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Launched Aug 26 1996.


Source: National Bureau of Standards SPECIAL PUBLICATION 482

Foreword from the Webmaster Two papers from this publication dealing with investigations are posted. This paper addresses hypothesis generation during investigations, and how that can be done. The second paper by W Johnson describes the MORT safety assurance program, including investigation-related research findings, which can serve as a model for investigating management practices during investigations.

Though twenty years old, the papers still provide useful insights into the thinking of the times for investigation researchers.

Rare Event/Accident Research Methodology

Proceedings of a Workshop held at the National Bureau of Standards

Gaithersburg, Maryland, May 26-28, 1976

Edited by V. J. Pezoldt

Institute for Applied Technology
National Bureau of Standards
Washington, D.C. 20234

Juanita M. Kreps, Secretary
Dr. Sidney Harman, Under Secretary
Jordan J. Baruch, Assistant Secretary for Science and Technology

Ernest Ambler, Acting Director

Issued July 1977


  • Acknowledgments v
  • Abstract vi
  • Introduction vii

      Presented at the Workshop
      • Safety Engineering as the Integrator of Accident Prevention Activities
        Willie Hammer --1
      • Methods Useful in Safety
        W. G. Johnson, presented by Robert Eicher --11
      • Hypothesis Generation for Rare Events Researchh
        Ludwig A. Benner, Jr --25
      • Approaches to Injury Research
        Julian A. Waller, M.D., M.P.H --29
      • Human Research and New Methodological Considerations Being Forced by the Law
        George A. Peters, Esq. --47
      • for Studying Complex Homemaking Tasks
        Rose E. Steidl, Ph.D.. --55
      • Data Collection for Hand Tool Injury: An Approach
        M. M. Ayoub, Ph.D., P.E --71
      • Simulation in Accident Research
        Stanley Rubinsky, Ph.D., P.E -- 105
      • Participants in the Workshop --111


    Ludwig A. Benner, Jr.

    National Transportation Safety Board

    LUDWIG BENNER, JR. is Chief of the Hazardous Materials Safety Division of the Bureau of Surface Transportation Safety, National Transportation Safety Board. Mr. Benner has long been involved with transportation safety in a number of capacities. His paper deals with the process of discovery, suggesting that hypothesis development in accident investigations and rare event research need not be a hit or miss proposition based primarily on "creative intuition" and "good luck." Rather, Benner proposes a multilinear events sequencing methodology to aid in the development and testing of research hypothesis. The interested reader is referred especially to Benner, L., Accident Investigations: Multilinear Events Sequencing Methods. Journal of Safety Research, 1975, 7(2), 67-73, for a more complete discussion of the proposed methods.


    This paper focuses on hypothesis generation. How does one generate propositions that can be tested by scientific methods? Popper (1959) says there is no logical path leading to new ideas- -they can only be reached by "emfuhlung" or creative intuition. Polya (1957) offers a "rule of discovery" that goes about like this: the first rule of discovery is to have brains and good luck; the second is to sit tight and wait until you get a bright idea. Their views are widely held.

    Surry's (1969) discussion of accident research methodology is useful if further understanding of some of the difficulties with existing accident research are of interest to the reader. But Surry does not discuss the discovery problem.

    The problem of structuring discovery, especially the discovery of hypothesis, has been with us for a long time. There may be a way to do it. I would like to share with you my method for generating hypotheses, derived from my work as an accident. investigator.


    After an accident, every investigator is. confronted with the need to answer the question "what happened?" regardless of the ultimate purpose of the investigation. The usual approach is to try to "reconstruct" the accident. The method used is to try to isolate events suggested or indicated by evidence acquired after the "accident". As the investigator becomes aware of events that occurred during the accident, outlines of what happened begin to emerge. As additional evidence of events comes to light, the investigator begins to speculate about possible hypotheses, that is, ways the accident might have happened. Each hypothesis is tested against the evidence subsequently developed, to arrive at the most likely explanation of what happened.

    As I have observed this process, elements common to the search for understanding of any phenomenon have been noted. These observations suggest that there may be a logical path leading to new ideas, and that a general method for generating hypothesis during the study of phenomena, including rare event phenomena, may be possible. The essential assumptions and principles follow.


