Compare methods

	Preliminary Hazard Analysis	FMEA	Hazard and Operability Study (HAZOP)	Semi-Quantitative Risk Matrix Analysis
Field	Disaster Studies	Decision-making	Disaster Studies	Disaster Studies
Family	Process / pipeline	MCDM	Process / pipeline	Process / pipeline
Year of origin	2008	1995	2016	2019
Originator	Military system-safety practice (MIL-STD-882); codified in CCPS guidelines	Stamatis, D. H.	ICI (1960s practice); codified in IEC 61882 and CCPS guidelines	ISO/IEC 31010 (standardized practice); critical analysis by L. A. Cox
Type	Early-stage qualitative hazard identification and ranking	Risk priority via product of O·S·D ratings	Structured guide-word deviation analysis of process designs	Semi-quantitative consequence-likelihood rating and ranking pipeline
Seminal source	Center for Chemical Process Safety (CCPS). (2008). Guidelines for Hazard Evaluation Procedures (3rd ed.). Wiley-AIChE, Hoboken, NJ. ISBN: 9780471978152	Stamatis, D. H. (1995). Failure Mode and Effect Analysis: FMEA from Theory to Execution. ASQ Quality Press ISBN: 978-0-87389-300-8	International Electrotechnical Commission. (2016). IEC 61882:2016 Hazard and operability studies (HAZOP studies) — Application guide (2nd ed.). IEC, Geneva.	International Organization for Standardization. (2019). IEC 31010:2019 Risk management — Risk assessment techniques. ISO/IEC, Geneva.
Aliases	PHA, Preliminary Hazard List Analysis, Early Hazard Analysis, Conceptual Hazard Analysis	—	HAZOP Study, Hazard and Operability Analysis, Guide-Word HAZOP, Deviation Analysis	Risk Matrix Analysis, Consequence-Likelihood Matrix, Probability-Impact Matrix, Risk Rating Matrix
Related	3	8	3	3
Summary	Preliminary hazard analysis, or PHA, is an early-stage, qualitative technique for identifying the hazards inherent in a system before its design is detailed enough for more rigorous methods, and for ranking those hazards so that the riskiest receive attention first. Conducted in the concept or preliminary design phase, it works from the system's energy sources, hazardous materials, intended functions and operating environment to compile a hazard list, postulate how each hazard could lead to harm, and assign each a risk level from severity and likelihood ratings. The CCPS Guidelines for Hazard Evaluation Procedures present it as a foundational hazard-evaluation method, and ISO/IEC 31010 includes it among standard risk-assessment techniques. Because it is applied when changing the design is still cheap, the PHA's chief value is steering early design decisions and identifying which hazards warrant deeper study by methods such as HAZOP, FMEA or quantitative risk assessment.	FMEA (Failure Mode and Effects Analysis) is a ranking multi-criteria decision-making (MCDM) method introduced by Stamatis, D. H. in 1995. It turns a decision matrix of alternatives scored on multiple criteria into a structured, reproducible result.	A Hazard and Operability Study, or HAZOP, is a structured, team-based examination of a process design that systematically searches for deviations from the design intent and judges whether each deviation could create a hazard or impair operability. Its signature device is the guide word: terms such as 'No', 'More', 'Less', 'Reverse' and 'Other than' are combined with process parameters like flow, pressure and temperature at each part of the system to provoke a complete and disciplined set of 'what if it went wrong this way?' questions. IEC 61882 is the international application guide that defines the technique, its guide words and its workflow, while the CCPS Guidelines for Hazard Evaluation Procedures situates HAZOP among the core hazard-evaluation methods of process safety. The method's power lies in its rigorous, qualitative completeness: by walking every node and every guide word, a multidisciplinary team aims to leave no credible deviation unconsidered.	Semi-quantitative risk matrix analysis rates each risk on ordinal likelihood and consequence scales and combines the two in a grid to assign a risk level that drives prioritization. It is the workhorse of practical risk management: ISO/IEC 31010 lists the consequence-likelihood matrix among its standard techniques precisely because it lets analysts compare many disparate risks quickly without the data demands of a full quantitative model. The 'semi-quantitative' label captures its hybrid character — ordinal categories such as 'rare' or 'catastrophic' are anchored to rough numeric bands, giving more discipline than a purely verbal judgment but far less than a probabilistic calculation. The method's popularity is matched by sharp critique: L. A. Cox's 2008 analysis in Risk Analysis showed that poorly designed matrices can rank risks incorrectly, compress very different risks into the same cell, and even perform worse than random, making careful scale design and consistency checks essential rather than optional.