Hazop Analysis in the Chemical and Process Industry

Table of Content


In the words of Jones (1992:4), a “hazard is a physical situation with a potential for human injury, damage to property, damage to the environment or some combination of these”. These hazards have several consequences ranging from death, illness, injury, damage to a person, property or plant, production and product loss. Hazards could either be;

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  • Chemical: Toxic spillages or leakages
  • Electrical: High voltage, Electrostatic phenomena
  • Thermodynamics: High pressure or temperature
  • Mechanical: Force strain or stress, High pressure fluid injection.
  • Health: Noise and pollution Ergonomics: Poor lighting, poor posture, frequent lifting
  • Environmental: Seismic activity, avalanche and volcanic eruptions.

All hazards cause accidents and these are not desirable in the chemical and process industry and must be eliminated to the barest minimum. Without a structured methodology, these hazards might be overlooked and not identified. According to the updated SEVESCO directive of 1996, all European Union (EU) member countries should work towards averting accidents involving harmful substances , man and the environment in a harmonious, capable and vigorous way.

This directive further emphasizes the need to take on and embrace guidelines that establishes consistently those hazards that occur from routine plant operation and look at their magnitude and propensity to occur. Several Process Hazard Analysis (PHA) techniques have been developed over the years like Failure Mode and Effects Analysis (FMEA) and Management Oversight and Risk Tree (MORT) and Task Analysis (Wells,2006). , but this review concentrates and highlights one of the most important techniques (HAZOP).

Hazard and Operability Studies (HAZOP) is a well thought out, planned and organized study of a process plant usually carried out by a team of multi – disciplinary professionals. The team carries out a point to point (often called node) investigation of a plant design. This investigation tends to find and identify possible causes of risk to plant personnel or equipment, and averts those causes that go against smooth plant operation. If the safeguards in place are insufficient to solve these cause-consequence problems, then the team can offer recommendations for consideration. It will be pertinent to point out that

HAZOP not only points out causes of risk but also identifies operability issues. Rausand (2006) has explained that the basic and fundamental feature of a HAZOP study involves the use of several guide-words like No (not, none), Less(less of, lower) and process parameters like flow, temperature and pressure to show deviation (like more pressure) from normal operation. It is qualitative in nature and should be carried out early in the design phase of a design to have an effect. Ideally, a HAZOP study should be carried out at the final design stage, usually on the Piping and Instrumentation Diagram (P). It may also be carried out on an existing facility to check risk and operability problems.

Types of HAZOP

  • As stated by Rausand (ibid. ), these types of HAZOP exist:
  • Process HAZOP – This HAZOP technique was initially developed to examine plants and process systems.
  • Human HAZOP – This is a group of specialized HAZOPs and is primarily focused on human errors and judgments rather than technical failures
  • Procedure HAZOP – This appraises and evaluates procedures or operational sequences
  • Software HAZOP – This HAZOP type encompasses identification of possible errors in the development of computer software.

Scope of Review

This review’s aim is to historically look at the origins of HAZOP and its adaptability to automation. Processes are becoming increasingly complex and high tech to operate and so its safety must be properly ensured. Different literature comprising mainly of textbooks and publications in major journals were looked at. Conclusions were then drawn from them.

Origins Kletz (1997:263) has accurately given a firsthand account of the early beginnings of HAZOP. HAZOP studies emanated in the Heavy Organic Chemical Division (HOC) of Imperial Chemical Industries (ICI) in 1963. A team comprising of three engineers was constituted to examine a phenol processing plant and determine if there were flaws in the design of the plant. The original aim of this study was to reduce the capital cost of the plant by “chopping” off unwanted areas of the plant. They looked at the engineering line diagram of the process and discovered many conceivable hazards, safety and operability issues which had not been imagined before. Kletz (ibid. :263) also noted that similar studies were carried out in other ICI locations and the results consolidated.

A distinction was made between the then existing methodology termed “critical reasoning” and results obtained from these studies. Several questions were asked and what is called HAZOP today was borne. Generally, at that point in time, the ultimate aim of HAZOP was to identify possible hazardous materials present in facilities which could cause harm.

