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5-Why Analysis

Risk & Failure Analysis
mechanicalprocesselectrical

Definition

An iterative root cause analysis technique that repeatedly asks 'Why?' (typically five times, though the actual number varies) to peel away successive layers of symptoms and intermediate causes until the fundamental root cause is identified. Each answer forms the basis of the next question. The method is effective for straightforward cause-and-effect chains but may need supplementing with other techniques for complex multi-causal events.

Context

A rapid RCA technique used for moderate-severity events where a single causal chain is suspected. It is often the starting point for investigation before escalating to more rigorous methods like fault tree analysis. In Reliatic, 5-Why analysis is one of the structured RCA templates available.

Examples

  1. Why did the pump fail? Bearing seized. Why? No lubrication. Why? Oil reservoir empty. Why? Oil leak at drain plug. Why? Drain plug gasket degraded and not replaced during last PM. Root cause: PM procedure does not include drain plug gasket replacement.
  2. A 5-Why analysis of a control valve failure identifies the root cause as inadequate valve sizing during the original design phase, not a maintenance deficiency.

Applicable Standards

  • IEC 62740:2015
  • Lean Six Sigma

Related Terms

Root Cause Analysis(RCA)

A systematic investigation methodology used to identify the fundamental underlying cause(s) of a failure, incident, or undesired outcome. RCA goes beyond the immediate or proximate cause to uncover the latent organizational, procedural, or design factors that created the conditions for the event. Common RCA techniques include 5-Why analysis, fishbone (Ishikawa) diagrams, fault tree analysis, and barrier analysis.

Fishbone Diagram

A cause-and-effect analysis tool (also called Ishikawa diagram or cause-and-effect diagram) that visually organizes potential causes of a problem into major categories branching from a central spine. Standard categories for manufacturing/maintenance include: Man (People), Machine (Equipment), Method (Procedure), Material, Measurement, and Mother Nature (Environment). Each category is explored for contributing causes.

Corrective Action

An action taken to eliminate the root cause of a detected nonconformity, failure, or undesirable situation to prevent its recurrence. Corrective actions address why something went wrong, not just the immediate symptoms. They are distinguished from immediate actions (containment) and preventive actions (proactive measures for potential future problems).

Where this appears in Reliatic

This concept is used in the FMEA & Risk module.