HAZOP Studies | Hazard and Operability Analysis
HAZOP studies 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 are 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 Guide Words
HAZOP Guide Words are simple words which are used to guide and stimulate the brainstorming process and so discover deviations. The guide words shown in the following table are the ones most often used in a HAZOP; some organisations have made this list specific to their operations, to guide the team more quickly to the areas where they have previously found problems.
| HAZOP Study Guidewords |
|---|
| Parameter | Guide Word | 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 |
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