Hazard Study 3 HAZOP Preliminaries

1 What the HAZOP Does. The HAZOP process is there to identify those situations which the designer has forgotten or ignored and which could lead to a hazard. It often will be looking for complex and abstruse failures and situations and rare events. It should be borne in mind that even rare events can represent considerable risks (recalling that risk is a combination of the consequences of an event and its likelihood). Despite often bad publicity, the chemical industry is a very safe one and rare events need to be addressed. 

3 Study Team Composition. HAZOP study is a team effort. The team consists of the leader, a scribe and working team members. The ideal size seems to be 6-7 (including the leader and scribe). The 

It is important that the following expertise and functions are present on the team - of course, one person may carry out more than one function. For different types of process the list may be modified, or people can join the discussion when sections of interest to them are being examined. 

Leader - who will direct and control the study. The leader should be trained and independent. 

Scribe - who will record the discussion (see the separate section on recording). 

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Many companies and facilities use the term HAZID or Hazard Identification for preliminary studies. Generally, HAZIDs are less formal and thorough than a full HAZOP, and are often conducted during the early stages of a project when it is important to identify major potential problems, without having to go into a lot of detail. 

In the previous chapter, it was established that in industry, plant hazards can cause harm to property (plant—machinery, asset), people, or the environment. So, it is important to develop some means of analyzing these and come up with a solution. Unfortunately, it is not as straightforward as it sounds. There are plenty of plant hazard analysis (PHA) techniques and each of them has certain strengths and weaknesses. Also each specific plant and associated hazard has specific requirements to be matched so that hazard analysis will be effective. In this chapter, various hazards (in generic terms) will be examined to judge their importance, conditions, quality, etc. so that out of so many techniques available for PHA it is possible to select which one is better (not the best because that needs to be done by experts specifically for the concerned plant) suited for the type of plant. So, discussion will be more toward evaluation of PHA techniques. Some PHA is more suited for process safety management (PSM) and is sometimes more applicable for internal fault effects [e.g., hazard and operability study (HAZOP)]. In contrast, hazard identification (HAZID) is applicable for other plants, especially for the identification of external effects and maj or incidents. HAZID is also covered in this chapter. As a continuation of the same discussion, it will be better to look at various aspects of risk analysis with preliminary ideas already developed in the previous chapter. In risk analysis risk assessment, control measures for safety management systems (SMSs) will be discussed to complete the topic. 

A hazard and opeiabilily study (Hazop), is a standard hazard analysis technique used worldwide in the process industries in the preliminary safely assessment of new systems or modihcations to existing ones. The Hazop study is a detailed examination, by a group of specialists, of components within a system to determine what would happen if that component were to operate outside its normal design mode. Each ccmponent will have one or more parameters associated with its operation such as pressure, flow rate, or electrical power. The Hazop study looks at each parameter in turn and uses guide words to list the possible off-normal behaviour such as more , less , high , low , yes , or no . The effect of such behaviour is then assessed. 

What if Approaches Hazind and Operability (HAZOP) Studies Preliminary Hazard Analysis (PLHA) Process Hazard Analysis (PHA)... 

Several qualitative approaches can be used to identify hazardous reaction scenarios, including process hazard analysis, checklists, chemical interaction matrices, and an experience-based review. CCPS (1995a p. 176) describes nine hazard evaluation procedures that can be used to identify hazardous reaction scenarios-checklists, Dow fire and explosion indices, preliminary hazard analysis, what-if analysis, failure modes and effects analysis (FMEA), HAZOP study, fault tree analysis, human error analysis, and quantitative risk analysis. 

XI. Preliminary Process Safety Studies A simple what-if study is generally performed to identify major safety concerns, if any, with the project scope. FMEA (failure modes and effects analysis) or HAZOP (Hazard and operability) study can also be performed if sufficient design documents are available. Otherwise, these detailed studies will be conducted in FEED. Necessary changes are made to the project scope for mitigating any significant process safety concerns. 

The HazOp study differs from the FMEA and ETBA in that some suggest that the best time to conduct a HazOp is when the design is fairly firm (Goldwaite 1987). Conventional system safety wisdom dictates that the system safety effort be as far upstream as practical, with a facility preliminary hazard analysis developed as part of the initial design effort and completed by the 35% stage. Also, a HazOp study tends to include human factors and operator errors whereas a traditional FMEA or ETBA normally examines hardware failures only. 

The predetermined safe position of the process equipment device under control, as determined by operational experience, a preliminary hazards analysis, or formal Hazard and Operability (HAZOP) study. Unless otherwise specified, the safe-state is de-energized, i.e., without power, pneumatic, or hydraulic supply. It is also the state of the process after acting to remove the hazard resulting in no significant harm. 

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