    My hypothesis generation method is based on the premise that the functioning of our universe and its constituent parts reflects a continuum of interacting events. Events, in this context, are used in the sense that someone or something does something (actor + action = event). Each event influences one or more events which follow that event in time. It is the precede follow logic of the related events that provides the key to the hypothesis generation method.

    The accident investigation process is based on a "break down events" principle. Take "an accident" and break it down into increasingly finite events in the following manner. "An accident occurred" describes a phenomenon as a gross event. "A sliding car struck a tree" breaks down the gross event into two sub-events. The car rolled onto an icy patch, began to slide, and struck a tree further breaks down the phenomenon into even more discrete events. This "break down" process can be continued for as long as necessary to gain the understanding of the phenomenon required by the purpose of the study. Each time an event is subdivided, the need for more precise understanding of the actor-action relationships arises. And each time the need arises, the last known action by an actor provides a starting point to hypothesize the next action or actions that must have been taken by that actor in order for him to arrive at the next known action supported by the evidence. Thus, the bridging of the events gaps is circumscribed by logical spatial and temporal relationships among the events as they progress through their precede/follow sequence. This method of "breaking down" the events sequence structures the discovery of unknown events required for the sequence to proceed from the beginning point to the end point of the phenomenon being studied.

    Usually for someone or something to do something (an event to occur) certain enabling conditions must exist. The creation of these conditions also flows from an event sequence. That is to say, events produce changes of state or outcomes. For any phenomenon under study, the chronological flow of events provides an explanation of what happened, just as we naturally try to create mental movies when we attempt to describe events. The existence of the enabling conditions, which must have been present for each event to occur, can be traced backward in time to explain "why" the events sequences occurred.

    A convention for displaying the events sequences, which further facilitates discussion and discovery, has been proposed where the events sequences involve two or more actors (Benner; 1975). This multilinear events sequencing method provides opportunity for a precede/follow logic check along both the horizontal time coordinate for a single actor as well as a vertical time coordinate for sequencing related events by two or more actors. In other words, the timing of any event by any actor can be compared with any other event by any other actor, and this chronological validation provides a method for "proving" the hypothesis that differs from traditional, statistical, or experimental approaches of the scientific method. The display has the further advantage of highlighting unknown "linking" events in the sequence. It can also structure speculations about their occurrence or guide the search for evidence to confirm these speculations.


    The multilinear events sequencing methodology can be useful for predictive study of rare events or accident phenomena. If one can accept that accidents are multi-event phenomena involving more than one actor, whose actions must occur in a specified chronological sequence to achieve a harmful or other outcome of interest, it can readily be seen that if any of the events occur out of sequence (or not at all) the outcome being studied will not occur. Thus the pattern of events describing the "rare event phenomenon" can be studied. It is the occurrence of the events sets in the necessary relationship which is rare, rather than the occurrence of individual events within the set.

    If this concept is valid, it suggests new approaches for the accumulation of data about rare events in the form of events sets, rather than in the form of individual conditions on events constituting the phenomenon. The manipulation of chronologically sequenced events sets in process flow chart form appears to hold more promise in understanding rare events phenomena than the present approaches. In the accident field, the need for a unifying theoretical framework to organize the events sets for research purposes can be shown to be increasingly urgent. A theory which would accommodate the sequential ordering of events sets in accident and other rare events research has been proposed by the author (1975).


    The sequential ordering and display of events and events sets constituting a rare phenomenon provide a reproducible method for structuring the discovery of a hypothesis explaining the phenomenon, and for testing the logic of the explanation. The application of probabilistic estimates of the frequency of occurrence of these events, both individually and in sets, provides an approach for predicting these phenomena. Time or spatial logic tests, as well as traditional mathematical or other experimental methods, can then be used to validate one's hypothesis.


    Benner, L ., Accident Investigations: Multilinear Events Sequencing Methods. Journal of Safety Research, 1975, 7(2), 67-73

    Polya, G. How to Solve It, Doubleday-Anchor Books, Second Edition, Garden City, New Jersey; 1957.

    Popper, Karl The Logic of Scientific Discovery, Basic Books, Inc., New York, New York, 1959.

    Surry, J. Industrial Accident Research, University of Toronto, 1969.

    Go to Johnson paper from same source.

Scanned from original document January 06, 1998