What FMEA is
FMEA stands for failure mode and effects analysis. It is a structured way of asking, for a piece of equipment or a process, three simple questions: how could it fail, what would happen if it did, and what should we do about it? The answers are written in a table so that a team can compare risks and decide where to act first.
The method is widely used in manufacturing, and it grew from the need to think about failures before they happen. Its value lies less in the paperwork than in the conversation. Putting operators, technicians and engineers in a room to describe failures they have seen, or fear, brings out knowledge that normally lives only in people’s heads.
Key terms
- Function. What the item is supposed to do, stated plainly. “Move water from the tank to the process at a steady flow.”
- Failure mode. The way the function can be lost. “No flow,” “reduced flow,” “leaks at the seal.”
- Effect. What happens as a result, for the process, product, people and environment.
- Cause. Why the failure mode might occur, such as wear, contamination or an operating error.
- Current controls. What already exists to prevent or detect it, such as inspection rounds, alarms or interlocks.
A failure mode is the way something fails, not the reason. “Bearing wear” is a cause; “pump stops delivering flow” is a mode. Mixing these up is the most common beginner mistake, and keeping them apart makes the worksheet much more useful.
Ranking the risks
After listing modes, effects and causes, teams usually score each line on three scales, commonly 1 to 10:
- Severity. How serious is the effect?
- Occurrence. How likely is the cause to happen?
- Detection. How likely are we to catch it before it causes the effect? Here a higher number conventionally means worse, meaning harder to detect.
The three scores are multiplied to give a risk priority number. Here is a hypothetical line, with invented scores:
| Failure mode | Cause | Severity | Occurrence | Detection | Priority number |
|---|---|---|---|---|---|
| Seal leaks | Dry running | 6 | 4 | 3 | 72 |
| Pump stops | Bearing seizure | 8 | 3 | 7 | 168 |
The arithmetic is 6 x 4 x 3 = 72 and 8 x 3 x 7 = 168. In this made-up case the second line gets attention first, mainly because a seizure is poorly detected and has a more serious effect.
The number is a guide for discussion, not a measurement. Different teams use different scales, and two very different situations can produce the same product. A line with severity 10 and low occurrence may deserve action even if its total looks modest. Many teams therefore look at severity on its own first, particularly where safety is involved, before considering the combined number.
Running a session
A practical FMEA session usually follows these steps.
- Choose the scope. Pick one system or machine, ideally one that has been ranked as important. Trying to cover a whole plant in one go does not work.
- Gather the right people. Include someone who operates the equipment, someone who maintains it and someone who understands the process. A facilitator keeps the discussion moving.
- Define functions. Write what each part is meant to do before talking about failure.
- List failure modes, effects and causes. Use maintenance records, past breakdowns and the manufacturer’s documentation as prompts.
- Score and rank. Agree the scales beforehand so the team scores consistently.
- Decide actions. For the highest-ranked lines, assign a specific action and an owner.
- Re-score after actions. Check whether the risk has genuinely dropped.
The output is a living document. It should be updated when the equipment is modified, when new failures occur, or when assumptions turn out to be wrong.
What actions come out of it
Actions are where the method pays off. Typical results include:
- adding or changing inspection tasks, such as a periodic check for early warning signs of trouble with shaft seals or bearing wear patterns
- adding a sensor or alarm to improve detection
- changing an operating procedure
- stocking a spare part that has a long lead time
- redesigning or replacing a weak component
- training operators to avoid a damaging practice
Notice that some actions reduce the chance of failure, others reduce the consequences, and others only improve detection. Teams should be clear about which they are choosing.
Limits of the method
FMEA has real weaknesses worth knowing.
- It depends on the knowledge of the people in the room. Failure modes nobody thinks of will not appear.
- Scoring involves judgment, and scores can be inflated or deflated by who speaks loudest.
- It usually examines one failure at a time and so can miss combinations of faults.
- It can become a box-ticking exercise, producing a thick binder that nobody uses.
- The risk priority number can be misleading if treated as exact.
For these reasons it works best alongside other tools, not as a replacement. Investigating real breakdowns through root cause analysis feeds real examples back into the worksheet, and a good record of past work orders helps the team recall what has actually happened.
Starting small
A small plant does not need special software. A spreadsheet with columns for function, mode, effect, cause, scores and actions is enough. Start with a single important machine, perhaps one that has already surfaced in a criticality exercise, and complete a short session. The first worksheet will be imperfect, and that is acceptable; the discussion itself generally exposes gaps in inspection routines and spares.
This article is general information. For any equipment, follow the manufacturer’s manuals, the plant’s lockout and tagout style procedures, local regulations and the judgment of trained, certified personnel.