Hazard and Operability Studies (HAZOP) is a technique (almost like brainstorming) whereby a group of well informed people aim to identify all the ways in which hazards may appear in a system.
Its purpose is to:-
Establish hazardous failure modes, and
A measure of their effect by a systematic examination of the system and its components.
Notes on Hazop
HAZOP is applicable at all stages of the system lifecycle although it is of limited use until a relatively detailed description of the system has been developed.
Typically the selected members of the HAZOP team will have had previous experience of such systems, and complement one another (are from different backgrounds) so that the benefits of the team approach are apparent.
The Hazop Process
A disciplined and systematic approach is adopted to ensure there are no obvious omissions.
Each component of the system and each hazard is considered in turn.
The team employs a series of guidewords and variables to facilitate the process.
Questions arise about the design and these act as the basis of the formulation of solutions to mitigate the hazards that are identified.
Example in use of guidelines:
in analysing pipelines in a chemical plant, the guidewords:-
NO LESS MORE
could be applied to the variables
FLOW PRESSURE TEMPERATURE
to identify possible hazards.
Notes on hazop
The basis (paperwork or model of the system) of the activity must be accurate.
The HAZOP process for a large system may take several months - each major component is typically considered in turn.
A database of previous disasters can be used as a reminder of options to be looked at.
It is possible for the team to get 'carried away' and install expensive equipment to compensate for possible hazards.
Proposals for change should go through the HAZOP process.
The HAZOP process can be viewed as a process of looking at possible disturbances (events that may cause failure) to the system and considering the consequences.
The more formal the process the better. This can significantly influence the effectiveness of the whole process and the outcomes.
Some practitioners draw up definitions of terms that may cause ambiguity. For example some, several, many,...
Likewise, checklists of possible disturbances are often provided; these tend to be application dependent.
But other lists can also be present to cover other unusual situations. For example, considerations of the effects of holidays on plant operation, strikes, shift changes, illness,...
Prior to the study, agreed checklists are compiled to provide a systematic basis for the study.
Risk identification process
A summary of the risk identification process may be as follows:-
use Preliminary Hazard Analysis techniques at the appropriate stage of development
use the HAZOP process
use Fault Tree Analysis for situations where control is involved or a service has to be provided