Root Cause Failure Analysis. Trinath SahooЧитать онлайн книгу.
propeller was not rotating severely diminished the turning ability of the ship. It is one of the many bitter ironies of the Titanic tragedy that the ship might well have avoided the iceberg if Murdoch had not told the engine room to reduce and then reverse thrust.”
There were too few lifeboats: Perhaps the biggest tragedy is that there were not enough lifeboats to accommodate all of the TITANIC's more than 2200 passengers and crew members. The lifeboats could accommodate only about 1200 people.
Do these nine causes cover everything, or are there still more factors I'm forgetting? Are there some lessons still unlearned from the TITANIC tragedy?
What Is Root Cause Analysis?
Looking at the TITANIC failure report, it shows that there is no single cause and no single train of events that lead to a failure. Rather, there are factors that combine at a particular time and place to allow a failure to occur. Sometimes the absence of any single one of the factors may have been enough to prevent the failure. Sometimes, though, it is impossible to determine, at least within the resources allotted for the analysis, whether any single factor was key. If failure analysts are to perform their jobs in a professional manner, they must look beyond the simplistic list of causes of failure that some people still believe. They must keep an open mind and always be willing to get help when beyond their own experience.
Different Levels of Causes
A failure is often the result of multiple causes at different levels. Some causes might affect other causes that, in turn, create the visible problem. Causes can be classified as one of the following:
Symptoms. These are not regarded as actual causes, but rather as signs of existing problems.
First‐level causes. Causes that directly lead to a problem.
Higher‐level causes. Causes that lead to the first‐level causes. They may not directly cause the problem, but form links in the chain of cause‐and‐effect relationships that ultimately create the problem.
Some failures often have compound reasons, where different factors combine to cause the problem. Examples of the levels of causes follow.
The highest‐level cause of a problem is called the root cause:
Hence, the root cause is “the evil at the bottom” that sets in motion the entire cause‐and‐effect chain causing the problem(s).
TrevoKletz said
…root cause investigation is like peeling an onion. The outer layers deal with technical causes, while the inner layers are concerned with weaknesses in the management system. I am not suggesting that technical causes are less important. But putting technical causes right will prevent only the LAST event from happening again; attending to the underlying causes may prevent MANY SIMILAR INCIDENCES.
The difference between failure analysis and root cause analysis is that failure analysis is a discipline used for identifying the physical roots of failures, whereas the root cause analysis (RCA) techniques is a discipline used in exploring some of the other contributors to failures, such as the human and latent root causes. Root cause analysis is intended to identify the fundamental cause(s) that if corrected will prevent recurrence. The principles of RCA may be applied to ensure that the real root cause is identified to initiate appropriate corrective actions. RCA helps in correcting and preventing failures, achieving higher levels of quality and reliability, and ultimately enhancing customer satisfaction
Depending on the objectives of the RCA, one should decide how deeply one should analyze the case. These objectives are typically based on the risk associated with the failures and the complexity of the situation. The three levels of root cause analysis are physical roots, human roots, and latent roots. Physical roots, or the roots of equipment problems, are where many failure analyses stop. Physical root causes are derived from laboratory investigation or engineering analysis and are often component‐level or materials‐level findings. Human roots (i.e., people issues) involve human factors, where the error may be happened due to human judgment that may have caused the failure. Latent roots include roots that are organizational or procedural in nature, as well as environmental or other roots that are outside the realm of control.
Physical Roots
This is the physical mechanism that caused the failure, it may be fatigue, overload, wear, corrosion, or any combination of these. For example – corrosion damage of a pipeline, a bearing failed due to fatigue. Failure analysis must start with accurately determining the physical roots, for without that knowledge, the actual human and latent roots cannot be detected and corrected. The analysis may focus on physics of the incident. In the case of TITANIC, the iron rivets were too weak.
The steel plates of the TITANIC buckled as there were excessive stress applied to the hull when the ship hit the iceberg. The strength of steel and hull was not sufficient to prevent the hull from being breached by the steel plates buckling. The failure of the hull steel resulted from brittle fractures caused by the high sulfur content of the steel, the low temperature water on the night of the disaster, and the high impact loading of the collision with the iceberg. When the TITANIC hit the iceberg, the hull plates split open and continued cracking as the water flooded the ship.
Human Roots
The human roots are those human errors that result in the mechanisms that caused the physical failures. What is the error committed that lead to the physical cause?
Someone did the wrong thing knowingly or unknowingly. We asked what caused the person to commit this mistake. A good example is, the TITANIC was sailing full speed ahead despite concerns about icebergs was Smith’s biggest misstep. the TITANIC was actually speeding up when it struck the iceberg as it was White Star chairman and managing director, Bruce Ismay’s, intention to run the rest of the route to New York at full speed, arrive early, and prove the TITANIC’s superior performance. Ismay survived the disaster and testified at the inquiries that this speed increase was approved by Captain Smith and the helmsman was operating under his Captain’s direction.
Latent Roots
All physical failures are triggered by humans. But humans are negatively influenced by latent forces. The goal is to identify and remove these latent forces. Latent causes reveal themselves in layers. One after the other, the layers can be peeled back, similar to peeling the layers off an onion. It often seems as if there is no end. These forces within the organizations are causing people to make serious mistakes.
These are the management system weaknesses that include training, policies, procedures and specifications. People make decision based on these and if the system is flawed, the decision will be in error and will be the triggering mechanism that causes the mechanical failure to occur. These are the management system weaknesses. These include training, policies, procedures and specifications. The most proactive of all industrial action might be to identify and remove these latent traps. But all our attempts to identify and remove these latent causes of failure start at the human. Humans do things “inappropriately,” for “latent” reasons. In order to understand these reasons, we must first understand what “errors” are being made. This puts people at risk – especially the “culprits.” Once exposed. They are in danger of being inappropriately disciplined.
In the TITANIC case, the voyage had been so hastily pushed that the crew had no specific training or conducted any drills in lifesaving on the TITANIC, being unfamiliar with the lifeboats and their davit lowering mechanisms. Compounding this was a decision by White Star management to equip the TITANIC with only half the necessary lifeboats to handle the number of people onboard. The reasons are long established. White