volcanoes can spread ashes up to 100 miles as displayed in the below article. Therefore, this number should be revised to 105 miles based on the type of volcano.
Earthquake – Similar to the volcano this distance will probably be sufficient but why take the chance when there is evidence that a 7.8 earthquake ruptured 220 miles of a fault. Therefore, this number and the definition should be clarified to be at least 60 miles from a major fault line.