Since the events of 9/11, particularly following the creation of the Department of Homeland Security, much attention has been paid to the use of probabilistic or quantitative risk analysis methods for the purposes of informing security investment decisions.  The debate on the appropriateness of these techniques was quite intense for awhile (say 2003-2006), and to some extent I think there was no clear winner (though I think we are finally coming to grips with what “risk-informed decisions” really means, which in a sense weakens the need for this debate).  Among the fighting and debating, I often found myself wondering what the late Prof. Norm Rasmussen would say about the value of QRA for security.  Now, a number of well-respected scholars have spent quite a deal of time and effort writing on the issue (e.g., Apostolakis, Cox, Bier, Ayyub, Haimes, Kunreuther, Slovic, Pate-Cornell, Diesler, Lave, etc.).  But nowhere could I find even a comment from Rasmussen on the issue.

[NOTE: Norman C. Rasmussen was the director of the famous 1975 Reactor Safety Study, or WASH-1400.  Because of its extreme significance in those days, the report was nicknamed "The Rasmussen Report." I hope to have a copy of the WASH-1400 report posted to this site sometime really soon - oddly enough I can't find it anywhere online]

Then there was my visit to Sandia.  I was priviledged to sit in on a presentation delivered by a scientist at Sandia National Labs that walked through the history of Security Risk Analysis from the Sandia perspective.  On one of the slides there was a quote about the appropriateness of QRA for security attributed to Professor Rasmussen himself!  I was truly taken aback!  I asked whether there was citation I could use for this quote, and low-and-behold there was.  Thanks to the Sandia people, I was able to obtain a copy of this paper and post it here via Scribd:

The citation information is as follows:

• Rasmussen, N. C. (1976). “Probabilistic Risk Assessment: Its Possible Use in Safeguards Problems.” Presented at the Institute for Nuclear Materials Management meeting, Fall 1976, pp. 66-88.

Note the timing… this commentary was made just after the 1975 release of the WASH-1400 report.  My understanding was that many believed PRA/QRA could be applied to problems outside the domain of nuclear safety, perhaps to include nuclear safeguards.  Prof Rasmussen believed then that QRA methods, as outlined in WASH-1400, are NOT appropriate for quantifying safeguards risks (though he says nothing about their usefulness in empowering analysts with knowledge to better inform decision makers).

Just to quickly layout the outline for this paper, Prof Rasmussen begins by offering an overview of all three levels of QRA then comments on the differences between security and safety problems, the most clear being that terrorists are not random and that there is some deliberate attempt to maximize consequences.  Rasmussen also points out that the only practical conservative value to assume in security is one, which given the tendency for terrorists to maximize consequences, almost always results in an unacceptable quantitative risk.  His solution – “make the unauthorized access to special nuclear material very difficult,” that is, make the probability of access so small that even if all the other probabilities are unity, the benefit of having nuclear power still outweighs the risk of malicious terrorist use of nuclear material.  Basically, this amounts to a focus on vulnerability reduction, but only those aspects of vulnerability pertaining to the unauthorized access to special nuclear material (not egress, use, response, recovery, etc. dimensions).  The paper concludes with a short question and answer exchange between Prof. Rasmussen and several audience members, some of which is quite interesting (and clearly dated before the existence of the Design Basis Threat).

In the end, I believe this talk is where the idea of “assuming probability of attack is one” came from, though I could be wrong.

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