What Is HAZOP?

Quick Answer

A HAZOP (Hazard and Operability Study) is a structured, systematic method for identifying potential hazards and operability problems in a process plant design. A multidisciplinary team examines each section of the process using standardized guide words (No, More, Less, Reverse, etc.) applied to process parameters (flow, pressure, temperature, level) to identify deviations from the design intent. For each deviation, the team evaluates causes, consequences, existing safeguards, and recommends additional protective measures if needed.

HAZOP Methodology

The HAZOP technique was developed by ICI in the 1960s and is now the globally accepted standard for process hazard analysis in the oil and gas, chemical, and petrochemical industries. It is typically conducted on P&IDs during the detailed engineering phase, after the process design is substantially complete but before construction begins, allowing design changes to be implemented at reasonable cost.

The HAZOP examines the process node by node. A node is a section of the process with a defined design intent (e.g., “transfer crude oil from separator V-101 to heater E-101 at 15 barg and 80°C”).

HAZOP Element	Description	Example
Node	Section of process being studied	V-101 outlet to E-101 inlet
Design intent	Normal operating condition	Flow at 150 m3/hr, 15 barg, 80°C
Guide word	Deviation keyword	NO, MORE, LESS, REVERSE, OTHER THAN
Parameter	Process variable	Flow, pressure, temperature, level, composition
Deviation	Guide word + parameter	NO FLOW, MORE PRESSURE, LESS TEMPERATURE
Cause	What could cause the deviation	Pump trip, valve closed, exchanger fouling
Consequence	What happens if the deviation occurs	Vessel overpressure, dry running pump, off-spec product
Safeguard	Existing protection	PSV, high-pressure alarm, shutdown system
Recommendation	Additional action needed	Add high-level trip on V-101, add check valve on pump discharge
Action party	Responsible discipline	Process, instrumentation, operations

HAZOP Guide Words

The standard guide words, applied systematically to each process parameter, generate a comprehensive list of deviations:

Guide Word	Meaning	Applied to Flow	Applied to Pressure
NO / NOT	Complete negation	No flow	No pressure
MORE	Quantitative increase	More flow (high flow)	More pressure (overpressure)
LESS	Quantitative decrease	Less flow (low flow)	Less pressure (underpressure)
REVERSE	Opposite direction	Reverse flow	Vacuum
AS WELL AS	Additional element	Contamination in flow	Two-phase flow
PART OF	Component missing	Loss of one component	Partial blockage
OTHER THAN	Complete substitution	Wrong material routed	Different phase
EARLY / LATE	Time deviation	Batch too early	Delayed response

HAZOP Team

A HAZOP study requires a multidisciplinary team:

• HAZOP chairman/facilitator: Leads the study, ensures systematic coverage (independent, experienced in HAZOP methodology)
• Scribe/recorder: Documents all deviations, causes, consequences, and recommendations
• Process engineer: Explains the design intent and process conditions
• Instrument/control engineer: Identifies existing instrumented safeguards
• Operations representative: Provides practical plant operating experience
• Mechanical/piping engineer: Addresses equipment and piping design issues
• HSE representative: Ensures safety and environmental aspects are covered

Common Mistake

Conducting a HAZOP too early (before P&IDs are mature) wastes time because the study must be repeated after major design changes. Conducting it too late (after equipment is ordered and construction started) makes it prohibitively expensive to implement recommendations. The optimal timing is when P&IDs are at IFD (Issued for Design) or IFA (Issued for Approval) status—approximately 60-70% engineering completion. At this stage, the design is stable enough for meaningful analysis but flexible enough to accommodate changes.

HAZOP is required by international safety standards (IEC 61882) and is typically a mandatory deliverable in EPC project execution. HAZOP recommendations often drive the design of Safety Instrumented Systems (SIS) and the determination of Safety Integrity Levels (SIL).

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