Hazard and Operability Analysis (HAZOP)

Scenario	Guide Word	Cause	Effect / Consequence	C	F	RPN	Protection / Mitigation	F	RPN	Fault Tolerance Time	Sensor	Final Element	Action SIF	Verification

C=Criticality / F = Frequency / SIF = Safety Instrumented Function

Guidewords to consider during HAZOP

Guide Word	Deviation	Example
Flow	More	Increased pumping capacity - increased suction pressure - reduced delivery head - greater fluid density - exchanger tube leaks - restriction orifice plates deleted - cross connection of systems - control faults - control valve trim changed - running two pumps - etc.
	No	Wrong routing - blockage - incorrect slip plate - incorrectly fitted check valve - burst pipe - large leak - equipment failure (isolation valve, pump vessel , etc.) - incorrect pressure differential - isolation in error - etc
	Less	Line restrictions - filter blockage - defective pumps - fouling of vessels, valves, orifice plates - density or viscosity changes - etc.
	Reverse	Defective check valve - siphon effect - incorrect pressure differential - two way flow -emergency venting - incorrect operation - in line spare equipment - etc.
	Other
Pressure	More	Surge problems - connection to high pressure system - gas breakthrough (inadequate venting) - defective isothermal overpressure - positive displacement pumps - failed open PCV's design pressures, specifications of pipes, vessels, fittings, instruments - etc.
	No	See Less
	Less	Generation of vacuum condition - condensation - gas dissolving in liquid - restricted pump / compressor suction line - undetected leakage - vessel drainage - blockage of blanket gas reducing valve etc.
	Other
Level	More	Outlet isolated or blocked - inflow greater than outflow - control failure - faulty level measurement - gravity liquid balancing - etc.
	Less	Inlet flow stops - leak - outflow greater than inflow - control failure - faulty level measurement - draining of vessel - etc.
	Other
Temperature	More	Ambient conditions - fouled or failed exchanger tubes - fire situation - cooling water failure - defective control - heater control failure - internal fires - reaction control failures - heating medium leak into process - escalation procedures for relief valves
	Less	Ambient conditions - reducing pressure - fouled or failed exchanger tubes - loss of heating - depressurization of liquefied gas - Joule / Thompson effect - etc.
	Other
Viscosity	More	Incorrect material or composition - incorrect temperature - high solids' concentration - setting of slurries - etc.
	Less	Incorrect material or composition - incorrect temperature - solvent flushing -etc.
	Other
Relief	Other	Relief philosophy (process / fire etc) - type of relief device and reliability - relief valve discharge location - pollution implications - two phase flow - effect of de-bottlenecking on relief capacity - inlet and outlet piping -etc.
Samples	Other	Sampling procedure and operator safety -time for analysis result - calibration of automatic samplers - reliability / accuracy of representative sample - diagnosis of result - loss of sample flow - etc.
Instruments - Control philosophy	Other	Location of instruments -response time - set points of alarms and trips and ability to change - time available for operator intervention - alarm and trip testing - fire protection - trip / control amplifiers - panel arrangement and location - auto / manual facility and human error - fail safe philosophy - etc.
Corrosion / Erosion	Other	Cathodic protection arrangements - internal / external corrosion protection - engineering specifications - zinc embrittlement - stress corrosion cracking - fluid velocities - etc.
Service	Other	Failure of instrument air / steam / nitrogen / cooling water / hydraulic power / water or other - contamination of instrument air, nitrogen etc. - telecommunication - heating and ventilating systems - computers etc.
Composition change		Leaking isolation valves - leaking exchanger tubes - phase change - incorrect feedstock / specification - inadequate quality control - process control upset - reaction intermediates / by-products - settling of slurries - etc.
Contamination		Leaking exchanger tubes - leaking isolation valves - incorrect operation of system - interconnected systems (especially services, blanket systems) - effect of corrosion - wrong additives - ingress of air - shutdown and start up conditions - grade change - etc.
Abnormal operation		Purging - flushing - start-up - normal shutdown - emergency shutdown - emergency operations - inspection of operating machines - guarding of machinery - etc.
Maintenance		Isolation philosophy -drainage - purging - cleaning - drying - slip plates - access -rescue plan - training - pressure testing - work permit
Ignition		Grounding arrangements - insulated vessels / equipment - low conductance fluids - splash filling of vessels - insulated strainers and valve components - dust generation - powder handling equipment - electrical classification - flame arrestors - hot work - hot surfaces - auto ignition - pyrophoric materials - etc.
Spare equipment		Installed / non-installed spare equipment - availability of spares - modified specifications - storage of spares - catalogue of spares - test running of spare equipment - etc.
Safety		Toxic properties of process materials - fire and gas detection system - alarms - emergency shutdown arrangements - fire fighting response time - emergency and major emergency training - contingency plans - T.L.V.'s of process materials - first aid / medical resources - effluent disposal - hazards created by others ( adjacent storage areas / process plant etc.) - testing of emergency equipment - compliance with local / national regulations - etc.

PRIORITIZATION OF SAFETY, HEALTH AND ENVIRONMENT ISSUES

ASSESSMENT KEY (ALARP)

CONSEQUENCE CATEGORY	PROPOSAL FOR EXPENDITURE - SAFETY, HEALTH OR ENVIRONMENT IMPROVEMENT
CATEGORY 5 EXTREMELY SERIOUS CONSEQUENCE	TOLERABLE BAND
CATEGORY 4 MAJOR CONSEQUENCES		TOLERABLE BAND		UNACCEPTABLE
CATEGORY 3 SEVERE CONSEQUENCES			TOLERABLE BAND
CATEGORY 2 SERIOUS CONSEQUENCES		TOLERABLE