HAZOP - Basic Understanding

Hazard and operability studies are a methodology for identifying and dealing with potential processes, particularly those which would create a hazardous situation or severe impairment of the process. It is commonly known as HAZOP.

Definitions
HAZARD any operation that could possibly cause a catastrophic release of toxic, flammable or explosive chemicals or any action that could result in injury to personnel.

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


HAZOP Process
The HAZOP focuses on specific portions of the process called “nodes”. Generally these are identified from the P&ID of the process. A process parameter is identified, say flow, and an intention is created for the node under consideration.

Then a series of guidewords is combined with the parameter “flow” to create deviations. For Example, the guideword “no” is combined with the parameter flow to give the deviation “no flow”. Then focus is on listing all the credible causes of a “no flow” deviation beginning with the cause that can result in the worst possible consequence one can think of.

Once the causes are recorded, a list is made of the consequences, safeguards and any recommendations deemed appropriate. The process is repeated for the next deviation and so on until completion of the node.



Guidewords, Selection of Parameters and Deviations
The HAZOP process creates deviations from the process design intent by combining guide words (no, more, less, etc) with process parameters resulting in a possible deviation from design intent.



SPECIFIC PARAMETERS
These include Flow, Pressure, Temperature, Level, Time, Agitation, Reaction, Start-Up/Shut-Down, Draining/Venting, Utility Failure(instrument air, power), Maintenance, Vibrations etc.

Concept of Point Of Reference
When defining nodes and performing a HAZOP on a particular node it is useful to use the concept of point of reference (POR) when evaluating deviations.

Screening for Causes of Deviations
It is necessary to be thorough in listing causes of deviations. A deviation is considered realistic if there are sufficient causes to believe the deviation can occur. However, only credible causes should be listed.

There are three basic types of causes. They are:

• Human error which are acts of omission or commission by an operator, designer, constructor or other person creating a hazard that could possibly result in a release of hazardous or flammable material.


• Equipment failure in which a mechanical, structural or operating failure results in the release of hazardous or flammable material.


• External Events in which items outside the unit being reviewed affect the operation of the unit to the extent that the release of hazardous or flammable material is possible. External events include upsets on adjacent units affecting the safe operation of the unit (or node) being studied, loss of utilities, and exposure from weather and seismic activity.

By Associate Writer : Ms Nidhi Gupta