Compare methods

	Hazard and Operability Study (HAZOP)	Bow-Tie Risk Analysis	FMEA	Preliminary Hazard Analysis
Field	Disaster Studies	Disaster Studies	Decision-making	Disaster Studies
Family	Process / pipeline	Process / pipeline	MCDM	Process / pipeline
Year of origin	2016	2016	1995	2008
Originator	ICI (1960s practice); codified in IEC 61882 and CCPS guidelines	Synthesized review by de Ruijter & Guldenmund; standardized in ISO/IEC 31010	Stamatis, D. H.	Military system-safety practice (MIL-STD-882); codified in CCPS guidelines
Type	Structured guide-word deviation analysis of process designs	Barrier-centred cause-consequence risk diagram and analysis	Risk priority via product of O·S·D ratings	Early-stage qualitative hazard identification and ranking
Seminal source	International Electrotechnical Commission. (2016). IEC 61882:2016 Hazard and operability studies (HAZOP studies) — Application guide (2nd ed.). IEC, Geneva.	de Ruijter, A., & Guldenmund, F. (2016). The bowtie method: A review. Safety Science, 88, 211-218.	Stamatis, D. H. (1995). Failure Mode and Effect Analysis: FMEA from Theory to Execution. ASQ Quality Press ISBN: 978-0-87389-300-8	Center for Chemical Process Safety (CCPS). (2008). Guidelines for Hazard Evaluation Procedures (3rd ed.). Wiley-AIChE, Hoboken, NJ. ISBN: 9780471978152
Aliases	HAZOP Study, Hazard and Operability Analysis, Guide-Word HAZOP, Deviation Analysis	Bowtie Method, Bow-Tie Diagram, Barrier Analysis (Bow-Tie), Cause-Consequence Barrier Model	—	PHA, Preliminary Hazard List Analysis, Early Hazard Analysis, Conceptual Hazard Analysis
Related	3	3	8	3
Summary	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.	Bow-tie risk analysis is a barrier-centred technique that places a single top event — the moment control over a hazard is lost — at the knot of a diagram, branches its possible causes to the left and its possible consequences to the right, and arrays along each pathway the barriers meant to prevent or mitigate it. The shape gives the method its name: the fanning threats and consequences form the two halves of a bow tie around the central event. de Ruijter and Guldenmund's 2016 review in Safety Science documents how the approach grew popular precisely because it combines, in one readable picture, the cause logic of a fault tree and the consequence logic of an event tree while foregrounding the controls that managers actually own. ISO/IEC 31010 lists bow-tie analysis among standard risk-assessment techniques, used both qualitatively to communicate risk and barrier coverage and quantitatively to estimate consequence likelihoods.	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.	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.