HAZOP - Hazard and Operability Studies

HAZOPs are used to identifying both hazards and operability problems. Although hazard identification is the main focus, operability problems are also identified to the extent that they have the potential to lead to safety or environmental hazards, or have a negative impact on plant profitability.
 

Hazards

Hazards are any operation that could possibly cause a release of toxic, flammable or explosive chemicals (including oil and gas) or any action that could result in injury to personnel or harm to the environment.
 

Operability

Operability considers any operation inside the design envelope that would cause a shutdown that could possibly lead to a violation of environmental, health or safety regulations or negatively impact profitability.
 

The HAZOP Process

The HAZOP team focuses on specific portions of the process called "nodes". Generally these are identified from the P&ID prior to the study by the Hazop chairman. A process parameter is identified, e.g. flow. Then a series of guidewords is combined with the parameter "flow" to create a deviation. For example, the guideword "no" is combined with the parameter flow to give the deviation "no flow". The team then focuses on listing all the credible causes of a "no flow" deviation beginning with the cause that can result in the worst possible consequence the team can think of at the time. Once the causes are recorded the team lists the consequences, safeguards and any recommendations deemed appropriate. The process is repeated for the next deviation and so on until completion of the node. The process is repeated for all other nodes.
 

HAZOP Study Guidewords
Guideword	Deviation	Examples of Potential Problems
FLOW	NO/LESS	Hi Pressure: stagnant lines, instrument tapping blockage, filter blockage.
	MORE	Undesireable flow, leakages, Hi velocity/erosion, seal/gasket failure, overflows
	REVERSE	Utility contamination, reverse rotation
TEMPERATURE	HIGH	Thermal expansion, location of instrumentation, fire
	LOW	Hydrates/freezing, flashing liquids, depressurisation
PRESSURE	HIGH	Hydraulic surge, gas breakthrough, tube rupture, thermal expansion
	LOW	Air ingress, vacuum failure
LEVEL	HIGH	Vessel overfill, hi static head
	LOW	Dead legs, cavitation, gas blowby
COMPOSITION	CHANGE	Contamination, slugging, corrosion products
ERROSION	HIGH	Localised failure, chocked valves
DEPOSITION	PROBLEMS	Sand, wax
CORROSION	HIGH	Dissimiliar materials, under lagging, stress corrosion
SERVICES	FAILURE	Power, heating/cooling medium, instrument air, HVAC
STARTUP / SHUTDOWN	PROBLEMS & REQUIREMENTS	Human error, sequential operations, ESD
MAINTENANCE, INSPECTION / TEST	PROBLEMS & REQUIREMENTS	Access, layout, isolation, lifting, vessel entry
OTHER	An opportunity for the chair person to prompt team members to raise any other concerns