Page 22 - Root Cause Failure Analysis

General Analysis Techniques 13
Active Descriptions

Event boxes in a sequence-of-events diagram should contain action steps rather than
passive descriptions of the problem. For example, the event should read: “Operator A
pushes pump start button” not “The wrong pump was started.” As a general rule, only
one subject and one verb should be used in each event box. Rather than “Operator A
pushed the pump stop button and verified the valve line-up,’’ two event boxes should
be used. The first box should say “Operator A pushed the pump stop button” and the
second should say “Operator A verified valve line-up.”

Do not use people’s names on the diagram. Instead use job functions or assign a code
designator for each penon involved in the event or incident. For example, three oper-
ators should be designated Operator A, Operator B, and Operator C.

Be Precise

Precisely and concisely describe each event, forcing function, and qualifier. If a con-
cise description is not possible and assumptions must be provided for clarity, include
them as annotations. This is described in Figure 2-5 and illustrated in Figure 2-6. As
the investigation progresses, each assumption and unconfirmed contributor to the
event must be either confirmed or discounted. As a result, each event, function, or
qualifier generally will be reduced to a more concise description.

Define Events and Forcing Functions
QualiJiers that provide all confirmed background or support data needed to accurately
define the event or forcing function should be included in a sequence-of-events dia-
gram. For example, each event should include date and time qualifiers that fix the time
frame of the event.

When confirmed qualifiers are unavailable, assumptions may be used to define uncon-
firmed or perceived factors that may have contributed to the event or function. How-
ever, every effort should be made during the investigation to eliminate the
assumptions associated with the sequence-of-events diagram and replace them with
known facts.