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Empirical Root Cause Analysis for Human Error
Because people often can’t remember what they forgot
PUBLISHED: MONDAY, JANUARY 22, 2024 - 12:03

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Aroot cause analysis (RCA) should be empirical; however, this can be
difficult when dealing with human error. A typical human failure is a
missed operation, such as when a process step isn’t carried out. This
could mean a part wasn’t installed, a bolt wasn’t tightened, or a server didn’t deliver a food item that had been ordered.

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The simplest answer in such a situation is “the employee forgot.”
Perhaps, but there’s often more to the situation than simple
forgetting—and forgetting isn’t so easy to evaluate empirically. We
can’t ask somebody who assembles hundreds of parts a day, “Did you
forget to tighten a bolt four months ago?” We have only the evidence, in
the form of an untightened bolt, and the untestable hypothesis,
“employee forgot.” Fixating on the untestable hypothesis does little to identify the cause of the problem so that adequate corrective actions
can be implemented. This is the point in supplier quality where the
supplier often submits an 8D report listing both the root cause,
“employee forgot,” and the corrective action, “employee retrained.” Such
actions do little to prevent a reoccurrence of the failure.

Instead, it’s better to look at the entire system that led to the
failure. W. Edwards Deming tells us that 85% of all problems are due to
the system and solvable by management only, and 15% of problems are due
to employees. Somebody may have forgotten, but how was it possible for
one act of forgetting to cause the problem? Is there any way to reduce
the chance of somebody forgetting in the future?

Investigating to identify the weak points in the process is the first
step. Here, a flowchart of the process may be helpful. This flowchart shouldn’t be created in a meeting room based on knowledge of the
process; the process should be followed and mapped to see how it truly operates. The objective is to identify improvement areas that can
prevent the failure from happening again as well as to prevent the
failure from escaping if it does occur. This second point is especially important when the only line of defense against an occurrence is hoping
nobody forgets.

Every organization has different processes, so the actual actions to
take will vary. Figure 1 shows a generic Ishikawa diagram for a missed operation, with various items to consider when dealing with such a problem.


Figure 1: Ishikawa diagram for a missed operation

People
A person may have made a mistake, but there could be contributing
factors that need to be addressed by the organization’s management.
Could fatigue have contributed to the failure? If so, there may not be sufficient break time, or breaks may be long enough but too infrequent.
This is especially important if the operation requires intensive
concentration for long periods of time.

Is the person even capable of correctly performing the operation? More
mistakes could happen if an inexperienced person was never shown how to
perform the operation, or a person was placed in the job without any
training in how to perform the task. If one person was untrained, then
there may be many more. So formal employee training and training
tracking should be instituted.

Method
Ensure that procedures or work instructions are up to date and available
at the place of work. Also, make sure they are written in a way the
operator can understand. Technical instructions written at a graduate
school level might not be understandable to a production operator. Be
sure to determine whether the operator is capable of reading the
language used for the work instructions. If not, update the instructions
to be more graphic or translate them into the appropriate language.

Are part counters available? If so, were they turned on? If not, perhaps
a part counter should be installed. Is there a check to ensure that
there are no unused parts left after the operation is completed? This is
an indication that there is a part from the last order still around. One
simple solution is to ensure that only parts used for the current order
are on the work surface.

Machine
Is there a poka-yoke system in place to ensure the machine automatically
stops when a process step is missed? Poka-yoke can remove the need to
depend on people not forgetting. Was a poka-yoke in place but turned off
or removed? One organization received customer complaints due to mixed
parts. The subsupplier that produced the parts kept reporting that there
was nothing more they could do because a divider was in place, and
production employees still mixed up parts. The root cause was clear
after a visit to the subsupplier’s production floor: All dividers had
been removed. During previous complaints, the supplier had not thought
to actually check to ensure that the dividers were still being used. The problem was blamed on employees, but a simple solution was available.

An operation may be stopped in the middle for an operator to collect the correct tool. Stopping an operation in the middle and a simple “don’t
stop till finished” procedure would be insufficient if the operation
can’t continue until the required tool is available. In such a
situation, all required tools and equipment should be made available in
the work area.

Environment
Lighting for people isn’t a typical item on an Ishikawa diagram, but it should still be considered. It would be difficult to correctly complete
many detailed operations with insufficient lighting, so this is an item
that should be checked.

Are there loud sounds in the work area? Some people might not be able to concentrate with the constant thump of a machine, so noise mitigation
efforts or hearing protection may be needed to help employees
concentrate in a loud work area.

Are co-workers interrupting the operator? A machine operator who needs
to frequently stop to assist others might not restart an operation at
the correct step. If interruptions are unavoidable, it may be necessary
to implement a policy requiring the current operation to be completed
before stopping to respond to the interruption.

The temperature in the work area should also be considered. Heating or
cooling may be necessary; it can be difficult to perform tasks requiring
fine motor skills in a very cold environment, or it could be difficult
to maintain concentration in an overly hot room.

Employees might also forget to install a part if they are working in a cluttered work area. Parts from various work orders may get mixed up,
making it difficult to notice if there is an extra part left over after
an operation. Implementing 5S may be helpful. The work area should be
sorted to remove unneeded items, straightened to ensure things are
stored in an orderly manner, scrubbed to clean the work area, and
standardized. Self-discipline should be used together with the
assistance of a regular cleaning schedule to make sure the work area
stays clean and orderly.

Measurement
Is there sufficient time to complete the operation? Assembly personnel
might be expected to move quickly, but is the takt time for the
operation too short for the operation to be correctly completed?

Material
Was the part delivered to the work area? The employee might have missed
the operation because the part was never there in the first place. In
such a situation, there’s the failure of “part not delivered” in
addition to somebody forgetting. Here, the failures should be
investigated to ensure that proper corrective action is implemented.

People make mistakes, but...
People do make mistakes. But often the process or organization
contributes to the mistake happening. Reminding an employee to “stop forgetting” isn’t a sufficient corrective action. The organization must investigate the underlying factors that helped to contribute to the
failure; otherwise, another employee can be expected to make the same
mistake. Wherever possible, poka-yoke should also be implemented to
ensure that failures can’t happen. Such actions are far more effective
that telling people to remember to stop forgetting.

Originally presented at the IAQ Quality Forum in Bled, Slovenia.

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