Regrettably, I did not consult Guidelines for Developing Quantitative Safety Risk Criteria [1], before writing my original paper on risk assessment criteria. In truth, the final paper evolved from a dissimilar topic initiated in 2008. The paper was not meant to displace the excellent CCPS text on risk acceptance that I now own. Furthermore, I am at a loss to explain my phrasing of goal setting by CCPS. I found articles referencing the 1989 version of CCPS Guidelines for Chemical Process Quantitative Risk Analysis [2]. I see “example” and “for illustrative purposes” used frequently. For instance, The Guidelines for Hazard Evaluation Procedures references JBF Associates and Stone and Webster as the sources for Tables 7.7, 7.8, and 7.9 [3]. The Guidelines have been referenced many times and not always as an example [4]. Notwithstanding reprinted examples, tables and graphs over decades with numbers and lines may have become an established practice (and not a stated policy), I erred in affirming CCPS had a set goal.

However, the provenance of the original risk matrix is important, as it is widely used and furthers the point. It can be traced back to reliability engineering MIL-STD-882 (1969) as correctly referenced by CCPS. Revisions C and D contain quantitative rankings that were arbitrarily set during a meeting [5,11]. These seem to be the same regions in print and widely in use today. Again, does restating existing levels and methods validate these levels? Should not we re-evaluate the roots of our studies? A better commentary on issues with risk matrices is contained elsewhere [6, 7,12].

Moreover, my article intended to introduce a new basis for risk acceptance. Hitherto, there were three methods for the generation of acceptance criteria: utility based, rights based, and technology based [8]. A fourth category was borrowed where acceptable level of risk is founded apart from risky occupations, expert opinions, or historical tradition. Furthermore, there are universal risk scales for viewing. One paper includes graphics on the occupations, personal and regulatory risk exposures of individuals at work, home, and leisure. This type of comparison has been done in other assessment arenas for many years [9].

“Risk acceptance” and “risk tolerance” were used interchangeably. Perhaps this is an oversimplification or dreadful error on my part but risk analysis has issues with phraseology and consistency [10].

I advocate no changes to existing US regulations or process safety management but advocate harmony across all elements of process safety. No doubt that dozens of assessments were completed during the Deep Water Horizon design showing it to be acceptable. Yet, five to ten risky “go” decisions with compromised critical safety equipment suggest a distorted risk strategy. I recommend an organizational Fingerspitzengefühl which, in German, means a great situational awareness where go/no-go decisions are made during operations, management of change, or emergency response situations based on real conditions, life safety, and a minimal risk acceptance. There is no time for the complex decision making advised in advanced texts. Management needs to communicate a single, unambiguous message about the control of risk across all operations and functions.


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  • 1
    Wiley CCPS, Guidelines for Developing Quantitative Safety Risk Criteria, Wiley CCPS, New York, 2009.
  • 2
    AIChE-CCPS, Guidelines for Chemical Process Quantitative Risk Analysis, 2nd ed. AIChE-CCPS, New York, 1999.
  • 3
    AIChE-CCPS, Guidelines Hazard Evaluation Procedures, AIChE-CCPS, New York, 1992 AIChE-CCPS, Tools for Making Acute Risk Decisions, AIChE-CCPS, New York, 1995.
  • 4
    G.A. Melham andR.P. Stickles, Enhancing Safety through risk management. Chem Eng 104 ( 1997) 118124.
  • 5
    B. McAllistar, “Evolution of MIL-STD-882E,” 8th Annual Systems Engineering Conference, San Diego, October 2005. Available at: (accessed 02.12.2012).
  • 6
    J. Louis Anthony Cox, What's wrong with risk matrices? Risk Anal 28 ( 2008), 497512.
  • 7
    J. Talbot, What's right with risk matrices? An great tool for risk managers [Internet], Version 13, Knol, April 9, 2011. Available from: (accessed 05.02.2012).
  • 8
    V.M. Trbojevic, “Risk acceptance criteria in Europe,” Safety and Reliability of Industrial Products, Systems and Structures, C. Guedes Soares (Editor), Taylor & Francis Group ( 2010), pp. 6573.
  • 9
    B. Pfitzer, Universal Risk Scales-A Tool for Developing Risk Criteria by Consensus, 2012. Available at:–00600_UseOfURSScalesPaper.pdf.
  • 10
    C.A. Ericson, Concise Encyclopedia of System Safety, Wiley, Singapore, 2011.
  • 11
    Henry Ozog “Designing an Effective Risk Matrix”, Mosaic Corporation whitepaper 2009 (accessed 02.22.2012).
  • 12
    DOD (1977, 1979, 1984, 1993), MIL-STD-882 ver. A,B,C,D.