A very simple sample case was provided to explain how to make FTA and how to utilize the FTA charts.
"Mr. A spilled some oil on the floor but Mr. B did not realize the oil. Mr. B fell on the floor and broke his wrist".
According to Maslow's Hierarchy of Needs, Safety comes next to Physiological needs. But we experience a lot of incidents. Safety is our important needs and we intend to decrease incidents as well as possible. To realize a safer world, we need to learn each incident and prevent the same mistakes.
IA&C (Incident Analysis and Communication) is focussing on FTA (Fault Tree Analysis) and analysing various incidents. And we are studying the measures to prevent the same type of incidents in
the future. Also it includes communication of people to prevent incidents.
1. Why Analysis
Why Analysis is well known as a method of analysis for incidents which requires "Why questions more than 5 times". This method is often used because it is easy to use.
Now let's think about a simple incident shown as Sample Case.
The result of Why Analysis is often as follows.
1. Why Mr.B broke his wrist? Because Mr. B fell and dropped from hand.
2. Why Mr.B fell and dropped from hand? Because Mr. B slipped by oil.
3. Why Mr.B slipped by oil? Because Mr. A spilled oil on the floor.
4. Why Mr. A spilled oil on the floor? Because Mr. A carried oil with a small pail.
5. Mr. A carried oil with a small pail? Because Mr. A did not go to get a large pail.
6. Why Mr.A did not goto get a large pail? Because Mr.A was in a hurry to recover the production line.
7. Why Mr. A was in a hurry to recover the production line? Because the due date to the client was coming close.
As you see the above, "Why?" questions continue endlessly and many of cases can not reach to the effective preventive measures. I saw many incident investigation reports that the result was "Mr. A was wrong to spill the oil" and the measure was like "Make Mr. A to promise not to spill the oil". Many Japanese companies tend to require a letter of apology but it will not prevent the next similar incident. Even Mr. A will not spill the oil, some other person may spill the oil.
Of course, there may be a lot of people who can do good analysis with Why Analysis, but it is true that there are many miserable cases too.
2. Fault Tree Analysis (FTA)
Then I would like to show how this incident could be analyzed by FTA.
The first question is "what is the incident to prevent?"
Of course you can take it as "broken wrist" but I would take it as "slipped on the oil".
The reason is "broken wrist" was a result of the incident "slipped on the oil". Mr. B could be dead if he had hit his head by the incident. Or Mr. B could be OK. Just hit his ass and felt
some pain, only. The incident we want to prevent is "slip on the oil".
When we do FTA, we place the "Incident" at top event. And we analyze how it could happen. In case of injury, there must be an "encounter of a danger and a person". We
start the analysis from "what was the danger" and "why the person encountered with the danger".
Danger is a status or a condition which may harm a person. We need to think if it was there from the first or the danger was made by something. And then we think why the
status or condition was kept dangerous. This stage is very important to consider the preventive measures, but this consideration is rare without FTA.
The next is the human error. Nobody want to be injured, but we sometimes make mistakes which are the errors on our action. Human action can be in success only when all the next stages were successful. "Acknowledgement", "Judgment", "Transmission" and "Execution". If we made an error at any stage of these four, the activity become an error. If we did not realize the "red signal", the result will be "ignoring red light". Even we realized the "red signal", if we made a judgment to ignore it, it result in "ignoring red light". While we may had a right judgment to stop, we may miss the right timing as we were answering to the mobile phone. And we may fail to pedal the brake. All the results above are "ignoring red light" but we don't know at which stage the person made an error. We have to interview the person to know this as an incident investigation team. The most difficult stage is "Transmission". The typical error of transmission is like the next. "When I was about go to work, my wife asked me to post a letter on the way. I agreed and decided to post it near the station. When I came close to the station I met an old friend and talked a bit and I totally forgot of the letter. I brought back the letter in my pocket to home." This is an error of transmission from myself of the past to myself of the future. In an organization like in a company, the decision of boss sometimes not done by workers. This is a transmission error from person to person.
Now we will go back to the case of "Mr. B broke his wrist".
The incident was "Mr. B fell on the floor". The status of danger was "oil on the floor". And Mr. B stepped in the oil without realizing it. Namely it was an error of acknowledgement.
Let's analyze the status first. The status of "oil on the floor" was made by spilling oil on the floor by Mr. A and the status was maintained as dangerous. If someone wiped off the
oil, the dangerous status could be disappeared. It means nobody cleaned the floor after the oil was spilled. Even though a dangerous status was made once, if it was eliminated soon,
the incident could be prevented. Then we need have an interview to Mr. A. Why Mr. A did not clean the floor soon? Did he realize the oil spilling? Did he decided not to
clean while he realized it? Did he forget to clean while he wanted to clean? Or he could not find the cleaning tools nearby? The preventive measure will be totally different by
the cause which can be obtained by his interview.
Then we will go back to Mr. B. As he did not realize the oil on the floor, it was an error of acknowledgement. Then why did not he realize it? Was the path very dark? Were there many stains on the floor and was hard to distinguish? Was he walking with something in mind? Or was he walking the path looking at his mobile phone? Here again, we need to find the truth through an interview.
Now you may be realized that FTA can raise many questions to find what must be investigated and what must be asked at the interviews.
Here I have shown a very simple case of FTA but actual incidents are more complicated and hard to analyze correctly without good tools. I hope you to utilize the FTA method to
Continue to Standard Approach to FTA
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