However, the Flixborough Disaster of 1974,  highlights the inherent risks in modifying a plant’s design without considering the operability issues. Wells (op cit. 91) has also asserted this fact. This has also been corroborated by Swann and Preston (1995). Lawley, (1974) as cited in Dunjo et al. , (2009) was the first to visually portray the basic understanding required to undertake a HAZOP analysis due to the ever changing processes at that time which could not be investigated using the then equipment -oriented approach. This was followed by the first major guideline publication by the Chemical Industries Association in the UK (CIA, 1977,) as cited in (Crawley & Tyler 2008).

Many years have elapsed since the publication of this historic guideline. Many important publications have also emerged on changing the requirements of the HAZOP technology for the process industry. Nolan (1994) discussed HAZOP and What If Techniques as it affected the petroleum, petrochemical and chemical industries. He also looked at scheduling and cost estimates. Lees (1996) cited in Dunjo(2009) and Wells (op cit. ) both looked at HAZOP at a wider scope of identifying hazards and reducing losses. A very important document BS IEC 61882 (2001) was released in the UK which established HAZOP as the most broad and extensively expended safety procedure in industrial plants and other chemical facilities.

Finally, Crawley and Tyler (op cit. ) have the latest guidelines in HAZOP analysis, with the first edition written in 2003. HAZOP indeed is most versatile and has diverse applications and has been used in facilities like medical diagnostic systems (Chudieigh, 1994), road-safety measures (Jagman et al. , 2003), and photovoltaic facilities (Fthenakis & Trammell, 2003) amongst others all cited in (Dunjo et al. , op cit. ). Jorgenssen et al (2009) has shown using an Industrial Vapor Recompression Distillation pilot plant that the functional HAZOP methodology s indeed a useful model in revealing potential hazards in safety critical operations. They have also suggested that this functional methodology can even be used by inexperienced chemical engineers.

Automation of the HAZOP Methodology

The HAZOP methodology is slow and time consuming. Often, it requires series of meetings. These bottlenecks have been addressed over the years by different authors. Efforts have been made to automate this very important process safety methodology. Galluzzo et al. 2000) have enhanced a computer support system aimed at minimizing the time involved in HAZOP analysis and also increased its reliability. Some of these support systems can be sourced openly in the market and includes various spreadsheet applications.

They are of the opinion that the methodology for the automation of a batch process is distinctly different for a continuous process. They came up with an archetypal for the most necessary everyday process plant equipment units, and incorporated it into their support system termed „HAST? which could be used both for batch and continuous processes.

Zhao et al. (2005) have laid a framework for the automation of HAZOP analysis termed PHA Suite. They state that the framework has the following characteristics – “appropriate representation of HAZOP analysis procedure for chemical processes, supporting abstraction and analysis on different levels of the process, incorporating general domain knowledge, as well as experience, learning ability, i. e. , the analysis, capability and quality should increase as more processes are applied”.

Chung and Palmer (2009) dedicated their automation of the HAZOP methodology to batch processes solely. They have come up with a batch HAZOP identification system (CHECKOP), which considers operating procedures, variable deviations and the effects of the operators actions. CHECKOP uses inputs like process description/layout and a set of operating instructions to generate a HAZOP report automatically. 7 Khan et al (2009) have also technologically advanced a classified structure for the automation of the HAZOP methodology (ExpHAZOP).

ExpHAZOP works by the smooth synergy between an expert knowledge base and a well organized fault transmission algorithm. Its uniqueness from other automated tools is the addition of a graphical user interface (GUI). This makes the tool easy to use as minimum know-how is required.


This review covered the early beginnings of the HAZOP methodology to date. It also critically examined its development over the years – from human experise to sophisticated Programmable Expert Systems (PES). HAZOP is quite extensive in nature, but the above scope acted as limiting in this review.

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Hazop Analysis in the Chemical and Process Industry. (2018, Apr 10). Retrieved from


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