HAZOP Guide words and Example causes:

NO FLOW : 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.

REVERSE FLOW : Defective check valve - siphon effect - incorrect pressure differential - two way flow -emergency venting - incorrect operation - in line spare equipment - etc.

MORE FLOW : 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.

LESS FLOW : Line restrictions - filter blockage - defective pumps - fouling of vessels, valves, orofice plates - density or viscosity changes - etc.

MORE LEVEL : Outlet isolated or blocked - inflow greater than outflow - control failure - faulty level measurement - gravity liquid balancing - etc.

LESS LEVEL : Inlet flow stops - leak - outflow greater than inflow - control failure - faulty level measurement - draining of vessel - etc.

MORE PRESSURE : 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.

LESS PRESSURE : 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.

MORE TEMPERATURE : 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 - etc.lation procedures for relief valves -

LESS TEMPERATURE : Ambient conditions - reducing pressure - fouled or failed exchanger tubes - loss of heating - depressurisation of liquefied gas - Joule / Thompson effect - etc.

MORE VISCOSITY : Incorrect material or composition - incorrect temperature - high solids' concentration - setting of slurries - etc.

LESS VISCOSITY : Incorrect material or composition - incorrect temperature - solvent flushing -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.

RELIEF : 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.

INSTRUMENTATION Control philosophy - 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.

SAMPLING : Sampling procedure and operator safety -time for analysis result - caliberation of automatic samplers - reliability / accuracy of representative sample - diagnosis of result - loss of sample flow - etc.

CORROSION/ EROSION : Cathodic protection arrangements - internal / external corrosion protection - engineering specifications - zinc embrittlement - stress corrosion cracking - fluid velocities - etc.

SERVICE FAILURES : 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.

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.