Question 2 of 7: FMEA in Reliability Engineering, Preliminary Hazard Analysis, and Design Deficiencies Causing Safety Hazards

Question 2: FMEA in Reliability Engineering, Preliminary Hazard Analysis, and Design Deficiencies Causing Safety Hazards (20 marks: 7/6/7)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(i) Failure Modes and Effects Analysis (FMEA) in Reliability Engineering

FMEA is a bottom-up, inductive reliability technique that works from individual components upward, in contrast to fault tree analysis's top-down deductive approach. For each component or subsystem, the analyst systematically identifies:

• Every credible failure mode — the specific way that component can fail (fracture, short circuit, seizure, leak, drift out of tolerance).
• The effect of each failure mode at the local (component), next-higher (subsystem), and system level, tracing how a single component failure propagates through the design.
• Severity, occurrence likelihood, and (where FMECA/quantified) a criticality ranking combining the two, so the analysis produces a prioritized list rather than an undifferentiated catalogue.
• Existing detection/compensating provisions and recommended corrective or design actions for the highest-criticality failure modes.

In reliability engineering specifically, FMEA identifies which components are most critical to overall system reliability, directly informing redundancy decisions, component derating, spare-parts stocking policy, and preventive-maintenance/inspection intervals — because it is exhaustive at the single-component level, it will not miss a failure mode of any component actually included in the analysis, though (unlike FTA) it is weaker at capturing combination or interaction failures across multiple components.

(ii) Elements of a Preliminary Hazard Analysis (PHA)

A preliminary hazard analysis is a qualitative, early-design-stage technique used before detailed design is committed, so hazards can be designed out while change is still cheap. Its standard elements are:

• Identification of hazardous elements/energy sources present in the system concept — hazardous materials, stored energy, moving parts, electrical sources.
• Identification of hazardous events that could result from those elements (a release, an uncontrolled energy transfer, a structural failure).
• Potential causes of each hazardous event, at a conceptual, not yet component-level, of detail.
• Potential effects and severity of each hazardous event on personnel, equipment, and the environment.
• Existing or planned safeguards already assumed in the concept design.
• A risk ranking (typically a probability × severity matrix) used to prioritize which hazards need design attention first.
• Recommended actions feeding directly into the detailed design phase, and into which hazards warrant a more detailed technique (FMEA, FTA, HAZOP) later.

(iii) Design Deficiencies or Defects Causing Product or Process Safety Hazards

• Inadequate factor of safety in structural, pressure, or load-bearing elements relative to actual operating and foreseeable overload conditions.
• Failure to anticipate foreseeable misuse — a design that is safe only under ideal, textbook operating conditions but not under the way the product or process is actually used in the field.
• Inadequate or absent guarding designed into the product, rather than treated as an accessory added later, leaving points of operation or power transmission exposed.
• Poor human-factors/ergonomic design — controls, displays, or access points that invite an error mode the operator cannot help but eventually commit.
• Incorrect material selection for the actual service environment (corrosion, fatigue, temperature extremes not accounted for).
• Absence of fail-safe behaviour — a component or control-system failure that defaults to a hazardous state rather than a safe one.
• Missing or inadequate interlocks preventing hazardous operation under an unsafe configuration (guard open, pressure out of range).
• Inadequate warnings and instructions for hazards that could not practically be designed out entirely.
• Poor provision for maintenance access, which pushes maintainers toward defeating guards or working in awkward, hazardous positions simply to reach the equipment.