By now, I explained how to make FTA charts. And you may realized that FTA suggest more to think and what information to obtain from interview.
The section of "continuity of undesirable condition" explained that it was made from "creation of undesirable condition" and "did not make it to desirable condition". The
important thing is who could make it to desirable condition. We expect someone to do that, but nobody done it. This is considered as "omission error". We have to find who
could realize the "undesirable condition" and have an interview to know if the person really knew the condition and what was the decision, and how come the decision was not
executed. These information is very important to make recommendations.
Many of the cases, there are many people who realized the undesirable condition and they all have good reasons why they did not. What does this mean? In such case, I feel the safety level of the organization is poor. We will find it rather easily by checking their safety activity records. If so, we don't have to interview to all to confirm their omission error.
Now we will move to preventing errors.
In the Standard Approach to FTA, I explained that human errors can happen somewhere in the four stages of "Acknowledgement", "Judgment", "Transmission" and "Execution". Here we need to
think how we could prevent the errors of each stage.
Prevent "Acknowledgement Error"
The first stage, "Acknowledgement" was error, the following tree cannot successful. Then we need to have a good idea to prevent this error. As it was explained before, we rely on our five senses to realize something. When we expect a person realize something by "sight", we have to consider the followings. "Is the brightness proper?", "Is the object size and color proper?", "Is a time given to notice it?" and so on.
Similarly there are many conditions to consider for "hearing", "smell", "touch" and "taste" to make the person be successful on "acknowledgement". To prevent "acknowledgement error", we
need sufficient knowledge. When our electrical equipment made some smell like plastic burn, we detect the strangeness by "smell" before "sight". But a small child cannot detect it
while the child felt the smell, because the child do not have knowledge. There are many ways to obtain the knowledge to convey something detected to "Judgment" stage. I hear a super
artisan can detect the difference of one micron on the metal surface. That sense was obtained from his long experiences and it is not just a knowledge.
To sharpen the senses, lectures are not enough. Please remember that trainings are also important, when you consider the measures to prevent "acknowledgement errors".
Prevent "Judgment Error"
When judgment error happened while "acknowledgement" was successful, we have to find what made him error on judgment. This is one of the most difficult thing on an interview, because he may not tell the truth as he afraid of punishment later. Sometimes he loses his temper. In such case, we are forced to decide what happened from other evidences and/or witnesses. But once we obtained the reason of the error, we can provide a measure of prevention.
In many cases, error on judgment happens when the person's safety mind set is low. It can be a personal issue but also can be an organizational issue. When safety activities and/or safety trainings are not enough, people tend to have this error.
Mental pressure can also lead an error on judgment. When a person is in a hurry, sometimes people forget the priority of safety and others. When we made a mistake and got a late, we want to recover it. To simulate the possible pressure and provide right answer when we do not feel pressure is a good measure to this kind of error. I would recommend this practice to include in your safety trainings.
When the health condition is not good, people tends to make an error of judgment. Some kind of job need to have a check on the health condition of people. Many people know that pilots
of airplane take a heath check before flight. An error of judgment by captain may expose all passengers and crews to death. A death of family or a heartbreak are also known as a
source of psychological damage. It is a good practice that managers sometimes forbid workers to do a dangerous job when the worker's health condition is doubtful.
Prevent "Transmission Error"
When there are plenty of time before execution from judgment, or when a person's judgment must be conveyed to others to do, transmission have more chance of disturbance. The sources of disturbance have a lot of variety and hard to eliminate all. Then the preventive measure is not to eliminate the disturbances but to build a transmission system which is strong against any disturbances. Already many people record their schedules and check periodically or set alarm to remind. This is a typical measure to prevent transmission error. But it is not all mighty. It cannot prevent an error of posting a letter. Checklist is also a typical measure to prevent this type of error. We have to select the best measure case by case.
Prevent "Execution Error"
While it was successful on "acknowledgement", "judgment" and "transmission", we sometimes fail at the last stage of "execution". When a small child failed to hold a glass of milk, he
may drop it on the floor. There was no error by transmission but he failed at the execution stage. There was nothing wrong with what he tried to do. Maybe the glass
was too large, or the surface was wet and slippery. In such case, we should not scold the child. Yes, the child need training and we need to give more chances of training to the
child. But if it was an old man who is very sick and may go to heaven in near future, we will not let him to do training. Even to the same error, the measure can be different on the
Physical Measure to Prevent Human Error
If a person made an error on acknowledgement, are there no way to stop the human error? These days, there are some cars which can detect an obstacle and stop to avoid a clash. As the
car stop by itself, it seems we can prevent a clash without acknowledgement. This kind of physical measure is sometimes worth to consider. Many chemical plants provide different type
of hose connection to air and nitrogen. We can prevent to connect air hose to nitrogen supply line by this measure.
Interlock system which is used in many plants, is also a measure to prevent the process to run into incident. Like this we already use a lot of physical measures to prevent human
errors. But one thing we must remember that any machine can fail and we shall not rely too much on the machine. When we use the physical measure, I would recommend you to have another
measure to prevent human error.
As described above, a lot of measures to prevent a similar incident come up from the FTA chart. Some of them are not so effective and some may not be affordable. But do not eliminate
those candidates at this stage. Please leave them in a candidates list. The measure which is not practical now may become available tomorrow. A car with automatic stop system
was a dream in the past, but it is available today. Some measures which looks not effective may give a good idea as our world is changing day by day.
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