Failure mode and effects analysis (FMEA) is also known as “failure Modes”. It is referred as one of the most systematic technique for failure analysis & hazard analysis. It was developed in 1950s by reliability engineers to evaluate and understand problems that might have arise due to military systems malfunction. When it comes to process safety management analysis FMEA is often the first step of reliability study of any system. In hazard risk assessment we review many components with the help of FMEA, components like assemblies, and subsystems as possible to identify failure modes, and their causes and effects, the all are reviewed in the process. A FMEA sheet is prepared and every variation of components, failure modes and their resulting effects on the entire system is recorded. All these worksheets have multiple variations in order to get the most accurate results. This industrial safety technique when calculated on the basis of mathematical failure rate model, it turns out to be the best quantitative & qualitative analysis
WHEN TO USE FMEA IN PRELIMINARY HAZARD ANALYSIS
- When a process, product, or service is being designed or redesigned, after risk management process
- When an existing process, product, or service is being applied in a new way
- Before developing control plans for a new or modified process
- When improvement goals are planned for an existing process, product, or service
- When analyzing failures of an existing process, product, or service
- Periodically throughout the life of the process, product, or service
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FMEA PROCEDURE FOR PROCESS SAFETY MANAGEMENT
- Assemble a cross-functional team of people with diverse knowledge about the process, product or service, and customer needs. Functions often included are: design, manufacturing, quality, testing, reliability, maintenance, purchasing (and suppliers), sales, marketing (and customers), and customer service.
- Identify the scope of the FMEA. Is it for concept, system, design, process, or service? What are the boundaries? How detailed should we be? Use flowcharts to identify the scope and to make sure every team member understands it in detail.
- Fill in the identifying information at the top of your FMEA form.The remaining steps ask for information that will go into the columns of the form.
- Identify the functions of your scope. Ask, “What is the purpose of this system, design, process, or service? What do our customers expect it to do?” Name it with a verb followed by a noun. Usually one will break the scope into separate subsystems, items, parts, assemblies, or process steps and identify the function of each.
- For each function, identify all the ways failure could happen. These are potential failure modes. If necessary, go back and rewrite the function with more detail to be sure the failure modes show a loss of that function.
- For each failure mode, identify all the consequences on the system, related systems, process, related processes, product, service, customer, or regulations. These are potential effects of failure. Ask, “What does the customer experience because of this failure? What happens when this failure occurs?”
- Determine how serious each effect is. This is the severity rating, or S. Severity is usually rated on a scale from 1 to 10, where 1 is insignificant and 10 is catastrophic. If a failure mode has more than one effect, write on the FMEA table only the highest severity rating for that failure mode.
- For each failure mode, determine all the potential root causes
- For each cause, determine the occurrence rating, or O. This rating estimates the probability of failure occurring for that reason during the lifetime of your scope. Occurrence is usually rated on a scale from 1 to 10, where 1 is extremely unlikely and 10 is inevitable. On the FMEA table, list the occurrence rating for each cause.
- For each cause, identify current process controls. These are tests, procedures or mechanisms that you now have in place to keep failures from reaching the customer. These controls might prevent the cause from happening, reduce the likelihood that it will happen or detect failure after the cause has already happened but before the customer is affected.
- For each control, determine the detection rating, or D. This rating estimates how well the controls can detect either the cause or its failure mode after they have happened but before the customer is affected. Detection is usually rated on a scale from 1 to 10, where 1 means the control is absolutely certain to detect the problem and 10 means the control is certain not to detect the problem (or no control exists). On the FMEA table, list the detection rating for each cause.
- Optional for most industries:Ask, “Is this failure mode associated with a critical characteristic?” (Critical characteristics are measurements or indicators that reflect safety or compliance with government regulations and need special controls.) If so, a column labeled “Classification” receives a Y or N to show whether special controls are needed. Usually, critical characteristics have a severity of 9 or 10 and occurrence and detection ratings above 3.
- Calculate the risk priority number, or RPN, which equals S × O × D. Also calculate Criticality by multiplying severity by occurrence, S × O. These numbers provide guidance for ranking potential failures in the order they should be addressed.
- Identify recommended actions. These actions may be design or process changes to lower severity or occurrence. They may be additional controls to improve detection. Also note who is responsible for the actions and target completion dates.
As actions are completed, note results and the date on the FMEA form. Also, note new S, O, or D ratings and new RPNs.