FINDING EVENT BLOCKS WITH THE
CHANGE TRACKING METHOD
Table of Contents
FINDING EBs WITH CTMA continuing challenge to incident investigators is trying to find data to transform into Event Blocks. One technique is to track changes. To do this, investigators develop a list of sequential changes, identifying what changed and what produced the changes. The latter is used for EBs.
Procedures for this task are contained in this Guide. INTRODUCTION
The Change Tracking Method uses the traditional method of difference to identify changes that occur during a process. CTM's primary value is in guiding the thinking required to trace the "change makers" and their actions as the occurrence progresses. OBJECTIVEThe objective of this Guide is to present ways to identify the changes of state that occurred during an occurrence, and the actors and actions that produced those changes of state. APPLICABILITYThis change tracking method is applicable during any stage of an investigation, but is most useful during the early stages to help identify the actors about whom the investigator(s) should acquire additional action data. The changes identified should be used to support EB and MES Matrix development.
DATA REQUIREDThis method requires a cursory awareness of the nature of the occurrence being studied. It also requires a modest understanding of a process's expected operations within which changes of state occurred during the occurrence, and data about the actual state of the system and its environment at the time the occurrence began and ended. DATA SOURCESCTM requires concrete observations of, or data from, any person, document or animate or inanimate source, including the description of things remaining after an occurrence. CTM uses direct observation, sequential logic and deductive reasoning from data sources. DATA PRESENTATIONThe work product of the CTM is a list of sequential changes of state that begin with the initial deviation from a normal state of the system. It documents the changes that led to the outcome of interest. A typical format for CTM documentation is shown in Figure 4-1.
Use comparisons to identify changes. Begin by considering circumstances when no mishap occurred, and then considering the circumstances present when the mishap occurred. When differences are observed, compare the mishap circumstances with the no-mishap circumstances to isolate changes that had occurred.
EXAMPLE: A container used to store fluids has been functioning without overflowing for years. Today the container overflowed. What changed? CHANGE TRACKING METHOD1. Try to identify the actual state of dynamic equilibrium of the system immediately before the occurrence of interest began. That state may be considered the state at a time when the system was functioning normally, or as desired or designed. While functioning normally, the system was probably adjusting continuously to potentially disruptive occurrences, but continuing to function as intended and produce the intended outputs. The changes of interest are any changes to which the system had to react to maintain its dynamic equilibrium, but didn't. These changes may be simple or compound changes, and the time spans involved may be moments or years.
Q: What changed before or around the time the occurrence began?
EXAMPLE: The container was filled with more fluid than usual, and the fluid overflowed. The same quantity of fluid had been piped to the container previously but it hadn't overflowed, because a drain pipe had diverted the excess fluid into a sump. This time it didn't. Thus the change of interest is in the overflow system that did not function as it had previously.
2. Any previous or subsequent changes of state leading to or resulting from that change of state are then explored, by naming the person or thing involved, and examining its state during or before the occurrence.
Q: What changed before (after) the first change?
EXAMPLE: As the container was being overfilled, the fluid could not be diverted by the drain pipe because it was partially plugged. Residue was found on the drain pipe walls, reducing its cross-sectional area. The last time spilled fluid was washed off the side of the tank, a new cleaner was used that coagulated and left the residue in the drain pipe. So the excess fluid could not run through the drain at a fast enough rate to keep from overflowing the container. The new cleaner was a "before" change of state, as was the partially plugged pipe. To avert the overflow, an adaptive response (counter-change) had to be initiated but the operators who used the new cleaner were unaware of the change in the drain pipe. The overflow was an "after" change of state around the container that resulted from the earlier changes.
3. Track and list, in sequence, the changes involved in the occurrence. Start with the first change that was introduced, for which a counter-change was necessary, and then list the subsequent changes that you found.
Q: What were the changes, in the order of their initiation, that may have had a bearing on the occurrence.
EXAMPLE: List changes in Event Block (EB) format, in proper sequence:
2. Cleaner formed coagulants with fluid residues. 3. Coagulant residues changed pipe flow capacity. 4. Pipe impaired routine overflow protection. 5. Excess fluid overflowed around container. COMMENTSUse the results of this change analysis to support EB preparation and modeling of scenario. The change analysis may provide a method of defining what information you should consider with a logic tree or MES Matrix.
For additional discussion of change and change analysis, refer to original work in Johnson, W.G., MORT SAFETY ASSURANCE SYSTEMS, Marcel Dekker, Inc. NY 1980, p 53-72.
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