The other evaluation tool mentioned in the Risk Analysis discussion is Fault Tree Analysis (FTA). The fault tree explicitly shows all the different relationships that are necessary to trigger the undesired state. Through the process of constructing the fault tree, you will gain a thorough understanding of the basic causes that led to the current situation. It also provides a framework for a thorough qualitative and quantitative evaluation of the event. This method is backward looking, and uses a top-down approach which can be used to:
- Understand the logic that lead to the undesired state
- Provide evidence of compliance to the requirements – both internal and regulatory
- Prioritize the items contributing to the undesired state, as a way to identify which items need to be addressed first
- Monitor the safety performance of the device
- Optimize resources while minimizing the amount needed
- Act as a diagnostic tool to identify and correct the causes of the undesired state
With FTA, your initial step is to identify the undesired state. From there, you work backwards to figure out what could cause this end-result – there will most likely be more than one possible cause (see diagram below). These are either “and” or “or” situations (for example, the cause of the machine breaking was this AND that; the machine could have broken because of this situation OR that one). FTA involves 5 steps:
- Define the undesired state to study: Defining the undesired state can be very difficult to identify, even if it is obvious to observe.
- Obtain an understanding of the system: Once the undesired state is identified, all causes that could have led to this event are studied and analyzed. Each of these causes is numbered and sequenced in the order of occurrence and then used in constructing the fault tree.
- Construct the fault tree: The fault tree is based on AND and OR identifiers, which define the major characteristics in the tree.
- Evaluate the fault tree: Evaluate and analyze the results to identify any areas for improvement.
- Control the hazards identified: All possible methods are pursued to decrease the probability of the undesired state occurring again.