Change Analysis - nst10040019

This diagram is a graphical display of what is known. Since all conditions are a result of prior

actions, the diagram identifies what questions to ask to follow the path to the source or root cause. In

real life, the causal factor chain will usually be complex with many branches. In such cases, a diagram will

be necessary to understand what happened and why. The cause and effect block diagram offers these

advantages:

It provides a means for organizing the occurrence data

It provides the investigator with a concise summary of what is known and what is

unknown; thus, it serves as a guide to direct the course of the investigation

It results in a detailed display of the sequence of facts, conditions, and activities

It assists in organization of the report data and provides a picture format for briefing

management.

Appendix D describes this technique.

Change Analysis is used when the problem is obscure. It is a systematic process that is generally

used for a single occurrence and focuses on elements that have changed. It compares the previous trouble-

free activity with the occurrence to identify differences. These differences are subsequently evaluated to

determine how they contributed to the occurrence. Appendix E describes this technique.

Barrier Analysis is a systematic process that can be used to identify physical, administrative, and

procedural barriers or controls that should have prevented the occurrence. This technique should be used

to determine why these barriers or controls failed and what is needed to prevent recurrence. Appendix F

describes this technique.

MORT/Mini-MORT is used to used to prevent oversight in the identification of causal factors. It

lists on the left side of the tree specific factors relating to the occurrence and on the right side of the tree,

it lists the management deficiencies that permit specific factors to exist. The management factors all

support each of the specific barrier/control factors. Included is a set of questions to be asked for each of

the factors on the tree. As such, it is useful in preventing oversight and ensuring that all potential causal

factors are considered. It is especially useful when there is a shortage of experts to ask the right questions.

However, because each of the management factors may apply to the specific barrier/control factors,

the direct linkage or relationship is not shown but is left up to the analyst. For this reason, Events and

Causal Factor Analysis and MORT should be used together for serious occurrences: one to show the

relationship, the other to prevent oversight. A number of condensed versions of MORT, called Mini-

MORT, have been produced. For a major occurrence justifying a comprehensive investigation, a full

MORT analysis could be performed while Mini-MORT would be used for most other occurrences.

Appendix G describes the Mini-MORT technique.